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Clinical performance of resin composite restorations: the value of accelerated in-vitro testing

Garcia-Godoy, F.

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Citation for published version (APA):Garcia-Godoy, F. (2012). Clinical performance of resin composite restorations: the value of accelerated in-vitrotesting.

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CClliinniiccaall ppeerrffoorrmmaannccee ooff rreessiinn ccoommppoossiittee rreessttoorraattiioonnss

The predictive value of accelerated in vitro testing

Franklin García-Godoy

Clinical perform

ance of resin com

posite restorations

F. G

arcía-Godoy

2012

UUiittnnooddiiggiinngg

Voor het bijwonen van de

openbare verdediging van

het proefschrift

Clinical performance of resin composite

restorations The predictive value of

accelerated in vitro testing

Op dinsdag 5 juni 2012 om

12:00 uur in de

Agnietenkapel

Ouderzijdsvoorburgwal 231

in Amsterdam

Na afloop van de promotie is

er een receptie ter plaatse


[email protected]

Franklin Garcia-Godoy was born in 1952 in Santo Domingo, Dominican Republic. He graduated in Dentistry in the University of Santo Domingo in 1976 with the degree of Doctor of Odontology Cum Laude. He obtained a specialty degree in Pediatric Dentistry from the College of Dentistry, University of Illinois, in Chicago, USA in 1979 and also in 1979 a Master of Science degree from the Graduate College of the University of Illinois, in Chicago, USA. He has been a Professor with Tenure at the University of Texas Health Science Center at San Antonio, Texas, USA, Tufts University, Boston, USA and University of Tennessee, Memphis, Tennessee. He is also a Senior Clinical Investigator at the Forsyth Dental Research Center, in Cambridge, Massachusetts, USA and Adjunct Professor at the University of Munich, Germany. Currently, he is Senior Executive Associate Dean for Research, Chair, Department of Bioscience Research, and Director, Bioscience Research Center, College of Dentistry, University of Tennessee Health Science Center. He is also the Editor of the American Journal of Dentistry. He has published over 450 scientific articles. He began his PhD program in 2005 conducting the long-term clinical results presented in this thesis and is conducting research in areas ranging from sealants to stem cells.

Clinical performance of resin composite restorations:

The predictive value of accelerated in vitro testing


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Copyright: © F. Garcia-Godoy

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system, or transmitted in any form or by any means, mechanically, by photocopy, by

recording or otherwise, without permission by the author.

Clinical performance of resin composite restorations:

The value of accelerated in-vitro testing

ACADEMISCH PROEFSCHRIFT

Ter verkrijging van de graad van doctor

aan de Universiteit van Amsterdam

op gezag van de Rector Magnificus

Prof.dr. D.C. van den Boom

ten overstaan van een door het college voor promoties ingestelde

commissie, in het openbaar te verdedigen in de Agnietenkapel

op dinsdag 5 juni 2012, te 12:00 uur

door

Franklin Garcia-Godoy

Geboren 11 november 1952

te Santo Domingo, Dominicaanse Republiek

Promotiecommissie

Promotor : Prof. dr. A.J. Feilzer

Co-promotores : Prof.dr. R. Frankenberger

Prof.dr. N. Krämer

Overige leden : Prof.dr. R. Hickel

Dr. C.J. Kleverlaan

Prof.dr. J. McCabe

Prof.dr. F.J.M. Roeters

Faculteit der Tandheelkunde

Contents

Chapter 1 Introduction 7

Chapter 2 Degradation of resin-bonded human dentin after 3 years of

storage

17

Chapter 3 Long-term degradation of enamel and dentin bonds: 6-year

results in vitro vs. in vivo.

31

Chapter 4 Fatigue behavior of dental resin composites: Flexural fatigue in

vitro vs. six years in vivo

45

Chapter 5 Microhybrid vs. nanohybrid resin composites in extended

cavities after 6 years.

59

Chapter 6 General discussion: Is the clinical performance of bonded

restoratives predictable in the lab?

82

Summary 106

Samenvatting 112

Acknowledgement 118

7

CHAPTER 1

Introduction

Chapter 1

8

Tooth-colored materials such as resin-based composites are today the treatment option

of choice for the majority of patients.1-6 This is mainly attributed to esthetic reasons

and not primarily related to lifetime-expectancy of individual restorative approaches.

Amalgam was a successful dental restorative material for over 200 years.7-9 However,

on one hand it was repeatedly alleged to be toxic,10-12 and on the other hand it is dark

or at best argentic and therefore simply not invisible nor tooth-colored.13 Today we

also know that amalgam, among all toxicologic issues, also has clinical disadvantages:

missing adhesive stabilization of remaining tooth hard tissues, cracked teeth after long

service times, and mandatory cement linings are not desirable in today's restorative

therapy of carious lesions.13 Resin composites are invisible, adhesively stabilizing to

both enamel and dentin, and appropriately sealing.1-4;14-16 Nevertheless, is the distinct

change towards resin composites really better in terms of overall clinical

performance? What are resin composite restorations able to perform, especially

compared to amalgam in larger stress-bearing posterior cavities? Today it is well-

proven that adhesive restorations are successful, having been repeatedly reported for

pit and fissure sealings, direct and indirect resin composites, and bonded indirect

ceramic restorations.1;2;4;13;15;17-22 In the focus of the present thesis only directly

applied resin composite restorations were investigated, especially as posterior

rsestorations for amalgam replacement.

It is well-known from several studies in the field of adhesive dentistry that durable

adhesion to enamel and dentin is a fundamental prerequisite for successful adhesive

dentistry because polymerization shrinkage of resin-based composites is still a major

issue.2;3;5;6;23-27 Bonding to phosphoric acid etched enamel is generally accepted as

clinically successful.13;15;17;28;29 The same is true for dentin, however, it is not

completely understood whether the etch-and-rinse or the self-etch approach may

represent the ultimate way of durable bonding to dentin.14;15;18;23;24;26;28;30-32 And

technique sensitivity with bonded restorations still is problematic facing a 1:12 failure

rate ratio in a clinical trial with identical materials but different clinical operators.33

Beside technique sensitivity, long-term performance of adhesion to enamel and dentin

is one of the most interesting issues.1;6;13;14;18;19;21;22;30-32;34 In the literature, many short

term evaluations are published, but medium to long-term investigations are still

needed. Therefore, bonding degradation over time is an important aspect. In dentin,

the last decade revealed an array of innovative findings with regards to bond

Introduction

9

degradation, especially in dentin.14;35-38 Both water treeing and enzymatic degradation

investigations clearly showed that there is a long way to go for durable dentin bonding

also in the nanoscale aspect.14;30;31;36-38 Results up to three years are presented here,

giving some more aspects of longevity in vitro (Chapter 2).

Moreover, adhesion to enamel is even more important because the main retention is

provided by appropriate bonding to enamel margins, and the absence of marginal

staining is primarily provided by a tight enamel seal.4;17-19;28;32;39 When cavities get

larger and larger, dentin support of the biomechanical tooth-restoration complex gets

lost and restoration margins in enamel receive even more stress besides residual

shrinkage stress and intraoral chewing forces.19;20;23-27 Therefore, long-term

evaluations over six years also were carried out (Chapter 3). In this chapter, in vitro

results were not thought to stand alone. When the setups for a clinical study were

designed, it was an aim of the author to simultaneously start both in vivo and in vitro

studies; i.e. in vitro evaluations regarding marginal quality were started with the same

materials at the same time like the prospective randomized clinical trial dealing with

posterior resin composite restorations. So after several years of clinical service, one

should be able to directly compare in vitro results with in vivo outcomes.

Resin-dentin and resin-enamel bonding behavior is important for clinical success, but

resin composite research is not adhesion alone. Adhesion is certainly an important

issue as described above, but restorative material properties such as wear, flexural

strength, and flexural fatigue behavior are important as well.2;3;32;40-45 In former times

(being represented by older studies in the literature of the field), the predominant

failure mechanism of resin composite restorations was gap formation and subsequent

recurrent caries.34 Residual stresses led to gap formation over time, supported by

different coefficients of thermal expansion.1-3;32;34;40 Gaps are colonized by biofilms

consequently resulting in secondary caries. This scenario was believed to be the major

failure reason for decades and is still in the back of dentists’ minds all over the world.

However, facing more recent prospective clinical trials dealing with modern resin

composite materials for posterior use, it becomes evident that more material-

dependent issues like bulk fractures and chipping have displaced secondary caries as

the No 1 failure scenario with this class of materials.2;3;13;16;19;20;26;27;40;42;46-48 This may

be due to the better understanding of long-term bonding to both enamel and dentin,

Chapter 1

10

but it may also be attributed to enhanced materials properties in terms of shrinkage

and shrinkage stress.2;5;23;25;32

Randomized prospective clinical trials are still the ultimate instrument for evaluating

dental restoratives such as resin composites, ceramics, cements, and prosthodontic

restorations.4;15;16;46-49 However, the predominant problem with these clinical trials is

that once valuable results are available after several years of clinical service, the

material under investigation may not be in the market anymore. This is a frustrating

situation which often occurred with many research groups. Another problem is when

publishable results are obtained, the peer review periods and publication backlog of

top dental journals add considerable time and actual publication is postponed

significantly. Legislation in the field of medical products also contributes negatively

here; it becomes harder and harder to get ethical permission to carry out clinical trials,

costs for clinical centers have to be readjusted, and finally the manufacturer may not

have enough budget for the study anymore. Due to this considerable number of

reasons, preclinical in vitro investigations are more important than ever, but it is still

not fully understood whether these tests are able to reliably predict clinical behavior.

As already mentioned, the performance of bulky resin composites is of importance to

counteract bulk fractures over time.17;32;40-42;50;51 Therefore, a thorough in vitro vs. in

vivo comparison of flexural fatigue characteristics of resin composites must be

addressed here (Chapter 4). In this case, the strategy was the same as in bonding

investigations of Chapter 3. Again, we simultaneously started both in vitro and in vivo

branches of the overall investigation plan. However, compared to the informative

value of thermomechanical loading for marginal quality estimation, loading of resin

composite beams is controversially discussed. On one hand, any fatigue loading

design is superior to pure initial loading alone.17;32;40-42;50;51 Initially, high loading

forces seldomly lead to clinical failures in real life.13;20;43 It is more the subcritical,

repeated load that degrades dental restorations over several years of clinical service.

Loading of beams - with fatigue or not - may not be very close to the clinical

situation, because in the oral cavity no resin composite beam may be found to be

loaded. Intraorally, resin composites are always bonded more or less successfully to

dental hard tissues, i.e. bending forces such as those observed in a classical three- or

four-point flexural strength evaluation may not occur similarly.13;20;43 Nevertheless,

the practical advantage of the presented four-point flexural fatigue evaluation design

Introduction

11

is of a very thoroughly standardized quality and moreover, a sound database of many

restoratives exists for comparison.32;41;42 So we decided to include this particular way

of stressing resin composite specimens in order to simulate bulk fatigue over time.

And finally, again we were able to correlate the results to clinical outcome directly.

The ultimate instrument is still the randomized clinical trial. Therefore, a prospective

clinical long-term trial was set up and reported (Chapter 5). As mentioned above,

both materials under investigation are no longer on the market. . On the other hand, a

certain amount of valuable information results from the present long-term evaluation

of Grandio and Tetric Ceram. The longitudinal approach allows for the correlation of

initial cavity size with marginal degradation over time. It is possible to measure wear

in both areas, occlusal contact area and contact-free area, and distinct differences

among materials can be worked out. Chapter 5 is the heart and center of the present

thesis, because it allows a clear view on what is happening with adhesively bonded

resin composites in stress-bearing areas of posterior teeth.4;16;18;46-48 It is possible to

distinguish between smaller, minimally invasive resin composite restorations, and

larger restorations with considerable occlusal contacts in resin composite instead of

being underpinned by more wear resistant enamel cusps. Last but not least, a

prospective clinical long-term trial offers the possibility of getting hints about the

ultimate question of how resin composite restorations behave over time and what

failure scenarios are really in the center of interest. This is the clear advantage

compared to cross-sectional studies offering important observation, but unfortunately

in a clearly retrospective nature.25;34

The final question remains and should be addressed with the last issue of the present

thesis, i.e. what is this all about or in different words: Is clinical performance of

bonded restoratives predictable in the lab (Chapter 6)? It was extensively discussed

previously, and it has to be the final statement of the present thesis. The key idea for

valuably estimating this particular and ultimate question was to start with in vitro and

in vivo research simultaneously.17;29 Only in this way was it possible to truly compare

preclinical outcome and clinical observations. And only when evaluated parameters in

both branches approximately match, the predictive quality of the chosen in vitro setup

is appropriate. This is the simple truth regarding the major question of the present

thesis, before smart materials avoiding classical material disadvantages are considered

as alternative.52

Chapter 1

12

References 1. Da Rosa Rodolpho PA, Donassollo TA, Cenci MS et al. 22-Year clinical

evaluation of the performance of two posterior composites with different filler characteristics. Dent Mater 2011.

2. Ferracane JL. Buonocore Lecture. Placing dental composites--a stressful experience. Oper Dent 2008;33:247-257.

3. Ferracane JL. Resin composite--state of the art. Dent Mater 2011;27:29-38.

4. Hickel R, Manhart J. Longevity of restorations in posterior teeth and reasons for failure. J Adhes Dent 2001;3:45-64.

5. Mjor IA. Esthetic dentistry--the future. J Esthet Dent 2000;12:281-283.

6. Mjor IA. Minimum requirements for new dental materials. J Oral Rehabil 2007;34:907-912.

7. Maserejian NN, Trachtenberg F, Hayes C, Tavares M. Oral health disparities in children of immigrants: dental caries experience at enrollment and during follow-up in the New England Children's Amalgam Trial. J Public Health Dent 2008;68:14-21.

8. Richardson GM, Wilson R, Allard D, Purtill C, Douma S, Graviere J. Mercury exposure and risks from dental amalgam in the US population, post-2000. Sci Total Environ 2011.

9. Trachtenberg F, Maserejian NN, Tavares M, Soncini JA, Hayes C. Extent of tooth decay in the mouth and increased need for replacement of dental restorations: the New England Children's Amalgam Trial. Pediatr Dent 2008;30:388-392.

10. Mutter J, Naumann J, Sadaghiani C, Walach H, Drasch G. Amalgam studies: disregarding basic principles of mercury toxicity. Int J Hyg Environ Health 2004;207:391-397.

11. Mutter J, Naumann J. Blood mercury levels and neurobehavior. JAMA 2005;294:679-680.

12. Mutter J. Is dental amalgam safe for humans? The opinion of the scientific committee of the European Commission. J Occup Med Toxicol 2011;6:2.

13. Manhart J, Chen H, Hamm G, Hickel R. Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Oper Dent 2004;29:481-508.

14. Carvalho RM, Chersoni S, Frankenberger R, Pashley DH, Prati C, Tay FR. A challenge to the conventional wisdom that simultaneous etching and resin

Introduction

13

infiltration always occurs in self-etch adhesives. Biomaterials 2005;26:1035-1042.

15. Hickel R, Manhart J, Garcia-Godoy F. Clinical results and new developments of direct posterior restorations. Am J Dent 2000;13:41D-54D.

16. Hickel R, Peschke A, Tyas M et al. FDI World Dental Federation - clinical criteria for the evaluation of direct and indirect restorations. Update and clinical examples. J Adhes Dent 2010;12:259-272.

17. Frankenberger R, Garcia-Godoy F, Lohbauer U, Petschelt A, Krämer N. Evaluation of resin composite materials. Part I: in vitro investigations. Am J Dent 2005;18:23-27.

18. Gordan VV, Shen C, Watson RE, Mjor IA. Four-year clinical evaluation of a self-etching primer and resin-based restorative material. Am J Dent 2005;18:45-49.

19. Krämer N, Garcia-Godoy F, Reinelt C, Frankenberger R. Clinical performance of posterior compomer restorations over 4 years. Am J Dent 2006;19:61-66.

20. Krämer N, Reinelt C, Richter G, Petschelt A, Frankenberger R. Nanohybrid vs. fine hybrid composite in Class II cavities: clinical results and margin analysis after four years. Dent Mater 2009;25:750-759.

21. Manhart J, Chen HY, Mehl A, Hickel R. Clinical study of indirect composite resin inlays in posterior stress-bearing preparations placed by dental students: results after 6 months and 1, 2, and 3 years. Quintessence Int 2010;41:399-410.

22. Manhart J, Chen HY, Hickel R. Clinical evaluation of the posterior composite Quixfil in class I and II cavities: 4-year follow-up of a randomized controlled trial. J Adhes Dent 2010;12:237-243.

23. Opdam NJ, Loomans BA, Roeters FJ, Bronkhorst EM. Five-year clinical performance of posterior resin composite restorations placed by dental students. J Dent 2004;32:379-383.

24. Opdam NJ, Bronkhorst EM, Roeters JM, Loomans BA. Longevity and reasons for failure of sandwich and total-etch posterior composite resin restorations. J Adhes Dent 2007;9:469-475.

25. Opdam NJ, Bronkhorst EM, Roeters JM, Loomans BA. A retrospective clinical study on longevity of posterior composite and amalgam restorations. Dent Mater 2007;23:2-8.

26. Opdam NJ, Bronkhorst EM, Loomans BA, Huysmans MC. 12-year survival of composite vs. amalgam restorations. J Dent Res 2010;89:1063-1067.

Chapter 1

14

27. Opdam NJ, Bronkhorst EM, Cenci MS, Huysmans MC, Wilson NH. Age of failed restorations: A deceptive longevity parameter. J Dent 2011;39:225-230.

28. Frankenberger R, Tay FR. Self-etch vs etch-and-rinse adhesives: effect of thermo-mechanical fatigue loading on marginal quality of bonded resin composite restorations. Dent Mater 2005;21:397-412.

29. Frankenberger R, Krämer N, Lohbauer U, Nikolaenko SA, Reich SM. Marginal integrity: is the clinical performance of bonded restorations predictable in vitro? J Adhes Dent 2007;9 Suppl 1:107-116.

30. Breschi L, Cammelli F, Visintini E et al. Influence of chlorhexidine concentration on the durability of etch-and-rinse dentin bonds: a 12-month in vitro study. J Adhes Dent 2009;11:191-198.

31. Breschi L, Mazzoni A, Nato F et al. Chlorhexidine stabilizes the adhesive interface: a 2-year in vitro study. Dent Mater 2010;26:320-325.

32. Ilie N, Hickel R. Resin composite restorative materials. Aust Dent J 2011;56 Suppl 1:59-66.

33. Frankenberger R, Reinelt C, Petschelt A, Krämer N. Operator vs. material influence on clinical outcome of bonded ceramic inlays. Dent Mater 2009;25:960-968.

34. Mjor IA, Moorhead JE, Dahl JE. Reasons for replacement of restorations in permanent teeth in general dental practice. Int Dent J 2000;50:361-366.

35. Kim YK, Mai S, Mazzoni A et al. Biomimetic remineralization as a progressive dehydration mechanism of collagen matrices--implications in the aging of resin-dentin bonds. Acta Biomater 2010;6:3729-3739.

36. Sadek FT, Braga RR, Muench A, Liu Y, Pashley DH, Tay FR. Ethanol wet-bonding challenges current anti-degradation strategy. J Dent Res 2010;89:1499-1504.

37. Sadek FT, Castellan CS, Braga RR et al. One-year stability of resin-dentin bonds created with a hydrophobic ethanol-wet bonding technique. Dent Mater 2010;26:380-386.

38. Tay FR, Frankenberger R, Krejci I et al. Single-bottle adhesives behave as permeable membranes after polymerization. I. In vivo evidence. J Dent 2004;32:611-621.

39. Frankenberger R, Pashley DH, Reich SM, Lohbauer U, Petschelt A, Tay FR. Characterisation of resin-dentine interfaces by compressive cyclic loading. Biomaterials 2005;26:2043-2052.

Introduction

15

40. Ilie N, Hickel R. Investigations on mechanical behaviour of dental composites. Clin Oral Investig 2009;13:427-438.

41. Ilie N, Hickel R, Valceanu AS, Huth KC. Fracture toughness of dental restorative materials. Clin Oral Investig 2012, in press.

42. Keulemans F, Palav P, Aboushelib MM, Van DA, Kleverlaan CJ, Feilzer AJ. Fracture strength and fatigue resistance of dental resin-based composites. Dent Mater 2009;25:1433-1441.

43. Mjor IA. In vivo versus in vitro. J Am Dent Assoc 2004;135:1370, 1372.

44. Mjor IA. A recurring problem: research in restorative dentistry... But there is a light at the end of the tunnel. J Dent Res 2004;83:92.

45. Roeters FJ, de Jong LC, Opdam NJ. [Change to a new composite with low shrinkage not sensible at this point]. Ned Tijdschr Tandheelkd 2009;116:10-15.

46. Hickel R, Roulet JF, Bayne S et al. Recommendations for conducting controlled clinical studies of dental restorative materials. J Adhes Dent 2007;9 Suppl 1:121-147.

47. Hickel R, Roulet JF, Bayne S et al. Recommendations for conducting controlled clinical studies of dental restorative materials. Int Dent J 2007;57:300-302.

48. Hickel R, Roulet JF, Bayne S et al. Recommendations for conducting controlled clinical studies of dental restorative materials. Clin Oral Investig 2007;11:5-33.

49. Wilson NH, Gordan VV, Brunton PA, Wilson MA, Crisp RJ, Mjor IA. Two-centre evaluation of a resin composite/ self-etching restorative system: three-year findings. J Adhes Dent 2006;8:47-51.

50. Palaniappan S, Bharadwaj D, Mattar DL, Peumans M, Van MB, Lambrechts P. Nanofilled and microhybrid composite restorations: Five-year clinical wear performances. Dent Mater 2011;27:692-700.

51. Palaniappan S, Elsen L, Lijnen I, Peumans M, Van MB, Lambrechts P. Nanohybrid and microfilled hybrid versus conventional hybrid composite restorations: 5-year clinical wear performance. Clin Oral Investig 2012;16:181-190.

53. McCabe JF, Yan Z, Al Naimi OT, Mahmoud G, Rolland SL. Smart materials in dentistry. Aust Dent J 2011;56: Suppl. 1, 3-10.

Chapter 1

16

17

CHAPTER 2

Degradation of resin-bonded human dentin after 3 years of storage

Chapter 2

18

Introduction

Considerable evidence in adhesive dentistry has accumulated over the past decade,

based on in vitro and in vivo work. Dentin bonds created by resin-based adhesives

may not be as durable as previously conjectured.1 Although the current strategies of

incorporating ionic and hydrophilic resinous components in etch-and-rinse and self-

etch adhesives arise from the need to bond to an intrinsically wet substrate,2 they

create potentially unstable resin matrices that slowly degrade via water sorption.3 This

is particularly so when resin-dentin bonds are not protected by enamel, and when the

durability of these bonds was challenged by reducing adhesive interfaces into smaller

portions, to expedite aging effects and increasing their interactions with water.4-6

Another mechanism of bond degradation is the potential instability of the

demineralized dentin collagen matrix, that was manifested as the thinning or

disappearance of collagen fibrils from aged, bonded dentin,7,8 or the failure of aged

hybrid layers to take up heavy metal stains.4 This issue of collagen instability has

caused concern, with the demonstration of the potential involvement of host-derived

matrix metalloproteinases (MMPs), a class of independent endopeptidases, in the

breakdown of the collagen matrices in dentin caries9-11 and the periodontium.12-14 In

the context of dentin bonding, residual collagenolytic activity was observed in

mineralized dentin of extracted teeth that accounted for the disintegration of collagen

fibrils from unbonded, aged acid-etched dentin, in the absence of the contribution

from bacterial or salivary MMPs. This low but persistent endogenous collagenolytic

activity was strongly inhibited by the use of protease inhibitors, the incorporation of

which preserved the structural integrity of the collagen fibrils.1 In that study, the

demineralized collagen matrices were not protected by adhesives. Thus, it remains to

be resolved whether these endogenous enzymatic activities can result in the

proteolysis of the resin-infiltrated collagen network in aged, adhesive-bonded dentin.

Using a model that consisted of soluble fluorescein-labeled Type I collagen and

gelatin in a previous study, both collagenolytic and gelatinolytic activities were

identified in powdered mineralized human dentin. Retention of these activities was

evident even upon autoclaving of the mineralized dentin power in water. Conversely,

these activities were sufficiently suppressed after treatment of the powder with

phosphoric acid. The results derived from this model suggested that if resin-bonded

dentin is permeable to endogenous enzymes released from the underlying mineralized

dentin, complete cleavage of the collagen fibrils within the hybrid layer is possible,


19

first into ¾- and ¼-length fragments,15 and subsequently into smaller peptides.16 Thus,

the objective of the present study was to investigate the morphologic correlations of

these endogenous enzymatic activities in aged, adhesive-bonded dentin. As water

molecules are putatively required for the activity of zinc-dependent MMPs,17,18 the

null hypothesis tested was that there was no difference in the ultrastructure of resin-

dentin bonds that were aged in mineral oil or artificial saliva.

Materials and Methods

Twenty-one non-carious human third molars were collected after the subject’s

informed consent had been obtained under a protocol reviewed and approved by the

Human Assurance Committee of the Medical College of Georgia, USA. Within 1

month of extraction, the occlusal enamel and roots of these teeth were removed using

a slow-speed saw (Isometa) under water-cooling. The exposed dentin surfaces were

polished with wet 180-grit silicon carbide papers.

Experimenlal design - Three total-etch adhesives were examined. They included two

two-step systems (Prime&Bond NTb and Excitec), and a multi-step system (All-Bond

2d). Six teeth were used for each adhesive. Each tooth was etched with 32-37%

phosphoric acid gel for 15 seconds, and rinsed with water for 20 seconds. The teeth

were then bonded with the respective adhesives according to the manufacturers’

instructions, and restored with a microfilled resin composite (EPIC-TMPTe). After

allowing the bonds to mature for 24 hours, each tooth was sectioned longitudinally

into 0.9 mm-thick serial slabs. Two slabs from the center part of each tooth were

further sectioned into 0.9 x 0.9 mm beams. The composite-dentin beams from each

adhesive group were randomly divided into two equal portions and stored respectively

in 5 ml aliquots of artificial saliva or mineral oil at 55°C for 3 years, according to the

accelerated aging protocol described by Tay et al.19 The artificial saliva contained

(mmoles/L): CaCI2 (0.7), MgCl2 • 6H20 (0.2), KH2P04 (4.0), KCI (30), NaN3 (0.3) and

HEPES buffer (20). The rationale for using artificial saliva was to prevent

demineralization of the mineralized dentin during aging. The artificial saliva was

replaced every month during the 3-year period. Sodium azide was added to prevent

bacterial growth, and to ensure that the only available source of MMPs was derived

from the dentin substrate.1 The resin-bonded dentin beams that were to be aged in

mineral oil (Dow-Coming 200 Fluidf), were wiped with lint-free gauze and briefly air-

dried to remove excess water prior to immersion in oil. They served as controls in that

collagenolytic and gelatinolytic activity cannot occur in a non-aqueous medium.

Chapter 2

20

To further ensure that degenerative changes observed after accelerated aging were not

caused by the increased aging temperature (55°C), an "extreme" control was

performed for each adhesive, using an additional tooth that was bonded in the same

manner. Composite-dentin beams prepared from these teeth were subjected to an

autoclave cycle at 121°C and 103 kPa for 30 minutes in water before further

laboratory processing.

Transmission electron microscopy (TEM) - For each adhesive, 10 specimens were

randomly retrieved from those aged in mineral oil, and another 10 from the artificial

saliva at time zero and after 3 years of incubation. Half of the specimens were

immersed in a 50 wt% ammoniacal silver nitrate solution for 24 hours, according to

the tracer protocol for nanoleakage examination.2 These specimens were processed for

TEM examination without further laboratory demineralization. The remaining

specimens were completely demineralized in ethylene diamine tetra-acetic acid. Both

undemineralized and demineralized, epoxy resin-embedded, 90 µm-thick sections

were prepared according a TEM protocol.20 Undemineralized sections were examined

without further staining. Demineralized sections were stained with 2% uranyl acetate

and Reynold's lead citrate for examining the characteristics of the resin-dentin

interfaces, and with a specific collagen staining technique (1% phosphotungstic acid

and 2% uranyl acetate) for examination of the status of the collagen fibrils. The

sections were examined using a TEM (Philips EM208Sg) operating at 80 kV.

Results

The "extreme" control specimens that were autoclaved at 121°C showed that collagen

fibrils were not denatured at this temperature when they were protected by adhesive

resin or apatite minerals (not shown). Their ultrastructural features were similar to

those observed in control specimens that were aged in mineral oil at 55°C for 3 years.

For example, in undemineralized sections of Prime&Bond NT that were aged in

mineral oil, a 5-7 µm thick zone of demineralized dentin with sparse silver deposits

was observed (Fig. 2.1A), that corresponded with the electron-dense hybrid layer in

stained, demineralized sections (Fig. 2.1B). Collagen fibrils with normal dimensions

and organization could be identified both within the hybrid layer (Fig. 2.1C) and the

underlying dentin (Fig. 2.1D).

By contrast, extensive nanoleakage was observed in Prime&Bond NT specimens that

were aged in artificial saliva (Fig. 2.2A). The corresponding hybrid layer was


21

abnormal and only discontinuous patches of stained fibrillar remnants were observed

(Fig. 2.2B). They consisted of grossly disintegrated, short microfibrillar fragments

(Fig. 2.2C). The collagen matrix from the underlying mineralized dentin was also

denatured, but to a lesser extent, and appeared as swollen, partially unraveled fibrils

that lacked cross banding (Fig. 2.2D).

Whereas the Excite specimens that were aged in mineral oil exhibited minimal

nanoleakage (Fig. 2.3A) and a highly electrondense hybrid layer (Fig. 2.3B), those

that were aged in artificial saliva demonstrated substantial degenerative changes.

Extensive patches of nanoleakage could be seen in the zone of demineralized dentin

that extended into the underlying mineralized dentin (Fig. 2.3C). In such regions,

stained fibrillar components were absent from tbe hybrid layer. Collagen fibrils from

the underlying dentin were sparsely distributed among abnormally wide interfibrillar

spaces (Fig. 2.3D).

Stained fibrillar components were evident throughout the entire hybrid layer in All-

Bond 2 specimens that were aged in mineral oil (Fig. 2.4A). These banded collagen

fibrils exhibited the characteristic unraveling of their severed ends along the dentin

surface (Fig. 2.4B). In specimens that were aged in artificial saliva, crystalline

deposits (Fig. 2.4C) derived from the supersaturated artificial saliva (Pashley et al.1)

were seen along the adhesive-hybrid layer interface. Although nanoleakage was only

identified in discrete parts of the demineralized collagen matrix (Fig. 2.4C), the entire

hybrid layer was completely devoid of stained fibrillar components (Fig. 2.4D).

Chapter 2

22

Figure 2.1: Control resin-bonded dentin beams of Prime&Bond NT that were aged in mineral oil for 3 years. C: resin composite; A: adhesive; D: intertubular dentin. A. Unstained, undemineralized section of a specimen that has been immersed in ammoniacal silver nitrate. The electron-lucent zone of demineralized dentin (between open arrows) corresponded with the stained hybrid layer in Fig.2. lB. Areas of incomplete resin infiltration within this zone are represented by reticular patterns of silver deposits (nanoleakage; pointer). B. The corresponding image of the electron-dense hybrid layer (H) from a demineralized section that was stained with uranyl acetate and lead citrate. C. A demineralized section that was stained with phosphotungstic acid and uranyl acetate. Although the hybrid layer was electron-dense due LO the intense mordanting effect of the adhesive solution, cross banding could be identified in longitudinaHy-oriented collagen fibrils (arrow). D. Normal collagen dimensions and organization could

be identified from the laboratory demineralized, epoxy resin-infiltrated dentin beneath the hybrid layer.

Figure 2.2: Experimental resin-bonded beams of Prime&Bond NT that were aged in artificial saliva for 3 years. C: resin composite; A: adhesive; D: intertubular dentin. A. Unstained, undemineralized section after immersion in ammoniacal silver nitrate. Extensive silver impregnation (arrow) was present in the hybrid layer (between open arrows). The intertubular dentin appeared normal in the undemineralized section. B. Phosphotungstic acid and uranyl acetate stained, demineralized section showing the breaking down of collagen fibrils (pointer) within the hybrid layer (H). A substantial part of the hybrid layer was devoid of stainable fibrillar components. Oblique sections of resin tags (open arrowheads) could also be seen in the disintegrated hybrid layer. No bacteria was observed in the section. C. A high magnification view of the adhesive-hybrid layer interface, showing the stainable fibrillar remnants that were present within the hybrid layer (H). Collagenolysis resulted in the appearance of loose

strands of gelatin microfibrils (arrow). D. A high magnification view of the hybrid layer dentin junction where grossly disintegrated fibrillar remnants (pointer) were observed at the base of the hybrid layer (H). Further gelatinolysis by matrix metalloproteinases that diffused from the underlying dentin probably resulted in the breakdown of the gelatin strands into smaller peptides. This may account for the absence of stainable fibrillar components from the rest of the hybrid layer. Collagen fibrils in the laboratory demineralized dentin were denatured to a lesser extent, probably due to the protection rendered by the mineral phases. There was a loss of cross banding from these partially denatured and swollen fibrils, in which only the microfibrillar architctture could be identified (arrow).


23

Figure 2.3: Control (Figs. A, B) and experimental (Figs. C, D) resin-bonded dentin beams of Excite after 3 years of accelerated aging. C: resin composite; A: adhesive; D: intertubular dentin. A. Unstained, undemineralized section following immersion in ammoniacal silver nitrate. The control specimen that was aged in mineral oil exhibited relatively little silver uptake (pointer) within the demineralized dentin zone (between open arrows). B. The corresponding uranyl acetate and lead citrate-stained, demineralized section showing the presence of a highly electron dense hybrid layer (H) in which collagen fibrils could be clearly distinguished (arrow). C. Unstained, undemineralized section following immersion in ammoniacal silver nitrate. The experimental specimen that was aged in artificial saliva exhibited extensive areas of heavy silver deposits within the demineralized dentin zone (between open arrows) that extended into the underlying mineralized dentin (asterisk). The rest of the mineralized dentin appeared normal when

undeminera1ized sections were examined. D. The corresponding uranyl acetate and lead citrate-stained, demineralized section demineralized section showing a palely-stained hybrid layer (H) in which fibrillar components could not be identified. Stained collagen fibrils in the underlying intertubular dentin were sparse and separated by abnormally wide interfibrillar spaces (open arrow).

Figure 2.4: Control (Figs. A, B) and experimental (Figs. C, D) resin-bonded dentin beams of All-Bond 2 after 3 years of accelerated aging. C: resin composite; A: adhesive; D: intertubular dentin. A. Phosphotungstic acid and uranyl acetate stained, demineralized section of a control specimen that was aged in mineral oil, showing the presence of stained fibrillar components within the 5-6 µm thick hybrid layer (H and between open arrows). B. A high magnification view of the area depicted by the box in Fig.2. 4A. Collagen fibrils within the hybrid layer (H) were partially obscured by the infiltrated adhesive resins. Nevertheless, banded collagen fibrils could be identified (pointer), with unraveling of microfibrillar strands along the surface of the cut dentin (arrow). C. Unstained, undemineralized section of an experimental specimen that was aged in artificial saliva and examined after immersion in ammoniacal silver nitrate. Crystalline deposits (open arrowhead) derived from the supersaturated artificial saliva were

present between the adhesive and the surface of the cut dentin. The presence of segregated silver deposits within demineralized dentin zone (between open arrows) indicated that the latter was an intact layer, despite the absence of stainable fibrillar components (Fig 2..4D). D. The corresponding phosphotungstic acid and uranyl acetate-stained, demineralized section of a specimen that was aged in artificial saliva. The hybrid layer (H) was completely devoid of stainable fibrillar components, and exhibited a similar staining characteristic as the underlying resin tag (pointer) that is supposed to consist predominantly of adhesive resin. The activity of the phosphotungstic acid dissolved the crystalline deposits along the cut dentin surface (open arrowhead). At higher magnification (not shown), collagen fibrils within the underlying dentin were denatured and appeared as microfibrillar strands that were devoid of cross banding (Fig. 2.2D).

Chapter 2

24

Discussion

The null hypothesis had to be rejected as pronounced differences were present

between the mineral oil and artificial saliva specimens. The extent of nanoleakage,

interfacial staining characteristics, and the conditions of the collagen fibrils in both the

hybrid layers and the underlying dentin from all the adhesives were examined. As the

glass transition temperature of mineralized dentin is 166.7°C,21 it is not surprising that

the temperature of superheated steam (121°C) was insufficient to denature collagen in

mineralized or resin-infiltrated dentin. As the structural integrity of the collagen fibrils

were also preserved in all control specimens that were aged at 55°C in mineral oil, one

may confidently assert that the degenerative changes that occurred after accelerated

aging in artificial saliva was not caused by the increase in aging temperature. In the

absence of salivary and bacterial MMP activities, these changes must have been

initiated by the endogenous collagenolytic and gelatinolytic activities of the

mineralized dentin, confirming the results of our previous long-term study.1

The inability to take up heavy metal stains from water-aged hybrid layers has

previously been reported by DeMunck et al.4 The authors surmised that such a

phenomenon was due to the decline in polar groups along the surfaces of degrading

collagen fibrils. Using a specific collagen stain, we demonstrated the existence of

discontinuous patches of grossly disintegrated microfibrillar fragments in some of the

artificial saliva-aged interfaces (Fig. 2.2C). These fragments probably represented

remnant ¾- and ¼-length fragments that resulted from collagenolysis,22 but were

retained by the adhesive resins within the hybrid layer. The existence of mild to

moderate nanoleakage (i.e. silver uptake) in the hybrid layers that were aged in oil

suggested that these hybrid layers were initially permeable to water that was utilized

by residual MMP hydrolases to degrade the collagen matrix of the hybrid layer and

the underlying mineralized dentin. In resin-bonded specimens incubated in artificial

saliva for 3 years, the coexistence of areas that did and did not take up specific

collagen stains and areas exhibiting a complete lack of stainable fibrillar components

from other specimens (Figs. 2.3D, 2.4D) indicates that the degenerated microfibrillar

fragments have further been degraded beyond detection. Such a process may occur via

gelatinolytic MMPs released from the mineralized dentin, with the gelatin breaking

down into peptides of lower molecular weight (kDa). Such a phenomenon is

analogous to the appearance of clear bands in Coomassie bluestained gels, when the

cleavage products of gelatin were subjected to Western blotting after treatment with

MMP-2 (Gelatinase A) or MMP-9 (Gelatinase B).23,24


25

Although the collagenase MMP-8 has been shown to exist in carious human dentin,9

its endogenous origin has not been established. Conversely, the gelatinase MMP-2 has

been shown to be present in human dentin.25 Apart from its gelatinolytic activity via

fibronectin-like domains, MMP-2 is also capable of collagenolysis,26 albeit at a slower

rate, via its hemopexin domain.27 Thus, even in absence of an endogenous collagenase

source, endogenous MMP-2 from the dentin matrix can apparently result in the slow

but complete cleavage of the entire resin-infiltrated collagen network over 3 years.

Further immunolabeling of MMP-2 within freshly-prepared and aged dentin hybrid

layers should be performed to establish the role played by this proteolytic enzyme in

the degradation of the demineralized collagen matrix.

It is disturbing to observe consistent partial degradation of the underlying mineralized

dentin. Degradation was less severe than the hybrid layers, probably because the

collagen fibrils were better protected by apatites than by adhesive resins.

Nevertheless, this provides evidence that under specific circumstances, mineralized

dentin is capable of self-destruction by its own matrix-bound enzymes. Such a process

may require the activation of host-derived MMPs with acids, as purported in the

pathogenesis of dentin caries,l1 A provocative clinical concern is why self-degradation

and accompanying weakening of mineralized dentin has not been reported in teeth

bonded in vivo with dentin adhesives. A possible explanation is the disturbance of the

balance between MMPs and their natural inhibitors, TIMPs (tissue inhibitors of

metalloproteinases) when extracted teeth are used for aging experiments. It is known

that both TIMP-l and TIMP-2 can complex with active MMP-2 and inhibit proteolytic

activity.28,29 As these natural MMP inhibitors have shorter half-lives30 than MMPs,

prolonged interruption of MMP-TIMP interaction such as the cessation of dentin fluid

flow (i.e. in vitro conditions) may prevent the replenishment of pulpal TIMPs out into

peripheral dentin. While such ideas remain highly speculative, a similar degradation

of collagen fibrils has recently been shown in endodontically-treated teeth that have

undergone long-term clinical function.31 Clearly, more work is required to establish

the relationship between MMPs and their natural inhibitors, or the use of synthetic

inhibitors such as chlorhexidine or doxycycline, in prolonging the longevity of resin-

dentin bonds and or non-vital dentin in endodontically-treated teeth.

a. Buehler Ltd., Lake Bluff, IL, USA.

b. Dentsply DeTrey, Konstanz, Germany.

Chapter 2

26

c. Ivoclar-Vivadent, Schaan, Liechtenstein.

d. Bisco Inc., Schaumburg, IL, USA.

e. Parkell Inc., Edgewood, NY, USA.

f. Dow-Corning Corp., Midland, MI, USA.

g. Philips, Eindhoven, The Netherlands.


27

References

1. Pashley DH, Tay FR, Hashimoto M, Breschi L, Carvalho RM, Ito S.

Degradation of dentin collagen by host-derived enzymes during aging. J Dent

Res 2004;83:216-221.

2. Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can

Dent Assoc 2003;69:726-731.

3. Yiu CK, King NM, Pashley DH, Suh BI, Carvalho RM, Carrilho MR, Tay FR.

Effect of resin hydrophilicity and water storage on resin strength. Biomaterials

2004;25:5789-5796.

4. DeMunck J, Van Meerbeek B, Yoshida Y, Inoue S, Vargas M, Suzuki K,

Lambrechts P, Vanherle G. Four-year water degradation of total-etch adhesives

bonded to dentin. J Dent Res 2003;82: 136-140.

5. Shono Y, Terashita M, Shimada J, Kozono Y, Carvalho RM, Russell CM,

Pashley DH. Durability of resin-dentin bonds. J Adhes Dent 1999;1: 211-218.

6. Hashimoto M, Ohno H, Sano H, Tay FR, Kaga M, Kudou Y, Oguchi H, Araki

Y, Kubota M. Micromorphological changes in resin-dentin bonds after 1 year

of water storage. J Biomed Mater Res 2002;63:306-311.

7. Hashimoto M, Ohno H, Sano H, Kaga M, Oguchi H. In vitro degradation of

resin-dentin bonds analyzed by microtensile bond test, scanning and

transmission electron microscopy. Biomaterials 2003;24:3795-3805.

8. Yoshida E, Hashimoto M, Hori M, Kaga M, Sano H, Oguchi H. Deproteinizing

effects on resin-tooth bond structures. J Biomed Mater Res Part B

2004;68B:29·35.

9. Tjaderhane L, Larjava H, Sorsa T, Uitto V-J, Larma M, Salo T. The activation

and function of host matrix metalloproteinases in dentin matrix breakdown in

carious dentin. J Dent Res 1998;77: 1622·1629.

Chapter 2

28

10. Sulkala M, Wahlgren I, Lannas M, Sorsa T, Teronen O, Salo T, Tjaderhane L

The effects of MMP inhibitors on human salivary MNIP activity and caries

progression in rats. J Dent Res 2001;80: 1545-1549.

11. van Strijp AJ, Jansen DC, DeGroot J, Ten Cate JM, Everts V. Host-derived

proteinases and degradation of dentine collagen in situ. Caries Res 2003;37:58-

65.

12. Kinane DF. Metalloproteinases in the pathogenesis of periodontal diseases.

Curr Opin Dent 1992;2:25-32.

13. Ryan ME, Ramamurthy S, Golub LM. Matrix metalloproteinases and their

inhibition in periodontal treatment. Curr Opin Periodontol 1996;3:85-96.

14. Gapski R, Barr JL, Sannent DP, Layher MG, Socransky SS, Giannobile WV.

Effect of systemic matrix metalloproteinase inhibition on perio-dontal wound

repair: A proof of concept trial. J Periodontol 2004;75:441-452.

15. Lauer-Fields JL, Iuska D, Fields GB. Matrix metalloproteinases and collagen

catabolism. Biopolymers 2002;66: 19-32.

16. Seltzer JL, Akers KT, Weingarten H, Grant GA, McCourt OW, Eisen AZ.

Cleavage specificity of human skin type IV collagenase (gelatinase).

Identification of cleavage sites in type I gelatin, with confirmation using

synthetic peptides. J Biol Chem 1990;265:20409-29413.

17. Overall CM. Molecular determinants of metalloproteinase substrate specificity:

Matrix metalloproteinase substrate binding domains, modules, and exosites.

Mol Biotechnol 2002;22:51-86.

18. Pelmenschikov V, Siegbahn PE. Catalytic mechanism of matrix metallo-

proteinases: Two-layered ONTOM study. Inorg Chem 2002;41:5659-5666.

19. Tay FR, Hashimoto M, Pashley DH, Peters MC, Lai SCN, Yiu CKY, Cheong

C. Aging affects two modes of nanoleakage expression in bonded dentin. J

Dent Res 2003;82:537-541.


29

20. Tay FR, Moulding KM, Pashley DR. Distribution of nanofillers from a

simplified-step adhesive in acid conditioned dentin. J Adhes Dent 1999;1: 103-

117.

21. Annstrong SR, Jessop JL, Winn E, Tay FR, Pashley DH. Denaturation

temperatures of dentin matrices. I. Effect of demineralization and dehydration.

J Endod 2006; 32:638-641.

22. Gross J, Nagai Y. Specific degradation of the collagen molecule by tadpole

collagenolytic enzyme. Proc Natl Acad Sci USA 1965;54: 1197-1204.

23. Gendron R, Grenier D, Sorsa T, Mayrand D. Inhibition of the activities of

matrix metalloproteinases 2, 8, and 9 by chlorhexidine. Clin Diag Lab Immunol

1999;6:437-439.

24. Smith PC, Munoz VC, Collados L, Oyarzún AD. In situ detection of

matrixmetalloproteinase-9 (MMP-9) in gingival epithelium in human

periodontal disease. J Periodont Res 2004;39:87-92.

25. Martin-DeLas Heras S, Valenzula A, Overall CM. The matrix

metalloproteinase gelatinase A in human dentine. Arch Oral BioI 2000;45:757-

765.

26. Aimes RT, Quigley JP. Matrix metalloproteinase-2 is an interstitial

collagenase. Inhibitor-free enzyme catalyzes the cleavage of coHagen fibrils

and soluble native type I collagen generating the specific 3/4 and 1/4-length

fragments. J Biol Chem 1995;270:5872-5876.

27. Patterson ML, Atkinson SJ, Knauper V, Murphy G. Specific collagenolysis by

gelatinase A, MMP-2, is detennined by the hemopexin domain and not the

fibronectin-like domain. FEBS Lett 200 I ;503: 158-162.

28. Ward RV, Hembry RM, Reynolds JJ, Murphy G. The purification of tissue

inhibitor of metalloproteinases-2 from its 72 kDa progelatinase complex.

Demonstration of the biochemical similarities of tissue inhibitor of

Chapter 2

30

metalloproteinases-2 and tissue inhibitor of metalloproteinases-l. Biochem J

1991 ;278: 179-187.

29. Palosaari H, Pennington CJ, Lannas M, Edwards DR, Tjäderhane L, Salo T.

Expression profile of matrix. metalloproteinases (MMPs) and tissue inhibitors

of MMPs in mature human odontoblasts and pulp tissue. Eur J Oral Sci 2003;

111: 117-127.

30. Bode W, Fernandez-Catalan C, Grams F, Gomis-Ruth FX, Nagase H,

Tschesche H, Maskos K. Insights into MMP-TIMP interactions. Ann N Y Acad

Sci 1999;878:73-91.

31. Ferrari M, Mason PN, Goracci C, Pashley DH, Tay FR. Collagen degradation in endodontically treated teeth after clinical function. J Dent Res 2004;83:414-419.

31

CHAPTER 3

Long-term degradation of enamel and dentin bonds:

6-year results in vitro vs. in vivo.

Chapter 3

32

Introduction

Tooth-colored materials such as resin-based composites are today the treatment option

of choice for the majority of patients18,22,22,29, primarily due to esthetic demands. It is

well-proven that adhesive restorations are successful e.g. pit and fissure sealings,

direct and indirect resin composites, and bonded indirect ceramic

restorations.19,20,22,28,30,32,36 Durable adhesion to enamel and dentin still represents the

fundamental prerequisite due to polymerization shrinkage of resin-based

composites.2,8,9,21,23,24 Bonding to phosphoric acid etched enamel is widely accepted as

clinically viable,5,6,9,30,33-36 however, in dentin it is not completely clear whether the

etch-and-rinse or the self-etch approach may be more successful in getting durable

bonds.11,15,22,28,30,35 Irrespectively, technique sensitivity with bonded restorations

remains problematic facing a 1:12 failure rate ratio in clinical trials with identical

materials but different clinical operators.12,13

The primary goal of preclinical screening of dental materials should be to mimic the

clinical situation in order to predict clinical behavior. Therefore, researchers try to

predict clinical behavior of restoratives with laboratory in vitro investigations. Of

course, randomized clinical trials remain the ultimate instrument for evaluating dental

restoratives, however, a major problem with clinical trials is that when they give

valuable results after several years of clinical service, the material under investigation

may no longer be available in the market.3,4,24,27,31 Thus, preclinical in vitro

investigations are more important than ever, however, it is still not fully understood

whether these tests are able to reliably predict clinical behavior. So the aim of this

investigation was to compare preclinical results of a large marginal quality in vitro

database with clinically recorded marginal qualities of the same materials.


In vitro study: Thirty-two intact, non-carious, unrestored human third molars,

extracted for therapeutic reasons with patients’ approval, were stored in an aqueous

solution of 0.5% chloramine T at 4°C for up to 30 days. The teeth were debrided of

residual plaque and calculus, and examined to ensure that they were free of defects

under a light microscope at x20 magnification. Standardized class II cavity

preparation (MO, 4mm in width bucco-lingually, 2mm in depth at the bottom of the

proximal box) with proximal margins located 1-2 mm below the cementoenamel

Long-term degradation of enamel and dentin bonds: 6-year results in vitro vs. in vivo

33

junction were performed. The cavities were cut using coarse diamond burs under

profuse water cooling (80 µm diamond, Komet, Lemgo, Germany), and finished

with a 25 µm finishing diamond (one pair of diamonds per four cavities). Inner angles

of the cavities were rounded and the margins were not bevelled to deliver comparable

results to previous experiments.11,15

The prepared cavities (n=8) were treated with two different adhesives according to the

manufacturers’ instructions (n=16 with Syntac, Ivoclar Vivadent, Schaan, Principality

of Liechtenstein, and n=16 with Solobond M, Voco, Cuxhaven, Germany; Table 3.1).

The dentin adhesives and resin composite were polymerized with a Translux CL light-

curing unit (Elipar Trilight, 3M Espe, Seefeld, Germany). The intensity of the light

was checked periodically with a radiometer (Demetron Research Corp, Danbury, CT,

USA) to ensure that 600 mW/cm2 was always delivered during the experiments. The

adhesive was polymerized for 40 s prior to application of the resin composite in all

cases. The resin composites Tetric Ceram (Ivoclar Vivadent; shade A2) and Grandio

(Voco; shade A2) were used for all experimental restorations. Each cavity preparation

was bonded with the respective adhesive and restored incrementally with the resin

composite in layers up to 2 mm thickness. The increments were separately light-cured

for 40 s each with the light source in contact with the edge of the cavity. Prior to the

finishing process, visible overhangs were removed using a posterior scaler (A8 S204S,

Hu-Friedy, Leimen, Germany). Margins were finished with flexible disks (SofLex

Pop-on, 3M ESPE, St. Paul, USA).

After storage in distilled water at 37°C for 21 days, impressions (Provil Novo,

Heraeus Kulzer, Hanau, Germany) of the teeth were taken and a first set of epoxy

resin replicas (Alpha Die, Schuetz Dental, Rosbach, Germany) was made for SEM

evaluation. One pair of groups was subjected to storage in distilled water at 37°C for

2190 days.14 After storage, impressions were taken and thermo-mechanical loading of

specimens was performed in an artificial oral environment (“Quasimodo” chewing

simulator, University of Erlangen, Germany).

Chapter 3

34

In vitro specimens (n=32)

Syntac/Tetric Ceram (n=16) Solobond M/Grandio (n=16)

replicas after 21 days water storage

(baseline / n=16)

replicas after 21 days water storage

(baseline / n=16)

TML

100,000 x 50 N

2,500 x 5°C/55°C

WS

2190 days

TML

100,000 x 50 N

2,500 x 5°C/55°C

WS

2190 days

replicas (n=8) replicas (n=8) replicas (n=8) replicas (n=8)

TML

100,000 x 50 N

2,500 x 5°C/55°C

TML

100,000 x 50 N

2,500 x 5°C/55°C

replicas (n=8) replicas (n=8)

Table 3.1: Experimental setup in laboratory groups (TML: thermomechanical loading / WS: water storage).

Two specimens were arranged in one simulator chamber in proximal contact, similar

to the oral situation with the two restored marginal ridges in a normal intercuspation.15

The two adjacent lateral ridges were occluded against a steatite (a multi-component

semi-porous crystalline ceramic material) antagonist (6 mm in diameter) for 100,000

cycles at 50 N at a frequency of 0.5 Hz. The specimens were subjected to 2,500

thermal cycles between +5°C and +55°C by restoration the chambers with water in

each temperature for 30 s. The mechanical action and the water temperature within the

chewing chambers were checked periodically to ensure a reliable thermo-mechanical

loading (TML) effect. After completion of TML, a second set of replicas was

manufactured for later SEM analysis. The other pair of groups was subjected to TML

only.

In vivo study: In the course of a randomized clinical study with approval of a local

ethics committee, 30 subjects (23 female, 7 male, mean age 32.9 (24-59) years) with a

minimum of two restorations to be replaced in different quadrants received at least

two different Class II restorations (52 MO/OD, 16 MOD or more surfaces, no cusp

replacements) in a random decision.26 Thirty six Grandio restorations were bonded

with Solobond M (Voco) and 32 Tetric Ceram restorations were bonded with Syntac


35

(Ivoclar Vivadent). The cavities were cut using coarse diamond burs under profuse

water cooling (80 µm diamond, Komet, Lemgo, Germany), and finished with a 25 µm

finishing diamond. Inner angles of the cavities were rounded and the margins were not

bevelled. After cleaning and drying under rubber dam isolation (Coltene/Whaledent

Inc., Altstätten, Switzerland), adhesive procedures were performed with Solobond M

(2-step etch-and-rinse adhesive) and Syntac (4-step etch-and-rinse adhesive). The

resin composite materials were applied into the cavity in layers of approximately 2

mm thickness and adapted to the cavity walls with a plugger. Each layer was light

cured for 40 s (Elipar Trilight, 3M Espe, Seefeld, Germany). The occlusal region was

modeled as exactly as possible under intraoral conditions, avoiding visible overhangs.

The light-emission window was placed as close as possible to the cavity margins. The

intensity of the light was checked periodically with a radiometer (Demetron Research

Corp., Danburg, CT, USA) and was found to be consistently above 650 mW/cm2.

As soon as polymerization was completed, the surface of the restoration was

checked for defects and corrected when necessary. Visible overhangs were removed

with a scaler and the rubber dam was removed. Contacts in centric and eccentric

occlusion were checked with foils (Roeko, Langenau, Germany) and adjusted with

finishing diamonds (Komet Dental, Lemgo, Germany), shaped with flexible discs (3M

Dental, St. Paul, USA), super-fine discs (3M Dental, St. Paul, USA) and polishing

brushes (Hawe-Neos Dental, Bioggio, Switzerland). A fluoride varnish (Elmex Fluid,

GABA, Lörrach, Germany) was used to complete the treatment. Impressions were

used to make epoxy replicas (Alpha Die, Schütz Dental, Germany); 22 of them (n=11

per group) were subjected to scanning electron microscopic (SEM) analysis (Table

3.2). The replicas with the longest evaluable margins were selected randomly.

In vivo specimens (n=22)

Syntac/Tetric Ceram (n=11) Solobond M/Grandio (n=11)

replicas at initial recall (baseline / n=11) replicas at initial recall (baseline / n=11)

6 years of clinical function

replicas (n=11) replicas (n=11)

Table 3.2: Procedure for in vivo groups.

Chapter 3

36

All in vitro and in vivo replicas were mounted on aluminum stubs, sputter-coated with

gold and examined under a SEM (Leitz ISI 50, Akashi, Tokyo, Japan) at x200

magnification. SEM examination was performed by one operator having experience

with quantitative margin analysis who was blinded to the restorative procedures. The

marginal integrity between resin composite and enamel was expressed as a percentage

of the entire judgeable margin length. Marginal qualities were classified according to

the criteria “continuous/gap-free margin” and “gap/irregularity”, non-judgeable parts

and artifacts were excluded. Afterwards the percentage “gap-free margins” in relation

to the individual judgeable margins was calculated as marginal integrity. For in vivo

specimens, all non-judgeable parts such as overhangs were excluded with the

remaining criteria having been either “continuous margin” or “gap/irregularity”

(crevice, negative step formation, or marginal fracture in enamel or resin composite).

For better comparison with in vitro results, gap-free margins were added whether

there was a crevice or not. Marginal quality in dentin was not recordable with the

impression/replica technique. However, clinical criteria such as secondary caries were

evaluated.

Statistical analysis was performed using SPSS 14.0 (SPSS Inc., Chicago, IL, USA).

As the majority of groups in each of the two investigations did not exhibit normal data

distribution (Kolmogorov-Smirnov test), non-parametric tests were used (Wilcoxon

matched-pairs signed-ranks test, Mann-Whitney-U test) for pairwise comparisons at

the 95% significance level.

Results

An overview of the results is shown in Table 3.3. In both the in vitro and in vivo

scenario, marginal quality of resin composite restorations was significantly

deteriorated over time (p<0.05; Wilcoxon test).

In the laboratory processed specimens, all restorations initially revealed nearly 100%

gap-free margins (p>0.05; Mann-Whitney U-test). After TML alone, continuous

margins dropped to 87-90% in enamel and 55-66% in dentin (p<0.05; Wilcoxon test;

in dentin with a significantly higher portion of gap-free margins for Syntac/Tetric

Ceram; p<0.05; Mann-Whitney U-test). After water storage for 6 years alone, gap-

free margins dropped to 97-99% in enamel and 67-75% in dentin (p<0.05; Wilcoxon

test; in dentin with a significantly higher portion of gap-free margins for

Syntac/Tetric Ceram; p<0.05; Mann-Whitney U-test). After water storage and TML,


37

marginal quality in enamel ranged from 85-87%, and in dentin 42-52% (p<0.05;

Wilcoxon test; in dentin with a significantly higher portion of gap-free margins for

Syntac/Tetric Ceram; p<0.05; Mann-Whitney U-test). Thermomechanical loading

had a more detrimental effect on marginal quality than 6 years water storage alone

(p<0.05).

In vitro In vivo

Materials Substrate Initial TML WS WS +

TML

Initial 6 years

Syntac +

Tetric Ceram

Enamel 100 90(3) 99 (2) 87 (8) 90 (9) 80 (18)

Dentine 100 66 (11) 75 (10) 52 (16) n.a. n.a.

Solobond M +

Grandio

Enamel 100 87 (4) 97 (2) 85 (9) 86 (10) 74 (19)

Dentine 98 (2) 55 (14) 67 (11) 42 (14) n.a. n.a.

Table 3.3 Overview of results with percentages of gap-free margins in % (SD). TML: Thermomechanical loading; WS: Water storage for 2190 days.

For the in vivo replicas, only marginal quality in enamel was recordeable by the

impression/replica technique. In enamel, continuous margins were initially at 86-

90% and after 6 years of clinical service at 74-80%, however, whether initially (1-

3%) nor after 6 years (4-5%) severe gap formation was found. Non-continuous

margins were attributed to clinical wear and consecutive negative step/crevice

formation/marginal fractures having been slightly more pronounced for Grandio

(p<0.05; Mann-Whitney U-test). For proximal margins being located in dentin,

clinical observations neither revealed severe staining nor secondary caries formation

over 6 years, so the absence of enamel at the bottom of the proximal box did not

affect results.

Chapter 3

38

Discussion

The idea to compare in vitro and in vivo outcome of resin-based composite

restorations is not new. As first approach in the history of the field, Abdalla and

Davidson published their “comparison of the marginal integrity of in vitro and in

vivo Class II composite restorations” in 1993, dealing with microleakage scores in

both laboratory and ex vivo specimens.1 In this paper, microleakage was

substantially more severe in the in vivo group, so the unanimous conclusion was that

it may not be possible to reliably predict clinical behavior of bonded restorations in

the lab. In this context, Peumans et al. reported the clinical outcome of different

adhesives in non-carious cervical lesions, because Class V setups do not provide

macromechanical retention but considerable amounts of dentin margins. However,

Class V trials completely fail to prove whether bonded resin-based composites may

compete with amalgam in posterior cavities under occlusal load. Although in Class II

setups macro-retention is normal, at least in replacement cavities and considerably

less dentin margins are routinely found, there are also advantages. Recording of

postoperative hypersensitivities is a valid instrument to estimate dentin seal, and

secondary caries is a well-suited indicator of loss of bonding performance, especially

in proximal areas of the restorations.

Former publications of our workgroup already dealt with resin composites and their

corresponsing adhesives in both aspects, in vitro and in vivo. The first one aimed to

elucidate in vitro performance of resin composites focusing on microtensile bond

strengths to enamel and dentin, flexural fatigue behavior, and wear behavior.10

Ariston pHc and Solitaire showed some differences compared to other contemporary

resin composites, Ariston provided significantly less adhesion to enamel and dentin,

Solitaire provided inferior flexural fatigue behavior.10 The corresponding part

showed clinical findings of the previously described resin composites being

completely unacceptable.18 So in both cases, clinical performance of resin

composites in Class II cavities was predictable from laboratory results.

However, the literature in the field of adhesive dentistry still requires some evidence

given from in vitro – in vivo comparisons. Based on the previously described

prospective clinical trial, also in vitro experiments with the identical materials were

performed. As artificial aging protocol six years water storage was chosen with and

without thermomechanical loading. TML setups are frequently used to mimic the

clinical situation, however, it is unclear how many cycles mean how much lifetime in


39

the mouth of the patient. Therefore, setups and cycle numbers are subjected to a wide

variation from 4,000 to 1.2 million cycles combined with separate or simultaneous

thermocycling. Derived from Swiss data from the 1980’s, it was widely accepted that

in vitro fatiguing of resin-tooth interfaces for 1.2 million cycles may be somewhat

equivalent to 5 years of clinical service.3,7,20,21 Even for fatigue simulations on core

build-up restorations as postendodontic restorations, this benchmark was used from

time to time.25,26. However, the basis of this approach was just counting chewing

cycles and not a true in vitro – in vivo comparisons of dental restoratives under

simulated and clinical load.

A previous study of our workgroup demonstrated that 100,000 load cycles combined

with 2,500 thermocycles was able to simulate clinical behavior of a 2-year period for

Class I cavities restored with bonded resin composites.11 A distinct advantage for

etch-and-rinse adhesives compared to self-etch adhesives was also shown.11

Also the results of the present in vitro – in vivo comparison revealed a certain

relationship between preclinical and clinical observations. Percentage of gap-free

margins was chosen as a main criterion, because this way it was possible also to

include clinical crevices without detectable gap formations. The present results

indicate that TML alone led to a higher loss of marginal integrity than 6 years’ water

storage (Table 3.3). On the other hand, a combined WS/TML scenario exhibited the

most pronounced effect on marginal quality over time. Nevertheless, in vitro and in

vivo results show a certain similarity. However, this is also attributed to the fact that

gap-free irregularities were also included in “gap-free” margins. Otherwise,

completely perfect margins in vivo (i.e. without any crevice or negative step

formation were ~55% initially and 20-30% after 6 years of clinical service.

Thus, marginal quality prediction is possible from laboratory findings, however,

marginal integrity is only one among several crucial factors responsible for clinical

success or clinical failure over time, meaning that more interfacial gaps after thermal

and mechanical stressing in vitro raise the probability of the same scenario to occur

under clinical circumstances in the oral cavity. However, some important

publications about secondary caries clearly demonstrated that the presence of

marginal gaps in vivo do not necessarily have to be accompanied with secondary

caries.16,17

Chapter 3

40

Altogether, a particular problem with adhesive restorations remains in general: A

given combination of adhesive and resin composite may obtain high percentages of

gap-free margins in vitro, so it may consequently have also a promising clinical

behavior related to marginal quality. The residual question is: What percentage of

marginal quality may be promising or below what borderline is there no guarantee

for clinical success? In the present case, in both groups (Syntac/Tetric Ceram vs.

Solobond M/Grandio) the in vitro results were promising, so also clinical outcome

was sufficient. For inferior materials, not enough data are collected and furthermore

ethically doubtful.

Facing the ultimate question, it has to be taken into account that several studies

dealing with evaluated marginal quality of restorations in vitro were designed in

order to elucidate primarily experimental questions where clinical trials would never

pass an ethics committee. In these cases only in vitro studies are possible, showing

appropriate ways for clinical application of dental materials. Facing different

laboratory approaches to predict clinical behavior such as bond strength testing or

microleakage assessment, thermomechanical loading with a SEM marginal analysis

still is the setup being closest to the clinical situation, however, it is still the most

extensive and time-consuming way of evaluating restorative materials.


41

References

1. Abdalla AI, Davidson CL. Comparison of the marginal integrity of in vivo and

in vitro Class II composite restorations. J Dent 1993;21:158-162.

2. Baratieri LN, Ritter AV. Four-year clinical evaluation of posterior resin-based

composite restorations placed using the total-etch technique. J Esthet Restor

Dent 2001;13:50-57.

3. Bortolotto T, Onisor I, Krejci I. Proximal direct composite restorations and

chairside CAD/CAM inlays: Marginal adaptation of a two-step self-etch

adhesive with and without selective enamel conditioning. Clin Oral Investig

2007;11:35-43.

4. da Cunha Mello FS, Feilzer AJ, de Gee AJ, Davidson CL. Sealing ability of

eight resin bonding systems in a Class II restoration after mechanical fatiguing.

Dent Mater 1997;13:372-376.

5. De Munck J, Van Landuyt K, Peumans M, Poitevin A, Lambrechts P, Braem

M, Van Meerbeek B. A critical review of the durability of adhesion to tooth

tissue: methods and results. J Dent Res 2005;84:118-132.

6. De Munck J, Van Meerbeek B, Yoshida Y, Inoue S, Vargas M, Suzuki K,


bonded to dentin. J Dent Res 2003;82:136-140.

7. Dietschi D, Herzfeld D. In vitro evaluation of marginal and internal adaptation

of class II resin composite restorations after thermal and occlusal stressing. Eur

J Oral Sci 1998;106:1033-1042.

8. Feilzer AJ, de Gee AJ, Davidson CL. Setting stress in composite resin in

relation to configuration of the restoration. J Dent Res 1987;66:1636-1639.

9. Ferrari M, Yamamoto K, Vichi A, Finger WJ. Clinical and laboratory

evaluation of adhesive restorative systems. Am J Dent 1994;7:217-219.

10. Frankenberger R, Garcia-Godoy F, Lohbauer U, Petschelt A, Krämer N.

Evaluation of resin composite materials. Part I: in vitro investigations. Am J

Dent 2005;18:23-27.

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11. Frankenberger R, Krämer N, Lohbauer U, Nikolaenko SA, Reich SM.

Marginal integrity: is the clinical performance of bonded restorations

predictable in vitro? J Adhes Dent 2007;9 Suppl 1:107-116.

12. Frankenberger R, Krämer N, Petschelt A. Technique sensitivity of dentin

bonding: effect of application mistakes on bond strength and marginal

adaptation. Oper Dent 2000;25:324-330.

13. Frankenberger R, Reinelt C, Petschelt A, Krämer N. Operator vs. material

influence on clinical outcome of bonded ceramic inlays. Dent Mater

2009;25:960-968.

14. Frankenberger R, Strobel WO, Lohbauer U, Krämer N, Petschelt A. The effect

of six years of water storage on resin composite bonding to human dentin. J

Biomed Mater Res B Appl Biomater 2004;69:25-32.

15. Frankenberger R, Tay FR. Self-etch vs etch-and-rinse adhesives: effect of

thermo-mechanical fatigue loading on marginal quality of bonded resin

composite restorations. Dent Mater 2005;21:397-412.

16. Kidd EA, Beighton D. Prediction of secondary caries around tooth-colored

restorations: a clinical and microbiological study. J Dent Res 1996;75:1942-

1946.

17. Kidd EA, Toffenetti F, Mjör IA. Secondary caries. Int Dent J 1992;42:127-138.

18. Krämer N, Garcia-Godoy F, Frankenberger R. Evaluation of resin composite

materials. Part II: in vivo investigations. Am J Dent 2005;18:75-81.

19. Krämer N, Reinelt C, Richter G, Petschelt A, Frankenberger R. Nanohybrid vs.

fine hybrid composite in Class II cavities: clinical results and margin analysis

after four years. Dent Mater 2009;25:750-759.

20. Lutz F, Krejci I. Resin composites in the post-amalgam age. Compend Contin

Educ Dent 1999;20:1138-44, 1146, 1148.

21. Lutz F, Krejci I, Barbakow F. Quality and durability of marginal adaptation in

bonded composite restorations. Dent Mater 1991;7:107-113.


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22. Manhart J, Chen H, Hamm G, Hickel R. Buonocore Memorial Lecture. Review

of the clinical survival of direct and indirect restorations in posterior teeth of

the permanent dentition. Oper Dent 2004;29:481-508.

23. Mjör IA. The reasons for replacement and the age of failed restorations in

general dental practice. Acta Odontol Scand 1997;55:58-63.

24. Mjör IA, Toffenetti F. Secondary caries: a literature review with case reports.

Quintessence Int 2000;31:165-179.

25. Naumann M, Preuss A, Frankenberger R. Load capability of excessively flared

teeth restored with fiber-reinforced composite posts and all-ceramic crowns.

Oper Dent 2006;31:699-704.

26. Needleman I, Worthington H, Moher D, Schulz K, Altman DG. Improving the

completeness and transparency of reports of randomized trials in oral health:

the CONSORT statement. Am J Dent 2008;21:7-12.

27. Nikolaenko SA, Lohbauer U, Roggendorf M, Petschelt A, Dasch W,

Frankenberger R. Influence of c-factor and layering technique on microtensile

bond strength to dentin. Dent Mater 2004;20:579-585.

28. Opdam NJ, Roeters FJ, Feilzer AJ, Verdonschot EH. Marginal integrity and

postoperative sensitivity in Class 2 resin composite restorations in vivo. J Dent

1998;26:555-562.

29. Ottenga ME, Mjor I. Amalgam and composite posterior restorations:

curriculum versus practice in operative dentistry at a US dental school. Oper

Dent 2007;32:524-528.

30. Peumans M, Kanumilli P, De MJ, Van Landuyt K., Lambrechts P, Van

Meerbeek B. Clinical effectiveness of contemporary adhesives: A systematic

review of current clinical trials. Dent Mater 2005;21:864-881.

31. Roulet JF. Marginal integrity: clinical significance. J Dent 1994;22 Suppl 1:S9-

12.

32. Tay FR, Frankenberger R, Carvalho RM, Pashley DH. Pit and fissure sealing.

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Bonding of bulk-cured, low-filled, light-curing resins to bacteria-contaminated

uncut enamel in high c-factor cavities. Am J Dent 2005;18:28-36.

33. Van Meerbeek B, Kanumilli P, De Munck J, Van Landuyt K, Lambrechts P,

Peumans M. A randomized controlled study evaluating the effectiveness of a

two-step self-etch adhesive with and without selective phosphoric-acid etching

of enamel. Dent Mater 2005;21:375-383.

34. Van Meerbeek B, Kanumilli PV, De Munck J, Van Landuyt K, Lambrechts P,

Peumans M. A randomized, controlled trial evaluating the three-year clinical

effectiveness of two etch & rinse adhesives in cervical lesions. Oper Dent

2004;29:376-385.

35. Van Meerbeek B, Perdigao J, Lambrechts P, Vanherle G. The clinical

performance of adhesives. J Dent 1998;26:1-20.

36. Van Meerbeek B, Peumans M, Gladys S, Braem M, Lambrechts P, Vanherle

G. Three-year clinical effectiveness of four total-etch dentinal adhesive

systems in cervical lesions. Quintessence Int 1996;27:775-784.

45

CHAPTER 4

Fatigue behavior of dental resin composites: Flexural fatigue in vitro vs. six years in vivo

Chapter 4

46

Introduction

During the last decades, resin-based composite materials were optimized with a

special focus on amalgam replacement.1-4 Thus, resin composites were more and

more improved for application even in occlusally stressed areas.5-10 In order to

simulate clinical conditions in the laboratory, it is important to observe fatigue

phenomena as an important factor during biodegradation processes of dental

biomaterials.11-15

In former times that have been characterized by less effective adhesive technology

and higher polymerization stresses generated by older resin composite materials, gap

formation and recurrent decay were the predominant reason for failures of bonded

resin composite restorations.5,16 Today, this is still true, but fatigue fractures after

several years under clinical load gain importance as reason for failure.2-4, 9,10,22

Fatigue in dental restoratives is influenced by corrosive water attack at 37°C and by

subcritical cyclic masticatory forces having been estimated to be 5-20 MPa.6,17,18

Contemporary approaches to fatigue principles describe fracture processes in three

stages: crack initiation, slow crack growth, fast fracture.6,17,18 Especially crack

initiation time and slow crack growth time are determining fatigue resistance of an

individual material. Crack initiation originates from surface and subsurface

microcracks, porosities, or filler particles.11,14,15,19 Cyclic loading is able to drive a

crack, and additional water exposure causes a variety of further weakening effects on

resin composite materials, i.e. degradation of the filler–matrix interface, swelling, or

visco-elastic effects on the matrix which all are able to accelerate slow crack

growth.11,14,15,19

Today it is still not fully understood whether and to what extent we are able to predict

clinical behavior of dental biomaterials such as resin composites based on in vitro

research. Therefore, the aim of this study was to compare fatigue behavior of two

different resin composites using an array of laboratory parameters (Young's modulus,

flexural strength, flexural fatigue limit) and analyze resin composite restorations in the

course of a randomized prospective clinical long-term trial over 6 years. This is the

maxiumum approach to thoroughly evaluate dental materials simultaneously in vitro

and in vivo.


47


Grandio

Grandio (shade A3, Voco, Germany), a nanofilled hybrid resin composite, was used in

this study. The resin matrix consisted of bisphenol glycidyl methacrylate (BisGMA)

and triethylene glycol dimethacrylate (TEGDMA), mixed in a ration of 3:1. Further

71.4 vol% (87 wt%) inorganic fillers were compounded, being 30% nanosized fillers.

Camphoroquinone served as photoinitiator. Grandio is clinically indicated as a

universal composite for anterior and posterior restorations.

Tetric Ceram

The light-curing dental restorative Tetric Ceram (shade A3, Ivoclar Vivadent,

Liechtenstein) was used in this study. The material was based on a bisphenol glycidyl

methacrylate (BisGMA)/urethane dimethacrylate (UDMA)/triethylene glycol

dimethacrylate (TEGDMA) resin matrix, with camphoroquinone as photoinitiator and

60 vol % (78 wt%) inorganic filler content. Tetric Ceram is clinically indicated as a

universal fine particle hybrid resin composite for anterior and posterior restorations.

Specimen preparation

Rectangular specimens with the dimension 2 x 2 x 25 mm were produced using a

metal/glass mold and light-curing on five overlapping spots of 8 mm diameter. The

upper and lower side of the bar were cured with a commercial halogen light curing

unit (Elipar Trilight (750 mW/ cm²), 3M Espe, Germany). The illumination time on a

single spot was 40s. The procedure followed the manufacturers’ recommendation and

ISO 4049 standard. The specimen flanges were ground under an angle of 45° using

SiC paper (1200 grit). All specimens were stored for 14 days in distilled water at

37°C, deviating from the ISO 4049 standard.

Elastic Modulus (EM)

To determine the elastic response of the composites, the Young’s moduli were

calculated from load-displacement curves in a four-point bending test setup. The

specimens (n=10) were positioned in the test rig (distance between the lower supports:

20mm, upper fins: 10mm) of a universal testing machine (Zwick Z2.5, Zwick, Ulm,

Germany) and loaded up to 20 MPa with a crosshead speed of 0.75 mm/minute. By

the linear-elastic relationship between stress (in the range between 10 to 20 MPa) and

Chapter 4

48

strain the EM was calculated. An extensometer served to measure the true deflection

(system compliance) directly at the lower side of the specimen.

Fracture strength (FS)

To evaluate the initial flexural strength (FS), the four-point bending test was used (n =

15). Fifteen bars of each material were brought into the four-point test rig and loaded

until fracture with a crosshead speed of 0.75 mm/minute in a universal testing

machine (Z 2.5, Zwick, Germany).6,17,18,22 The measurements were carried out in

distilled water at 37°C.

Flexural Fatigue Limit (FFL)

The flexural fatigue limits (FFL) of the composite materials were determined for 105

cycles under equivalent test conditions at a frequency of 0.5 Hz (n=25). The

“staircase” approach was used for fatigue evaluation.12,13,20,22 For every cycle the

stress alternated between 1 MPa and the maximum stress. Tests were conducted

sequentially, with the maximum applied stress in each succeeding test being increased

or decreased by a fixed increment (5 MPa) of stress, according to whether the

previous test resulted in failure or not. The first specimen was tested at approximately

50% of the initial flexural strength value. As the data are cumulated around the mean

stress, the number of specimens required is less than with other methods (n=25). The

test stopped at a certain level below which no further failure occured. 6,12,13-15

The mean flexural fatigue limit (FFL) was determined using Eq. 1 and standard

deviation, using Eq. 2, respectively:

5.00

i

i

n

indXFFL (1)

029.062.1

2

22

i

iii

n

innindSD (2)

where X0 is the lowest stress level considered in the analysis and d is the fixed stress

increment.6,13,17 To determine the FFL, the analysis of the data was based on the least

frequent event (failures versus non failures). In Eq. 1 a negative sign was used when


49

the analysis was based on failures. The lowest stress level considered was designated

as i = 0, the next as i = 1, and so on, and ni was the number of failures or non-failures

at the given stress level. 6,13,17

Statistical treatment

The strength data (FS and FFL) were statistically treated using a one-way ANOVA

test followed by a modified LSD post-hoc routine (p < 0.05).

Clinical study

In the course of a randomized clinical study with approval of a local ethics committee

(University of Erlangen, Germany), 30 subjects (23 female, 7 male, mean age 32.9 (24-

59) years) with a minimum of two restorations to be placed in different quadrants

received at least two different Class II restorations (52 MO/OD, 16 MOD or more

surfaces, no cusp replacements) in a random decision.26 Thirty six Grandio restorations

were bonded with Solobond M (Voco) and 32 Tetric Ceram restorations were bonded

with Syntac (Ivoclar Vivadent). The cavities were cut using coarse diamond burs under

profuse water cooling (80 µm diamond, Komet, Lemgo, Germany), and finished with a

25 µm finishing diamond. Inner angles of the cavities were rounded and the margins

were not bevelled. After cleaning and drying under rubber dam isolation

(Coltene/Whaledent Inc., Altstätten, Switzerland), adhesive procedures were performed

with Solobond M (2-step etch-and-rinse adhesive) and Syntac (4-step etch-and-rinse

adhesive). The resin composite materials were applied into the cavity in layers of

approximately 2 mm thickness and adapted to the cavity walls with a plugger. Each

layer was light cured for 40 s (Elipar Trilight, 3M Espe, Seefeld, Germany). The

occlusal region was sculpted as exactly as possible under intraoral conditions, avoiding

visible overhangs. The light-emission window was placed as close as possible to the

cavity margins. The intensity of the light was checked periodically with a radiometer

(Demetron Research Corp., Danburg, CT, USA) and was found to be consistently above

650 mW/cm2. Visible overhangs were removed with a scaler and the rubber dam was

removed. Contacts in centric and eccentric occlusion were checked with foils (Roeko,

Langenau, Germany) and adjusted with finishing diamonds (Komet Dental, Lemgo,

Germany), shaped with flexible discs (3M Dental, St. Paul, USA), super-fine discs (3M

Dental, St. Paul, USA) and polishing brushes (Hawe-Neos Dental, Bioggio,

Switzerland). A fluoride varnish (Elmex Fluid, GABA, Lörrach, Germany) was applied

with a foam pellet (Pele-Tim, Voco, Cuxhaven, Germany) to complete the treatment.

Chapter 4

50

Impressions (Dimension Penta and Garant, 3M ESPE, Seefeld, Germany) were taken at

baseline, after 4 and 6 years and were used to make epoxy replicas (Alpha Die, Schütz

Dental, Germany) for x30 magnification cast analysis under a scanning electron

microscope (SEM) evaluating fatigue characteristics such as voids, chippings or cracks

within the resin composite, and 22 of them (n=11 per group) were subjected to SEM

margin analysis at x200. The replicas with the longest evaluable margins were selected

randomly. All in vitro and in vivo replicas were mounted on aluminum stubs, sputter-

coated with gold and examined under a SEM (Leitz ISI 50, Akashi, Tokyo, Japan) at

x200 magnification. SEM examination was performed by one operator having

experience with quantitative margin analysis who was blinded to the restorative

procedures. The marginal quality between resin composite and enamel was expressed as

percentage of the entire judgeable margin length, i.e. margins having been accessible by

the impression material in vivo. Marginal qualities were classified according to the

criteria “continuous/gap-free margin” and “gap/irregularity” for another study, here the

focus was set on marginal breakdown and cracks. Non-judgeable parts and artifacts

were excluded. Afterwards the percentage of “marginal fracture areas” in relation to the

individual judgeable margin was calculated as marginal fracture score. For better

comparison with in vitro results, gap-free margins were scored whether there was a

negative step or not.

Statistical analysis was performed using SPSS 14.0 (SPSS Inc., Chicago, IL, USA).

As the majority of groups in each of the two investigations did not exhibit normal data

distribution (Kolmogorov-Smirnov test), non-parametric tests were used (Wilcoxon

matched-pairs signed-ranks test, Mann-Whitney-U test) for pairwise comparisons at

the 95% significance level.

Results

Results of the laboratory part are displayed in Table 1. It was shown that Grandio

exhibited a significantly higher elastic modulus (p<0.05) and flexural fatigue limit

(p<0.05). Initial fracture strengths were not significantly different (p>0.05). Results

of the clinical investigation are shown in Tables 3 and 4. Irrespective of the resin

composite used, significant changes over time were found for all criteria applied in

clinical examinations (Friedman test; p<0.05). The main reason for the degradation

of the occlusal surface of the restorations was an increased surface roughness (41%


51

after 4 and 27% after 6 years) and more chipping especially in the proximal ridge

area (36% after 4 and 35 % after 6 years; Fig. 2). Voids were obvious mainly after 6

years (clinically 44% and SEM 73 %; Table 3 and 4). Except for the criterion “wear”

after 6 years (Pearson correlation coefficient 0.671) no correlation was calculated

between the clinical and cast evaluation (p>0.05; two-tailed correlation). Neither

restorative materials nor localization of the restorations (upper or lower jaw) had a

significant influence on the surface degradation at baseline and after 4/6 years

(p>0.05; Mann‐Whitney U-test). However, molar restorations performed worse than

premolar restorations regarding the clinical criterion “wear” after both 4 and 6 years

(premolars: 22% bravo after 4 and 44% after 6 years vs. molars: 61% bravo after 4

and 69% after 6 years).

Criteria and results of the x30 magnification cast analysis under the SEM are

displayed in Table 4. Here also, no significant differences were computed between the

materials Grandio and Tetric Ceram. Only in the x200 SEM analysis of restoration

margins, marginal breakdown areas were more often recorded for Tetric Ceram

(7.9%) vs. Grandio (4.8%). Examples for clinical images and corresponding SEM

pictures are explained in Figures 1-5. Predominant findings in both species of

investigations were slightly exposed restoration margins after 6 years of clinical

service due to mainly wear in the contact free areas (CFA; Figures 1b, 2b, 3b, 4b) and

more roughened surfaces in the occlusal contact areas (OCA).

Discussion

Biomaterials labs daily try to simulate clinical conditions in order to predict clinical

behavior of dental biomaterials.5,20-23 This is the only and most important justification

of the existence of this kind of laboratory. Without clinical relevance, what should be

the reason for in vitro research?

Beside other co-factors for clinical success with resin-based composites such as

marginal integrity, wear, biocompatibility and absence of postoperative

hypersenstivities2,3,9,10,24,25, fatigue is a major factor during biodegradation of

restorative materials. Fatigue loading has gained importance in materials science not

only regarding adhesion,5,22-24,26 since even for restorative materials the initially high

flexural strength values suffered a reduction of 50% after fatigue loading.

Chapter 4

52

The chosen in vitro setup of the present study was shown to give reliable and

reasonable results in several studies with an array of different classes of

materials.14,15,30-32 On first sight it may be awkward to evaluate a restorative material

as simple beam in a 4-point bending device, since the same material is always

adhesively bonded under clinical conditions. However, results from previous studies

as well as the present results demonstrate that FFL analysis of dental biomaterials

gives important results for their intraoral use in stress-bearing restorations.14,15,30-32

Facing the present results in both aspects in vitro and in vivo, it is crucial to achieve

equal or even similar test conditions in both setups.

One fundamental point here is light polymerization. On one hand, we had to stick to

previously published curing protocols to get comparable results to former

investigations;6,13,17 on the other hand, light-curing under clinical conditions should at

least be achievable. So it might be a consequence that in vitro specimens are still more

intensively light-cured than the same materials having been applied in vivo. The same

is true for storage times in vitro, so we used the well-established protocol of 2 weeks

water storage6,13,17 whereas loading began immediately intraorally.

Another critical point in the present simulation of clinical circumstances is the in vitro

setup in general. In vitro we used simple beams having been mechanically loaded as

bars and not as bonded resin composite restorations being stabilized inside the tooth.

Here, thermomechanical loading may be much closer to the real clinical situation,

however, also in a chewing simulation chamber with more complex and individually

styled restorations in natural teeth forces are more complex to handle.23

The normal way of testing dental biomaterials is to conduct preclinical issues first and

then carry out clinical trials. However, when in vitro and in vivo research is carried

out simultaneously as in the present paper, an appropriate comparison of both ways of

investigations is possible.4,23,26 So since 1998, we decided to perform in vitro and in

vivo research with the same materials simultaneously with both resin composites and

ceramic materials. This may be the most appropriate way to explain what happened

clinically and why it happened as well. Furthermore it is easier to determine

predictable parameters in the laboratory.

Compared to other classes of restorative materials such as glass ionomer cements,

both resin composites under investigation provided sufficient initial flexural strengths


53

of >100 MPa. However, both Young’s modulus and flexural fatigue limit were

significantly higher for Grandio. In the present study, FFL of investigated materials

was 63 MPa for Grandio and 44 MPa for Tetric Ceram. These findings were not

statistically different at the initial stage of flexural strength. After mechanical fatigue,

the FFL of Grandio was 55% of the initial flexural strength, whereas Tetric Ceram

dropped to 45% of its initial flexural strength values. Regarding both aspects,

physicochemical characteristics were slightly better for Grandio which also exhibited

a somewhat increased filler load of 87%wt vs. 78%wt in Tetric Ceram. Facing the

overall clinical performance of both materials, slightly superior materials

characteristics for Grandio did not result in a significantly better clinical outcome, at

least after 6 years of clinical service. Only when dental restorative materials have

flexural fatigue limits of less than 20 MPa, it seems to be critical for clinical survival

with more frequent catastrophic bulk fractures even after considerably shorter clinical

observation periods.4 In a previous study under identical test conditions in vitro as

well as in vivo, Solitaire provided a FFL of 18 MPa which lead to unacceptably high

marginal and bulk fracture rates in vivo in the course of a prospective clinical study.4

Finally, the significantly higher FFL for Grandio when compared to Tetric Ceram led

to clinical consequences having been detected under the SEM during the marginal

quality evaluation: Grandio restorations exhibited significanlty less marginal

breakdown (4.8%) than Tetric Ceram restorations (7.9%). Although Grandio

restorations showed inferior marginal quality in a previous clinical trial,26 they

performed slightly better according to marginal fatigue characteristics in the present

investigation. However, these are microscopic findings suffering limited clinical

impact for the present observation period of 6 years when it comes to clinical survival

as the major criterion.

Up to now, wear was the predominantly detected degradation factor over time.14,15,25

In contrast, the influence of the clinical operator is still a major factor for clinical

success, maybe more than the difference between an FFL of 40 MPa vs. 50 MPa.33

Chapter 4

54

References

1. Kleverlaan CJ, Feilzer AJ. Polymerization shrinkage and contraction stress of

dental resin composites. Dent Mater 2005;21:1150-1157.

2. Hickel R, Manhart J, Garcia-Godoy F. Clinical results and new developments

of direct posterior restorations. Am J Dent 2000;13:41D-54D.

3. Hickel R, Manhart J. Longevity of restorations in posterior teeth and reasons

for failure. J Adhes Dent 2001;3:45-64.



5. Lambrechts P, Braem M, Vanherle G. Buonocore memorial lecture. Evaluation

of clinical performance for posterior composite resins and dentin adhesives.

Oper Dent 1987;12:53-78.

6. Lohbauer U, von der Horst T, Frankenberger R, Krämer N, Petschelt A.

Flexural fatigue behavior of resin composite dental restoratives. Dent Mater

2003;19:435-440.

7. Manhart J, Kunzelmann KH, Chen HY, Hickel R. Mechanical properties and

wear behavior of light-cured packable composite resins. Dent Mater

2000;16:33-40.

8. Manhart J, Chen HY, Hickel R. The suitability of packable resin-based

composites for posterior restorations. J Am Dent Assoc 2001;132:639-645.




10. Manhart J, Chen HY, Hickel R. Clinical evaluation of the posterior composite

Quixfil in class I and II cavities: 4-year follow-up of a randomized controlled

trial. J Adhes Dent 2010;12:237-243.

11. Braem M, Lambrechts P, Van Doren V, Vanherle G. The impact of composite

structure on its elastic response. J Dent Res 1986;65:648-653.


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12. Braem M, Davidson CL, Vanherle G, Van Doren V, Lambrechts P. The

relationship between test methodology and elastic behavior of composites. J

Dent Res 1987;66:1036-1039.

13. Braem MJ, Davidson CL, Lambrechts P, Vanherle G. In vitro flexural fatigue

limits of dental composites. J Biomed Mater Res 1994;28:1397-1402.

14. Keulemans F, Palav P, Aboushelib MM, van Dalen A, Kleverlaan CJ, Feilzer

AJ. Fracture strength and fatigue resistance of dental resin based composites.

Dent Mater 2009;25:1433-1441.

15. Turssi CP, Ferracane JL, Ferracane LL. Wear and fatigue behavior of nano-

structured dental resin composites. J Biomed Mater Res B Appl Biomater

2006;78:196-203.

16. Wilder AD, Jr., May KN, Jr., Bayne SC, Taylor DF, Leinfelder KF. Seventeen-

year clinical study of ultraviolet-cured posterior composite Class I and II

restorations. J Esthet Dent 1999;11:135-142.

17. Lohbauer U, Frankenberger R, Krämer N, Petschelt A. Time-dependent

strength and fatigue resistance of dental direct restorative materials. J Mater

Sci Mater Med 2003;14:1047-1053.

18. Lohbauer U, Rahiotis C, Krämer N, Petschelt A, Eliades G. The effect of

different light-curing units on fatigue behavior and degree of conversion of a

resin composite. Dent Mater 2005;21:608-615.

19. Abe Y, Braem MJ, Lambrechts P, Inoue S, Takeuchi M, Van MB. Fatigue

behavior of packable composites. Biomaterials 2005;26:3405-3409.

20. Drummond JL, Lin L, Al-Turki LA, Hurley RK. Fatigue behaviour of dental

composite materials. J Dent 2009;37:321-330.



Chapter 4

56



Dent 2005;18:23-27.







25. Gaengler P, Hoyer I, Montag R, Gaebler P. Micromorphological evaluation of

posterior composite restorations - a 10-year report. J Oral Rehabil

2004;31:991-1000.

26. Garcia-Godoy F, Krämer N, Feilzer AJ, Frankenberger R. Long-term

degradation of enamel and dentin bonds: 6-year results in vitro vs. in vivo.

Dent Mater 2010;26:1113-1118.

27. Braem MJ, Lambrechts P, Gladys S, Vanherle G. In vitro fatigue behavior of

restorative composites and glass ionomers. Dent Mater 1995;11:137-141.

28. Krämer N, Reinelt C, Garcia-Godoy F, Taschner M, Petschelt A,

Frankenberger R. Nanohybrid composite vs. fine hybrid composite in extended

class II cavities: clinical and microscopic results after 2 years. Am J Dent

2009;22:228-234.




30. Drummond JL. Cyclic fatigue of composite restorative materials. J Oral

Rehabil 1989;16:509-520.

31. Drummond JL, Bapna MS. Static and cyclic loading of fiber-reinforced dental

resin. Dent Mater 2003;19:226-231.


57

32. Ferracane JL, Condon JR. In vitro evaluation of the marginal degradation of

dental composites under simulated occlusal loading. Dent Mater 1999;15:262-

267.

33. Frankenberger R, Reinelt C, Petschelt A, Krämer N. Operator vs. material

influence on clinical outcome of bonded ceramic inlays. Dent Mater

2009;25:960-968.

Chapter 4

58

59

CHAPTER 5

Microhybrid vs. nanohybrid resin composites in extended cavities after 6 years.

Chapter 5

60

Introduction

Although a prospective clinical trial is not an in vitro study as reflected by the topic of

the present thesis, clinical data are the one and only desirable comparison tool for

dental restorative materials. Moreover, they can be linked to preclinically evaluated in

vitro data. Therefore, it is important to compare the presented in vitro data with

clinical outcome of directly bonded dental biomaterials such as resin-based

composites.

Cavitated carious lesions are today predominantly restored by use of resin

composites.1-4 Durable adhesion to tooth hard tissues still is the fundamental

prerequisite for pit and fissure sealings, direct and indirect resin composites, and

bonded all-ceramic restorations 5-9. When adhesion mechanisms fail, gap formation

and secondary caries corroborate clinical success of restorations 10-13.

Bonding to enamel is clinically durable at least when the etch-and-rinse approach is

applied,1,6,12,14-16 dentin still provides inferior adhesion,8,9,13,17-20 but also clinically

acceptable sealing is obtainable to limit the occurrence of postoperative

hypersensitivity.4,6,7,11,12,21,22 Although bonded resin composites have proven to

durably seal dentin especially with multi-step adhesives,14,17,19,23-25 it is still unclear

whether it is possible to maintain a stable proximal seal in Class II cavities with

proximal margins extending beyond the amelocemental junction. In vitro studies give

varying results after thermomechanical loading and/or long-term storage, mostly with

distinct advantages for two- or three-step adhesives compared to simplified adhesive

systems.23,24,26-28 Prospective clinical trials remain ultimate instruments, but preclinical

in vitro investigations are still needed for experimental questions and preclinical

screening.17,26,29

One of the most severe problems of clinical trials of dental materials is apparent: while

affording acceptable results after some years of clinical service, there is a certain risk

that the adhesive and/or resin composite under investigation is not in the market

anymore.1,11,12,15,16,30,31 However, it is not a matter of course that this kind of clinical

trial reveals favorable results, so also catastrophic outcomes were observed when

fundamental prerequisites are neglected such as hygroscopic expansion or flexural

fatigue behavior.15 And it may be still true that, e.g. amalgam, may be superior to resin

composites for restoration of very extended defects,21

Microhybrid vs. nanohybrid resin composites in extended cavities after 6 years

61

Research and development of resin-based composites during the last decade generated

different subspecies of restorative materials, such as hybrid resin composites, fine

hybrid resin composites, nanohybrid resin composites, or even nano resin composites

(Filtek Supreme XTE, 3M ESPE, Seefeld, Germany). Especially the latter ones

entered the market with claims of less polymerization shrinkage, lowered shrinkage

stress and even higher wear resistance.32-37 In most of the cases, however, a truly better

clinical outcome is not proven. On the other hand, it is stated from recent in vivo

results that modern nano hybrid resin composite may provide an enamel-like wear

behavior.38,39

Therefore, the aim of this clinical trial was to investigate two different restorative

material systems (i.e. adhesive and resin composite) in extended Class II cavities over

6 years in order to observe differences between conventional (Tetric Ceram) and

partially nanofilled (Grandio) resin composites. The null-hypothesis tested was that

there would be no difference between the different resin composites with their

respective adhesives under investigation.

Methods and Materials

Patients selected for this study met the following criteria: 1) Absence of pain from the

tooth to be restored; 2) possible application of rubber dam during luting of restoration;

3) no further restorations planned in other posterior teeth; 4) high level of oral

hygiene; 5) absence of any active periodontal and pulpal desease; 6) restorations

required in two different quadrants (split mouth design).

Thirty patients (23 female, 7 male, mean age 32.9 (24-59) years) with a minimum of

two restorations to be replaced in different quadrants received at least two different

restorations in a random decision according to recommendations of the CONSORT

statement.40 Thirty-six Grandio restorations were bonded with Solobond M (Voco,

Cuxhaven, Germany) and 32 Tetric Ceram restorations were bonded with Syntac

(Ivoclar Vivadent, Schaan, Liechtenstein). All restorations (only Class II, 52 MO/OD,

16 MOD or more surfaces, no cusp replacements) were re-restorations made by one

dentist in a private practice (31 upper bicuspids, 12 upper molars, 14 lower bicuspids,

11 lower molars). Reasons for replacement were caries (n=19), insufficient esthetics

(n=2), and secondary caries (n=47). For all teeth receiving restorations, current X-rays

(within 6 months of the procedure) were present. After evaluating the radiographs, 53

Chapter 5

62

cavities (78%) were treated as caries profunda. Twenty-four cavities (35%) revealed

no enamel at the floor of the proximal box, while 33 cavities (49%) exhibited a

proximal enamel width of <0.5 mm.

All restorations were inserted in permanent vital teeth without pain symptoms. An

extension for prevention was disregarded for maximal substance protection; however,

the majority of restorations were previously prepared with undercuts for amalgam

retention. The cavities were cut using coarse diamond burs under profuse water cooling

(80 µm diamond, Komet, Lemgo, Germany), and finished with a 25 µm finishing

diamond. Inner angles of the cavities were rounded and the margins were not bevelled.

After cleaning and drying under rubber dam isolation (Coltene/Whaledent Inc.,

Altstätten, Switzerland), adhesive procedures were performed with Solobond M (2-step

etch-and-rinse adhesive) and Syntac (4-step etch-and-rinse adhesive). The resin

composite materials were applied into the cavity in layers of approximately 2 mm

thickness and adapted to the cavity walls with a plugger. Each layer was light cured for

40 seconds (Elipar Trilight, 3M ESPE, Seefeld, Germany). The occlusal region was

modeled as exactly as possible under intraoral conditions, avoiding visible overhangs.

The light-emission window was placed as close as possible to the cavity margins. The

intensity of the light was checked periodically with a radiometer (Demetron Research

Corp., Danburg, CT, USA) and was found to be constantly above 650 mW/cm2.

As soon as polymerization was completed, the surface of the restoration was checked for

defects and corrected when necessary. Visible overhangs were removed with a scaler

and the rubber dam was removed. Contacts in centric and eccentric occlusion were

checked with foils (Roeko, Langenau, Germany) and adjusted with finishing diamonds

(Komet Dental, Lemgo, Germany), shaped with flexible discs (3M Dental, St. Paul,

USA), super-fine discs (3M Dental, St. Paul, USA) and polishing brushes (Hawe-Neos

Dental, Bioggio, Switzerland). A fluoride varnish (Elmex Fluid, GABA, Lörrach,

Germany) was used to complete the treatment.

At the initial recall (baseline, i.e. within 2 weeks), and after 6 months, 1, 2, 4, and 6

years, all restorations were assessed according to the modified United States Public

Health Service (USPHS) criteria (Tables 5.1 and 5.2) by two independent

investigators using loupes with x3.5 magnification, mirrors, probes, bitewing

radiographs, impressions (Dimension Penta and Garant, 3M-ESPE, Seefeld,

Germany), and intraoral photographs. Replicas were collected for later marginal and


63

wear analysis (studies in preparation). Recall assessments were not performed by the

clinician who initially placed the restorations.

Statistical appraisal was computed with SPSS for Windows XP 14.0 (SPSS Inc.,

Chicago, IL, USA). Statistical unit was one tooth, differences between groups were

evaluated using Mann-Whitney U-test, changes over time were calculated with the

Friedman test (p=0.05).

Modified

criteria Description

Analogous USPHS

criteria

“Excellent” Perfect

“alpha” “Good”

Slight deviations from ideal performance,

correction possible without damage to tooth or

restoration

“Sufficient”

Few defects, correction impossible without

damage to tooth or restoration.

No negative effects expected “bravo”

“Insufficient”

Severe defects, prophylactic removal for

prevention of severe failures “charlie”

“Poor” Immediate replacement necessary “delta”

Table 5.1: Evaluated clinical codes and criteria.

Results

The overall success rate was 100% after 6 years of clinical service, while drop out of

patients was 0%. Results of the clinical investigation are displayed in Tables 5.2‐5.7.

Neither restorative material nor localization of the restoration (upper or lower jaw)

had a significant influence on any criterion after 6 years (p>0.05; Mann‐Whitney U

test). However, molar restorations performed worse than premolar restorations

regarding marginal integrity (4 years), restoration integrity (6, 12, 24, 48 months),

and tooth integrity (4 and 6 years; Table 5.8). Irrespective of the resin composite

used, significant changes over time were found for all criteria applied in clinical

Chapter 5

64

examinations (Friedman test; p<0.05). Marginal integrity started with a major portion

of overhangs in all marginal areas having been detected until the 1‐year recall and

distinctly dropping afterwards (overhangs at baseline 44%; 6 months: 65%; 1 year:

47%; 2 years: 6%; 4 years: 4%; and 6 years: 3%). Beyond the 1‐year recall, more and

more negative step formations due to wear were detected (Table 5.5). This

phenomenon was earlier seen in molars (87 % bravo after 4 years) than in premolars

(51 % bravo after 4 years; Table 5.8a).

Baseline (n=68) 2 Years (n=68) 4 Years (n=68) 6 Years (n=68)

Alpha1 Alpha2 Bravo Alpha1 Alpha2 Bravo Alpha1 Alpha2 Bravo Alpha1 Alpha2 Bravo

[%] [%] [%] [%] Date of investigation

1.2 months 24.4 months 49.2 months 73.3 months Criterion

Surface roughness

100

99 1

93 7

82 18

Color match 94 6 93 7 84 13 3 84 16

Marginal integrity

44 54 2

60 40

34 66

41 59

Tooth Integrity 91 9

40 47 13 29 56 15 31 48 21

Restoration Integrity 93 4 3 9 41 50 1 25 74 3 34 63

Proximal contact

94 4 2 82 16 2 91 7 1 85 13 2

Change of sensitivity

97

3 100

100

98

2

Hyper- 91 7 2 100

100

100

sensitivity

Radiographic assessment

91 4 5

96 1 3

Table 5.2: Descriptive statistics for all assessed restorations.


65



[%] [%] [%] [%] Criterion

Surface roughness

100

97 3

92 8

78 22

Color match 92 8 92 8 81 14 5 78 22

Marginal integrity

50 47 3

53 47

36 64

39 61

Tooth integrity 86 14

47 42 11 31 58 11 33 50 17

Restoration integrity

100

11 45 44 3 28 69 3 39 58

Proximal contact

94 3 3 89 11 94 6 83 17 Change of sensitivity

100 100 100 100 Hyper-

97 3 100 100 100 sensitivity

Radiographic assessment

89 3 8 97 3

Table 5.3: Descriptive statistics for all Grandio restorations. *

Chapter 5

66



[%] [%] [%] [%]

Criterion

Surface roughness 100

100

94 6

87 13

Color match 97 3 94 6 88 13 91 9

Marginal integrity 37 63

69 31

31 69

44 56

Tooth integrity 97 3

31 53 16 28 53 19 28 47 25

Restoration integrity

85 9 6 6 38 56

22 78 3 28 69

Proximal contact 94 3 3 75 22 3 88 9 3 88 9 3

Change of sensitivity 94

6 100

100

97

3

Hyper- 84 13 3 100

100

100

sensitivity

Radiographic assessment 94 6

94 3 3

Table 5.4: Descriptive statistics for all Tetric Ceram restorations.

Criterion Baseline (n=68)

24 months (n=68)

48 months (n=68)

72 months (n=68)

Alpha I Excellent

44.1 % 0.0 % 0.0 % 0.0%

Alpha II Negative step 8.8 % 44.1 % 29.4% 38.2% Slight defects, easily Overhang 44.1 % 5.9 % 4.4% 1.5% correctable Stained

overhang 1.5 % 10.3 % 0.0 % 1.5%

Bravo Slight defects, not

Gap / negative step

1.5 % 16.2 % 23.5% 11.8%

correctable without damage

Staining 0.0 % 23.5 % 42.6% 47.2%

Table 5.5a: Descriptive statistics regarding “marginal integrity” (all restorations).


67


24 months (n=36)

48 months (n=36)

72 months (n=36)

Alpha I Excellent

50.0 % 0.0 % 0.0% 0.0%

Alpha II Negative step 5.6 % 38.9 % 27.8% 33.3% Slight defects, easily

Overhang 38.9 % 2.8 % 8.3% 2.8%

correctable Stained overhang

2.8 % 11.1 % 0.0 % 2.8%

Bravo Slight defects,

Gap / negative step

2.8 % 19.4 % 25.0% 8.3%

not correctable without damage

Staining 0.0 % 27.8 % 38.9% 52.8%

Table 5.5b: Descriptive statistics regarding “marginal integrity” (Grandio restorations).


24 months (n=32)

48 months (n=32)

72 months (n=32)

Alpha I Excellent 37.5 % 0.0 % 0.0% 0.0%

Alpha II Negative step 12.5 % 50.0 % 31.3% 43.8% Slight defects, easily Overhang 50.0 % 9.4 % 0.0 % 0.0 %

correctable Stained overhang

9.4 % 0.0 % 0.0 %

Bravo Gap / negative step

0.0 % 12.5 % 21.9% 15.6%

Slight defects, not correctable without damage

Staining 0.0 % 18.8 % 46.9% 40.6%

Table 5.5c: Descriptive statistics regarding “marginal integrity” (Tetric Ceram restorations).

Chapter 5

68


24 months (n=68)

48 months (n=68)

72 months (n=68)


Alpha II Enamel chipping

1.5 % 4.4 % 0.0 % 5.9 %

Slight defects, easily

Enamel crack 7.4 % 42.6 % 55.9% 41.2%

correctable Wear 0.0 % 0.0 % 0.0 % 1.5 %

Bravo Enamel chipping

0.0 % 10.3 % 14.7% 13.2%


Enamel crack 0.0 % 2.9 % 0.0 % 5.9 %

Wear 1.5 %

Table 5.6a: Descriptive statistics regarding “tooth integrity” (all restorations).


24 months (n=36)

48 months (n=36)

72 months (n=36)



2.8 % 2.8 % 0.0 % 5.6 %


Enamel crack

11.1 % 38.9 % 58.3% 41.7%

correctable Wear 0.0 % 0.0 % 0.0 % 2.8 %


0.0 % 8.3 % 11.1% 8.3 %


Enamel crack

0.0 % 2.8 % 0.0 % 5.6 %

Wear 0.0 % 0.0 % 0.0 % 2.8 %

Table 5.6b: Descriptive statistics regarding “tooth integrity” (Grandio restorations).


69


24 months (n=32)

48 months (n=32)

72 months (n=32)



0.0 % 6.3 % 0.0 % 6.3 %


Enamel crack

3.1 % 46.9 % 53.1% 40.6%

correctable


0.0 % 12.5 % 18.8% 18.8%


Enamel crack

0.0 % 3.1 % 0.0 % 6.3 %

Table 5.6c: Descriptive statistics regarding “tooth integrity” (Tetric Ceram restorations).

Criterion

Baseline (n=68)

24 months (n=68)

48 months (n=68)

72 months (n=68)


Alpha II Chipping 2.9 % 0.0 % 0.0% 1.5% Slight defects, easily

Crack 0.0 % 1.5 % 0.0% 0.0%

correctable Roughness / Abrasion

1.5 % 39.7 % 25.0% 32.4%

Bravo Chipping 0.0 % 2.9 % 7.4% 2.9% Slight defects, not correctable without damage

Crack probing 2.9 % 0.0 % 4.4% 1.5%

Abrasion 0.0 % 30.9 % 51.5% 58.8% Roughness 0.0 % 4.4 % 7.4% 0.0% Void 0.0 % 11.8 % 2.9% 0.0%

Table 5.7a: Descriptive statistics regarding “restoration integrity” (all restorations).

Chapter 5

70


24 months (n=36)

48 months (n=36)

72 months (n=36)


Alpha II Chipping 0.0 % 0.0 % 0.0 % 0.0 % Slight defects, easily

Crack 0.0 % 0.0 % 0.0 % 0.0 %


0.0 % 44.4 % 27.8% 38.9%


Crack probing 0.0 % 0.0 % 2.8% 0.0 %

Abrasion 0.0 % 16.7 % 50.0% 55.6% Roughness 0.0 % 5.6 % 8.3% 0.0 % Void 0.0 % 16.7 % 0.0% 0.0 %

Table 5.7b: Descriptive statistics regarding “restoration integrity” (Grandio restorations).


24 months (n=32)

48 months (n=32)

72 months (n=32)

Alpha I Excellent

84.4 % 6.3 % 0.0 % 3.1 %


Crack 0.0 % 3.1 % 0.0 % 0.0 %


3.1 % 34.4 % 21.9% 25.0%


Crack probing 6.3 % 0.0 % 6.3% 3.1%

Abrasion 0.0 % 46.9 % 53.1% 62.5% Roughness 0.0 % 3.1 % 6.3% 0.0 % Void 0.0 % 6.3 % 6.3% 0.0 %

Table 5.7c: Descriptive statistics regarding “restoration integrity” (Tetric Ceram

restorations).


71

48 months 72 months

Criterion premolars (n=45)

molars (n=23)

premolars (n=45)

molars (n=23)

Alpha I Excellent

2.2 % 4.3 % 0.0 % 0.0 %

Alpha II Negative step

40.0% 8.7 % 44.4% 26.1 %

Slight defects, easily Overhang 6.7 % 0.0 % 2.2 % 0.0 % correctable Stained

overhang 0.0 % 0.0 % 2.2% 0.0%

Bravo Gap /

negative step

20.0% 26.1 % 8.9 % 17.4%


Staining 31.1% 60.9 % 42.2% 56.5%

Table 5.8a: Descriptive statistics of premolars vs. molars regarding “marginal integrity”. No significant difference could be calculated after 72 months (p=0.073) in contrast to the result after 48 months (p=0.007; Mann‐Whitney U‐test).

48 months 72 months


molars (n=23)

premolars (n=45)

molars (n=23)

Alpha I Excellent

37.8 % 13.0 % 42.2% 8.7 %


0.0 % 0.0 % 6.7 % 13.0 %

Slight defects, easily Enamel crack

53.3% 60.9 % 35.6% 52.2 %

correctable Wear 0.0 % 0.0 % 2.2% 0.0 %


8.9 % 26.1 % 6.7 % 26.1 %


Enamel crack

0.0 % 0.0 % 4.4 % 8.7 %

Wear 0.0 % 0.0 % 2.2 % 0.0 % Table 5.8b: Descriptive statistics of premolars vs. molars regarding “tooth integrity”. Significant differences could be calculated after 48 (p=0.013) and 72 months (p=0.003; Mann‐Whitney U‐test).

Chapter 5

72

48 months 72 months


molars (n=23)

premolars (n=45)

molars (n=23)

Alpha I Excellent

2.2 % 4.3 % 0.0 % 8.7 %


Crack 0.0 % 0.0 % 0.0 % 0.0 %


33.3 % 4.3 % 40.0% 17.3%

Bravo Chipping 4.4 % 8.7 % 4.4 % 0.0 % Slight defects, not correctable without damage

Crack probing

4.4 % 4.3 % 2.2 % 0.0 %

Abrasion 40.0 % 73.9 % 51.1 % 73.9% Roughness 8.9 % 4.3 % 0.0 % 0.0 % Void 4.4 % 0.0 % 0.0 % 0.0 %

Table 5.8c: Descriptive statistics of premolars vs. molars regarding “restoration integrity”. No significant difference was calculated after 72 months (p=0.321) in contrast to the 48 month findings (p=0.018; Mann‐Whitney U‐test).

Tooth integrity significantly deteriorated due to increasing enamel cracks over time

(p<0.05; Table 5.6). Enamel chippings or cracks were significantly more frequently

observed in molars (26% bravo after 4 years / 35 % bravo after 6 years) than in

premolars (9% bravo after 4 years/11% bravo after 6 years). The main reasons for

decreasing “restoration integrity” were visible signs of surface roughness and distinct

wear traces (28% after 1 year, 75% after 2 years, 84% after 4 years, 91% after 6

years; Table 5.7). Visible wear of both materials under investigation was detectable

earlier in molars (74% bravo after 4 years) than in premolars (40% bravo after 4

years; Table 5.8c, Figures 5.1 and 5.2).


73

Figure 5.1

Clinical view of a Grandio restoration after 6 years (upper left first premolar). A discoloration at the palatal proximal margin was detectable, probably due to a small overhang. Wear and negative step formation in the occlusal portion of the restoration was obvious. The surface appears rough.

Figure 5.2

Clinical view of a Tetric Ceram restoration after 6 years (upper right first premolar, same patient as in Figure 5.1). No discoloration was detectable clinically. Wear and negative step formation in the occlusal portion of the restoration was detectable. In the occlusal contact area of the lateral ridge, the surface show signs of surface fatigue (small cracks) and the surface appears rough.

Discussion

Fundamental prerequisites for clinical success with resin-based composites as

posterior restorative material still must be met in order to achieve clinical success

with this particular group of dental materials.10-12,18,30,41 There is no doubt that resin

composites are almost perfect for minimally invasive posterior cavities, however, it

is to the date not fully understood how far we can go in terms of cavity extension. So

it is still frequently argued that resin composites suffer some disadvantages in very

Chapter 5

74

extended cavities and should therefore be replaced by other materials and techniques

such as indirectly bonded restorations.21 When large cavities need to be restored, the

major objections against resin composites are the dangers of developing recurrent

caries and the non-predictable wear rates over time.42 The problem with secondary

caries is even more common when proximal Class II margins are located in dentin.

At least from in vitro and in vivo investigations dealing with indirect ceramic inlays

and onlays, it is proven that even margins extending beyond the amelocemental

junction can be safely restored.6,16,25,42 For Class V restorations it is similar, although

50% of margin length is located in dentin.4,19,20,22 On the other hand, proximal

marginal seal in dentin-bordered cavities restored with direct resin composite

restorations, is underrepresented in the literature of the field.21 Thus, the setup of this

clinical trial excluded minimally invasive cavities and was mainly restricted to

amalgam replacement restorations resulting in 35% of cavities with no proximal-

cervical enamel and 49% with <0.5 mm proximal enamel width. Finally, after 6

years of clinical service, these restorations did not reveal significantly worse clinical

outcomes, and moreover, neither recurrent caries nor severe marginal staining was

detected.

The most recent recommendations for clinical trials with restorative materials 31

could not be addressed, because these recommendations were published considerably

after the beginning of the present study. Therefore, it was not possible to include

more evaluation aspects among well-suited protocols such as the CONSORT

statement.15,16,40,42

Direct and indirect resin composites as well as all-ceramic inlays have to be bonded

for acceptable clinical outcome.5,10,11,14,30 The selection of materials for this study

was carried out after thorough in vitro testing with promising results for both

materials used, in terms of good marginal adaptation and long-term stability,24,27,28,43

because previous studies clearly indicated that it may be dangerous to make clinical

trials with materials having failed some preclinical screenings.15,43

Although the different adhesives used in the present investigation required special

bonding protocols, i.e. wet bonding with the acetone-based Solobond M, this

obviously did not negatively influence clinical results in terms of postoperative

hypersensitivities. Initially, restorations bonded with Syntac exhibited slightly more

hypersensitivities (baseline to 6 months) (3% vs. 0% bravo scores), but this played


75

no role past the 1-year recall. Therefore, both the internal sealing of dentin and tight

dentin margins were possible with both adhesives under investigation. Even so,

dealing with the clinical outcome of complete restorative systems (i.e. adhesive plus

resin composite) always is more complicated than evaluating two adhesives with one

resin composite in order to minimize variables. This paper is not able to completely

elucidate this particular problem, but the promising results over the 6-year period

support the assumption that both systems are clinically acceptable.

Including nanofillers in recent resin composites is widespread in adhesive dentistry

today. Major advantages are primarily enhanced translucency effects and increased

polishability.12,44,45 Irrespective of these aspects, clinical reports dealing with this

class of materials exhibited no significant advantages in vivo.12 In the present

investigation, Tetric Ceram was used as fine hybrid resin composite (without

nanofillers), and Grandio was used as one of the first resin composites with

incorporated nanofillers among conventional hybrid type fillers as so-called

nanohybrid resin composite.12,32,37

Altogether, the null hypothesis of the present investigation was confirmed because

there was no difference in the clinical behavior between Grandio and Tetric Ceram

used for extended Class II posterior restorations.

Chapter 5

76

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results and new developments. Dent Clin North Am 2002; 46:303-339.


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3. Mjor IA. The reasons for replacement and the age of failed restorations in

general dental practice. Acta Odontol Scand 1997; 55:58-63.

4. Van Meerbeek B, Peumans M, Verschueren M et al. Clinical status of ten

dentin adhesive systems. J Dent Res 1994; 73:1690-1702.

5. Bergenholtz G. Evidence for bacterial causation of adverse pulpal responses in

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the permanent dentition. Oper Dent 2004; 29:481-508.

7. Manhart J, Chen HY, Hickel R. Three-year results of a randomized controlled

clinical trial of the posterior composite QuiXfil in class I and II cavities. Clin

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8. Peumans M, Kanumilli P, De Munck J, Van Landuyt K, Lambrechts P, Van

Meerbeek B. Clinical effectiveness of contemporary adhesives: A systematic

review of current clinical trials. Dent Mater 2005; 21:864-881.

9. Tay FR, Frankenberger R, Krejci I et al. Single-bottle adhesives behave as

permeable membranes after polymerization. I. In vivo evidence. J Dent 2004;

32:611-621.

10. Baratieri LN, Ritter AV. Four-year clinical evaluation of posterior resin-based

composite restorations placed using the total-etch technique. J Esthet Restor

Dent 2001; 13:50-57.

11. Efes BG, Dorter C, Gomec Y, Koray F. Two-year clinical evaluation of

ormocer and nanofill composite with and without a flowable liner. J Adhes

Dent 2006; 8:119-126.


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12. Ernst CP, Brandenbusch M, Meyer G, Canbek K, Gottschalk F, Willershausen

B. Two-year clinical performance of a nanofiller vs a fine-particle hybrid resin

composite. Clin Oral Investig 2006; 10:119-125.


relation to configuration of the restoration. J Dent Res 1987; 66:1636-1639.

14. De Munck J, Van Landuyt K, Peumans M et al. A critical review of the

durability of adhesion to tooth tissue: methods and results. J Dent Res 2005;

84:118-132.


materials. Part II: in vivo investigations. Am J Dent 2005; 18:75-81.

16. Krämer N, Taschner M, Lohbauer U, Petschelt A, Frankenberger R. Totally

bonded ceramic inlays and onlays after eight years. J Adhes Dent 2008;

10:307-314.

17. Frankenberger R, Perdigao J, Rosa BT, Lopes M. "No-bottle" vs "multi-bottle"

dentin adhesives--a microtensile bond strength and morphological study. Dent

Mater 2001; 17:373-380.

18. Nikolaenko SA, Lohbauer U, Roggendorf M, Petschelt A, Dasch W,

Frankenberger R. Influence of c-factor and layering technique on microtensile

bond strength to dentin. Dent Mater 2004; 20:579-585.


performance of adhesives. J Dent 1998; 26:1-20.

20. Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, Van

Landuyt K, Lambrechts P, Vanherle G. Buonocore memorial lecture. Adhesion

to enamel and dentin: current status and future challenges. Oper Dent 2003;

28:215-235.

21. Van Nieuwenhuysen JP, D'Hoore W, Carvalho J, Qvist V. Long-term

evaluation of extensive restorations in permanent teeth. J Dent 2003; 31:395-

405.

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of enamel. Dent Mater 2005; 21:375-383.

23. De Munck J, Van Meerbeek B, Yoshida Y et al. Four-year water degradation

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composite restorations. Dent Mater 2005; 21:397-412.



predictable in vitro? J Adhes Dent 2007; 9 Suppl 1:107-116.

26. Dietschi D, De Siebenthal G, Neveu-Rosenstand L, Holz J. Influence of the

restorative technique and new adhesives on the dentin marginal seal and

adaptation of resin composite Class II restorations: an in vitro evaluation.

Quintessence Int 1995; 26:717-727.

27. Frankenberger R, Strobel WO, Krämer N et al. Evaluation of the fatigue

behavior of the resin-dentin bond with the use of different methods. J Biomed

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28. Frankenberger R, Strobel WO, Lohbauer U, Krämer N, Petschelt A. The effect

of six years of water storage on resin composite bonding to human dentin. J

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adaptation. Oper Dent 2000; 25:324-330.

30. Dresch W, Volpato S, Gomes JC, Ribeiro NR, Reis A, Loguercio AD. Clinical

evaluation of a nanofilled composite in posterior teeth: 12-month results. Oper

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31. Hickel R, Roulet JF, Bayne S et al. Recommendations for conducting


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controlled clinical studies of dental restorative materials. Science Committee

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partial crowns. J Adhes Dent 2007; 9 Suppl 1:121-147.



Oper Dent 1987; 12:53-78.

33. Lohbauer U, Frankenberger R, Krämer N, Petschelt A. Strength and fatigue

performance versus filler fraction of different types of direct dental

restoratives. J Biomed Mater Res B Appl Biomater 2006; 76:114-120.

34. Clelland NL, Pagnotto MP, Kerby RE, Seghi RR. Relative wear of flowable

and highly filled composite. J Prosthet Dent 2005; 93:153-157.

35. Schwartz JI, Söderholm KJ. Effects of filler size, water, and alcohol on

hardness and laboratory wear of dental composites. Acta Odontol Scand 2004;

62:102-106.

36. Turssi CP, De Moraes PB, Serra MC. Wear of dental resin composites: insights

into underlying processes and assessment methods--a review. J Biomed Mater

Res B Appl Biomater 2003; 65:280-285.


dental composites under simulated occlusal loading. Dent Mater 1999; 15:262-

267.

38. Palaniappan S, Elsen L, Lijnen I, Peumans M, Van Meerbeek B, Lambrechts P.

Three-year randomised clinical trial to evaluate the clinical performance,

quantitative and qualitative wear patterns of hybrid composite restorations.

Clin Oral Investig 2010;14:441-458.

39. Palaniappan S, Bharadwaj D, Mattar DL, Peumans M, Van Meerbeek B,

Lambrechts P. Three-year randomized clinical trial to evaluate the clinical

performance and wear of a nanocomposite versus a hybrid composite. Dent

Mater 2009; 25:1302-1314.

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40. Needleman I, Worthington H, Moher D, Schulz K, Altman DG. Improving the

completeness and transparency of reports of randomized trials in oral health:

the CONSORT statement. Am J Dent 2008; 21:7-12.


in vitro Class II composite restorations. J Dent 1993; 21:158-162.

42. Krämer N, Garcia-Godoy F, Reinelt C, Frankenberger R. Clinical performance

of posterior compomer restorations over 4 years. Am J Dent 2006; 19:61-66.



Dent 2005; 18:23-27.

44. Attar N. The effect of finishing and polishing procedures on the surface

roughness of composite resin materials. J Contemp Dent Pract 2007; 8:27-35.

45. Jung M, Sehr K, Klimek J. Surface texture of four nanofilled and one hybrid

composite after finishing. Oper Dent 2007; 32:45-52.

81

CHAPTER 6

General discussion:

Is the clinical performance of bonded restoratives predictable in the laboratory?

Chapter 6

82

Introduction

Dental biomaterials are subjected to considerable degradation processes during

clinical service over time.1-5 After amalgam, having been the standard restorative for

posterior restorations for more almost two centuries, today tooth-colored materials

such as resin-based composites are the treatment option of choice for the majority of

patients.6-13 Adhesive dentistry's long-term success is proven for pit and fissure

sealing, direct and indirect resin composites, and ceramic inlays.11,13-25 Nevertheless,

even in the era of nano-optimized resin-based composites, polymerization shrinkage

still relies on durable adhesion to enamel and dentin as a fundamental prerequisite, and

vice versa, without successful adhesion, gap formation potentially jeopardizes clinical

long-term success.4,26-36

Adhesion to phosphoric acid etched enamel is no longer a concern for dentists due to

its clinically proven durability,4-6,31,35,37-40 however, durability of self-etch adhesives in

heavily loaded Classes I and II is still not clinically proven, whereas in cervical

lesions, medium-term results are promising.12,21,22,41,42 Knowledge about adhesion to

dentin is different; the self-etch approach - at least with two steps - seems to be the

most promising way to get durable bonds beside multi-step etch-and-rinse

systems.30,31,35,40,43,44 Comparing enamel and dentin as adhesive substrates still reveals

dentin to be the weaker substrate due its tubular structure and intrinsic wetness which

leads to permeability problems with all-in-one self-etch adhesives.27,31,33-35,44-47

More or less all degradation processes found for dental biomaterials are related to

fatigue.10,37,48-55 Especially with resin-based composites, fatigue is not only a matter of

loss of adhesive performance over time (adhesive fatigue) but also of bulk fatigue

(fracture) and surface fatigue (wear). For resin composites, two fatigue phenomena

(adhesive fatigue leading to recurrent caries and bulk fatigue leading to fractures) are

responsible for the vast majority of clinical failures observed during clinical long-term

trials.6,7,11,16,56 Wear is in most of the cases less clinically relevant because worn resin

composites may still be clinically serviceable, however, loss of anatomic form over

time may lead to occlusal interferences.10,57-59 Research in restorative dentistry is,

since decades, focused on predicting clinical issues in the lab.60 Of course, clinical

long-term trials remain the ultimate instrument for thoroughly evaluating dental

biomaterials. However, the main problem with clinical trials is that when they give

General discussion

83

valuable results after several years of observation time, the adhesive and/or resin

composite may no longer be on the market.

Therefore, preclinical in vitro investigations are very important, however, it is

contradictorily reported in the literature whether these tests are able to reliably predict

clinical behavior. So the aim of this paper was to investigate this particular question

with a special focus on marginal integrity, bulk fatigue (fracture), and surface fatigue

(wear).


Publications in dental and biomaterial journals with dental materials since 1990 were

retrieved in PubMed, MedLine, Dimdi, and Embase. Search key words were: margin,

gap, marginal integrity, marginal adaptation, enamel margin, dentin margin, marginal

quality, fracture, chipping, bulk fracture, abrasion, and wear. We only chose papers

dealing with resin composites. Congress abstracts were completely ignored. Top

cited papers were retrieved from www.scopus.com in order to prioritize publications

that were frequently referred to39. As indicator for top cited papers, the frequency of

citations per year (CPA) was set >5.

Results

An overview of top cited papers dealing with marginal integrity, fatigue, and wear of

bonded restorations is displayed in Tables 6.1-6.3.

Marginal quality

Papers reporting direct comparisons between in vitro and in vivo results are scarce in

the literature in the field of adhesive dentistry. However, several evaluations of

marginal integrity from the preclinical point of view exist as do a few papers

focusing on marginal adaptation in vivo. Marginal integrity papers in vitro repeatedly

report a superior performance of etch-and-rinse adhesives in enamel

bonding,16,18,19,22,31,35,36,39,40,48,61,62 however, again there are contradictory reports of

Hannig et al. claiming self-etch adhesives being an alternative to phosphoric acid

even in stress-bearing cavities.63,64 For dentin bonding, Frankenberger and Tay

Chapter 6

84

reported equal results for etch-and-rinse adhesives and two-step self-etch adhesives

in dentin margins of Class II cavities after thermomechanical loading, and

significantly worse results when all-in-one adhesives were used for bonding of resin

composites in vitro.35

Abdalla and Davidson directly compared in vitro and in vivo applied resin composite

restorations in Class II cavities with less microleakage in the laboratory.65 Two

papers of our group investigated the resin composites Ariston pHc and Solitaire both

in vitro and in vivo. In the in vitro part, both restoratives exhibited some

shortcomings,36 however, these previously reported materials properties led to

catastrophic outcomes in vitro with mean survival times for both materials of 2.4

years.66 Frankenberger et al. also compared the same materials in vitro and in vivo

with respect to marginal adaptation of Class I resin composite resotrations in

molars.39 Here, some minor differences were noticed between the in vitro and the in

vivo situation, however, the rankings regarding the adhesive’s performances were the

same, revealing superior results for etch-and-rinse adhesives when compared to self-

etch adhesives.39 And among the self-etch adhesives, two-step self-etch adhesives

were more effective than one-step self etch adhesives.39 Another publication

observed marginal quality for Grandio and Tetric Ceram restorations both in vitro

and in vivo over 6 years.4 Also here, in vitro and in vivo results for marginal quality

were similar until the 6-year recall with a combined 6-year water

storage/thermomechanical loading scenario.4 Heintze et al. compared results of

clinical studies with bonded Class V resin composite restorations with two different

in vitro stressing regimens for a variety of 37 adhesives.44 They concluded that the

systematic analysis of the correlation between laboratory data of marginal adaptation

and the outcome of clinical trials of Class V restorations revealed that the correlation

was weak and only present if studies were compared which used the same composite

for the in vitro and in vivo evaluation.44

Bulk fatigue / fracture behavior

Regarding the fatigue behavior related to flexural strength, some studies evaluated the

flexural fatigue behavior in terms of a so-called flexural fatigue limit (FFL).48,49,67-79

The flexural fatigue limits (FFL) of the composite materials were determined for 105

General discussion

85

cycles under equivalent test conditions at a frequency of 0.5 Hz (n = 25). The

“staircase” approach was used for fatigue evaluation.70 For every cycle the stress

alternated between 1 MPa and the maximum stress. Tests were conducted

sequentially, with the maximum applied stress in each succeeding test being increased

or decreased by a fixed increment of stress, according to whether the previous test

resulted in failure or not. The first specimen was tested at approximately 50% of the

initial flexural strength value. As the data are cumulated around the mean stress, the

number of specimens required is less than with other methods. The mean flexural

fatigue limit (FFL) is determined using Eq. 1 and standard deviation, using Eq. 2,

respectively:

5.00

i

i

n

indXFFL (1)

029.062.1

2

22

i

iii

n

innindSD (2)

X0 is the lowest stress level considered in the analysis and d is the fixed stress

increment. To determine the FFL, the analysis of the data was based on the least

frequent event (failures versus nonfailures). In Eq. 1 a negative sign was used when

the analysis was based on failures. The lowest stress level considered was designated

as i = 0, the next as i = 1, and so on, and ni was the number of failures or non-failures

at the given stress level. Turssi et al. evaluated FFLs of microfill versus nanfilled resin

composite with equal to worse outcome for the nanomaterials.80 Abe et al. compared

an array of resin composites with results having been inferior for most of the packable

resin composites under investigation.81 Lohbauer et al. evaluated the FFL behavior of

different resin composites for posterior use and concluded that high initial flexural

strengths do not automatically mean high FFLs.77,78 In a direct in vitro - in vivo

comparison of resin-based materials regarding FFL and clinical outcome, the low FFL

for the resin composite Solitaire led to unacceptably high fracture rates in vivo, so the

authors concluded that FFL >30 MPa is the critical threshold value for bulk fatigue in

order to withstand masticatory forces and clinical fatigue life over time.66,77,78

Chapter 6

86

Surface contact fatigue/clinical wear

Early abrasion studies during the first stages of resin composite testing were cast

analyses according to some scales such as the Leinfelder scale allowing estimates of

clinical wear in terms of calibrated casts in 50 µm steps.1,52,53,82-88 Compared to

preclinical screenings where normally only the test material is abraded,54,55,89,90

clinical wear measurements in restorative dentistry always deal with enamel and

restorative materials and an exact determination of reference points is only possible

with demanding 3D laser devices.57-59,91-93 Due to the expensive tool and

sophisticated software issues, very few 3D laser scan studies dealing with clinical

wear phenomena are available in the literature, reporting wear rates after 3 years of

clinical service of ~80 µm.91,92

Discussion

In vitro research on dental adhesive biomaterials is necessary, because a) special

experimental research questions would never pass an ethics committee and b) not

every adhesive and/or resin-based composite can be the subject of randomized

prospective clinical trials because these are time-consuming and expensive.

Nevertheless, it is still not fully understood whether and what we can really simulate

in the lab and where major shortcomings are. So, the objective of this paper was to

clarify the question “Is clinical performance of dental biomaterials predictable in the

lab?”. Roulet thought about this topic years ago indicating that in vitro research

suffers from interpretation problems and even in vivo studies always reveal

significant limitations.94

Today, there are still only a handful of studies directly comparing in vitro with in

vivo results from the same workgroup. Abdalla and Davidson published the first

“Comparison of the marginal integrity of in vitro and in vivo Class II composite

restorations” being unique so far. This investigation dealt with microleakage in

laboratory and ex vivo specimens.65 Whereas only 40% of in vitro specimens

revealed microleakage after mechanical loading, 100% of in vivo restorations

exhibited microleakage.65 Therefore, the authors concluded that laboratory studies

may not be able to completely predict clinical behavior of adhesive junctions in the

oral cavity.65

General discussion

87

Clinical studies are mainly peformed in Classes V or II cavities being the latter the

most difficult to obtain. Major advantages of clinical trials in Class V cavities were

referred to as non-existing macromechanical retention, considerable amounts of

dentin margins, probably less influence of the particular resin composite, and easy

judgement of retention vs. retention loss.20-22,43,44,62 However, the main problem in

adhesive dentistry is not retention of Class V restorations, it is still to prove whether

bonded resin compositess are able to fully replace amalgam in stress-bearing

posterior cavities. However, disadvantages of Classes I and II are that retention is

often provided by undermining dentin decay and subsequent undercuts, and less

presence of clinically judgeable dentin margins.4,6,9 So marginal quality assessments

in posteror stress-bearing resin composite restorations may be less suitable to

investigate adhesives alone compared to non-carious Class V restorations, however,

clinical importance facing millions of stress-bearing posterior resin composite

restorations is great.6

Opdam et al. reported marginal integrity and postoperative sensitivity in Class II

restorations in vivo finding that etch-and-rinse adhesives showed good results in

enamel bonding and self-etch adhesives produced less postoperative

hypersensitivity.17 When clinical staining is related to inferior or loss of enamel

bonding durability, and postoperative hypersensitivities are linked to inferior or loss

of dentin bonding quality, this was predictable from laboratory investigations.39

Four recent publications of our workgroup aimed to evaluate resin composites and

their corresponding adhesives in both aspects, in vitro and in vivo.4,36,39,66

Frankenberger et al. reported in vitro performance of resin composites by means of

microtensile bond strenghts to enamel and dentin, flexural fatigue behavior, and wear

behavior. The resin composites Ariston pHc and Solitaire were different from

contemporary resin composites, i.e. Ariston exhibited significantly less adhesion,

Solitaire revealed an inferior flexural fatigue limit.36 Krämer et al. reported clinical

findings of identical materials demonstrating catastrophic clinical outcome with

several bulk fractures of Solitaire, and even more failures of Ariston restorations

caused by postoperative hypersensitivities and enamel fractures.66 Frankenberger et al.

compared different classes of adhesives in vitro and in vivo with identical enamel

bonding rankings for the different bonding approaches.39 The same was true for a

recent publication showing 6-year results in vitro and in vivo with again similar

Chapter 6

88

outcomes over time.4 So in all cases, clinical performance of resin composites in

Classes I and II cavities was predictable from laboratory results, especially significant

differences between etch-and-rinse adhesives and self-etch adhesives in enamel

bonding durability. So even the results of Heintze et al.43,44 actually match the

outcome of our workgroup where always the same resin composites were used in vitro

and in vivo which may have contributed to the more consistent values.4,39

All these findings clearly reflect that marginal quality prediction is possible from

laboratory studies, however, marginal integrity is only one among several crucial

factors for clinical outcome with bonded tooth-colored materials. A high amount of

gaps after thermomechanical challenge in vitro increases the probability of the same

scenario in vivo. However, this does not necessarily lead to recurrent decay because

the presence of marginal gaps in vivo does not necessarily lead to secondary caries.

One ultimate question is still unclear: when e.g. resin composite restoration achieves

good results in an in vitro marginal quality assessment, it is rather predicable that its

clinical marginal quality will not cause significant problems. On the other hand, can

we conclude this also from the other side of the scale? Probably not. We still do not

know below which percentage of gap-free margin it is not safe to use the material

combination also clinically.

The final reason in favor of in vitro research regarding marginal quality is that many

studies focus on experimental questions that would never pass an ethics committee

for a clinical trial. In these cases in vitro studies are the only way, giving important

tendencies for clinical application of dental biomaterials. Among all in vitro

approaches to predict clinical outcome, thermomechanical loading and subsequent

marginal analysis is the closest scenario to the clinical situation, however, it is almost

as intricate as a clinical trial.

As the frequency of citations as well as the presence of top cited papers clearly

reflects, flexural fatigue behavior of dental biomaterials receives far less attention.

However, a few top papers indicate that flexural fatigue behavior of dental

biomaterials is closely related to clinical outcome in terms of fracture

behavior.36,48,49,66,67,70,71,95 Compared to the multiple questions about marginal quality,

FFL measurements in vitro are able to exactly define a kind of lower borderline at

~30 MPa flexural fatigue limit, because below that level clinically much more

fractures were observed.66 On the other hand, there are still not enough clinical data

General discussion

89

proving that higher and higher initial and fatigue values for flexural strength

automatically lead to less fractures observed in clinical recalls after several years of

clinical service.96

Wear is an important consequence of occlusal interactions.10,16,91,97,98 If not

controlled, wear could lead to poor masticatory function with a concomitant

reduction in quality of life.99-102 However, for most of the investigated resin-based

composites this is simply not the case.10,16,91,97,98 Compared with other modes of in

vitro testing of dental biomaterials, preclinical wear simulation is the most

sophisticated branch.52,53,86,98,103,104 Clinical wear is a very complex scenario being

influenced by several factors such as pH, contact-free abrasion, occlusal contact

fatigue, and antagonist structure and material.52,53,86,98,103,104 Most of the in vitro

regimens are only able to mimic one of these several co-factors. Analyzed as an

array, many different wear simulation scenarios could finally result in an appropriate

estimation of clinical wear.52,53,86,98,103,104 Also here it is clearly visible in Table 6.3

that the scientific importance of wear investigations decreased during the last decade

and top cited papers are scarce. 3D laserscans are the ultimate instrument to evaluate

clinical wear, however, there is an urgent need for more clinical data with different

restoratives.98

In times of ranking publications according to their journal impact factor (JIF),

citations are an important tool in order to judge the importance of individual papers

in the literarure. High JIF regularly result from frequently cited papers. As performed

before with a substantial amount of citations, the authors again decided to include

this aspect by focussing on frequently cited papers being indicated by CPA (citations

per anno; Tables 6.1-6.3). For the top cited paper published by Van Meerbeek et al.

this means that this single publication receives an individual or "true" impact factor

of 50 compared to the journal impact factor of ~3 meaning that the importance of the

paper exceeds the importance of the journal by means of 16. Although citation

rankings and measurement are always criticized to be somewhat subjective, it is the

only way to judge or rank scientific outcome. The same is true for the journal impact

factor, i.e. it may not be an optimum tool for author evaluations, however, is there a

better alternative? So finally, the inclusion of top cited papers is of at least some

relevance and should not be underestimated.

Chapter 6

90

Conclusions

Clinical marginal quality is predictable from in vitro adhesive fatigue investigations

with thermomechanical loading, but it is not possible to determine a cut off for

clinically successful marginal quality. Flexural fatigue can be appropriately

determined in the lab as well, having been successful in defining lower borderlines for

additional clinical safety. To compare in vitro and in vivo results according to wear

phenomena, valid in vivo results are too seldom. Altogether, it has to be taken into

account that the described co-factors are only a few among several important aspects

in restorative dentistry, i.e. overall clinical performance is not predictable from fatigue

aspects alone.

Year Author Title Citations per year (CPA)

2003 Van Meerbeek et al.13 Adhesion to enamel and dentin: Current status and future challenges

50.9

1997 Mehl at al.23 Physical properties and gap formation of light-cured composites with and without softstart polymerization

14.5

1995 Feilzer et al.24 Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface

12.1

2005 Frankenberger & Tay35

Self-etch vs etch-and-rinse adhesives: effect of thermo-mechanical fatigue loading on marginal quality of bonded resin composite restorations

10.8

1990 Kemp-Scholte et al.41 Complete marginal seal of Class V resin composite restorations effected by increased flexibility

10.3

1999 Hannig et al.63 Self-etching primer vs. phosphoric acid: an alternative concept for composite-to-enamel bonding

10.0

2000 Peumans et al. 25 Porcelain veneers: A review of the literature 9.0 2000 Frankenberger et al.45 Technique sensitivity of dentin bonding: Effect of

application mistakes on bond strength and marginal adaptation

8.6

1998 Opdam et al.17 Marginal integrity and postoperative hypersensitivity in Class II resin composite restorations in vivo

6.8

2007 Heintze43 Systematic reviews: I. The correlation between laboratory tests on marginal quality and bond strength. II. The correlation between marginal quality and clinical outcome

6.0

2000 Frankenberger et al.2 Leucite-reinforced glass ceramic inlays and onlays after six years: clinical behavior

6.0

1990 Kemp-Scholte & Davidson60

Marginal integrity related to bond strength and strain capacity of composite resin restorative systems

5.8

2007 Frankenberger et al. 39

Marginal integrity: Is the clinical performance of bonded restorations predictable in vitro?

5.7

Table 6.1: Top cited papers (CPA >5) regarding marginal adaptation of resin composites.

General discussion

91


1997 Gladys et al.95 Comparative physico-mechanical characterization of new hybrid restorative materials with conventional glass-ionomer and resin composite restorative materials

11.4

2003 Drummond et al.73 Static and cyclic loading of fiber-reinforced dental resin

8.9

2005 Lohbauer et al.78 The effect of different light-curing units on fatigue behavior and degree of conversion of a resin composite

5.6

Table 6.2: Top cited papers (CPA >5) regarding bulk fatigue behavior of resin composites.


1998 Bayne et al.99 A characterization of first-generation flowable composites

11.3

2005 Sarrett et al.101 Clinical challenges and the relevance of materials testing for posterior composite restorations

9.6

1996 Mair et al.100 Wear: Mechanisms, manifestations and measurement. Report of a workshop

7.4

2005 Turssi et al.102 Filler features and their effects on wear and degree of conversion of particulate dental resin composites

7.4

Table 6.3: Top cited papers (CPA >5) regarding surface fatigue / wear of resin composites.

Chapter 6

92

Figure 6.1: Biodegradation of a resin composite restoration in a lower first molar after 6 years of clinical service. R: Resin composite. E: Enamel. Clinical wear is clearly visible around the occulsal margins. Gap formation does not play a major role in this case.4

General discussion

93

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General discussion

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97. Sarrett DC, Ray S. The effect of water on polymer matrix and composite wear.

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148.

101. Sarrett DC. Clinical challenges and the relevance of materials testing for

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102. Turssi CP, Ferracane JL, Vogel K. Filler features and their effects on wear and

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2005;26:4932-4937.

General discussion

103

103. Heintze SD, Cavalleri A, Forjanic M, Zellweger G, Rousson V. A comparison

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Chapter 6

104

105

Summary

106

Tooth-colored materials such as resin composites should be safely used for patients in

terms of clinical behavior. Esthetics are more or less a side aspect in the posterior

region. However, it is probably the most important issue for patients all over the world

to receive invisible restorations. This summary section picks up relevant issues having

been addressed in the introduction section (Chapter 1) to build a thematic bridge in

this thesis and to provide some framework for future thoughts.

Resin composite materials are well-suited materials to bond to tooth hard tissues and

furthermore to support enamel and dentin in terms of cuspal adhesive stabilization. It

is well-proven that adhesion in dentistry can be safely applied in many ways, such as

pit and fissure sealings, direct and indirect resin composites, and bonded ceramic

restorations. Bonding to phosphoric acid etched enamel is accepted to be clinically

successful, however, marginal staining or gap formation have been also reported as

major incidents already after medium-term observations. Also dentin can be bonded

and sealed successfully, being rather quickly represented by the absence of

postoperative hypersensitivities. When no hypersensitivities occur, the dentin seal

should be estimated to be sufficient, at least to avoid fluid movement inside the dentin

tubules. Long-term bonding degradation over time is interesting to observe, therefore

it was the topic of the second part of the thesis to do so (Chapter 2). Also, the central

idea was to accelerate degradation in vitro, in this case degeneration of resin-dentin

bonds by artificial saliva compared to mineral oil (control). Resin-dentin beams

bonded with three different etch-and-rinse adhesives (two-step: Prime&Bond NT,

Excite/three-step: All-Bond 2) were prepared after 3 years of storage in the described

media and subjected to transmission electron microscopy (TEM). An "extreme

control" was introduced by autoclaving at 121°C and 103kPa. The TEM images

clearly showed that the extreme control scenario did not result in denatured collagen

when having been protected by adhesive resin. The control group with mineral oil

exhibited almost intact hybrid layers over 3 years with minimal silver deposits,

whereas in the test group with artificial saliva, extensive nanoleakage was observed.

All ultrastructural parameters, i.e. extent of nanoleakage, interfacial staining

characteristics, and the structure of the collagen fibrils in hybrid layers and underlying

dentin were completely different and revealed considerable aging processes when

storage was accelerated using artificial saliva.

Summary

107

Dentin bonding is more responsible for proper dentin seal and consequent reduction of

postoperative hypersensitivities. In contrast, enamel bonding is important for

restoration retention and marginal integrity, i.e. unstained margins, especially in the

visible area. Therefore, in the next stage marginal quality in enamel and dentin was

evaluated simultaneously in vitro and in vivo. This was achieved by starting both

investigations at the same time to get comparable results between preclinical and

clinical investigations (Chapter 3). In this section, 32 in vitro specimens were

compared to 22 in vivo specimens regarding marginal adaptation in enamel and

dentin. Clinically, replicas of baseline investigations and 6-year recalls were

compared, and in vitro we investigated replicas initially and after 2190 days of water

storage with and without thermomechanical loading for accelerated aging processes

under a SEM. Due to inferior proximal access to dentin margins, marginal adaptation

to dentin was only assessed in vitro. Here, percentages of gap-free margins dropped

from 98-100% at the beginning to 55-66% after thermomechanical loading alone and

67-75% after water storage alone and to 42-52% after both accelerated aging

mechanisms together. Enamel margins remained 100% gap-free in vitro and 86-90%

in vivo at the beginning, dropping to 85-87% after water storage and

thermomechanical loading in vitro and 74-80% in vivo. So besides some more

artifacts and overhangs due to the more challenging clinical situation, results in

marginal quality were almost identical between in vitro and in vivo specimens.

After having worked out the value of accelerated aging on resin-dentin and resin-

enamel bonding behavior, the following step was to focus on material properties of

resin composites for posterior use. Especially flexural strength and flexural fatigue

behavior have been of special interest for us due to the fact that it received increased

attention facing increasing marginal and bulk fracture rates in clinical trials dealing

with direct resin composites. A thorough evaluation of flexural fatigue characteristics

was therefore the aim of the next chapter of the present thesis (Chapter 4). Following

the same strategy as in Chapter 3, here we also simultaneously started both in vitro

and in vivo evaluations. For the in vitro part, elastic modulus, flexural strength, and

flexural fatigue limit according to the staircase method were assessed. In vivo, clinical

fracture behavior in terms of marginal breakdown and bulk fractures/chippings were

observed and correlated to the outcome detected in vitro. In vitro results showed

similar values initially, however, flexural fatigue limits were higher for Grandio

compared to Tetric Ceram. In contrast, no such differences occured in vivo up to the

108

6-year recall of the same materials having been under investigation. Only at a closer

view, facing x200 magnification of marginal breakdown sites, revealed that Tetric

Ceram showed more areas of marginal defects (7.9%) compared to Grandio (4.8%).

The ultimate instrument for definitive estimation and judgement of dental biomaterials

is still the randomized clinical long-term trial. A prospective clinical long-term trial

was carried out over a 6-year observation time, using the same restorative materials

(Solobond M/Grandio, Syntac/Tetric Ceram) previously described (Chapter 5).

Thirty patients received at least two different restorations in a random decision

according to recommendations of the CONSORT statement. Thirty-six Grandio

restorations were bonded with Solobond M, 32 Tetric Ceram restorations were bonded

with Syntac (only Class II, 52 MO/OD, 16 MOD or more surfaces). Twenty-four

cavities (35%) revealed no enamel at cervical margin, 33 cavities (49%) exhibited less

than 0.5 mm cervical enamel width. At the baseline initial recall, after 6 months, 1, 2,

4, and 6 years, all restorations were assessed according to modified United States

Public Health Service (USPHS) criteria by two independent investigators using loups

with x3.5 magnification, mirrors, probes, bitewing radiographs, impressions, and

intraoral photographs. The overall success rate was 100% after 6 years of clinical

service, while drop out of patients was 0%. Neither restorative materials nor

localization of the restorations had a significant influence on any criterion after 6

years. However, molar restorations performed worse than premolar restorations

regarding marginal integrity (4 years), restoration integrity (6, 12, 24, 48 months), and

tooth integrity (4 and 6 years). Irrespective of the resin composite used, significant

changes over time were found for all criteria applied in clinical examinations.

Marginal integrity started with a major portion of overhangs in all marginal areas

having been detected until the 1‐year recall and distinctly dropping afterwards

(overhangs at baseline 44%; 6 months: 65%; 1 year: 47%; 2 years: 6%; 4 years: 4%;

and 6 years: 3%). Beyond the 1‐year recall, more and more negative step formations

due to wear were found. Tooth integrity significantly deteriorated due to increasing

enamel cracks over time. Enamel chippings or cracks were significantly more

frequently observed in molars than in premolars. Main reasons for decreasing

“restoration integrity” were visible signs of surface roughness and distinct wear traces.

Visible wear of both materials under investigation was earlier detectable in molars

(74% bravo after 4 years) than in premolars (40% bravo after 4 years).

Summary

109

The final question remains and is addressed with the last issue of the present thesis,

i.e. what is this all about or in different words: Is clinical performance of bonded

restoratives predictable in the lab (Chapter 6)? It could be repeatedly shown that the

easiest way of predicting clinical behavior is assessment of marginal integrity. Here

the best correlation between in vitro and in vivo results can be found. The explanation

is clear: restoring real teeth with real restorations and loading them with real forces

being similar to subcritical loads in vivo finally results in realistic estimations of later

observable clinical behavior. It was clearly shown that by use of etch-and-rinse

adhesives a tight enamel seal is provided both in vitro and in vivo being well-suited to

counteract polymerization forces and to withstand occlusal stresses in the oral cavity.

However, this estimation is not correlated to the risk for secondary caries, because gap

formation not always, nor quickly results in the formation of secondary caries. Here a

complex biofilm acts on different tooth hard tissues, which is extremely hard to

simulate under in vitro conditions using an artificial mouth. So the final correlation

gap-caries is clearly not yet achieved with present investigations having been carried

out for the present thesis. Regarding fatigue behavior related to flexural strength, the

literature reveals that promising initial flexural strengths do not logically mean high

FFLs and an FFL of >30 MPa may be the critical threshold value for bulk fatigue in

order to withstand masticatory forces and clinical fatigue over its lifetime. This

furthermore supports the aspect that thorough in vitro screening of dental biomaterials

is only sufficient when long-term fatigue phenomena are considered in order to get

accelerated aging. Regarding clinical wear, few 3D laser scan studies are available in

the literature, reporting wear rates after 3 years of clinical service of ~80 µm.

Altogether, there is a certain value for accelerated in vitro testing of dental

biomaterials which is very highly esteemed because financial resources get smaller,

and ethics committees’ approval are harder to obtain.

In conclusion, the present thesis clearly shows that in vitro research will be even more

important during the next decade of research in restorative dentistry.

111

Samenvatting

112

Voor een veilige toepassing van tandkleurige vulmaterialen, zoals kunststof

composieten (hierna zonder meer aangeduid als composiet), is het klinisch gedrag

van groot belang. Esthetiek is in het posterieure gebied minder van belang.

Desondanks hechten onze patiënten wereldwijd veel belang aan ‘onzichtbare’

restauraties. Deze samenvatting richt zich op de relevante zaken die aan de orde

komen in de inleiding (hoofdstuk 1) van dit proefschrift om een thematische brug op

te bouwen en om een zeker kader te bieden voor toekomstige gedachtenvorming.

Composiet restauratie-materialen zijn zeer geschikt om te hechten aan de harde

tandweefsels (glazuur en dentine) wat van belang is om het tandweefsel te

ondersteunen waardoor het herstel van sterkte van het gebitselement wordt

ondersteund. Het is aangetoond dat hechting in de tandheelkunde in vele klinische

situaties veilig kan worden toegepast. Bijvoorbeeld in fissuur-afdichtingen, directe en

indirecte composietrestauraties, en in adhesief bevestigde keramische restauraties.

Hechting aan met fosforzuur geëtst glazuur is klinisch een betrouwbaar gebleken

methode. Desondanks zijn randverkleuring en rand-spleetvorming gerapporteerd als

optredende verschijnselen bij middellangetermijnonderzoek. Ook kan aan tandbeen

(dentine) worden gehecht waarbij dit levende weefsel met succes wordt afgedicht en

afgeschermd van omgevings-invloeden wat de afwezigheid van postoperatieve

overgevoeligheden verklaart. Als er geen hypergevoeligheid optreedt, wordt de

dentine afdichting als voldoende ingeschat om de vloeistofbeweging in de

dentinetubili te voorkomen. Degradatie van de hechting aan dentine met de tijd, op de

lange termijn, is een interessant fenomeen dat het onderwerp van onderzoek is van het

tweede deel van het proefschrift (Hoofdstuk 2). Het centrale uitgangspunt van dit

onderzoek was om de degradatie te versnellen in vitro door de kunststof-dentine-

verbinding aan kunstspeeksel of minerale olie (controle) bloot te stellen. Kunststof-

dentine-staafjes, aan elkaar gehecht door middel van drie verschillende ets-en-spoel

adhesiefsystemen (twee-staps systemen: Prime & Bond NT, Excite; drie-staps

systeem: All-Bond 2) werden toegepast. Na 3 jaar opslag in de beschreven media

werd het hechtvlak met transmissie elektronenmicroscopie (TEM) beoordeeld. Een

"extreme controlegroep" werd in de autoclaaf aan 121°C en 103kPa druk blootgesteld.

De TEM-beelden laten duidelijk zien dat dit extreme controle scenario niet leidt tot

het ontstaan van gedenatureerd collageen wanneer het dentine is afgedekt met een

kunststof van een dentine hechtsysteem. De hybride laag van de controlegroep die

werd blootgesteld aan minerale olie bleef vrijwel intact over de onderzoeksperiode

Samenvatting

113

van 3 jaar met een minimum aan zilverneerslag, terwijl in de testgroep blootgesteld

aan kunstmatig speeksel, uitgebreide nanolekkage werd waargenomen. Alle

ultrastructurele parameters, dat wil zeggen: de omvang van nanolekkage, interface

verkleuringen en de structuur van de collageenfibrillen in de hybride lagen en in het

onderliggende dentine waren totaal verschillend en illustreren intense

verouderingsprocessen die in dit onderzoek werden versneld met behulp van

kunstmatig speeksel.

Hechting aan dentine is verantwoordelijk voor een goede afdichting van het tandbeen

en de daaruit voortvloeiende vermindering van postoperatieve overgevoeligheden.

Daarentegen is hechting aan glazuur van belang om de restauratie houvast te geven en

voor een goede ‘onzichtbare’ overgang tussen tandweefsel en restauratie, de

randaansluiting. Daarom werd in de volgende fase van het onderzoek van dit

proefschrift de kwaliteit van de randaansluiting van een vulling met glazuur en met

dentine gelijktijdig in vitro en in vivo geëvalueerd. Dit werd gerealiseerd door het

gelijktijdig starten van beide onderzoeken om zo vergelijkbare resultaten tussen de

preklinische en klinische onderzoeken (hoofdstuk 3) te verkrijgen. In dit

deelonderzoek is de randaansluiting van composiet restauraties aan glazuur en aan

dentine met elkaar vergeleken, in vitro met 32 monsters en in vivo met 22 monsters.

Klinisch werden replica's van de baseline-resultaten met die van 6-jaar recalls

vergeleken, en in vitro werden baseline replica’s vergeleken met replica’s na 2.190

dagen blootstelling aan water met of zonder thermomechanische belasting. De

(versnelde) verouderingsprocessen werden met Scanning Electron Microscopy (SEM)

geëvalueerd. Vanwege de met direct zicht slecht toegankelijke approximale dentine-

randaansluitingen werd de randaansluiting aan dentine alleen in vitro onderzocht. In

vitro daalde het percentage van de lekvrije randaansluitingen van 98-100% bij

aanvang tot 55-66% na uitsluitend thermomechanische belasting en tot 67-75% na het

uitsluitend blootstellen aan water en tot 42-52% na blootstelling aan beide versnelde

verouderingsmechanismen. De glazuurrandaansluiting was voor de in vitro monsters

aan het begin 100% lekvrij terwijl in vitro dit variëerde van 86 - 90%. Blootstelling

aan water en thermomechanische belasting leidde tot een daling naar 85 - 87% in vitro

en naar 74 - 80% in vivo. Ondanks het feit dat de klinische situatie gepaard gaat met

wat meer artefacten en overhangende restauraties, waren de gevonden in vitro en in

vivo onderzoeksresultaten nagenoeg identiek.

114

Na meer zicht te hebben gekregen op de waarde van versnelde veroudering van de

kunststof hechting aan dentine en aan glazuur was de volgende stap in dit onderzoek

om zich te concentreren op de materiaaleigenschappen van composieten voor

toepassing in de posterieure delen van het gebit. Vooral inzicht in buigsterkte en

(buig-)vermoeiingsgedrag zijn van bijzonder belang voor het verklaren van de

randlekkage en bulkfracturen die in klinische studies met directe composieten vaak

worden gevonden. Een grondige evaluatie van de buig-vermoeidheid karakteristieken

was dan ook het doel van het volgende hoofdstuk van dit proefschrift (hoofdstuk 4).

Volgens dezelfde strategie als in hoofdstuk 3, werd hier ook tegelijkertijd

aangevangen met zowel in vitro als in vivo onderzoek. In het in vitro deel werd de

elasticiteitsmodulus, buigsterkte en buigingsvermoeiingsgrens volgens de “staircase”

methode bepaald. In vivo, werd het klinisch gedrag in termen van randbreuk,

bulkfracturen en ‘chipping’ beoordeeld en gecorreleerd met de uitkomsten van het in

vitro onderzoek. In vitro resultaten tonen bij aanvang dezelfde waarden voor de

verschillende vulmaterialen, echter de buigings/vermoeiingsgrenzen waren hoger voor

Grandio in vergelijking met Tetric Ceram. Daarentegen werden in vivo, waarbij

dezelfde materialen zijn onderzocht, geen verschillen gevonden, zelfs niet na 6 jaar.

Alleen bij een beter zicht, met x200 vergroting van de plaatsen waar randbreuk werd

gevonden, bleek dat Tetric Ceram meer randafwijkingen (7,9%) liet zien ten opzichte

van Grandio (4,8%).

Het ultieme instrument voor de definitieve bepaling van de klinische geschiktheid van

tandheelkundige biomaterialen is nog steeds gerandomiseerd klinisch onderzoek. Met

gebruikmaking van dezelfde vulmaterialen (Solobond M / Grandio, Syntac / Tetric

Ceram), eerder beschreven in de vorige hoofdstukken, werd een prospectieve

klinische langetermijnstudie uitgevoerd met een observatietijd van 6-jaar (hoofdstuk

5). Dertig patiënten ontvingen ten minste twee verschillende restauraties waarbij de

materiaalkeuze op basis van aanbevelingen van de CONSORT verklaring willekeurig

werd bepaald. Zesendertig Grandio restauraties werden met Solobond M als dentine

hechtsysteem geplaatst, 32 Tetric Ceram restauraties werden met Syntac als dentine

hechtsysteem geplaatst (alleen Klasse II, 52 MO / OD, 16 MOD of meer

oppervlakken). In vierentwintig caviteiten (35%) was geen glazuur op de cervicale

rand aanwezig, 33 caviteiten (49%) vertoonden minder dan 0,5 mm cervicale

glazuurbreedte. De restauraties werden bij aanvang, na 6 maanden, 1, 2, 4 en 6 jaar

beoordeeld, op basis van de gemodificeerde United States Public Health Service

Samenvatting

115

(USPHS) criteria door twee onafhankelijke onderzoekers met behulp van loepen met

x3.5 vergroting, spiegels, sondes, bitewing röntgenfoto's, afdrukken, en intra-orale

foto's. Het totale succespercentage van klinisch functioneren was 100% na 6 jaar, alle

patiënten zijn gedurende deze periode in onderzoeksgroep gebleven. Noch

vulmaterialen, noch lokalisatie van de restauraties hebben een significante invloed

gehad op het bepalen van de kwaliteit van functioneren na 6 jaar. Echter,

molaarrestauraties presteerden slechter dan premolaarrestauratiesmet betrekking tot de

integriteit van de randaansluiting (4 jaar), restauratie integriteit (6, 12, 24, 48

maanden), en tand integriteit (4 en 6 jaar). Ongeacht het gebruikte composiet, werden

significante veranderingen in de tijd gevonden voor alle criteria die in het klinisch

onderzoek werden geëvalueerd. De beoordeling van de randaansluiting bij aanvang

leidde tot de constatering van relatief veel overhangende randen (1 jaar) en namen

daarna af (overhang baseline 44%, 6 maanden 65%; 1 jaar: 47%; 2 jaar: 6%; 4 jaar:

4% en 6 jaar: 3%). Naast de 1-jaar recall, werden meer en meer randhoogteverschillen

als gevolg van slijtage gevonden. Tandintegriteit verslechterde als gevolg van het

toenemen van glazuurbarsten in de tijd. Glazuur-‘chipping’ of -barsten werden

significant vaker waargenomen in molaren dan in de premolaren. De belangrijkste

redenen voor het verminderen van "restauratie integriteit" waren zichtbare tekenen

van ruwheid van het oppervlak en duidelijke slijtagesporen. Voor beide materialen

was de zichtbare slijtage eerder detecteerbaar in molaren (74% bravo na 4 jaar) dan bij

premolaren (40% bravo na 4 jaar).

In hoofdstuk 6 wordt de vraag waar het in dit proefschrift om draait behandeld: zijn

klinische prestaties van adhesief geplaatste restauraties te voorspellen met

laboratoriumonderzoek? Meerdere malen is aangetoond dat de makkelijkste manier

van het voorspellen van het klinische gedrag de evaluatie van de marginale integriteit

is. Op dit gebied kan de optimale correlatie tussen in vitro en in vivo resultaten

worden gevonden. De verklaring hiervoor is duidelijk: testresultaten met natuurlijke

tanden en kiezen die zijn voorzien van echte restauraties die worden belast met de

krachten die vergelijkbaar zijn met de subkritische belastingen in vivo resulteren

uiteindelijk in een realistische inschatting van het latere klinisch waarneembare

gedrag. Het is duidelijk aangetoond dat door toepassing van ets- en spoel adhesief

systemen een stevige afdichting van het glazuur, zowel in vitro als in vivo, wordt

verkregen en dat deze hechting zeer geschikt is om de polymerisatiekrachten op te

vangen en om de functionele occlusale spanningen in de mondholte te weerstaan.

116

Echter deze schatting is niet gecorreleerd met het risico op secundaire cariës.

Randspleetvorming leidt niet altijd tot de vorming van secundaire cariës. Een

complexe biofilm ontstaat in de randspleet welke verschillend werkt op de

verschillende harde tandweefsels. De biofilm is uiterst moeilijk te simuleren onder in

vitro omstandigheden. Dus inzicht in de correlatie tussen randspleetvorming en

hetontstaan van cariës is duidelijk nog niet verkregen met de onderzoeken uit dit

proefschrift. Met betrekking tot vermoeiingskarakteristieken in relatie tot buigsterkte,

blijkt in de wetenschappelijke literatuur dat een veelbelovende buigsterkte waarde bij

aanvang niet per definitie betekent dat dit resulteert in een hoge vermoeiingslimiet

(FFL). Een FFL-waarde van > 30 MPa lijkt een kritische drempelwaarde voor

bulkvermoeidheid te zijn om de kauwkrachten langdurig te weerstaan. Dit ondersteunt

het feit dat grondige in-vitro screening van tandheelkundige biomaterialen slechts

toereikend is wanneer vermoeidheidskarakteristieken worden meegewogen. Met

betrekking tot klinische slijtage zijn er enkele studies beschikbaar in de literatuur

waarbij gebruik wordt gemaakt van 3D laser scantechnologie, waarbij de

gerapporteerde slijtage na 3 jaar klinische dienst is in de orde van grootte van ~ 80

µm. De waarde voor versnelde in-vitro testen van tandheelkundige biomaterialen is

van groot belang, de financiële middelen voor klinisch onderzoek nemen af en de

goedkeuring van ethische commissies is steeds moeilijker te verkrijgen.

Tot slot, dit proefschrift laat duidelijk zien dat het belang van in-vitro-onderzoek in de

restauratieve tandheelkunde tijdens het komende decennium zal toenemen.

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Acknowledgements

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To my wife Katherine Garcia-Godoy, who has been a constant beacon in my life and career. Without her this thesis would not have been possible.

To Prof. Albert Feilzer, for his constant support to this project.

To my co-promoters, Prof. Roland Frankenberger and Prof. Norbert Krämer for their vital support to this thesis. With their help this project has been possible.

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