MORPHOLOGICAL ANALYSIS AND MICROTENSILE BOND …

MORPHOLOGICAL ANALYSIS AND MICROTENSILE BOND

STRENGTH EVALUATION OF A SELF-ETCH ADHESIVE TO

CARIES EXCAVATED HUMAN DENTIN PREPARED BY

MECHANICAL, CHEMOMECHANICAL AND Er, Cr: YSGG

LASER SYSTEMS: AN IN VITRO STUDY.

Dissertation submitted to

THE TAMILNADU Dr. M. G. R. MEDICAL UNIVERSITY

In partial fulfillment for degree of

MASTER OF DENTAL SURGERY

BRANCH IV – CONSERVATIVE DENTISTRY &

ENDODONTICS

APRIL 2012

RR AA JJ AA SS DD EE NN TT AA LL CC OO LL LL EE GG EE

RAJA NAGAR, KAVALKINARU - 627 105, TIRUNELVELI DISTRICT.

DCI Recognition No.DE-3 (44) - 93/2246, dated 09/11/1993

Affiliated to The Tamil Nadu Dr. M.G.R. Medical University, Chennai.

DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS

CERTIFICATE

This is to certify that this dissertation entitled “Morphological Analysis and Microtensile Bond

Strength Evaluation of a Self-Etch Adhesive to Caries Excavated Human Dentin Prepared

by Mechanical, Chemomechanical and Er, Cr: YSGG Laser Systems: An in vitro study” is

a genuine work done by Dr. S. K. AJILAL under my guidance during his postgraduate study

period between 2009-2012.

This dissertation is submitted to THE TAMILNADU Dr. M. G. R. MEDICAL UNIVERSITY, in

partial fulfillment for the degree of MASTER OF DENTAL SURGERY in

CONSERVATIVE DENTISTRY & ENDODONTICS – BRANCH IV. It has not been

submitted (partial or full) for the award of any other degree or diploma.

HOD, Professor & Guide

Dr. R. Jonathan Emil Sam. MDS.

Professor & HOD

Department of Conservative Dentistry & Endodontics

Rajas Dental College & Hospital, Raja Nagar, Kavalkinaru.

ACKNOWLEDGEMENT

I take this opportunity to express my sincere and heartfelt gratitude to my postgraduate

teacher and guide Prof. Dr. R. Jonathan Emil Sam, Professor and Head of the department of

Conservative Dentistry & Endodontics, Rajas Dental College, for his inspiring guidance,

constant encouragement, advice, unlimited help and kind support throughout the course of this

study as well as during my entire course.

I express my profound gratitude to co-guide Dr. Renjith Babu, Senior Lecturer,

Department of Conservative Dentistry & Endodontics, Rajas Dental College, for having

reviewed my work and for his support, valuable guidance and supervision during the preparation

of this dissertation.

My sincere gratitude to Dr. Suresh Mohan Kumar professor, Dr. Arvind.V, assistant

professor, Department of Conservative Dentistry & Endodontics, Rajas Dental College, for their

invaluable guidance, constant encouragement and constructive suggestions throughout the course

of my study.

It had been a privilege and honor to have worked under esteemed teachers, Dr. Kashi

Vishwanath. P, Dr. Bejoy John Thomas, Dr. T S P Ram Balaji, Dr. Anoop Samuel, Dr.

Saravanan. Their in-depth knowledge and authority on subject has helped me to learn scientific

look approach to the subject.

I owe my sincere thanks to Dr. Premila Suganthan BDS, Diploma in Laser Dentistry

(IALD, AALZ Aachen University), Director, KP Tooth Care Clinic, Chennai, for her valuable

suggestions, sound advices and for granting me permission to make use of the facilities needed

for this work.

I wish to thank Dr. Neeraja Raju, Associate Professor, Deparment of Pedodontics,

Oxford Dental College Banagalore, for her valuable help during the study.

I sincerely thank Dr. Prabhakar Rao. Senior Principal Scientist & Mr. M. R.

Chandran Senior Technical Officer, of Electron Microscopy & Materials Characterization

Division of National Institute of Interdisciplinary Science & Technology (NIIST)

Thiruvananthapuram, for granting me permission to use the facilities needed for SEM study.

I am extremely thankful to Dr. Narayana Swamy, Scientist-F & Mr. Eldhose. K,

Technical Officer, Geo Science Division, Centre for Earth Science Studies (CESS), Akkulam,

Thiruvananthapuram, for their esteemed co-operation in utilizing the facilities for the

microtensile sample preparation.

My sincerely grateful to Mr. Muraleedharan C V, Engineer-G, Mr. Renjith G,

Engineer-C & Ms. Sreedevi V, Project Assistant, Organ Testing Department, BMT wing, Sree

Chitra Tirunal Institute of Medical Science & Technology (SCTIMST), Poojappura,

Thiruvananthapuram, for their valuable guidance and help in carrying out the microtensile bond

strength determination.

I am thankful to Mr. Muraleedharan Nair, Retired Associate Professor & Consultant

Bio Statistician, Government Medical College, Thiruvananthapuram for the statistical analysis.

It is my extreme pleasure to extend my gratitude to my beloved chairman Dr. Jacob

Raja and founder Chairman Dr. S. A. Raja for their valuable support and constant

encouragement throughout the period of my study.

It gives me immense pleasure to convey my deep indebtness to our respected Principal,

Dr. Suresh Sathiasekhar, Academic Director and Professor Dr. Marykutty Joseph and

Administrative Director Dr. I. Pakiaraj for the permission, help and guidance throughout my

course.

I owe my sincere thanks to Dr. S. Ignatius Rex, former professor and HOD, for his

constant encouragement and unlimited help.

I express my sincere gratitude and is indebted to my colleagues Dr. Arun Mathew

Thomas, Dr. Pramod S Prasad, Dr. Arun Balakrishnan, Dr. Gnanaseelan, Dr. Joan

Mathew, for sharing their views and ideas all through my post graduation course.

I am obliged to Dr. Ambu Suresh and Dr. Segin Chandran for their invaluable

suggestions, help and support during the study.

I am greatly thankful to my Father (Late) S. Krishna pillai, Mother (Late) P.

Saraswathy Amma, Brother Mr. S. K. Anilal, in laws Commander (Rtd) K P Rajendran

Pillai and Mrs. Radhamany Amma, who helped me to tide through all my problems with their

understanding and timely advices.

Above all I bow in gratitude to God Almighty for showering his grace and blessings all

through my life in achieving unexpected goals and proceed towards new height of destination.

Dedicated to-

My beloved wife SINDHU R PILLAI

& my dearest son RIDHIMAN

CONTENTS

1.

INTRODUCTION

1 - 4

2.

AIMS & OBJECTIVES

5

3.

REVIEW OF LITERATURE

6 – 27

4.

MATERIALS & METHODS

28 - 32

5.

RESULTS

33 - 45

6.

DISCUSSION

46 - 58

7.

SUMMARY & CONCLUSION

59 - 61

8.

BIBLIOGRAPHY

62 - 70

LIST OF FIGURES

Fig 1 Extracted human carious tooth with grounding of occlusal surface

Fig 2 a, b, c Chemomechanical preparation with CarisolvTM

and special instruments

Fig 3 a, b, c Laser preparation with Er, Cr: YSGG laser (BIOLASETM

WATERLASE).

Fig 4 Scanning electron microscope (JEOL JSM – 5600 LV)

Fig 5 a, b, c Photomicrographs of tooth prepared with TC bur (X800, X2000 and X5000)

Fig 6 a, b, c Photomicrographs of tooth prepared with CarisolvTM

(X800, X2000 and

X5000)

Fig 7 a, b, c Photomicrographs of tooth prepared with Er: Cr: YSGG laser (BIOLASETM

)

(X800, X2000 and X5000)

Fig 8 Clearfil SE Bond (Kuraray Medical Inc, Tokyo, Japan)

Fig 9 QTH curing unit (Confident Dental – India)

Fig 10 Prepared samples for microtensile bond strength test

Fig 11 Buehler fine sectioning machine (Buehler – USA)

Fig 12 Prepared 1mm² samples

Fig 13 Universal Testing Machine (BIOPULS – INSTRON, USA)

Fig 14 Loading at Universal Testing Machine

Fig 15 Stereomicroscope (Leica, Switzerland)

Fig 16a, b, c, d Photomicrographs of the fractured specimens

LIST OF TABLES

Table I The Micro Tensile Bond Strength (µTBS) values in MPa for the ‘residual caries-

excavated dentin’ according to the caries excavation technique tested (Mechanical (G1).

Table II The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the ‘residual caries-

excavated dentin’ according to the caries excavation technique tested (Carisolv (G2).

Table III The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the ‘residual caries-

excavated dentin’ according to the caries excavation technique tested (Laser (G3).

Table IV Mean Micro Tensile Bond Strength (µTBS) values comparison between Mechanical

(G1), Carisolv (G2) and the Laser (G3) groups using Kruskal-Wallis test.

Table V Comparison of Mean Micro Tensile Bond Strength (µTBS) values of two groups at a

time. Inter group comparison was carried out using Man-Whitney ‘U’ test.

Table VI Distribution of fracture types using different caries removing techniques

LIST OF BAR-DIAGRAMS

Chart I

Bar diagram of Mean Micro Tensile Bond Strength (µTBS) values of different caries

removing techniques.

Chart II

Bar diagram of Distribution of tensile strength in different groups.

Chart III

Bar diagram of Mean Micro Tensile Bond Strength (µTBS) values of different caries

removing techniques in MPa.

Chart IV

Bar diagram of Distribution of type of fractures as seen using the stereomicroscope

Introduction

Introduction

1

Dental caries is ubiquitous in all populations throughout the world and is the

key factor responsible for dental pain and tooth loss in populations throughout the

world43

. It is a process that may take place on any tooth surface in the oral cavity

where dental plaque is allowed to develop over a period of time31

.

The advent of “Adhesive Dentistry” has simplified the guidelines for

cavity preparation enormously. The design and extent of the current preparations are

basically defined by the extent and shape of the caries lesion, potentially slightly

extended by beveling the cavity margins in order to meet the modern concept of

minimally invasive dentistry41

. The superficial necrotic zone of caries-infected dentin

that harbors the core bacterial biomass should be excavated, leaving only ‘residual’

caries-affected dentin lining the cavity with sound enamel margins and dentin

adjacent to the enamel dentin junction, which enables the best peripheral seal to be

achieved with the current adhesive dentin bonding system3.

Caries dentin removal by mechanical means is non-specific nature of

excavation that may result in excessive loss of tissue thus affecting the prognosis of

the treated tooth33

. Other inherent fundamental drawbacks of these approaches are

unpleasantness to patient, need for local anesthesia, and potential effect to the pulp

due to heat and pressure30

.

Numerous caries excavation techniques have been introduced such as plastic

and ceramic burs, caries-disclosing dyes, enzymatic caries dissolving agents, sono-

Introduction

2

abrasion, air abrasion, laser ablation, Photo active disinfection (PAD), Ozone therapy,

Chemical Vapor Deposition (CVD)13

and caries infiltration of low viscosity resin.

They all aim to remove caries-infected tissue as selectively as possible, while being

minimally invasive through maximum preservation of caries-affected tissue. Minimal

invasive preparation techniques claim to achieve controlled removal of infected and

softened dentin while preserving healthy and hard dental tissues and causes minimal

discomfort for the patient63

.

Chemomechanical caries removal system removes only the softened carious

dentin whilst preserving the healthy tissue. The CarisolvTM

system, based on non-

specific proteolytic effect of sodium hypochlorite into which three naturally occurring

amino acids, namely glutamic acid, leucin and lysine are incorporated to form a gel.

The amino acids involve in the chlorination of partially degraded collagen in carious

dentin and initiates disruption of the altered collagen fibers in carious dentin21

.

Recently fluorescence controlled laser was introduced for the selective

removal of carious dentin20.

Laser light on absorption, is converted to heat, which

overheats the water to vaporize and cause micro explosions that can carry away

surrounding tooth fragment. Carbon dioxide, Neodymium and Erbium lasers were

used for the removal of carious dentin. Among these, erbium lasers are more

commonly used due to their ability to ablate enamel and dentin more effectively

because of their highly efficient absorption in both water and hydroxyapatite. Er: Cr:

YSGG laser would be favorable for caries removal because it does not damage dental

pulp tissue62

. More over dentin irradiated using erbium lasers provide microscopically

irregular surfaces and open dentinal tubules without smear layer5.

Introduction

3

During cavity preparation, the surface to bond will be covered by a smear

layer, which is not attached firmly to the tooth surface. The basic mechanism of

bonding to enamel and dentin is essentially an exchange process involving

replacement of minerals removed from the hard dental tissues by resin monomers that

upon setting becomes micro mechanically interlocked in the created porosities37

.

Bonding effectiveness may be impaired by thick smear layers. The recognition of the

role of smear layer in dentin bond strength highlights the importance of the cavity-

preparation method. Current adhesives should be able to dissolve the smear layer

without demineralizing the tooth surface too profoundly, thereby removing

hydroxyapatite at the interface38

.

Mild self-etch adhesives demineralize the dentin surface sufficiently to

provide micro-mechanical retention, while preserving hydroxyapatite within the

hybrid layer to enable additional chemical interaction53

. Phosphoric-acid etching of

dentin could nowadays be considered too aggressive for dentin, given all the

consequences related to exposure of the vulnerable collagen46

. Selective phosphoric-

acid etching of the enamel cavity margins is therefore highly recommended, followed

by applying a mild self-etch procedure to both the beforehand etched enamel and

(unetched) dentin26

.

Micro Tensile Bond Strength (µTBS) test method is one of the most

commonly used methodology to mechanically assess the strength of the resin-dentin

interface complex, since it has several advantages over traditional Tensile and shear-

bond test methodologies, as µTBS test is more versatile as multiple specimens can be

obtained from a single tooth53

. Micro Tensile Bond Strength (µTBS) test produces

Introduction

4

more adhesive failure than cohesive failure, permits testing of bond to irregular

surfaces as well very small areas68

.

This invitro investigation was undertaken to evaluate the morphological

changes, microtensile bond strength and interfacial characteristics of three different

caries excavation techniques namely mechanical (rotary), chemomechanical

(CarisolvTM

) and Er, Cr: YSGG Laser ((BIOLASETM

WATERLASE-MD) using a

two-step self-etch adhesive (Clearfil SE Bond).

Aim & Objectives

Aims & Objectives

5

The aim of this in vitro study was to evaluate the surface characteristics of caries-excavated

dentin and to compare the microtensile bond strength values of an adhesive, bonded to the

residual dentin after three different contemporary caries-excavation methods namely Mechanical

(handpiece and bur), Chemomechanical (CarisolvTM

) and Laser Ablation ( Er, Cr: YSGG laser -

BiolaseTM

) and to assess the failure mode after microtensile testing.

The objective of this in vitro study was to compare the efficacy of three caries-excavation

methods as Mechanical (handpiece and bur), Chemomechanical (CarisolvTM

) and Laser Ablation

( Er, Cr: YSGG laser - BiolaseTM

).

Review of Literature


6

1. Tao L, Pashley DH and Boyd L (1988)67

in an in vitro study compared the effect of

different types of smear layers created on dentin, using burs or sandpaper. Clinically

dentin is shaped with burs prior to dentin bonding, and in laboratory studies bonding is

done on dentin prepared with sandpaper. Human third molars were selected and the

crowns were cemented to plastic cylinders. Teeth were sectioned along the long axis;

smear layer on the dentin and the enamel were created using either bur or sand paper. The

prepared surfaces were restored using composite resin and the shear bond test was

undertaken. There were no statistically significant differences among bond made to

enamel versus dentin smear layer. Dentin smear layer created with slow-speed burs and

silicon carbide sandpaper gave similar bond strengths. Microphotographs of the sides of

sheared surfaces indicated a cohesive failure of the smear layer. The authors suggested

that tooth surfaces prepared with rotary burs should be finished with silicon carbide

sandpaper.

2. Yip HK & Samaranayake LP (1998)77

reviewed the development of various caries

removal techniques and the evolutionary philosophies of cavity preparation which

promulgated over the last century. Caries excavation techniques such as hand

instruments, air-abrasion, air-polishing, atraumatic restorative technique, laser, enzymes,

ultrasonics and chemomechanical agents were discussed elaborately. The article

concluded that, the development of caries removal techniques in restorative dentistry is

progressing towards a more biological and conservative direction.


7

3. Ericson D et al (1999)21

conducted a multicentre clinical study to test the efficacy and

safety of Carisolv for chemomechanical removal of dentin caries. The mean caries

removal time of 10.62min with Carisolv and 4.42min with rotary instruments were

recorded. The volume of Carisolv used was 0.45ml per person. 64% experienced no taste,

77% no smell, 29% experienced taste and 20% experienced smell. 52% of the patients

perceived that Carisolv method was faster than drilling, 25% estimated it to have lasted

the same and 11% estimated it to have lasted longer or much longer. In the study, the

complete caries removal was obtained in 106 of 107 cases and no short-term adverse

effects were observed.

4. Banerjee A, Kidd E A M & Watson T F (2000)11

in an invitro study evaluated five

alternate methods of carious dentin excavation using rotary instruments (no.3 round

carbon-steel bur in a slow speed handpiece), air-abrasion, sono-abrasion and carisolv

with hand excavation. Though bur excavation was found to be quickest and carisolv the

slowest, it was found that bur excavation tended to over prepare, sono-abrasion under-

prepare and carisolv removed adequate amount of caries

5. Banerjee A, Watson T F & Kidd E A M (2000)9 reviewed and discussed some of the

techniques available to excavate demineralized dentin clinically. These methods can be

classified as mechanical rotary, mechanical non-rotary, chemomechanical and laser

photo-ablation that include: dental handpieces/burs, manual excavators, air-abrasion, air-

polishing, ultrasonication, sono-abrasion, chemo-mechanical methods, lasers and

enzymes. The advantages and disadvantages of each technique were discussed.


8

6. Banerjee A, Kidd EAM and Watson TF (2000)10

evaluated the time taken and quantity

of dentin removed using four caries-dentin excavation techniques namely bur, air-

abrasion, sono-abrasion and carisolv gel, and were compared to conventional hand

excavation. Eighty freshly extracted molars were assigned to four experimental groups of

20 teeth each, which were sectioned longitudinally through the occlusal lesion and pre-

excavation color microphotographs were obtained. Using natural autofluorescence of

carious dentin as an objective, carious dentin removal was assessed in each half of the

split-tooth sample. A confocal laser scanning microscope was used for this study. The

end-point of excavation was checked using a dental probe and the final color

microphotographs were taken. The study concluded that bur excavation was quickest but

resulted in over preparation. Carisolv excavation was the slowest, but removed adequate

amount of tissue. Sono-preparation tends to under prepare where as air- abrasion was

more comparable to hand excavation in both the time and the amount of dentin removed.

7. J. A. Beeley,1 H. K. Yip,2 and A. G. Stevenson (2000)8 reviewed Chemomechanical

caries removal techniques which involve the chemical softening of carious dentin

followed by removal with gentle excavation. The reagent involved is generated by

mixing amino acids with sodium hypochlorite; N-monochloroamino acids were formed

which selectively degrade demineralized collagen in carious dentin. The procedure

requires 5–15 minutes but avoids the painful removal of sound dentin thereby reducing

the need for local anaesthesia. It is well suited for the treatment of deciduous teeth, dental

phobics and medically compromised patients. The dentin surface formed is highly

irregular and well suited to bonding with composite resin or glass ionomer. When


9

complete caries removal is achieved, the remaining dentin is sound and properly

mineralized. The system was originally marketed in the USA in the 1980’s as Caridex.

Large volumes of solution and a special applicator system were required. A modification

of this system known as Carisolv was introduced in 1998, that comes as a gel, which

requires volumes of 0.2–1.0 ml and is accompanied by specially designed instruments.

8. Splieth et al (2001)60

assessed the efficacy of carisolv and rotary instruments in

removing dentin caries. Caries removal with Carisolv or rotating round bur was

monitored by checking the hardness of the dentin with a dental explorer and was stopped

when a leather hard texture was reached or a sharp scratching sound was heard. After

embedding and sectioning, caries activity of the residual dentin was assessed using

methyl red dye. Carisolv treatment resulted in higher mean depth of caries-active dentin

(71 to 78µm) than conventional caries removal using round bur (19-51 µm). The authors

concluded that carisolv treatment leaves about 50 µm more carious dentin than caries

removal with round burs.

9. Bart Van Meerbeek et al (2003)38

stated that bonding to tooth tissue can be achieved

through etch & rinse, self-etch or glass ionomer approach. The basic bonding mechanism

to enamel and dentin of these three approaches were demonstrated by means of ultra-

morphological and chemical characterization of tooth-biomaterial interfacial interactions.

Bond-strength testing and measurement of marginal-sealing effectiveness were evaluated

upon their value and relevance in predicting clinical performance. Benefits and

drawbacks of etch and rinse versus self-etch was thoroughly evaluated. It was concluded


10

that the conventional three-step etch & rinse adhesives performed more favorably and are

more reliable in long-term. Mild self-etch adhesives that bond through a combined

micromechanical and chemical interaction with tooth tissue were comparable with

conventional three-step systems in bonding performance.

10. Laura Ceballos (2003)14

evaluated the microtensile bond strength (µTBS) of total-etch

and self-etch adhesives to caries affected versus normal dentin. The bond strength results

were correlated with DIAGNOdent laser fluorescence and Knoop microhardness (KH)

measurements of the dentin substrates. Extracted carious human molars were ground to

expose flat surfaces with caries surrounded by normal dentin. Surfaces were bonded

respectively with Prime & Bond NT, Scotchbond 1, Clearfil SE Bond and Prompt L-

prop, and core build up was done using resin composite. 1 mm² samples were prepared

and the microtensile bond strength (µTBS) test was carried out. The results showed high

bond strength values for total-etch than self-etch samples. This study concluded that

total-etch adhesives produced higher bond strengths to normal and caries-affected dentin

than self-etching systems.

11. Sonada H, Banerjee A, Watson TF et al (2005)59

conducted an invitro study to

compare the micro-tensile bond strengths of two different adhesive systems, ABF

(Clearfil Protect Bond) and PBNT Prime & Bond NT, bonded to caries-affected dentin

retained after chemo-mechanical caries removal using Carisolv gel, and to the residual

dentin after conventional hand instrumentation. Matchstick-shaped samples were

prepared and the microtensile bond strength values were recorded. Scanning electron


11

microscope (SEM) was used to ascertain the mode of failure at the restoration–dentin

interface. ABF group showed no difference in bond strengths between the controls and

Carisolv group but these values were significantly higher than those for the hand-

excavated samples. PBNT samples showed no significant differences in any of the three

test groups. They concluded that microtensile bond strengths of PBNT/composite

restorations to caries-affected dentin in clinical cavities were statistically comparable to

those to sound dentin. In the ABF/composite restored group (self-etched), the use of

conventional hand excavation appeared to weaken the bond strength to the remaining

caries-affected dentin. However, the use of Carisolv gel excavation did not compromise

bond strengths to caries-affected dentin.

12. William J Dunn et al (2005)18

evaluated dentin and enamel bond strength to resin

composite following high-speed rotary or Er: YAG laser preparation with total-etch

adhesive system. Extracted human molar teeth without visible caries or surface defects

were selected. Specimens having enamel and dentin were prepared with high-speed

rotary or Er: YAG laser and etched either with 37% phosphoric acid or not etched.

Composite was bonded to specimens and after thermocycling, samples were tested for

shear bond strength. There was significant difference between the etched and the not-

etched samples. Acid etched specimens had higher mean bond strengths, with rotary

preparation specimens having significantly higher mean strength versus laser prepared

specimens. Within the group comparison, acid etching was better than laser etch, and

laser etch was better than nonetch samples. Scanning electron microscopy of laser ablated

specimens demonstrated significant surface scaling and subsurface fissuring beyond


12

normal resin penetration depth. This study concluded that adhesion to laser-ablated or

laser-etched dentin and enamel was inferior to that of conventional rotary preparation and

acid etching.

13. Inoue G et al (2006)28

conducted a study to examine the ultrastructure of both intact and

caries affected dentin-adhesive interface after artificial secondary caries formation, using

scanning electron microscope (SEM) and nanoindentation testing. Half of the prepared

specimens were bonded with Clearfil SE Bond and a resin composite for the

nanoindentation test. The other specimens were stored in a buffered demineralizing

solution for ninety minutes, and then observed under SEM. An acid-base resistant zone

(ABRZ) was observed beneath the hybrid layer. The ABRZ of caries-affected dentin was

thicker than that of normal dentin. It is suggested that, the monomer of Clearfil SE Bond

penetrated deeper into the residual dentin, which created a thicker hybrid layer.

14. Lennon AM et al (2006)35

conducted an in vitro study to compare the efficiency of four

caries excavation methods namely fluorescence aided caries excavation (FACE), caries

detector dye (CD), chemomechanical excavation (CS) and conventional excavation (CE);

and to compare the time taken to excavate and successfully remove bacterially infected

dentin. In the FACE group, the operating field was illuminated with violet light and the

operator observed the teeth through a 530nm yellow glass filter and removed the infected

dentin which was seen as orange-red fluorescing areas using a slow-speed bur. In the CS

group, Carisolv was applied to the cavity and allowed to act for 30 sec and the caries

excavation was performed using special hand instruments. In the CD group, caries was


13

removed using caries detector and in the CE group, conventional excavation was carried

out using visual tactile criteria. The excavation time was recorded. Results showed that

excavation time was significantly shorter for FACE (3min 3sec), compared to CS (5min

8sec), CD (5min 26sec) and CE (4min 2sec). Microscopic examination revealed; bacteria

were significantly less in FACE samples when compared to CS and CD groups, but the

bacterial count were comparable with CE group. The study concluded that the excavation

with fluorescence aided caries excavation (FACE) is equal to conventional excavation

(CE) and superior to caries detector dye (CD) and chemomechanical excavation (CS).

15. Nelson R F A Silva et al (2006)56

conducted a study to test the hypothesis that there is a

reduction in bond strength when a micro tensile load is applied to adhesive junctions

prepared at 10, 20 and 30 degrees to the usual perpendicular interface. Extracted human

third molars were selected, occlusal enamel was removed, self-etch adhesives were

applied, and composite resin restorations were done. The teeth were sectioned at 10, 20

and 30 degrees to the bond interface and the control group sectioned at 0 degree bond

angle. The bond strength resulted in lower values as the angle on the interface increases.

They proved that there is a reduction in bond strength when a micro tensile load is

applied to different angles.

16. Bor-Shiunn Lee et al (2007)34

investigated the tensile bond strength of composite resin

to Er:Cr:YSGG laser irradiated dentin. The study analyzed the resin-dentin interface

among bur-cut/acid etched, Er:Cr:YSGG laser ablated / acid etched and Er:Cr:YSGG

laser ablated dentin. Crown dentin disks were prepared from extracted human third


14

molars and SEM analysis was undertaken. SEM analysis showed all the three groups

were free of dentin debris and smear layer. The peritubular dentin was found protruded

from the surrounding intertubular dentin after laser irradiation. No statistical difference

was found in the tensile bond strength of the first and second groups, whereas the third

group values were lower. It was proved that Er:Cr:YSGG laser ablation adversely affects

the adhesion of resin to dentin and the acid etching followed by laser ablation method

was able to increase the tensile bond strength.

17. Omar H et al (2007)44

compared the ability of two self-etch adhesives and a

conventional three-step adhesive to bond composite to both intact and caries-affected

dentin with and without thermocycling. Thirty extracted human teeth with occlusal caries

were randomly assigned to three groups according to the adhesives used: Scotchbond

multi-purpose, Clearfil SE bond and Xeno IV. The occlusal surfaces were ground;

adhesives were applied, and restored using a composite material. 1mm² thickness sections

were obtained using a micro-slicer. Half the specimens were subjected to thermocycling

prior to testing. All the specimens were subjected to microtensile bond strength (µTBS)

testing. Mean µTBS values were: Scotchbond multi-purpose – 22.19 and 15.7MPa;

Clearfil SE bond – 24.25 and 22.3MPa and for Xeno IV – 21.43 and 18.3 MPa

respectively of initial and after thermocycling procedure. This study concluded that two-

step self-etch adhesives produced comparable µTBS values to both sound and residual

dentin and thermocycling significantly reduces µTBS values of specimens.


15

18. Zuhal Kirzioglu et al (2007)30

studied the clinical efficacy of Carisolv™ system and

hand excavation methods in the removal of occlusal dentin caries of primary molar teeth.

Both Carisolv system and hand excavation methods were applied for the removal of

caries on different teeth and were restored. The clinical follow-up was made every 3

months within a year. At the end of 1 year, outcome of the Carisolv and the hand

excavation groups in terms of marginal adaptation were found to be comparable.

19. Arlene Tachibana et al (2008)62

evaluated the influence of the dental surfaces obtained

after the use of different caries removal techniques on bonding of a self-etching system.

Extracted, carious, human molar teeth were selected and the caries lesions were removed

by mechanical, Carisolv and Er: Cr: YSGG laser. The prepared teeth were submitted to a

bonding system followed by construction of resin based composite crown. Hour glass

shaped samples were obtained and submitted to the micro-tensile bond strengths (µTBS).

The highest bond strengths were observed with the sound dentin treated with burs and

Carisolv. The samples of the sound dentin presented higher bond strength than samples of

the caries affected dentin. Among the caries removal methods tested, the Er: Cr: YSGG

laser ablation was the poorest in providing a substrate for bonding with the self-etch

system used.

20. J Eberhard et al (2008)20

evaluated the extension of cavities prepared conventionally by

bur or by Er:YAG laser. Extracted human teeth with dentin caries were bisected through

the caries lesion and was treated by Er:YAG laser and by mechanical caries removal. The

specimens were subjected to histological staining and a quantitative evaluation of the


16

cavity area (mm²) by computer-assisted alignment. 23 out of 29 cavities were smaller

after caries removal with laser compared to the bur. This invitro study indicates that

caries removal by Er:YAG laser resulted in less dentin than that of caries removal by a

rotary instruments.

21. Marcio V Cardoso, BV Meerbeek et al (2008)13

studied the influence of dentin cavity

surface finishing on microtensile bond strength (µTBS) of adhesives. Tooth preparation

techniques such as chemical vapor deposition (CVD), laser irradiation and conventional

mechanical methods were followed. The morphological characteristics of dentin prepared

with these techniques were also evaluated. Scanning electron microscopic examination

revealed different morphological features on the dentin surface depending on the caries

excavation method. Microtensile bond strength (µTBS) evaluation resulted in lower

values for chemical vapor deposition (CVD) and Er, Cr: YSGG laser irradiation

techniques than to conventional rotary prepared dentin. This study concluded that

alternate cavity preparation techniques negatively influenced the microtensile bond

strength (µTBS) of the adhesives.

22. Michal Staninec et al (2009)57

conducted a study to prove the hypothesis that, laser

initiated cracks resulted in lower bending strength of dentin tested. Dentin beam

specimens were prepared from human molar teeth and divided into three groups as

control, wet & dry and was irradiated with either Er:YAG or Er, Cr: YSGG laser. The

bending strength of each beam was tested in a universal testing machine. They concluded


17

that, Er:YSGG laser without water caused cracks in the surface that significantly

decreases the bending strength of dentin.

23. Mine A, De Munk, B Van Meerbeek et al (2009)39

in an invitro study, evaluated the

bonding effectiveness of two new self-etch adhesives (Adper Easy Bond and Adper

ScotchBond SE, 3M ESPE) to enamel and dentin and to characterize the interfacial ultra-

structure at enamel and dentin using transmission electron microscope (TEM). The

adhesives were applied to coronal human enamel and dentin surfaces and core build up

was done with micro-hybrid resin composite Z100 (3M ESPE). The ‘gold-standard’ two-

step self-etch adhesive Clearfil SE Bond (Kuraray) served as control. Results showed that

the µTBS of the two self-etch adhesives to enamel was significantly lower than that of

the control. To dentin, the µTBS of Adper Easy Bond was significantly lower than that of

Adper ScotchBond SE and the control. TEM showed a tight interface to enamel for all

the three self-etch adhesives but observed spot and cluster like nano-leakage in dentin.

This study concluded that the new two self-etch adhesives revealed a tight interaction at

both enamel and dentin, their bond strength to both tooth tissues was generally lower than

that of the adhesive Clearfil SE Bond (control).

24. Maria Paula Gandolfi Paranhos et al (2009)45

evaluated the Microtensile Bond

Strength (µTBS) of two adhesive systems to carious or normal dentin. Adhesives used

were Adper single bond plus and Clearfil SE bond. The prepared teeth were divided into

twelve groups: group one to six were submitted to pH cycling for artificial caries and

group seven to twelve with normal dentin. Dentin surfaces were treated with either, laser

Nd: YAG irradiation for one minute, laser Nd: YAG irradiation associated with fluoride


18

gel, or no treatment. Adhesive systems were applied and a composite resin block was

built up. Teeth were sectioned serially to get a 0.8 mm² samples and were submitted for

Microtensile Bond Strength (µTBS) testing. The study results showed the highest mean

bond strength was obtained in groups of normal dentin treated with Clearfil SE Bond

(40.65MPa). Laser irradiation with fluoride decreased the bond strength value of both the

adhesives. Presence of carious dentin significantly reduces the bond strength value of

both adhesive systems. This study concluded that after excavating the caries affected

dentin, the use of erbium laser followed by a self-etching adhesive system is the best

clinical choice when considering the bond strength; compared with the total-etching

based system.

25. Nathalie Brulat et al (2009)5 conducted a study to compare the shear bond strength of

composite resin bonded to Er:YAG laser or bur-prepared dentin surfaces using three self-

etching adhesive systems. Occlusal surface of the extracted human third molars were

grounded to expose dentin and the dentin was prepared using either a carbide bur or Er:

YAG laser. Three different self-etching adhesive systems were applied: iBondTM

, Xeno

IIITM

and Clearfil SE BondTM

. Samples were restored with composite resin and shear

bond tests were carried out. It was found that Xeno III showed no difference in shear

bond strength to bur and laser. Shear bond strength values of iBond and Clearfil SE Bond

to laser prepared dentin were lower than preparation with burs.

26. Avijit Banerjee et al (2010)3 evaluated the amount of residual dentin retained after using

three excavation techniques; namely hand, Carisolv and an enzymatic gel (SFC-V). The


19

microtensile bond strengths (µTBS) to residual dentin were assessed using an offset

micro-tensile testing device, comparing etch-rinse versus self-etching adhesives. They

found that surface roughness and smear layer formation is more with hand excavation

when compared with chemomechanical system. µTBS value from etch-rinse sample

showed statistical difference between hand and Carisolv groups. Self-etch samples

showed significant difference between hand and Carisolv as well hand and Biosolv. This

study concluded that different caries excavation techniques have an effect on the

microtensile bond strength (µTBS) of adhesives to dentin.

27. Snejana et al (2010)63

conducted an in vitro investigation aimed to study the

morphological changes in the hard dental tissues after using different caries removal

methods by means of scanning electron microscope. Caries excavations in freshly

extracted human teeth were done using Er: YAG laser, Carisolv gel and mechanical

preparation. Results showed considerable differences in surface characteristics of dental

tissues. This study concluded that, dental tissue prepared using steel and diamond burs

showed surfaces covered with a thick smear layer that may be relevant to the subsequent

bonding of adhesive restorative material. Carisolv samples showed a rough retentive

surface, where as Er: YAG laser prepared teeth surface remained without smear layer and

clearly exposed dentinal tubule orifices.

28. Sarr M et al (2010)53

evaluated mechanically and ultra-morphologically eleven different

adhesive systems bonded to dentin. The resultant interfacial ultra-structure in dentin was

characterized by Transmission electron microscope (TEM). The Micro Tensile Bond


20

Strength (µTBS) of eleven adhesives, including two three-step etch & rinse, three two-

step etch & rinse, two two-step self-etch and four one-step self-etch adhesives to dentin,

were measured. The microtensile bond strength (µTBS) varied from 11.1 to 63.6 MPa;

the highest bond strengths were obtained with the three-step etch & rinse adhesives and

the lowest with one-step self-etch adhesives. Mild self-etch adhesives demineralized the

dentin surface sufficiently to provide micro-mechanical retention, while preserving

hydroxyapatite within the hybrid layer to enable additional chemical interaction. This

study concluded that adhesives with simplified application procedure still underperform

when compared to conventional three-step adhesives. “Mild” two-step self-etch adhesives

provide additional chemical bonding, which appears to be the most acceptable bonding

effectiveness with a simplified application protocol.

29. J D Scholtanus et al (2010)55

conducted a study to determine the microtensile bond

strength of three different adhesive systems to caries-affected dentin. Extracted human

molars with primary carious lesions were ground flat to expose dentin and the caries-

infected dentin was excavated with the help of caries detector dye. Three adhesives

namely Adper Scotchbond(2 step etch & rinse adhesive), Clearfil S Bond(one step self-

etch) and Clearfil SE Bond(two step self-etch) were used and a resin composite buildup

was done. Specimens were sectioned into 1.0 x 1.0mm bars and µTBS was measured in a

UTM at a crosshead speed of 1 mm/min. All the three adhesives showed comparable

result to sound dentin whereas Scotchbond and Clearfil S bond showed significantly

lower bond strength value to caries-affected dentin. They concluded that two step self-


21

etch adhesive Clearfil SE Bond showed better result than etch & rinse and one step self-

etch adhesive.

30. Ahmed A EL Zohairy (2010)78

in an in vitro study evaluated the efficacy of the

microtensile bond strength (µTBS) and micro shear bond (µSBS) in ranking dental

adhesives according to bond strength tests. Forty four caries-free extracted human molars

were divided into two groups. After occlusal grinding, different types of adhesive

systems were applied and the resin core build was done. Samples were stored in water for

24h and the microtensile bond strength (µTBS) tests were carried out. The resulted test

ranks of adhesives were analyzed. The authors concluded that, microtensile bond strength

(µTBS) tests appeared to be more accurate in differentiating among adhesives.

31. Steve Armstrong et al (2010)1 reviewed the mechanics, geometry, load application and

other testing parameters of ‘micro’ tensile and shear tests, and to outline their advantages

and limitations. The testing of multiple specimens from a single tooth conserves

specimens and allows research designs not possible using conventional ‘macro’ methods.

Specimen fabrication, gripping and load application methods, in addition to material

properties of various components comprising of the resin-tooth adhesive bond, will

influence the stress distribution and consequently the nominal bond strength and failure

mode. For the foreseeable future, both ‘micro’ and ‘macro’ bond strength tests will be an

important tool for improving resin-tooth adhesion to increase the service life of dental

resin-based composite restorations.


22

32. Ulrich Salz & Thorsten Bock (2010)68

reviewed testing adhesion of direct restoratives

to enamel and dentin. They aimed to survey available methods of adhesion testing and

influential parameters affecting experimental outcome. The longevity and success of

modern dental restorations very often relies on potent dental adhesives to provide durable

bonds between the dental hard substance and the restorative composite. This review

provided a current overview of bond strength testing methods and their applicability to

the characterization of dental adhesives. Preparatory parameters possess tremendous

influence on the validity and scope of obtained data. A subtle variation in sample

preparation may severely impact test results. This article discusses the most influential

parameters, such as substrate nature, age, health status, storage, pre-treatment and sample

preparation.

33. A clinical study conducted by Yazici AR et al (2010)75

evaluated the two year clinical

performance of two minimally invasive cavity preparation techniques using bur and laser;

in class I occlusal resin composite restorations. Twenty seven patients, each having at

least one pair of occlusal caries, were selected for the study. For each patient, one cavity

was prepared with a diamond bur and the other was prepared with Er, Cr: YSGG laser

and the cavities were restored with a nano filled flowable resin composite using an etch

& rinse adhesive. The restorations were evaluated at baseline, 6, 12, 18 and 24 months

according to modified Cvar/Ryge criteria (alpha, Bravo & Charlie). Patient recall rate

was 100%. The retention rates of restorations at 24 months were 98.1% for bur and 100%

for the laser-prepared group. After 24 months, 5.6% of bur prepared and 7.4% of laser-

prepared were rated bravo in marginal discoloration. Marginal adaptation for bur


23

prepared was 9.3% and laser-prepared was 13% in 24 months and was rated bravo. This

study concluded that there were no significant difference between the two cavity

preparation techniques and both the techniques performed equally, with excellent

outcomes after a 24-month period.

34. Aline de A. Neves et al (2011)41

reviewed current concepts and techniques for caries

excavation and adhesion to residual dentin. New caries excavation techniques have been

introduced, such as the use of plastic and ceramic burs, improved caries disclosing dyes,

enzymatic caries-dissolving agents, caries-selective sono/air abrasion and laser ablation.

They all aim to remove or help remove caries-infected tissues as selectively as possible,

while being minimally invasive through maximum preservation of caries affected tissue.

Each technique entails a specific caries-removal endpoint and produces residual dentin

substrates of different natures and thus different receptiveness for adhesive procedures.

They summarized that bond strength of caries-affected dentin is lower than that at sound

dentin interfaces and also no difference in bond strength between etch and rinse as well

self-etch approach. They concluded that the design and extent of the current preparations

are basically defined by the extent and shape of the caries lesion, potentially slightly

extended by beveling the cavity margins in order to meet the modern concept of

minimally invasive dentistry.


determined the caries-removal effectiveness (CRE) and

minimal-invasiveness potential (MIP) of contemporary caries-removal techniques.

Carious molars were scanned using micro-CT, after which dentin caries was removed by


24

9 contemporary caries-removal techniques. The micro-CT was repeated and CRE was

determined on basis of the relative volume of residual caries and the mineral density

(MD) at the cavity floor. MIP was determined by measuring the cavity size relative to the

initial size of the caries lesion. The study concluded that, Er:YAG-laser aided by Laser

Induced Fluorescence resulted in non-selective caries removal. Rotary/ oscillating caries

removal may lead to over-excavation. The risk for over-excavation was reduced with

carisolv group and the chemo-mechanical methods were most selective in removing

caries, whilst preserving sound tissue.


evaluated the micro-tensile bond strength (µTBS) and

interfacial characteristics of adhesive–dentin bonds produced after caries-removal with

contemporary techniques. Carious molars were sectioned at the base of the fissure, and

after caries-excavation, a composite was bonded using a 2-step self-etch adhesive.

Results showed µTBS to residual caries-excavated dentin was lower than to sound dentin.

They found that various caries-removing techniques had different effects on the µTBS.

Er:YAG-laser excavation guided by a LIF-feedback system resulted in a statistically

significantly lower µTBS as compared to sound dentin and produced a thick layer of

demineralized/ unprotected collagen at the interface with the adhesive. Carisolv resulted

in the highest µTBS to ‘residual caries-excavated’ dentin, followed by the use of a

tungsten-carbide-bur.

37. Bart Van Meerbeek et al (2011)37

reviewed the current self-etch adhesives. After

presenting the general characteristics of self-etch adhesives, the major shortcomings of


25

the most simple-to-use one-step (self-etch) adhesives are addressed. Special attention was

devoted to the AD-concept and the benefit of chemical interfacial interaction with regard

to bond durability. Finally, issues like the potential interference of surface smear and the

more challenging bond to enamel for ‘mild’ self-etch adhesives are discussed. They

concluded that selective phosphoric-acid etching of the enamel cavity margins is highly

recommended, followed by applying a mild self-etch procedure to both the beforehand

etched enamel and (unetched) dentin. Phosphoric-acid etching of dentin is believed to be

too aggressive for dentin, given all the consequences related to exposure of the vulnerable

collagen.

38. David H Pashley et al (2011)46

conducted a study aimed to explore the therapeutic

opportunities of each step of three-step etch & rinse adhesives. Etch & rinse adhesive

systems are the oldest of the multi-generation evolution of resin bonding systems. The

three-step version involve acid-etching, priming and application of a separate adhesive.

Acid-etching, using 32-37% phosphoric acid (pH 0.1 to 0.4) etches enamel and dentin as

well destroys residual bacteria due to its low pH. Primers are water and HEMA-rich

solutions that ensure complete expansion of the collagen fibril meshwork and wet the

collagen with hydrophilic monomers. In the future, ethanol or water-free solvents may

serve as dehydrating primers which can increase the resin-dentin bond. Three-step Etch

& rinse adhesives produce higher resin-dentin bonds that are more durable than one and

two step adhesives. Incorporation of protease inhibitors in etchants and/or cross-linking

agents in primers may increase the durability of resin-dentin bonds.


26

39. Arlene Tachibana et al (2011)61

conducted a study to detect the influence of blood

contamination on bond strength and the efficacy of cleaning agents on contaminated

enamel and dentin during the adhesion process. One hundred and four extracted human

molars were sectioned into halves along the long axis. Heparinized and fresh blood were

obtained from the same donor, applied and dried to maintain a layer of dry blood on the

top of samples. The cleansing agents used were hydrogen peroxide, anionic detergent and

antiseptic solution. Adhesive was applied and composite resin core build up was done.

Bond strength result showed higher values for groups without contamination than of

contaminated group. There were no statistically significant difference among cleansing

agents and they were as effective as water stream in counter acting the effect of blood

contamination. The study concluded that a water stream is sufficient enough to remove

blood contamination from dental tissues, before the application of adhesive agent.

40. Cecilia Goracci et al (2011)26

conducted an in vitro study to determine the influence of

mechanical properties of resin based composites on the microtensile bond strength to

dentin. Three dimensional models of the microtensile beam were created for finite

element analysis. The tensile strength, flexural strength, tensile elastic modulus, shear

elastic modulus, poissons ratio, Vickers hardness and contraction stress of the resin

composite were assessed. The study found that adhesives did not significantly influence

the microtensile bond strength; but the properties of the resin composite were a

significant factor. The authors concluded that when comparing the bonding potential of

several adhesives with the microtensile technique, the same resin composite should be

used in all the experimental groups for building up of the coronal portion.


27

41. Anne-Maria Vuorinen et al (2011)70

in their study evaluated the effect of water storage

on the microtensile bond strength of composite resin to dentin. Experimental primers

were prepared and applied on to dentin and the resin build up was done. Teeth were

sectioned after 48h, 6 months and 12 months of water storage and tested for microtensile

bond strength. The authors found that long-term water storage decreased the microtensile

bond strength. The study concluded that one-year water storage lowered the dentin bond

strength.

42. Heintze et al (2011)27

evaluated whether the correlation between in vitro bond strength

data and estimated clinical retention rates of cervical restorations depends on pooled data

obtained from multicentre studies or single-test data. Pooled mean data for six dentin

adhesive systems ( Adper Prompt L-Pop, Clearfil SE, Optibond FL, Prime & Bond NT,

Single Bond and Scotchbond Multi-Purpose) and four laboratory methods (macroshear,

microshear, macrotensile and micro-tensile bond strength (µTBS) test) were correlated to

estimated pooled two-year retention rates of Class V restorations using the same adhesive

system. The results of the regression analysis of the pooled data revealed that only the

macrotensile and the micro-tensile bond strength (µTBS) tests correlated well with the

clinical findings. This study concluded that the tensile bond strength tests showed an

adequate correlation rate with the clinical data’s.

Materials & Methods

Materials and Methods

28

1. Sampling procedure.

Forty five extracted cavitated human permanent molars were used in this study. Teeth

with caries lesions limited to the occlusal surface and extending at least half the distance from

the enamel-dentin junction to the pulp chamber were included. Only central dentin portion that is

located directly above the pulp was used in order to minimize any regional variation between the

periphery and the central dentin substrate25

. These characters were determined by visual and

radiographical inspections.

2. Sample preparation.

The occlusal enamel was removed perpendicular to the long axis of the tooth to expose

the dentin surface completely, which contain a central zone of caries-infected dentin surrounded

by sound dentin, by using a low speed diamond saw ( IsoMetTM

Beuhler – USA) under running

water. The exposed flat surfaces were manually polished with a wet 600-grit silicon carbide

paper (Fig. 1).

3. Experimental groups.

The teeth were randomly divided into three groups (n=15), according to the caries

removal methods, as follows:


29

Group I : Mechanical rotary preparation by round tungsten carbide burs/air turbine (NSK

PANA-MAX, Japan).

Group II : Chemo-mechanical preparation with carisolvTM

gel (MediTeam Sweden).

Group III : Laser preparation by Er. Cr: YSGG Laser (BIOLASETM

WATERLASE-MD,

USA).

Preparations were made strictly according to the manufacturer’s instructions. For all the

caries-excavation methods, the infected dentin was removed till clinically detectable hardness of

the dentin was felt.

3.1. Mechanical rotary excavation (GI).

Round tungsten carbide burs No.2 and No.3 were used in an airotor handpiece ( NSK

PANA-MAX, Japan) to remove carious dentin. The full extent of carious dentin including a

periphery of sound dentin was excavated. A spoon shaped hand excavator was used for the

removal of softened caries. Infected-dentin removal was terminated when the soft dentin has

been removed from the cavity surface as clinically detected by using a probe to check the

firmness.


30

3. 2 Chemomechanical preparation with CarisolvTM

(G2).

Caries excavation using carisolvTM

(MediTeam Sweden) was done as per manufacturer’s

instructions. Pre-mixed gel was introduced into the carious dentin for 40sec. The mixture was

agitated against the dentin using a metal mace tip instrument. Once the gel has become cloudy

with a muddy consistency, it was rinsed away and a second fresh mix of gel was applied and

further agitated. Excavation was deemed complete, when the gel failed to become cloudy and the

cavity surface was checked with dental probe for hardness (Fig. 2 a, b, c).

3.3 Er, Cr: YSGG Laser preparation (G3).

Er: Cr: YSGG laser (BIOLASETM

WATERLASE-MD) with a power output of 3.5W,

pulse duration of 140µs, frequency of 20Hz, energy density of 175mj, and a Turbo handpiece

with MX700 micron focusing lens was used. The non-contact mode was used at a distance of 3-

5mm. Cooling was obtained by setting the equipment at the 80% air and 70% water level. (Fig: 3

a, b). caries-excavation was terminated once the firmness of the prepared surface was confirmed

with a probe.

4. Scanning Electron Microscopy (SEM).

After caries excavation, the samples were randomly selected from each group for

scanning electron microscopy (JEOL JSM – 5600 LV) (Fig. 4). These specimens were immersed

in 4% glutaraldehyde solution for 1hr at room temperature. Then they were rinsed in distilled


31

water. The samples were then placed in cold buffer solution of sodium cacodylate for 90 minutes

to fix the organic matter. Specimens were then dehydrated in ascending grades of ethanol (30,

50, 70, 80, 95 and 100% for one hour in each series) and then dried in a Critical Point Drier

based desiccator. The dried specimens were mounted on a metal stand and gold sputter coated

(200 – 250 nm) by cathode atomization under vacuum. SEM images of the caries excavated

surfaces were obtained. For each specimen, three microphotographs of different magnification

(X800, X2000 and X5000) were made. Each SEM photomicrographs were evaluated, described

and the morphological findings were compared.

5. Sample restoration.

After caries excavation, the samples were thoroughly washed with air-spray and gently

air-dried. Then the surfaces were bonded with a two-step self-etch adhesive; Clearfil SE Bond

(Kuraray Medical Inc, Tokyo, Japan) with the aid of a QTH curing unit (Confident Dental India)

according to the manufacturer’s instruction. The bonded surface was restored using a nanohybrid

resin composite (Filtek – Z 250, 3M ESPE. USA). Composite resin was constructed with 1.5mm

increments to reach a height of approximately 6mm. Each increment was light cured for 20

seconds. The samples were then immersed in water at 37°C for 24h.

6. Micro-tensile bond strength test (µTBS).

The specimens were serially sectioned into multiple slices using a low speed diamond

saw ( IsoMetTM

Beuhler – USA) under water cooling. Each slab was ground with an ultra-fine


32

diamond disc in a ‘high-speed precision saw’ (Buehler – USA) under water spray to create a

stick (rod) shaped configuration with a cross-sectional area of approximately 1mm2. The final

width and thickness of the samples prepared were 1mm X 1mm. The prepared rods comprised of

residual dentin, adhesive and composite resin. Silicon sleeves were attached to both the end of

the samples. Specimens were mounted on a pneumatic jig. The tests were taken out using a

universal testing machine (BIOPULS – INSTRON, USA), at a tension of 0.5mm/min until it

failed. Bond strengths were calculated by dividing the load at failure by the cross-sectional

bonding area. The pre-testing failures were considered as 0 MPa.

7. Failure modes analysis.

Dentin-resin samples after microtensile bond strength test were randomly selected and

the interfaces were analyzed using a digital stereoscopic microscope (Leica, Switzerland) at

X100 magnification to evaluate the fracture mode. To determine the fracture mode, the

classification used by Trajtenberg et al64

was adopted:

Type 1 - Complete adhesive failure between resin and dentin

Type 2 - Partial adhesive failure between resin and dentin and partial cohesive failure

within resin

Type 3 - Complete cohesive failure within resin

Type 4 - Partial cohesive failure within dentin.

Fig 1: Extracted carious tooth with Fig 2a: CarisolvTM

grounded occlusal surface

Fig 2b: Special instruments for CarisolvTM

Fig 2c: Chemomechanical preparation with

CarisolvTM

Fig 3a: Laser preparation with Fig 3b: BIOLASETM

WATERLASE

Er, Cr: YSGG laser

Fig 4: Scanning electron microscope (JEOL JSM – 5600 LV)

Fig: 5a

Fig. 5 a b c: SEM images of tooth prepared with TC bur (X800, X2000 and X5000)

Fig: 5b

Fig: 5c



Fig: 6a

Fig. 6 a b c: SEM images of tooth prepared with Carisolv

Fig: 6a Fig: 6b

Fig: 6c

Fig. 6 a b c: SEM images of tooth prepared with CarisolvTM

(X800, X2000 and X5000

(X800, X2000 and X5000

Fig: 7a

Fig. 7 a b c: SEM images of tooth prepared with Er: Cr: YSGG laser (BIOLASE

Fig: 7b

Fig: 7c

Fig. 7 a b c: SEM images of tooth prepared with Er: Cr: YSGG laser (BIOLASE

(X800, X2000 and X5000)

Fig. 7 a b c: SEM images of tooth prepared with Er: Cr: YSGG laser (BIOLASETM

)

Fig 8: Clearfil SE Bond Fig. 9. QTH curing unit

Fig 10a, b: prepared samples for microtesile bond strength test

Fig 11a, b: Buehler fine sectioning machine

Fig 12a, b: Prepared 1mm² samples

Fig 13: Universal Testing Machine Fig 14: Loading at UTM

Fig 15: Stereomicroscope

Fig 16a, b, c, d: Photomicrographs of the fractured specimens

Results

Results

33

Data from the bond strength testing were statistically compared using non-parametric

Kruskal-Wallis one-way ANOVA. Mann-Whitney ‘U’ test was used to identify

significant difference between the different caries removing techniques. A significant

level of 5% was employed for all analysis (p = ≤ 0.05)

1. Scanning Electron Microscopy.

Morphological analysis of the cavity floor prepared with tungsten carbide bur, air

turbine and water cooling appeared rougher with irregular particles scattered throughout

the surface area. A well defined smear layer was detected. Missing of smear layer was

observed in some areas (Fig 5a b c). In the areas of water turbulence; there were patent

dentinal tubule orifices, but without a clear outline of both tubule lumens and peri-

tubular as well intertubular dentin.

CarisolvTM

produced a reduced and more inconsistent smear layer with large areas of

open tubular orifices. The dentinal tubule orifices were visible and there were almost no

smear layer (Fig 6a b c). Preparing the organic matrix using chemo-mechanical

preparation with CarisolvTM

protected the mineralized dental tissue and at the same time

resulted in rough appearance of the treated surface.

Results

34

The dentin surfaces that received Er, Cr: YSGG laser irradiation showed a scaly,

irregular and rugged appearance (Fig 7a b c). There were rough and irregular surfaces

with no smear layer and dentinal tubule orifices were open without widening. The peri

tubular dentin protruded slightly from the surrounding intertubular dentin.

Results

35

Table I – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the ‘residual

caries-excavated dentin’ according to the caries excavation technique tested (Mechanical

(G1).

Frequency Percent

Valid

Percent

Cumulative

Percent

Valid

0.93513 1 6.7 6.7 6.7

2.73848 1 6.7 6.7 13.3

2.92532 1 6.7 6.7 20

3.51224 1 6.7 6.7 26.7

3.95952 1 6.7 6.7 33.3

4.43319 1 6.7 6.7 40

6.279 1 6.7 6.7 46.7

6.33294 1 6.7 6.7 53.3

6.93334 1 6.7 6.7 60

7.32774 1 6.7 6.7 66.7

8.306 1 6.7 6.7 73.3

8.60986 1 6.7 6.7 80

9.77605 1 6.7 6.7 86.7

9.8309 1 6.7 6.7 93.3

12.3649 1 6.7 6.7 100

Total 15 100 100

Results

36

Table II – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the

‘residual caries-excavated dentin’ according to the caries excavation technique tested

Carisolv(G2) group.

Frequency Percent Valid Percent Cumulative Percent

Valid

1.6044 1 6.7 6.7 6.7

3.113 1 6.7 6.7 13.3

3.28716 1 6.7 6.7 20

3.3461 1 6.7 6.7 26.7

4.07832 1 6.7 6.7 33.3

4.19492 1 6.7 6.7 40

4.3214 1 6.7 6.7 46.7

4.34274 1 6.7 6.7 53.3

5.80472 1 6.7 6.7 60

6.368 1 6.7 6.7 66.7

8.53832 1 6.7 6.7 73.3

8.6999 1 6.7 6.7 80

8.7961 1 6.7 6.7 86.7

9.64364 1 6.7 6.7 93.3

19.3857 1 6.7 6.7 100

Total 15 100 100

Results

37

Table III – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the

‘residual caries-excavated dentin’ according to the caries excavation technique tested:

Laser (G3) group.

Frequency Percent

Valid

Percent

Cumulative Percent

Valid

1.01609 1 6.7 6.7 6.7

1.15049 1 6.7 6.7 13.3

1.41134 1 6.7 6.7 20

1.47562 1 6.7 6.7 26.7

1.91447 1 6.7 6.7 33.3

3.34997 1 6.7 6.7 40

3.61219 1 6.7 6.7 46.7

4.17611 1 6.7 6.7 53.3

4.4698 1 6.7 6.7 60

5.42358 1 6.7 6.7 66.7

5.60265 1 6.7 6.7 73.3

7.03815 1 6.7 6.7 80

7.80213 1 6.7 6.7 86.7

8.39711 1 6.7 6.7 93.3

10.2984 1 6.7 6.7 100

Total 15 100 100

Results

38

Table IV – Mean Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the

‘residual caries-excavated dentin’ according to the caries excavation techniques tested

(Mechanical (G1), Carisolv(G2) and the Laser(G3) groups).

Caries

Removing

Agent

No of

Samples

Mean

Tensile

strength

Median

Tensile

strength

Standard

Deviation

Test of

Significance

Group – I

Mechanical

15 6.2843073 6.3329400 3.1818350 Kruskal-wallis

test

Chi-square

2.424

p-value 0.298

Group – II

Carisolv

15 6.3682973 4.4327400 4.3647770

Group – III

Laser

15 4.4758747 4.1761100 2.9174428

Chart I -

0

1

2

3

4

5

6

7

1 2 3

laser

carisolv

mechanical

Results

39

Table V – Comparison of Mean Micro Tensile Bond Strength (µTBS) values of two

groups at a time.

V A – Comparison between Mechanical (G1) and Carisolv (G2).

Caries

Removing

Agent

No of

Samples

Mean

Tensile

strength

Median

Tensile

strength

Standard

Deviation

Test of

Significance

Group – I

Mechanical

15 6.2843073 6.3329400 3.1818350

Man-

Whitney

‘U’=

106.000

p-value =

0.787

Group – II

Carisolv

15 6.3682973 4.4327400 4.3647770

V B - Comparison between Mechanical (G1) and Laser (G3).

Caries

Removing

Agent

No of

Samples

Mean

Tensile

strength

Median

Tensile

strength

Standard

Deviation

Test of

Significance

Group – I

Mechanical

15 6.2843073 6.3329400 3.1818350

Man-

Whitney

‘U’= 79.000

p-value =

0.165

Group – III

Laser

15 4.4758747 4.1761100 2.9174428

Results

40

V C - Comparison between Carisolv (G2) and Laser (G3).

Caries

Removing

Agent

No of

Samples

Mean

Tensile

strength

Median

Tensile

strength

Standard

Deviation

Test of

Significance

Group – II

Carisolv

15 6.3682973 4.4327400 4.3647770

Man-

Whitney

‘U’= 82.000

p-value =

0.206

Group – III

Laser

15 4.4758747 4.1761100 2.9174428

2. Micro tensile bond strength ( µTBS)

The highest bond strength values were observed in the Carisolv group (6.37MPa) and

the Mechanical group (6.25MPa), and the lowest value was found with the Laser group

(4.47MPa). The data was statistically analyzed using Kruskal-Wallis non-parametric one-

way ANOVA and Mann-Whitney ‘U’ test.

Results

41

Chart II

Chart III

Results

42

Table VI- Fracture Mode Analysis

Types Mechanical(G1) Carisolv(G2) Laser(G3)

1 – A 0 1 5

2 – B 9 5 8

3 – C 1 2 0

4 – D 5 7 2

Chart IV

3. Failure mode analysis

A substantial increase in cohesive dentin failure was observed in CarisolvTM

group. For

the mechanical caries excavation, fractured specimens typically showed a ‘mixed’

fracture pattern. The predominant fracture modes of laser-ablated dentin were Type II

(53%) followed by Type I (33%).

0

1

2

3

4

5

6

7

8

9

10

1 - A 2 – B 3 – C 4 – D

Mechanical(G1)

Carisolv(G2)

Laser(G3)

Results

43

Table I – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the ‘residual

caries-excavated dentin’ according to the caries excavation technique tested (Mechanical

(G1).

Table II – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the

‘residual caries-excavated dentin’ according to the caries excavation technique tested

Carisolv(G2) group.

Table III – The Micro Tensile Bond Strength (µTBS) values in MPa (SD) for the

‘residual caries-excavated dentin’ according to the caries excavation technique tested:

Laser (G3) group.

Table IV – Mean Micro Tensile Bond Strength (µTBS) values comparison between

Mechanical (G1), Carisolv (G2) and the Laser (G3) groups. The values for the ‘residual

caries-excavated dentin’ according to the caries excavation techniques tested were 6.28 ±

3.18, 6.36 ± 4.36 and 4.47 ± 2.91 respectively. Non-parametric Kruskal-Wallis test

analysis (0.298) indicated that they were not statistically significant (p� 0.05).

Results

44

Table V - Comparison of Mean Micro Tensile Bond Strength (µTBS) values of two

groups at a time. Inter group comparison was carried out using Man-Whitney ‘U’ test.

Table II A shows comparison between Mechanical (G1), Carisolv (G2), and the p-value

is 0.787, which is statistically not significant. Table II B is the Comparison

between Mechanical (G1), Laser (G3) and the p-value is 0.165, which is also statistically

not significant. Table II C represents the Comparison between Carisolv (G2), Laser (G3)

groups with the p-value of 0.206 and that showed no significant statistical difference

(p� 0.05).

Table VI – Distribution of fracture types for different caries removing techniques.

Fracture mode analysis exhibited an increase in the percentage of cohesive failure in

dentin with Carisolv (G2) group. The Mechanical (G1) group specimen showed a high

number of ‘mixed’ fracture pattern and the Laser (G3) group revealed a mixed failure

pattern.

Results

45

Chart I - Mean Micro Tensile Bond Strength (µTBS) values of different caries removing

techniques. Kruskal-Wallis test analysis indicated no significant difference (0.298)

between the caries-excavated groups.

Chart II – Distribution of tensile strength in different groups: Carisolv (G2), Laser (G3)

and Mechanical (G1). The dots represent the minimum and the maximum values.

Chart III – Mean Micro Tensile Bond Strength (µTBS) values of different caries

removing techniques in MPa. The boxes represent the spreading of the data between the

first and third quartile. The central line represents the median. The whiskers denote the

5th

and 95th

percentiles. Group I is Mechanical (6.28 ± 3.18), Group II Laser (4.47 ± 2.91)

and Group III is Carisolv (6.36 ± 4.36) in this chart.

Chart IV – Distribution of type of fractures as seen using the stereomicroscope after

Micro Tensile Bond Strength (µTBS) have been performed. An increased number of

cohesive dentin fractures were observed with carisolv group.The mechanical caries

excavation group, fractured specimens typically showed a ‘mixed’ fracture pattern. The

predominant fracture modes of laser-ablated dentin group were of mixed type.

Discussion

Discussion

46

Minimal Invasive Dentistry has gained popularity with the development of new adhesive

systems and technological improvements in tooth preparation75

. Minimal invasive techniques

claimed to achieve controlled removal of infected and softened dentin, while preserving healthy

and hard dental tissues and perform with a minimal discomfort to the patient63,66

. The superficial

necrotic zone of caries-infected dentin which harbors the core bacterial biomass should be

excavated leaving only “residual” caries-affected dentin lining the cavity with sound enamel

margins and dentin adjacent to the enamel-dentin junction3,23

.

Fusayama (1966) claimed that cariogenic bacteria were never found beyond the softening

front of dentin24

. Elimination of the heavily infected dentin and preservation of the residual

affected dentin were thus defined as pre-requisites for effectively arresting the carious process

without harming the long-term survival of the pulp and the restoration32

. This will enable the best

peripheral seal to be achieved with the current adhesive dentin bonding agents55

.

The transition zone between infected and affected dentin is difficult to assess. Change in

color is not a good indicator as the gradual pathologic changes are not consistently color-

dependent60

. Defining the actual end point of caries excavation is the start point of restoration

and is often clinically challenging40

. EAM Kidd (2004) suggested removing carious dentin to the

level where it is ‘firm’42

. The ability of a restorative material to achieve a strong and durable

Discussion

47

bond with the tooth substrate is of paramount importance for the clinical success56

. Complete

removal of infected-dentin is mandatory to attain this goal.

The conventional methods of carious dentin removal by using rotary instruments are

proved to be quick and efficient. However it may result in unnecessary removal of the healthy or

even the affected dentin that shows the ability for remineralization. Moreover this technique is

usually associated with pain and discomfort to the patient77

. As a result of the former drawbacks,

a growing interest has been noticed to develop alternative minimally invasive techniques. The

search for a more gentle, comfortable and conservative caries excavation has led to the

development of methods which aim at providing minimal thermal changes, less vibration and

removal of infected dentin only.

Techniques such as laser, chemomechanical excavation and air abrasion have been shown

to be more or less successful in overcoming these problems15

. These methods offer interesting

advantages in comparison to the conventional approach, but are still far from fulfilling all

requirements. In most cases they are more time consuming than bur preparation, require more

investment and space, and are still dependent on conventional burs to gain access to the lesion

and to finish the preparation margins. Moreover, many of these techniques tend to over or under

prepare or do not completely eliminate the smear layer9. Chemochemical caries removal involves

the selective removal of carious dentin and is proved to be clinically effective in the removal of

infected-dentin and also harmless to healthy tissue and bio-compatible to the pulp8. Carisolv

TM

system, provides efficient removal of dental caries with no harm expected either on the healthy

Discussion

48

dentin or the pulp tissues19

. The chemo mechanical caries removing agent ‘CarisolvTM

’ consists

of 0.5% w/v sodium hypochlorite, 0.1M of an amino acid mixture (glutamic acid, leucine and

lysine) and water11

. It is available in two tube system and the contents of the tubes were mixed

and introduced into the prepared cavity using specific instruments provided by the manufacturer.

The gel was applied in the cavity, after which the carious dentin is scrapped off using specially

designed non-cutting hand instrument30, 16

.

Lasers can be considered as a possible replacement for current caries excavation

methods. Erbium lasers have been pointed out as the most promising, due to their specificity in

ablating enamel and dentin without side effects to the pulp and surrounding tissue57

. The Er:

YAG (Erbium loaded Yttrium – Aluminum –Garnet) and the Er, Cr: YSGG (Erbium,

Chromium: Yttrium – Scandium – Gallium – Garnet) are the two types of erbium lasers currently

available. Both devices present very similar wavelength (2.78µm for Er, Cr: YSGG and 2.94µm

for Er: YAG), although the Er, Cr: YSGG laser is discretely more absorbed by hydroxyapatite

than Er: YAG41,71

. The wavelength emitted by Er, Cr: YSGG laser (2.78µm) coincides with the

absorption peak of water and is well absorbed by all biological tissues including enamel and

dentin34

.

The hard tissue erbium lasers have the capability to prepare enamel, dentin, caries,

cementum and bone in addition to cutting soft tissue. The ability of hard tissue lasers to reduce or

eliminate vibrations, the audible whine of drills, microfractures, and some of the discomfort that

many patients fear and commonly associate with high-speed handpieces is impressive. In

addition, these lasers can be used with a reduced amount of local anesthetic for many procedures,

Discussion

49

which is another feature that makes the hard tissue laser very exciting for needle-phobic

patients62

.

Lee et al (2007) claimed that the dentin irradiated with laser power output above 3.5W

would exhibit micro cracks under SEM examination. Hence in this study dentin surfaces were

irradiated with a laser power output of 3.5W to avoid the micro cracks. Frequency is fixed at

20Hz. Air pressure level of 80% could create the roughest surface and the water pressure level

was elevated to 70% to get a least charred or carbonated dentin surface34

.

Conventional excavation with burs and spoon excavators are the most popular current

caries excavation techniques. The selective removal of caries-infected dentin is not easily

achieved with this method due to relative tactile insensitivity and operator variability; which

leads to varying quantities of tissue removed35

. Most of the caries excavation techniques leave a

layer of smear layer in the residual dentin75

. A major factor to consider in terms of restoring a

cavity with current adhesives are the final dentin surface characteristics such as surface

roughness and the presence of smear layer, which can affect the final bond and the seal achieved

by adhesive systems3, 10, 72

.

The smear layer in caries-affected dentin may be more resistant to the action of self-

etching primers, as they include acid-resistant crystals and extrinsic proteins that might have

permeated into the mineral phase during demineralization cycles76

. If a residual smear layer is

Discussion

50

left on the surface, the adhesive resin will bond to crystals within it rather than to underlying

dentin49

. Moreover, the acidity of the primer could also be buffered by the mineral content of the

smear layer29

. D H Pashley (1995) found that, the presence of mineral casts within the tubules of

caries-affected dentin, would prevent the formation of resin tags in dentinal tubules, and it is

believed that tags are thought to contribute to bond strength67

.

Analysis of the morphological changes in the residual dentin is critical in assessing the

adherence capacity of the caries-excavated dentin. Arguably Scanning Electron Microscope

(SEM) is the best instrument for the topographical analysis as it is easy to operate, large depth of

field which allows more of a specimen to be in focus at one time, much higher resolution and the

data acquisition is rapid28

. Hence, this in vitro study aimed to evaluate morphological changes in

caries-excavated dentin using a scanning electron microscope52

.

Samples for scanning electron microscopic (SEM) evaluation were immersed in 4%

glutaraldehyde for one hour, rinsed in distilled water and placed for one hour in sodium

cacodylate for the fixation of the tooth substrate. Following fixation, the samples were placed in

ethanol in ascending series for the dehydration63

. For SEM analysis, the specimens should be

dried and gold sputter coated for electrical conduction.

Er, Cr: YSGG laser irradiation produced a scaly, irregular and rugged appearance of

dentin in SEM evaluation. Absence of smear layer and partially closed dentinal tubule orifices

Discussion

51

were observed. The peri-tubular dentin was found protruding from the intertubular dentin. It

could be due to the higher mineral content and the lower water content of peri-tubular dentin.

Signs of carbonation were not found. The marked surface irregularities and lack of smear layer

provided solid evidence for the physical mechanism of bonding with the composite material after

laser treatment34, 36

.

The dentin surface treated with CarisolvTM

observed under scanning electron microscope

in the present study showed uneven surface with many undermined areas leaving residual-caries

affected dentin which is partially demineralized and the intertubular dentin exhibiting a high

degree of porosity. There were partially patented dentinal tubules and residues of contaminant

smear layer covering the dentinal surfaces. The dentin topography after Carisolv treatment was

granular and rough comparable to laser prepared dentin. This surface roughness and structural

changes may play a crucial role in adhesion to the composite material, possibly without using

etching agents3, 12

. The ‘Mild’ two-step self-etch adhesives have a potential to penetrate deeper

and form a thick and homogenous hybrid layer.

The scanning electron microscopic examination of the dentin surfaces prepared using

tungsten carbide bur and spoon excavator produced smearing and smear plugs in the tubular

orifice. This method leaves a homogenous smear layer with more or less uniform roughness, and

dentinal tubules visibly obstructed with smear plugs. Though the residual dentin after mechanical

excavation showed similar hardness to that of sound dentin, there are chances of sclerotic dentin

formation within the dentinal tubules that can lead to complete obliteration14

. With regard to

Discussion

52

bonding receptiveness, the smear covered surface does not interfere with the etch-and-rinse

adhesive, but may reduce the bonding effectiveness of self-etching adhesives14, 59

.

The basic mechanism of bonding to enamel and dentin is essentially an exchange process

involving replacement of minerals removed from the hard dental tissues by resin monomers that

upon setting becomes micro mechanically interlocked in the created porosities37, 38

. The etch-

and-rinse and the self-etch methods are employed to produce an effective bond between the

direct restoration and dentin46

. The total-etch technique relies on the removal of the smear layer

and exposure of collagen matrix by acid-etching, followed by the application of a self-priming

agent that combines the primer and the adhesive resin into one solution51

, 37

. Self-etching

adhesive systems have been used to simplify adhesive procedure as it decreases technique

sensitivity45

. The self-etch approach is the use of self-etching primers, in which the acid and the

primer are combined in one solution to form a highly hydrophilic and acidic monomers, that

make hybrid layer more permeable and sensitive to water sorption from the underlying dentin65

.

A two-step mild self-etch adhesive (Clearfil SE Bond, Kuraray, Japan), which have

repeatedly shown to be excellent performer in clinical and laboratory studies and is considered to

be ‘gold-standard’ adhesives for their class, was used in this study39

. Two-step self-etch

adhesives were characterized by separate chemical formulations for priming and bonding,

utilizing a self-etching hydrophilic primer that is followed by the application of a comparatively

mild hydrophobic bonding agent22

. ‘Mild’ self-etch adhesives demineralize the dentin surface

sufficiently to provide micro-mechanical retention, while preserving hydroxyapatite within the

Discussion

53

hybrid layer to enable additional chemical interaction53, 69

. ‘Mild’ two-step self-etch adhesives

that provide additional chemical bonding and that appear to be the most optically combine

bonding effectiveness with a simplified application protocol 53, 74

. Omar et al (2007) proved that

the microtensile bond strength of residual dentin, when bonded with two-step self-etch adhesive

is comparable to that of sound dentin44

.

The performance of enamel and dentin adhesives can be investigated by shear or tensile

bond strength17

. Micro Tensile Bond Strength (µTBS) testing is one of the most commonly used

methodologies to mechanically assess the strength of resin dentin interface complex1. Adhesive

performance of the enamel and dentin can be tested by macro or micro bond strength approaches,

depending upon the size of the bonded area27

. The macro bond strength tests as tensile bond

strength and shear bond strength are performed in specimens with bond area of 3 mm² or more68,

4. The use of macro test methods has been eclipsed in the recent years because of the advantages

of micro test methods78

. Currently Micro Tensile Bond Strength (µTBS) test is the most popular

method47

.

The advantages of the Micro Tensile Bond Strength (µTBS) test can be enumerated as68, 48

:

1. More adhesive failure, fewer cohesive failure

2. Higher initial bond strength

3. Permits measurements of regional bond strength

4. Means and variances can be calculated for single teeth

Discussion

54

5. Permits testing bonds to irregular surface

6. Permits testing of very small areas

7. Facilitate SEM examination of the failed bonds since the surface area is

approximately 1 mm².

1 mm² samples were prepared for the Micro Tensile Bond Strength (µTBS) test. The

adhesive (Clearfil SE Bond, Kurraray, Japan) was applied over the prepared dentin and

composite resin was incrementally polymerized onto the adhesive26

. Four millimeter to six

millimeter thickness of composite resin was bonded over the prepared surface; which helped to

prepare samples containing residual dentin, adhesive junction and the composite resin, which

favors easy holding of samples during testing6. After a storage period of 24hours in water

70, the

specimen was sectioned to 1 mm² stick shaped samples using a high-speed precision saw

(Buehler – USA) under water spray50

.

Sample preparation for the Micro Tensile Bond Strength (µTBS) test can be of stick

shaped, dumbbell shaped or hour-glass shaped. Studies have shown that stick and dumbbell

shaped specimens with a rectangular bonded area shows similar bond strength and failure

modes54

. Sawing and trimming of the test samples appears to be the most technique-sensitive

part of the Micro Tensile Bond Strength (µTBS) test. The interfacial stress during the preparation

can leads to pre-test failure of samples. The hour-glass or dumbbell shaped trimming of the

samples places additional pre-test strain and stress concentration on the bonded area; hence a

stick shaped samples were preferred for this study.

Discussion

55

Following the sample preparations, the test specimens were mounted on a pneumatic jig

using suitable sized silicon-sleeves on both the end of the specimens. The conventional method

of using fast-setting adhesives for the fixation of samples to the jig which can lead to glue

contamination of the samples; as well it can influence the test results.

The Mean Micro Tensile Bond Strength (µTBS) value of the CarisolvTM

group (G2)

showed highest among the three groups: 6.36MPa (SD 4.36). This value was comparable with

the values of the Mechanical group G1 (6.28 MPa [SD 3.18]). The third group; Er, Cr: YSGG

laser showed lower values (4.47 MPa [SD 2.91]) than that of the other two groups. The higher

values shown by CarisolvTM

group could be because of the removal of smear layer by the action

of CarisolvTM

, which allowed the self-etch adhesive to penetrate deeper into the dentinal

surfaces; resulting in a thick and homogenous hybrid layer3, 59

.

Residual dentin which remained after chemomechanical (CarisolvTM

) excavation showed

a roughened surface, with minimum smear layer and many open tubular orifices. The rough and

granular dentin topography might have allowed the ‘Mild’ self-etch adhesive to penetrate deeper

and form a thicker and smoother hybrid layer; that resulted as the highest Mean Micro Tensile

Bond Strength (µTBS) value among all the experimental groups.

Discussion

56

Mechanical caries excavation exhibited over-preparation with more histologically sound

dentin at the cavity margins. SEM examination showed that hand excavation produced smearing

and smear plugs in the tubular orifice. Although the dentin that is left after caries removal with

hand excavation has similar hardness to that of normal sound dentin, there are ultra-structural

differences. It is well known that as caries progress; sclerotic dentin (translucent dentin) is

deposited within the tubules at the advancing front of the lesion, which can lead to their complete

obliteration58

. This factor, in conjunction with the formation of the smear layer that has a higher

organic content, due to the increased bacterial load, may interfere with the ability of the ‘Mild’

self-etch adhesive to penetrate deeper into smear layer and thus demineralizing the underlying

dentin, leading to a reduced Micro Tensile Bond Strength (µTBS) value.

Er, Cr: YSGG laser irradiation produced a scaly, irregular and rugged appearance with

the absence of smear layer with exposed dentinal tubule orifices. All these features could

increase the adhesive area and strength, but lack of good hybrid layer could counteract these

effects and cause a lower Micro Tensile Bond Strength (µTBS) value. The laser initially

vaporizes water and the other hydrated organic components of the dentin. During the process,

internal pressure increases in the dentin until the explosive destruction of inorganic substances

occurs. Since intertubular dentin contains more water and has a lower mineral content than the

peritubular dentin, it is selectively more ablated than the peritubular dentin, leaving protruding

dentinal tubules with a cuff-like appearance2. Thus it would be expected to have better bond

strength to irradiated dentin. However, not only the morphology of the dentin surface is

important for bonding, but the chemical composition of the intertubular dentin is also an

Discussion

57

important factor. During the bonding procedure, this dentin is demineralized and then permeated

by the hydrophilic monomers; the bonding resin can then hybridize with the network of collagen

fibers. Thus the bonding to irradiated dentin was less than the other groups; it can be assumed

that, the composition of the intertubular dentin has been modified by the laser irradiation. This

modification could have lead to a dentin surface more resistant to demineralization, impairing the

action of the mild pH hydrophilic primer used62

.

The fracture mode analysis of the resin-dentin interface revealed that the three caries

excavation techniques have no effect on the failure mode and loci of failure. It is apparent from

the data that samples in all groups suffered similar proportions of cohesive failure in the

composite aspect of the restorative interface. A substantial increase in cohesive dentin failure

was observed in the CarisolvTM

group. Sodium hypochlorite might have reduced the mechanical

properties of dentin, causing the specimens to fail more cohesively in dentin59, 7

. For the

mechanical caries excavation group, fractured specimens typically showed a ‘mixed’ fracture

pattern, including areas that fractured in dentin, composite and within the adhesive. The

predominant fracture modes of laser-ablated dentin were Type II (53%) followed by Type I

(33%). More number of adhesive failures could be because laser ablation did not create an

appropriate hybrid layer.

Within the limitations of this study it was concluded that; the surface remaining after

CarisolvTM

excavation and bonding with a mild self-etch adhesive seem to be very compatible,

allowing deeper penetration of the adhesive and resulted in a thick and homogenous hybrid layer.

Discussion

58

In this study, the inclusion criteria for samples were teeth with caries lesion limited to the

occlusal surface and extending at least half of the distance from the enamel-dentin junction to the

pulp chamber62

. This was to minimize any regional variation between the periphery and the

central dentin substrate and to increase the validity of the results53

. Generally micro specimens

for the microtensile bond strength studies were fixed to a jig with the aid of a cyanoacrylate-

based glue, whereas silicon sleeves were used in this study. This method might have resulted in

lower values when compared to the published data’s. Further studies are recommended with

larger number of samples for the microtensile bond strength evaluation.

Summary

Summary

59

The advent of ‘Adhesive Dentistry’ has simplified the guidelines for cavity preparation

enormously. In light of the minimally invasive dentistry concept, the macroretentive cavities

have been replaced by cavities limited to removal of carious dentin that are at most extended

with some additional rounding off sharp margin edges and/or beveling. Caries dentin removal by

mechanical means is non-specific nature of excavation that may result in excessive loss of tissue

thus affecting the prognosis of the treated tooth. This in vitro study was aimed to evaluate the

surface characteristics of caries-excavated dentin and to compare the microtensile bond strength

values of an adhesive bonded to the residual dentin remained after three different contemporary

caries-excavation methods namely Mechanical, Chemomechanical (CarisolvTM

) and Er, Cr:

YSGG laser (BiolaseTM

).

Forty five extracted cavitated human permanent molars with the lesion limited to the

central portion of the occlusal surface were selected. The teeth were randomly divided into three

groups (n=15), according to the caries removal methods, as follows: Group I: Mechanical rotary

preparation by diamond bur/air turbine. Group II: Chemo-mechanical preparation with

carisolvTM

gel. Group III: Laser preparation by Er. Cr: YSGG Laser(BiolaseTM

).

Morphological changes in the residual dentin surfaces were evaluated using scanning

electron microscopy (SEM). These specimens were immersed in 4% glutaraldehyde solution for

1hr at room temperature. Then they were rinsed in distilled water. The samples were then placed

in cold buffer solution of sodium cacodylate for 90 minutes to fix the organic matter. Specimens

were then dehydrated in ascending grades of ethanol and then dried in a Critical Point Drier

Summary

60

based desiccator. The dried specimens were mounted on a metal stand and gold sputter coated by

cathode atomization under vacuum. SEM images of the caries excavated surfaces were obtained.

After caries excavation the samples were bonded using a “Mild” two-step self-etch

adhesive, Clearfil SE Bond and then restored using a nanohybrid resin composite. The specimens

were serially sectioned into multiple slices with a diamond disc under water cooling to create a

1mm² stick shaped samples for the Micro-tensile bond strength test (µTBS). The prepared rods

comprised of residual dentine to which composite resin was bonded using suitable dentin

adhesive. Silicon sleeves were attached to both the end of the samples. Specimens were mounted

on a pneumatic jig. The test was taken out at a tension of 0.5mm/min until it failed. Bond

strengths were calculated by dividing the load at failure by the cross-sectional bonding area.

In this study, the morphological analysis of the residual dentin excavated with CarisolvTM

produced a reduced and more inconsistent smear layer with large areas of open tubular orifices.

The dentine surfaces that received Er, Cr: YSGG laser irradiation showed a scaly, irregular and

rugged appearance whereas the teeth prepared by mechanical method appeared rougher with

irregular particles scattered throughout the surface area. A well defined smear layer was

detected.

The results were subjected to statistical analysis by means of parametric Kruskal-Wallis

one-way ANOVA and Mann-Whitney ‘U’ test.

The Microtensile bond strength evaluation showed the highest bond strength values for

the CarisolvTM

group (6.37MPa) and the mechanical group (6.25MPa), and the lowest value was

found with the laser group (4.47MPa).

Conclusion

Conclusion

61

Within the limitations of this in vitro study it can be concluded that the caries-removal

effectiveness and minimal-invasiveness potential varied amongst the three caries-excavation

techniques tested. It was found that the surface remaining after CarisolvTM

excavation and

bonding with a mild self-etch adhesive seem to be very compatible, allowing deeper penetration

of the adhesive and resulted in a thick and homogenous hybrid layer.

The fracture mode analysis of the resin-dentin interface revealed that the three caries

excavation techniques have no effect on the failure mode and loci of failure. A substantial

increase in cohesive dentin failure was observed in the Carisolv group, whereas mechanical and

laser groups showed a mixed fracture pattern.

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