Evaluation of Bond Strength of Various Margin Ceramics to a Zirconia Ceramic

7/25/2019 Evaluation of Bond Strength of Various Margin Ceramics to a Zirconia Ceramic

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Evaluation of bond strength of various margin ceramics

to a zirconia ceramic

M. Erhan Comlekoglu a,*, Mine Dundara, Mutlu Ozcan b, M. Ali Gungora,Bulent Gokce a, Celal Artunca

aEge University, School of Dentistry, Department of Prosthodontics, Izmir, Turkeyb University Medical Center Groningen, University of Groningen, Academic Center for Oral Health,

Clinical Dental Biomaterials, Groningen, The Netherlands

1. Introduction

Various types of reinforced ceramic framework materials have

been introduced in restorative dentistry in an attempt to

improve the mechanical properties of ceramics.15 One such

example is zirconium dioxide (hereon: zirconia)-based mate-

rials. Zirconia is a biocompatible material with excellent

mechanical properties and low bacterial adhesion properties.

Restorations made of this material can be cemented with

conventional cements.4 Several different oxides such as

Magnesia (MgO), Yttria (Y2O3), and Calcia (CaO) are added to

zirconia in order to stabilize their tetragonal and/or cubic

phases to form partially stabilized zirconia. When zirconia

polycrystal is processed with yttria, yttrium-stabilized tetra-

gonal zirconium polycrystal (Y-TZP) is obtained.5 The high

initial strengthand fracture toughness of zirconia results from

a physical property of partially stabilized zirconia known as

transformation toughening.6

j o u r n a l o f d e n t i s t r y 3 6 ( 2 0 0 8 ) 8 2 2 8 2 7

a r t i c l e i n f o

Article history:

Received 13 March 2008

Received in revised form

30 May 2008

Accepted 31 May 2008

Keywords:

Shear bond strength

ZirconiaMargin ceramic

Copy-milling

a b s t r a c t

Objective: This study evaluated the bond strengths of four different margin ceramics based

on fluoroapatite and feldspath to a zirconia ceramic.

Methods: Zirconia cores (Zirconzahn) (N= 28, n= 7/margin ceramic group) were fabricated

according to the manufacturers instructions (diameter: 4 mm; thickness: 2 mm) and ultra-

sonically cleaned. Four different margin ceramics (thickness: 5 mm) (Cerabien Zr, Noritake;

Ceramco PFZ, Ceramco; e.max, Ivoclar Vivadent and Triceram, Dentaurum) were vibrated

and condensed in a stainless steel mould and fired onto their zirconia cores. After trying the

specimens in the mould for minor adjustments, they were again ultrasonically cleaned and

embedded in PMMA. The specimens were stored in distilled water at 37 8C for 1 week and

shear bond strength (MPa S.D.) tests were performed in a universal testing machine

(crosshead speed: 0.5 mm/min). Failure modes were recorded under SEM.

Results: Significant effect of margin ceramic types were found on the bond strength values

(P < 0.05). The mean bond strength values of Ceramco margin ceramic to zirconia was

significantly lower (25.4 4.5 MPa) (P < 0.05) than those of Cerabien (31.6 6.4 MPa), e.max

(35.9 8.4 MPa), and Triceram margin ceramic (38.8 7.1 MPa) systems.

Conclusions: Margin ceramics, compatible with zirconia framework material tested in the

present study, exhibited high bond strength values. Variations in thermal expansion

coefficients might influence their bond strength values.

# 2008 Elsevier Ltd. All rights reserved.

* Corresponding author at: Ege University, School of Dentistry, Department of Prosthodontics, Bornova 35100, Izmir, Turkey.Tel.: +90 2323880327; fax: +90 2323880325.

E-mail address:[email protected](M.E. Comlekoglu).

a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

j o u r n a l h o m e p a g e : w w w . i n t l . e l s e v i e r h e a l t h . c o m / j o u r n a l s / j d e n

0300-5712/$ see front matter # 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jdent.2008.05.019
mailto:[email protected]://dx.doi.org/10.1016/j.jdent.2008.05.019http://dx.doi.org/10.1016/j.jdent.2008.05.019mailto:[email protected]


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Zirconia frameworks can be fabricated mainly with the

help of CAD/CAM or copy-milling techniques by means of

grinding a zirconia block. These blocks can be milled either in

the green, pre-sintered or completelysintered stage.7,8 Frame-

works made from green andpre-sinteredzirconia aremilledin

an enlarged form to compensate for the shrinkage that occurs

during sintering, which usually equals to 2025% for partially

sintered frameworks.9,10 Completely sintered Y-TZP blocks areprepared by pre-sintering at temperatures below 1500 8C and

then processed by hot isostatically pressed (HIP) technique at

temperatures between 1400 and 1500 8C under high pressure

in an inert gas atmosphere. This leads to a very high density in

excess of 99% of the theoretical density.5 The blocks can then

be machined using a specially designed milling system.

The milling of pre-sintered zirconia blocks is faster and

causes less mechanical damage to the material than milling of

fullysinteredblocks.6Comparedtothemillingmethodbasedon

pre-sintering, milling of fully sintered zirconia blocks is a time

consuming process that causes greater wear of the diamond

burs and is more expensive. Moreover, it has recently been

reported thatquestions remained regarding to the surface stateafterhardmachining of Y-TZP, while soft machiningseemed to

lead to a more consistent final state, provided that the

machined restoration was left intact after sintering.5 Hence,

green-stage zirconia could be considered advantageous.

The milled frameworks are then veneered with feldspar or

glassy matrix ceramics appropriate for the zirconia ceramic

used. However, the mechanical properties of zirconia ceramic

areaffected during the veneering stage performed at relatively

higher temperatures.11 The framework suffers from distortion

and shrinkage during sintering and veneering stages but this

does not consequently have a negative effect on the marginal

adaptation. The quality of the marginal adaptation has been

shown to influence the long-term success of restorations.11 Interms of longevity, the clinically acceptable range of marginal

discrepancies is 120 mm. On the other hand, in CAD/CAM or

copy-milling systems, the marginal openinghas been reported

to range between 60 mm and 300 mm.11,12

Margin ceramics are therefore formulated to compensate

for the marginal impurities in orderto maintain accurate fit as

well as resistance to chewing forces. Their shrinkage after

firing/sintering has been minimized. Moreover, fluorescent

agents are added to optimize their aesthetics and opacity has

been balanced to mask the show-through of the more opaque

framework.13 In a recent clinical study on zirconia FPDs, the

overall survival rate was found to be 73.9% with marginal

integrity problems and thereby secondary caries (21.7%) and

ceramic chipping (15.2%) being major causes of failure.17 Also,the most common chippings were observed at the cervical

areas of the reinforced all ceramic fixed-partial-dentures

(FPDs).14

It has been previously demonstrated that marginal dis-

crepancies of conventional metalceramic systems decreased

after the application of margin ceramics.15 Although it is not

commonly practiced, such marginal ceramics, made of either

feldspath or fluoroapatite, are also available to be used in

conjunction withzirconiaFPDs. Since cervicalareas of the FPDS

were reported to be more prone to stresses,16 the adhesion of

such margin ceramics to the core ceramic is of clinical

importance in order not to experience chippings after cementa-

tion. No study to date evaluated their durability on zirconia.Although with fluoroapatite ceramic, high degree of luminous

reflectance andhigh translucencycould be delivered, sincethey

are all glassy matrix ceramics, it can be hypothesized that both

feldspath or fluoroapatite types of margin ceramics would

perform comparable bond strength to zirconia.

Therefore, the objectives of this study were to compare the

adhesion of four individual margin ceramics to a processed

zirconia framework and evaluate the failure modes after

debonding.

2. Materials and methods

Core/margin ceramic combinations (N= 28, n= 7 per group)

were fabricated by one experienced dental technician accord-

ing to each manufacturers instructions. The brand names,

types, compositions, manufacturer and batch numbers of the

margin ceramics, modelling liquid and liners used in this

study are presented inTable 1.

Table 1 Margin ceramics used in this study

Brand name of marginceramic, build-up liquidand liner

Ceramic type Chemical composition Manufacturer Batch number

Cerabien Zr Feldspathic SiO2, Al2O3,Na2O, CaOK2O,

MgO, LiO2, B2O3, pigments

Noritake Dental Supply Co.,

Nagoya, Japan

MB3 OD612

Cerabien Zr forming liquid APEJQ

Ceramco PFZ Feldspathic SiO2, Al2O3,Na2O, K2O,

SnO2,CeO2, pigments,

1.3-Butanediol Xi

Ceramco, Burlington,

NJ, USA

A3-06002487

Ceramco PFZ margin liquid 06003649

E.max margin Fluorapatite SiO2, Al2O3,Na2O, K2O,

ZnO, CaO, P2O5, F, oxides,

pigments

IvoclarVivadent,

Schaan, Liechtenstein

JO6301

E.max Zir liner build-up liquid H33669

E.max margin build-up liquid H32689

E.max Zir liner 2 H12845

Triceram Feldspathic SiO2, Al2O3, K2O, Na2O,

Li2O, CaO, BaO, MgO, B2O3, F

Dentaurum, Ispringen,

Germany

SMA 003F

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2.1. Preparation of the core ceramics

Zirconia core specimens (diameter: 4 mm, height: 2 mm) were

produced by a copy-milling system (Zirconzahn, Bruneck,

Italy) using prefabricated blanks of zirconia (ICE Zirkon,

Zirconzahn, Bruneck, Italy) and then sintered. All of the core

materials were ultrasonically cleaned (Quantrex 90, L&R

Ultrasonics, Kearny, NJ, USA) for 15 min in ethanol anddeionized water and air-dried.

2.2. Preparation of the core-veneer assemblies

The individual veneering ceramics for the zirconia ceramic

cores were condensed at a thickness of 2 mm, positioned on

top of a platinum foil and backed by a glass slide leading to

specimens with 5 mm in diameter and 5 mm in height.

Manufacturers of e.max and Triceram margin ceramics

required an obligatory liner application at the interface

whereas the other two were instructed to be applied directly

to the core ceramic without liners. Ceramic powder for dentin

of four different types of zirconium margin ceramics wasmixed on a glass slab using the mixing liquidas recommended

by each manufacturer. The mould was carefully filled with the

creamy mixture of margin ceramic and condensed. Excess

liquid was removed by applying a piece of adsorbing paper

(Kimwipes1Lite 200, Kimberly Clark Corp., Roswell, GA, USA)

onto the surface of the specimen. After condensation, the

mould was removed, leaving the non-sintered specimen

behind on the platinum foil. The test specimens on the

platinum foil, were then transferred to a firing tray, and

sintered in a calibrated ceramic furnace (Programat P90,

Ivoclar, Schaan, Liechtenstein) in accordance with each

manufacturers instructions. Following the firing process,

the specimens were tried in the mould for minor adjustments,ultrasonically cleaned as described above and embedded in

auto-polymerized polymethylmethacrylate (PMMA) resin

(Palapress, Vario, Heraeus Kulzer, Wehrheim, Germany).

The specimens were stored in distilled water at 37 8C for 1

week.

2.3. Shear bond strength test

Specimens were mounted in the jig of the universal testing

machine (Autograph Model AG-50kNG, Shimadzu, Kyoto,

Japan) and the shear force was applied to the core/veneer

ceramic interface until fracture occurred. They were then

loaded at a crosshead speed of 0.5 mm/min and the stressstrain curve was analysed.

2.4. Failure analysis

Complementary to the bond strength tests, failure modes

were examined at 150 magnification under the scanning

electron microscope (SEM) (JEOL JSM-5200, Kyoto, Japan) at the

fracture site. The failure between the zirconium framework

and margin veneering ceramic was defined as adhesive. The

failure within either the framework or margin ceramic

material was defined as cohesive. The term mixed failure

was used to describe the combination of these two failure

types.

2.5. Statistical analysis

Statistical analysis was performed using SPSS 15.0 for

Windows (Chicago, IL, USA). The means of each group were

analysed by one-way analysis of variance (ANOVA). Due to

significant difference between the groups, Tukeys test was

used to determine the significant differences between ceramic

systems. P values less than 0.05 were considered to be

statistically significant in all tests.

3. Results

Significant effect of margin ceramic types were found on the

bond strength values (P < 0.05). The mean bond strength

values of Ceramco margin ceramic (25.4 4.5 MPa) (P < .05) to

zirconia was significantly lower than those of Cerabien

(31.6 6.4 MPa), e.max (35.9 8.4 MPa), and Triceram margin

ceramic (38.8 7.1 MPa) systems (Fig. 1).

Failure analysis revealed predominantly adhesive type of

failures for Ceramco while in Cerabien, e.max and Triceram

mainly cohesive failures were observed (Table 2). Representa-

tive SEM pictures are presented inFig. 2ad.

4. Discussion

In this study,the shear bond strengths of four different margin

ceramics to a zirconia core ceramic were evaluated. Margin

ceramics have been developed to restore the marginal

impurities caused by the inherent shrinkage behavior of

framework materials. Their reduced shrinkage properties as

well as sealing ability for metal or opaque zirconia framework

collar show-through around the cervical region, propose

advantages for clinical use of margin ceramics.13 In addition

to their optical advantages, margin ceramics should basically

also demonstrate good adhesion to their frameworks. In all-

ceramic restorations, compressive and tensile stresses have

been reported to accumulate on heavy load bearing areas like

Fig. 1 Mean shear bond strength (MPa) of the tested

margin ceramics to zirconia.



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cervical finish lines.17 The margin ceramics should therefore

have highbond strengths to their frameworksin order to resist

these stresses and thereby prevent chipping of the restoration

at the cervical region. Thus,the bond strength test was used toevaluate the adhesion of margin ceramic to a zirconia

framework. The bond strength values of veneering ceramics

to their core ceramics were reported to range between 23 MPa

and 41 MPa.18,19 In this study, mean bond strength values of

the tested margin ceramics to zirconia framework ranged

between 25 MPa and 39 MPa. Although the tested ceramics

were not veneering ceramics, the results of the present study

were compared with the results obtained with veneering

ceramic in previous studies since no data on margin ceramic

bond strength to zirconia framework were available in

reviewed literature.

Several factors such as lack of proper framework support,

internal defects, mismatch between the thermal coefficients

(t) of the veneering and core materials, direction, magnitude

and frequency of the applied load, as well as the residual

stresses induced by processing, were reported to be respon-

sible for the cause of fracture of veneering ceramic on ceramic

core materials.2022 Compressive stresses are generated in the

veneering ceramic as a result of differences in t of both theframework and the veneering ceramics.19 Guazzato et al.23

found that crack propagation occurred very often in the

proximity of the interface in the veneering ceramic. This

phenomenon indicates a region of high stress just above the

ceramiccore interface, and becomes more apparent at higher

t mismatch between the core and the veneering ceramic.

Althought of the three margin ceramics and zirconia frame-

work used in this study were glassy matrix ceramics, t

mismatch of Ceramco-zirconia (9.1 106 K1) and zirconia

framework (11 106 K1) might have resulted in the sig-

nificantly lower SBS results than those of the other groups. In

fact, all the ceramics tested were glassy matrix ceramics but

particle sizes andtmay differ among different brands. In thiscontext, it can be anticipated that among the factors affecting

the bond strengths of the margin ceramics to the framework

material,tof the margin ceramics, rather than their chemical

compositions, might have influenced the results obtained.

Therefore the hypothesis was rejected.

Although failure types may not always correspond to bond

strength results, SEM images showedmainlyadhesive failures

for Ceramcowith which the lowest bond strengthresults were

obtained. On the other hand Cerabien, e.max and Triceram,

with higher bond strength values, exhibited more frequent

cohesive failures within the margin ceramic. However, since

Table 2 Failure types and distribution for each experi-mental group

Adhesive(A)

Cohesivemarginceramic

(CMC)

Cohesivesubstrateceramic

(CSC)

Mixed(M)

Cerabien 2 4 0 1

Ceramco 5 0 0 2E.max 1 4 0 2

Triceram 1 4 0 2

Adhesive (A) = failure between the zirconium framework and

margin veneering ceramic; cohesive in margin ceramic

(CMC) = failure only within the margin ceramic; cohesive in

substrate ceramic (CSC) = failure only within the zirconia ceramic;

mixed (M) = combination of A + CMC.

Fig. 2 SEM images (150T) of the typical failure types for each margin ceramic tested: (a) cohesive failure within the margin

ceramic Cerabien; (b) cohesive failure within the margin ceramic Ceramco; (c) mixed failure type in e.max. The arrow

indicates the cohesive failure in the margin ceramic; (d) cohesive failure within the margin ceramic Triceram.



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in all groups, also some mixed failures were observed, it

cannot be stated that the shear strength values correlate with

the failure types. The question remains to be answered in

future studies whether the bond strength results or solely the

failure types should be considered to assess the performance

of adhesion. The test method used in this study can still be

considered a practical option to monitor the adhesive

performance of ceramics. Considering the nature of themandibular movement against maxilla, shear forces do have

clinical relevance. However, the results should be confirmed

with supplementary data using fatigue tests in more complex

geometries such as an FPD. Also, the behavior in terms of

adhesion and microleakage of margin ceramics cemented to

the dentinwarrantsfurther research. To this point,shear bond

test could be considered as a screening test among all battery

of tests.24

Some ceramic systems advise application of liners on the

core ceramic. Selenium-based feldspathic porcelain liners are

used for masking the opaqueness of zirconia core ceramics.

Depending on the test method used, pretreatment of the core

with liners was not shown to affect the bond strength ofveneering ceramic to the core ceramic. While an increasing

effect was found in flexural strength tests,5 the use of a liner

between zirconia and veneering ceramic was not found to

increase the microtensile bond strengths.25 In this study,

manufacturers of some margin ceramics (e.max and Tri-

ceram) required an obligatory liner application at the interface

whereas others were instructed to be applied directly to the

core ceramic without liners. However, the obtained mean

bond strengths for Ceramco for instance did not reveal any

significant differences between liner applied e.max and

Triceram margin ceramics.

From the clinical point of view, the thickness of the core

ceramic is important and small variations can affect thestrength of the restoration.26 It hasbeen suggested that thicker

ceramic cores lead to bulk fractures in veneer ceramics under

fracture resistance tests. Zirconia core (2 mm)margin cera-

mic (2 mm) ratio in this study was 1:1. When nominal core

ceramic thicknesses (0.51 mm) in bilayered all-ceramic

materials are considered in single or multiple unit FPDs, this

may not seem clinically relevant.21 The objective of this study

was solely to observe the adhesion properties of margin

ceramics designed for zirconia framework and make compar-

isons between available products. Nevertheless, the obtained

bond results could be considered sufficient when compared to

bond strengths to the dental tissues. Future studies may

consider also the coremargin ceramic ratio. This may beparticularly important when tooth preparation has wider

finish lines especially when the abutment teeth are prepared

more than once such as replacement of existing metal

ceramic FPDs with zirconia-based ceramic materials. Further-

more, the right choice and use of margin ceramics may

eliminate chipping problems at the cervical margins of

zirconia FPDs.

5. Conclusions

Margin ceramics, compatible with zirconia framework mate-

rial tested in the present study, exhibited high bond strength

values. Variations in thermal expansion coefficients might

influence the bond strength values of margin ceramics to

zirconia.

Acknowledgements

The authors would like to thank Stephan Fiorillo, mastertechnician from IvoclarVivadent for supplying the zirconia

frameworks and ZirkonZahn Asya Dental Laboratory, Istan-

bul, Turkiye for the processing of the zirconia specimens.

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Evaluation of Bond Strength of Various Margin Ceramics to a Zirconia Ceramic

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