adhesion in dentistry

Dentin Bonding Agents

CONTENTS

SL.

NO.

TITLE PAGE NO.

01. INTRODUCTION 1

02. REVIEW OF LITERATURE 5

03. HISTORY 17

04. ADHESION 21

05. FACTORS AFFECTING ADHESION 34

06. CHEMISTRY OF ADHESION 50

07. PARAMETERS AFFECTING THE CLINICAL

PERFORMANCE OF ADHESIVES

61

08. STRUCTURE AND COMPOSITION OF ENAMEL AND

DENTIN

64

09. ENAMEL BONDING SYSTEM 74

10. SMEAR LAYER 81

11. DENTIN BONDING SYSTEM 84

12. CONDITIONING OF DENTIN SUBSTRATE 89

13. PRIMERS 99

14. HYBRID LAYER 107

15. CLASSIFICATION OF DENTIN BONDING AGENTS 113

16. AMALGAM BONDING SYSTEM 156

17. PULP CONSIDERATION OF ADHESIVE MATERIAL 158

18. CLINICAL APPLICATIONS OF DENTIN ADHESIVES 162

19. LIST OF GUIDELINES TO ENSURE CLINICAL SUCCESS 172

20. CONCLUSION 175

21. REFERENCES 176

1


INTRODUCTION

During the last three decades clinicians have been confronted with a

continuous and fairly rapid turnover in adhesive materials. It started in the

mid-’60s with the advent of the first commercialized restorative resin

composites, followed in the early ‘70s with the introduction of the acid etch

techniques clinical practice. Since then, there has been ongoing progress in

developing more refined and diversified restorative composites along with the

production of steadily improved bonding agents. Effective adhesion to enamel

has been achieved with relative ease and has repeatedly proven to be a durable

and reliable clinical procedure for routine applications in modern adhesive to

a restorative density. Although adhesion to dentin is not as reliable as adhesion

to enamel, today’s adhesives produce superior results in laboratories, along

with improved clinical effectiveness, approaching enamel-bonding

performance1.

Early one-step dentin bonding agents became multi-step systems with

more complicated, time-consuming and technique-sensitive application

procedures. In the early `90s, the selective enamel-etching technique was

replaced by a total-etch concept. Since then, universal enamel-dentin

conditioners have been simultaneously applied to enamel and dentin. Now that

today’s total-etch adhesives have reached a clinically acceptable bonding

effectiveness, most recent research and development efforts have focused on

simplifying the multi- step bonding process and reducing its sensitivity to

errors of inaccurate or incorrect clinical handling.

The concept and practice of esthetic dentistry now is common to most

clinicians around the world. Retention of restorative materials to the surface of

2


tooth structure by means of adhesion is carried out routinely. So successful

have been adhesion techniques that retentive pins are seldom, if ever,

incorporated into dental practice. The long sought after dream of bonding

virtually any type of material to the tooth surface has been realized2.

This momentous change in the way and dentistry currently is practiced

can be attributed to the contribution of many scientists. There are, however,

three individuals who made the most significant contributions. The first is

Michael Buonocore who demonstrated the concept of bonding acrylic resin to

the surface of enamel. The second is Rafael Bowen who developed composite

resin as an esthetic restorative material.

The third investigator who contributed to the field of esthetic restorative

dentistry is Nubuo Nakabayashi. His efforts have led to the techniques for

bonding resin composites to the surface of dentin.

The production of a stable, long-term bond to tooth substance is an ideal

requirement for the success of all restorations, both metallic and non-metallic.

The magnitude of this bond must be sufficient to with stand the stresses caused

by the polymerization contraction of resin-based materials and steps must be

taken to prevent these stresses from compromising the restoration3.

After observing the industrial use of phosphoric acid to improve

adhesion of paints and resin coatings to metal surfaces, Buonocore in 1955,

applied acid to teeth to “render the tooth surface more receptive to adhesion.

”Buonocore’s pioneering work led to major changes in the practice of

dentistry. Today, we are in the age of adhesive dentistry. Traditional

mechanical methods of retaining restorative materials have been replaced, to a

large extent, by tooth-conserving adhesive methods4.

3


One major problem in restorative dentistry is the lack of proper union

between the restorative material and the tooth surface. The process of

inventions over a period of time have led to the development of various

techniques and modalities, which help in adhesion there by reducing the tooth

restoration gaps5.

In the present era improved oral hygiene habits have resulted in a

dramatic decrease in the incidence of carious diseases and prosthetic treatment

needs. This has progressively called into question the traditional concepts of

the profession and placed restorative dentistry on a center stage, giving a new

impulse to the more conservative adhesive techniques.

During the last two decades adhesive restorative dentistry has

increasingly proven its tremendous clinical potential, first in the anterior and

more recently in the posterior segments of the mouth. The major driving force

for this evolution has been threefold i) The continuous search for specific, less

invasive restorative modalities, ii) The patients ever-increasing demand for

natural looking esthetics and iii) The intense controversy related to the use of

dental amalgam.

Adhesive techniques have greatly expanded the horizon of aesthetic

dentistry. Correction of shapes, positions, dimensions and shades of teeth are

now possible with the restorative materials. Repair of fractured teeth can be

carried out using the fractured tooth fragments there by maintaining original

esthetics5.

Although significant progress has been made in preventing the

premature loss of failure of restorative materials because of breakdown at the

tooth-restorative interface, many questions and challenges remain. The

4


continued developments of adhesive materials is now focused on gaining a

better understanding of factors affecting adhesion in the oral environment to

improve the clinical longevity of restorative materials.

5


REVIEW OF LITERATURE

JR Holtan et al (1995)22 compared the shear bond strength to enamel of

Scotch bond Multi purpose dental adhesive systems bonding resin following

etching of enamel with 10% maleic, 1.6% oxalic, 10% phosphoric, and 35%

phosphoric acid for 15,30 and 60 seconds and adhesive resin applied. They

found that significant differences exist for shear bond strength values by type

of etchant (10% phosphoric, 35% phosphoric > 10 % maleic > 1.6% oxalic

acid). Further analysis revealed that the bond strength values for three etchants

increased as the applications time increased from 15 to 30 seconds. Bond

strength values for the etchants used in this either decreased or did not

significantly improve as the application time increased from 30 to 60 seconds.

PT Triolo, EJ Swift, W.W. Barkmeier (1995)26 evaluated the shear

bond strength of All bond 2 (Bisco), Imperva bond (Shofu), Optibond (Kerr),

Permagen (Ultradent), Probond (dentsply) and Scotch bond Multipurpose (3M)

and found that the bond strength of Scotch bond Multi purpose and All bond 2

were significantly greater than those of Permagen and Probond. The bond

strength of Imperva bond and Optibond were statistically equivalent to Scotch

bond Multi purpose and All bond 2.

M. Miyazaki et al (1996)27 carried out a study to determine the

influence of dentin primer application methods on bond strength to human

dentin. Two dentin bonding restorative systems, Imperva bond /Lilefil IIA

(Shofu) and Scotch bond Multipurpose/Z-1 00 (3M) were employed. Two

experiments were designed 1) effect of the primer application procedures

(inactive and active application), and 2) effect of air-drying time (0,1,5,10,20

and 30 seconds). They found that the bond strength with active application

6


were higher than with inactive group. The maximum shear bond strength was

obtained with 20 seconds of air drying time for Imperva bond and with 5

seconds of air drying time for Scotch bond Multi purpose. The bond strengths

of each bonding system were lower when the primed dentin surface was not

air-dried.

T. Nikaido et al (1996)35 evaluated the effect of low-pressure air

abrasion with alumina and glass beads on bonding to tooth substrates. They

found that air abrasion with glass beads significantly decreased the bond

strengths to enamel and dentin, where as air abrasion with alumina decreased

adhesion to enamel but not to dentin. The SEM photographs suggested that air

abrasion might weaken the tooth surface, which could account for the decrease

of the bond strengths.

JC Meiers, GA Miller (1996)29 evaluated antibacterial effect of Syntac,

Probond, Gluma 3-step using cariogenic bacteria S. mutans, L salivarius and S.

sobrinus and A. viscosus in vitro with a modified cylinder drop plate agar

diffusion assay. They found that primer and adhesives of Probond and Syntac

and the conditioner and primer of Gluma 3 step displayed bacterial inhibition

against all four bacteria.

Geroge Eliades, Georgios Palaghias, George Vougiouklakis (1997)35

did a study to evaluate the effect of some acidic conditioners on dentin

morphology, molecular composition and collagen conformation in situ. The

specimens were subjected to conditioning treatments with CA agent (Kuraray),

Scotch bond Etchant (3M) and Scotch bond MP Etchant (3M) gels. They

concluded that all the conditioners removed the smear layer, funneled the

tubules, increased the intertubular roughness and contaminated the dentin

surface with residues from irreversibly adsorbed thickening agents. CA agent

7


manifested a significantly lower extent of dentin decalcification that Scotch

bond Etchants.

Richard B.T Price, Gordov C. Hall (1999)41 did a study to evaluate

24 hr shear bond strength of six dentin bonding systems with 10 minute dentin

bonding system and concluded that 10 minute shear bond strength were

significantly less than the 24 hour values.

P N R. Pereira et al (1999)54 investigated the influence of intrinsic

wetness on regional bond strength of adhesive resin to dentin

Group one- no pulpal pressure

Group two- pulpal pressure of 15cm H2O

Group three- dentin dried overnight in a dessicator

They found that no significant regional differences were observed for

group 1 and bond strengths significantly decreased at the pulp horn regions.

They concluded that dentin adhesive system should be chosen according to the

substrate and region to be bonded, since bond strength vary according to the

intrinsic wetness, region and the adhesive system.

C Prati, S. Chersoni, D.H Pashlay (1999)24 did a study to evaluate the

effects of NaOCl at removing the demineralized layer by examining the

morphology of hybrid layer and measuring shear bond strengths after dentin

treatments. They observed that collagen fibrils were completely removed from

acid- etched surface by NaOCl treatment. The diameter and size of dentinal

tubules and number of lateral branches of tubules were increased following

NaOCl treatment.

8


K Miyasaka, N. Nakabayashi (1999)55 did a study to examine a new

bonding system combining an ethylene diaminetetraaceticacid (EDTA)

conditioner and the 2 methacryloxyloxyethyl phenyl phosphoric acid (Phenyl

p)/2 hydroxyethyl methacrylate (HEMA) self etching primer with a dumb bell-

shaped specimen for tensile test. They found that combining the EDTA

conditioner and phenyl P/HEMA primer afforded high quality hybridization

and good bond strength.

M. Hashimoto et al (2000)36 evaluated the correlation between hybrid

layer thickness and bond strength using specimens acid conditioned for varying

lengths of time. They found that bond strength decreased with increase in

period of acid conditioning. The distance between resin tags within the hybrid

layer of the specimen acid conditioned for100 S can be seen to be less than that

between the resin tags in a specimen acid conditioned for 60 seconds.

H.LI, M.F. Burrow. M.J Tyas (2000)38 evaluated the nanoleakage

pattern of four dentin-bonding systems. They did study on Single bond, One

coat bond Prime and bond NT/Non rinse conditioner and Perma Quick samples

were immersed in a 50% solution of silver nitrate for 24 hrs. This study

demonstrated the nanoleakage pattern of four dentin-bonding systems.

Different leakage patterns were observed with the different type dentin

bonding agents employed. Prime and bond NT/NRC showed a dense silver

deposition. Perma Quick showed better sealing ability. Single bond and one

coat are intermediate.

Bruno T. Rosa, Jorge Perdigao (2000)29 did a study to determine

enamel and dentin bond strengths of non rinsing all in one adhesive and of a

non rinsing conditioner combined with a one bottle adhesive. Prompt L -Pop,

No etch plus Prime and bond NT, NRC plus prime and Bond NT, Phosphoric

9


acid plus prime and bond 2.1. They found that for resin composite, etching

with phosphoric acid resulted in the highest bond strength to enamel. For

compomer, the highest enamel bond strength was achieved with both

phosphoric acid and Prompt L- Pop. Treating dentin with Prime and bond NT

with out etching provided the highest mean bond strength for composite. For

compomer treating dentin with Prime and bond NT resulted in the highest

mean bond strengths, regardless of the conditioner.

M. Tanumiharja, M.F. Burrow, M.J. Tyas (2000)32 evaluated the

micro tensile bond strengths of seven dentin adhesive systems (Solid bond,

EBS Multi, Perma Quick, One coat bond, Gluma one bond, Prime and bond

NT/NRC and Clearfil liner bond 2V). They found that conventional and single

bottle systems had similar bond strengths except for one of the conventional

systems, Perma Quick. The self- etching priming systems, Clearfil liner bond 2

V and Prime and bond NT/NRC, had higher bond strengths than the other

systems.

Siavoljub Zivkovic (2000)28 assessed in vitro quality of marginal

sealing of composite dentin adhesive system and human dentin. After the

enamel layer was removed, class V cavity was formed on buccal surface, and a

wedge cavity was formed on lingual surface.

Denthesive/Charisma, Tripton/Opalux, Syntax/Helioprogres, Gluma/

Pekafil Scotchbond Multipurpose/Valux, XR- bond/Herculite, Superlux

universal bond 2/ Superlux solar. They found that best marginal sealing was

achieved by the Scotch bond Multi purpose /Ssyntac/helioprogres, XR bond/

Herculite, Gluma/ Pekafill, and Superlux Universal bond 2/ Superlux solar

system, the greatest microleakage was noted with the tripton/ Opalux and

Denthesive/charisma system.

10


Franklin R. Tay, David H, Pashley (2001)23 conducted a study on the

aggressiveness of three self-etching adhesive systems in penetrating dentin

smear layer of different thickness. Adhesive were Clearfil Megabond, Non-

Rinse conditioner/Prime and bond NT and Prompt L- Pop. They found that for

Mega bond, thin authentic hybrid layers between 0.4-0.5mm were found.

Smear layer and smear plugs were retained as part of the hybridized complex.

For non-rinse conditioner/Prime and bond NT, the authentic hybrid layers were

between 1.2-2.2 mm thick. Smear layer and smear plugs were completely

dissolved in dentin with thin smear layers, but were partially retained as part of

the hybridized complex in those with thick smear layers. For Prompt L-Pop,

authentic hybrid layers were 2.5-5mm thick and smear layer and smear plugs

were completely dissolved even in dentin with thick smear layers.

R. Frankenberger et al (2001)40 compared the adhesive capability of

the new adhesive Prompt L Pop (ESPE) with that of two total etch adhesive

systems- EBS multi (ESPE) and Prime and bond NT (Dentsply) combined with

Pertac II (Composite) or Hytac Aplitip (Compomer). They found that 1). The

use of prompt L-Pop as a multi step adhesive system resulted in higher bond

strengths than when used as per manufacturer directions 2.) When applied on

multiple coats, Prompt L- Pop resulted on bond strengths that were not

statistically different from those of P & B NT, a total etch adhesive. The bond

strengths obtained with EBS multi, a water- one -based total etch adhesive,

were significantly higher than those obtained with Prompt L-Pop.

David H. Pashley, Franklin R- Tay (2001)39 studied the

aggressiveness of three self-etching adhesives unground enamel.

Ultrastructural features and microtensile bond strength was examined. Study

group included Clearfil Mega bond, Non- rinse, conditioner or Prompt L-Pop

and a control group with 32% phosphoric acid. Clearfil Mega bond exhibited

11


the mildest etching patterns, while Prompt L-Pop produced an etching effect

that approached that of total etch control group. Microtensile bond strength of

three experimental groups was all significantly lower than control group.

G. Eliades, G. Vougiouklakis, G. Palaghias in (2001)53 did a study to

investigate whether monomer separation occurs in single bottle adhesives

applied on acid- etched dentin surfaces. The single bottle adhesives used were

One step, Prime and bond 2.1, Scotch bond 1 and Syntax- sprint All the

adhesives demonstrated separation of monomer components on etched dentin.

Atila Stephan, Zafer C. Cehreli and Burcin Sener (2001)52 studied

the antibacterial effects of dentin bonding systems Single bond, Prime and

bond NT, and Excite using the bacteria streptococcus mutans ATCC 25175,

Streptococcus intermedius, Lactobacillus acidophilus, Prevolella oris,

Prevolella denticola, Porphyromonas gingivalis, Porphyromonas endodontalis,

and Clostridum ramosum with a disk diffusion method. Prime and bond NT

showed growth inhibition for all bacterial strains. Lactobacillus acidophilus

and streptococcus mutans were remarkably resistant to Single bond, whereas

Excite produced no inhibitory effect on Porphyromnas edodontalis.

Johan Blomlof et al (2001)25 did a study to compare EDTA

conditioning and phosphoric acid conditioning of dentin in combination with

two principally different commercial dentin-bonding systems (All bond- 2 and

Prime and bond NT). They found that combination of conditioning with EDTA

and bonding with all bond 2 was significantly better than all other

combinations.

Jorge Perdigao et al (2001)50 did a study to determine the microtensile

bond strength of 3 dental adhesives (Clearfil SE bond, Prime and bond NT,

12


Single bond) when applied to dentin decalcified with EDTA.For each adhesive

the control group (not decalcified) resulted in higher bond strengths than the

treatment groups.

Lorenzo Breschi et al (2002)51 evaluated the ultra-morphological

effects of maleic acid and citric acid in dentin by means of a field emission in

lens scanning electron microscope. Both acids were tested on human dentin at

pH 0.7 and 1.4 in aqueous solutions. They found that both acids removed

smear layer and partially removed smear plugs. Maleic acid at pH 0.7 showed

the highest depth of demineralization of all the tested samples, citric acid,

showed a higher depth of demineralization values when tested at pH 1.4 than at

pH 0.7.

M. Miyazaki et al (2002)56 examined the relationship between the

bonding agent application duration and the dentin bond strength of several

single applications bonding systems. The restorative material/bonding systems

used were Reactmer, with Reactmer bond, Paltique Estelite with One up bond

F, and F 200 compomer adhesives were applied for 5,10,20,30 and 60 seconds.

No significant differences were found among the 10-60 second application

duration groups for the systems used. Demineralization of the dentin surface

was more pronounced with longer application duration.

Y. Shimada et al (2002)30 compared the microshear bond strength of

two adhesive systems to primary and permanent tooth enamel. Two

commercially available resin adhesives, a self etching primer system (Clearfil

SE bond) and a Single bottle adhesive system (Single bond) used with a total

etch wet bonding technique were tested. No statistically significant differences

of shear bond strength values were found between the primary and permanent

enamel in the adhesive systems used. The SEM observations showed that both

13


adhesive systems etched the primary enamel deeper than the permanent

enamel, suggestion that the action of acid etch seemed to be more intense on

primary enamel than on permanent enamel. Bonding of the adhesive systems to

primary enamel was almost identical to permanent enamel.

Y. Shimada et al (2003)31 investigated the bonding of current resin

adhesives to the region approximating the DEJ, where the etch pattern to

enamel or dentin may be different. Three kinds of tooth substrates were chosen

for testing enamel, dentin and the DEJ region. A self- etching primer system

(Clearfil SE bond) and total etch wet bonding systems (Single bond and One

step) were used. Confocal laser scanning microscopy observation showed that

the DEJ region was etched more deeply by phosphoric acid gel than enamel or

dentin. No significant differences of shear bond strength values were observed

between the DEJ region and enamel or dentin.

Amer Abu Hanna, Valeria V. Gordan Ivar Mjor (2003)34 studied the

effect of variation in etching times effect depth of dentin demineralization and

the thickness and morphology of the hybrid layer. Different etching times of

5,15 and 30 seconds. There was a direct correlation between etching time and

depth of demineralized zone.The hybrid layer thickness correlated directly to

the etching time. Reducing etching time reduces the depth of the demineralized

zone and may be effective for achieving complete penetration and for sealing

the dentin surface.

Sofia S.A et al (2003)57 did a study to determine the effect of dentin

smear layers created by various abrasives in the adhesion of a self etching

primer (SE) and total etch (SB) bonding systems. Shear bond strength of SB

system was not sensitive to the abrasive used except for the very smooth

surfaces produced by the 0.05mm-alumina slurry. Compared with those

14


produced by the diamond burs, the carbide bur yielded the highest bond

strength and the thinnest smear layer.

G.C. Lopes et al (2003)33 verified whether there are differences

between bonding to hypermineralized dentin and normal dentin and if longer

acid etching can improve the bond strength to this modified substrate without

damaging the bond to normal dentin. They found that the thickness of the

hybrid layer formed on sclerotic dentin is less than normal dentin, showing this

tissue to be more resistant to demineralization caused by acid etching. Bond

strength of sclerotic dentin is not as high as normal dentin.

Murat Turkun, Sebnem Turkun, Atakan Kalender (2004)42

evaluated the effect of three different cavity disinfectants on the microleakage

of two current non rinsing dentin bonding systems, Prompt L- Pop and Clearfil

SE bond. They found that consepsis and tubulicid red could be used as cavity

disinfectants with Clearfil SE bond and prompt L-Pop without affecting their

sealing ability. Ora- 5 is not an appropriate disinfectant to use with these

dentin-bonding systems because of alters their sealing abilities.

Sigurdur O. Eriksson et al (2004)46 evaluated the effects of saliva

contaminated on microtensile bond strength between resin interfaces and to

determine which decontamination methods best re-established the original

resinresin bond strength.. Saliva contamination significantly reduced bond

strength between resin composite surfaces regardless of materials evaluated.

Blowing the saliva off quickly or rinsing with water did not restore bond

strength to normal levels.

Sigurdur O., Eiriksson et al (2004)45 evaluated the effects of blood

contamination on microtensile bond strength between resin interfaces and to

15


determine the best decontaminaion method to re-establish the original resin-

resin bond strength Blood contamination significantly reduced the bond

strength between resin composite increments regardless of materials evaluated.

Rinsing with water restored the bond strength significantly for all materials.

G. Schmaiz, Z.Ergucu and K.A. Hiller (2004)47 examined the

antibacterial effects of different dentin bonding agents and two components of

dentin adhesives, HEMA and TEGDMA against carieogenic bacteria

Streptococcus mutans, S.Sorbinus and Lactobacillus acidophilus. Antibacterial

activities associated with some dentin bonding agents and chlorhexidine are

modified by the presence of dentin.

Bora Ozturk and Fusun Ozer (2004)58 evaluated the effects 5%

NaOCl on bond strengths of four bonding sytems- Clearfil SE Bond, Prompt

L-Pop, Prime and Bond NT, and Scotchbond Multi purpose plus- to pulp

chamber mesial walls. Results showed that, in general, NaOCl application

decreased the bond strength values of the bonding agents.

Esra Can Say et al (2004)44 evaluated the effect of two cavity

disinfectant, a 2% chlorhexidine and a 1% benzalkonium chloride solution on

the shear and tensile bond strengths of dentin bonding systems it denture.

Results indicate that the use of 2% cholrhexidene and 1% benzalkonium

chloride solution as cavity disinfectants after etching the dentin did not affect

the shear and tensile bond strength.

Hagay slulzky, Shlomo Matalon and Ervin I. Weiss (2004)43

evaluated the antibacterial surface properties of polymerized single bottle

bonding agents such as Bond-1, OptiBond sole, One-step, Gluma, Prime and

16


Bond NT and Synergy, using the direct contact test (DCT). The results

showed that all tested bonding agents exhibited potent antibacterial properties.

Arlin Kiremitci, Filiz Yalcin and Saadet Gokalp (2004)48 evaluated

the effectiveness of prime and Bond NT, Clearfil SE Bond and Prompt L-Pop

on adhesion of resin composite to both dentin and enamel. Results showed that

Prompt L-Pop exhibits significantly higher bond strength values to enamel than

all other groups. There were no statistically significant difference for shear

bond strength to dentin among adhesives.

Maria Carolina Guilherme Erhardt et al (2004)49 evaluated the

influence of carisolv on the shear bond strength of hydrophilic adhesives to

dentin. Results showed that carisolv did not interfere in the adhesion to dentin.

17


HISTORY

Pioneers of enamel and dentin bonding :

Research into bonding agents for attachment of resins to tooth structure

was started in early 1950’s. The first attempt to develop on adhesive system

for bonding acrylic resins to tooth structure was made by Hagger, a Swiss

chemist working for the Amalgamated Dental Company in London and Zurich

in 1949. A commercial product, Sevriton cavity seal was then marketed in

conjunction with a chemically cured resin, Sevriton for use in restorative

dentistry: A patent was applied for in Switzerland on July 21 1949, granted

November 15 1951 and expired on July 21 19645.

At that time, this invention by Hagger was revolutionary and almost

unrecognized in current literature since it was the first time that chemical

bonding to tooth structure became a commercial possibility. The system was

very sophisticated for that period and was based on glycerophosphoric acid

dimethacrylate, which could be catalytically polymerized by the action of

sulphinic acid in a 5 to 30 minute period at 200c.

In 1952, Kramer and Mc Lean were among the first to use

glycerophosphoric acid dimethacrylate (GPDM) to bond to dentin. Reports

soon demonstrate the interest in using these molecules to bond restorative

materials to dental tissues, and at the same time provided the first description

of what was to be called the “hybrid layer”.

In 1955 the foundation for adhesive restorative and preventive dentistry

was laid, when Buonocore proposed that acids could be used to alter the

surface of enamel to “ render it more receptive to adhesion”. His hypothesis

18


was based on the common industrial use of phosphoric acid to improve

adhesion of paints and acrylic coatings to metal surface.

In 1955 Buonocore, conducted experiments on enamel surfaces

employing a 30 seconds treatment of 85% phosphoric acid to achieve a simple

acid decalcification. In 1956 Michael Buonocore pioneered the work on

adhesion to dentin. Buonocore’s idea resulted in a bonding agent being used as

an intermediary between dentin and restoratives resin. The strength of this was

however low initially but later more effective systems of bonding based on the

original idea of Buonocore appeared. In 1956 Michel Buonocore, Wileman W

Brudevald reported a resin composition capable of bonding to human dentin

surfaces.

In 1957 R.L. Bowen did the initial work on Bis-phenol glycidyl

methacrylate resin systems. In 1962 R.L. Bowen conducted the first workshop

on adhesive restorative dental materials and demonstrated that surface active

agents having an affinity for the surface of hydroxyapatite powder contained

groups which were capable of forming five membered chelate ring with

calcium5.

In 1965 the infiltration of resin monomers into demineralized dentin

created a new structure, which was, first described invitro for enamel by

Gwinnett and Buonocore. Simultaneously R. L. Bowen advocated that

bonding to dentin could be improved by pre-treatment and the use of surface-

active co-monomer.

In 1968 Bunocore, Matsui, and Gwinnett conducted pioneering studies

in which the physical relationship between acrylic restorative resins and etched

enamel surfaces was clarified paving way for “ the acceptance of the acid etch

19


techniques “as an integral part of restorative procedures involving composite

restorative resins.

In 1970 Eick and others described the nature of smear layer for the first

time. In 1971 Lee and others developed a polymethane resin to be used as an

adhesive for composite restoration.

In 1974 R.L. Bowen in “ Adhesive bonding of various materials to hard

tooth tissues VII “ reported that metal salts acts as mordant for coupling agents.

In 1979 Fusayama and others were the first to report the successful use

of phosphoric acid to remove smear layer, etch the dentin and restore with

adhesive composite resin.

In 1979 Yamauchi, Nakabayashi, and Masuhara developed

methacryloxyethyl phosphoric acid ester, which appears to be the basis of the

Clearfil bond system.

In 1980 Nakabayashi and Masuhara developed acrylic bonding agents

containing the polymerization initiator tributyl boron, which is said to induce

grafting of the methyl methacrylate to dentin collagen. Brannstrom later in the

year 1981 reported that for clinical success the conditioned dentin must be

sealed to prevent sensitivity and to prevent the pathology associated with

increased permeability of the dentinal tubules.

Later Causton in the year 1982 illustrated the principle of primers,

which react with the tissue surface and which compete with and displace water

for durable bonding. Bowen, Cobb and Rapson later developed the multilayer

adhesive system.

20


In 1982 Nakabayashi reported the presence of hybrid layer of resin-

reinforced dentin.

In 1982 Den Mat separated enamel bonding from dentin bonding.

In 1987 -Tenure system was used.

In 1990 – Fourth generation dentin bonding agents was developed

Later in year 1991 Kanca technique, was introduced which is also

referred to as All-etch technique.

1995 –fifth generation bonding agent were developed.

2000 – New classification of adhesive was introduced – based on

number of different working steps and treatment of smear layers.

21


ADHESION

The word adhesion comes from the Latin word adhaerere (“to stick to”).

The American society for Testing and Materials (ASTM, specification No 907)

defines adhesion as” the state in which two surfaces are held together by

interfacial forces which may consist of valence forces or interlocking forces or

both. Adhesion describes the attachment of one substance to another whenever

they come into close contact with each other. Therefore it can be defined as a

force that binds two dissimilar materials together when they are brought into

intimate contact6.

Adhesion is the attraction of molecules at surfaces. The bond strength

depends on the amount of force present of each contact site. At an atomic level

solid often have rough surface, which means that they contact each other only

at certain points. To get a better contact between two materials, an intermediate

layer called “adhesive” has to be placed. An adhesive is a material frequently

a viscous fluid; that joins the two substrates together and solidifies, therefore

able to transfer a load from one surface to other. The surfaces or substrates

that are adhered to are termed the “adherends”. Adhesive strength is a measure

of load bearing capacity of an adhesive joint.

22


Schematic summary of dental adhesion and dental adhesive joint

Mechanism of adhesion:

1. Mechanical adhesion: Interlocking of adhesive with irregularities in

the surface of the substrate, or adherend.

2. Adsorption adhesion : Chemical bonding between the adhesive and the

adherend. The forces involved may be primary (ionic & covalent) or

secondary (hydrogen bonds, dipole interaction, or Vander waals valence

forces).

23


3. Diffusion adhesion: Interlocking between mobile molecules, such as

the adhesion of two polymers through diffusion of polymer chain ends

across an interface.

4. Electrostatic diffusion: an electrical double layers at the interface of a

metal with a polymer that is part of the total bonding mechanism.

Bonding of resins to tooth structure is a result of four possible

mechanisms:

1. Mechanical: Penetration of resin and formation of resin tags with in the

tooth surface.

2. Diffusion- Precipitation of substances in the tooth surface to which

monomers can bond mechanically or chemically.

3. Adsorption- Chemical bonding to the inorganic component

(hydroxyapatite) or organic components (mainly type 1 collagen) of

tooth structure.

4. A combination of the previous three mechanisms.

Theories of adhesion:

Two main theories for the observed phenomenon of adhesion are.

Mechanical theory: States that the solidified adhesive interlocks micro

mechanically with the roughness and irregularities of the adherend surfaces.

Adsorption theory: Includes all kinds of chemical bonds between the adhesive

and the adherend including primary and secondary valence forces.

24


Several types of bond may be classified under the two general headings.

ADHESIVE BOND

Mechanical adhesion Microscopic penetration

Primary valence forces

. Ionic bonds

Covalent bonds

Metallic bonds

Secondary valence forces

(Vander waal’s forces)

Vander waal’s forces

Hydrogen bonds

Chemical adhesion

MECHANICAL ADHESION :

Strong attachment of one substance to another can also be accomplished

by mechanical bonding or retention rather than by molecular attraction.

Mechanical bonding may also involve more subtle mechanisms such as the

penetration of the adhesive into microscopic or submicroscopic irregularities in

the surface of the substrate. On hardening the multitude of adhesive

projections embedded in the adhesive bond surface provides the anchorage for

mechanical attachment (retention).

An example of the mechanical adhesion is resin impregnation. Before

insertion of the resin, the enamel is treated with phosphoric acid for a short

period. The acid produces minute pores in the enamel surface into which the

resin subsequently flows when it is placed into the preparation. On hardening

25


these resin projections provide improved mechanical retention there by

reducing the possibility of interfacial marginal leakage.

Thus it is an example of how bonding between the dental material and

tooth structure can be attained through mechanical mechanisms ,not through

molecular adhesion.

CHEMICAL ADHESION:

The chemical adhesions are basically interatomic bonds, which may be

classified as primary or secondary. The strength of these bonds as well as their

ability to reform after breakage, determines the physical properties of the

material.

Primary atomic bonds may be of three different types

1. Ionic

2. Covalent

3. Metallic

Ionic Bonds :

These primary bonds are of simple chemical type, resulting from the

mutual attraction of positive and negative charges. The classic example is

sodium chloride (Na+ Cl-). Because the sodium atom contains one valence

election in its outer shell and the chlorine atom have seven electrons in its outer

shell, the transfer of the sodium valence electron to the chlorine atom results in

the stable compound NaCl.

26


Covalent bond:

In many chemical compounds, two valence electrons are shared by

adjacent atoms. The hydrogen molecule, H2 is an example of covalent

bonding.The single valence electron in each hydrogen atom is shared with the

other combining atom, and the valence shell become stable.

Covalent Bond

Metallic bonds :

Certain atoms of a few crystals like gold can easily donate electron from

their outer shell and form a gas of free electrons. The contribution of free

electrons to this cloud results in the formation of positive ions that can be

neutralized by acquiring new valence electrons from adjacent atoms.

27


Metallic Bond Formation

Interatomic secondary bonds:

In contrast with primary bonds, secondary bonds do not share electrons

instead; charge variations among molecules or atomic groups induce polar

forces that attract the molecules.

a. Hydrogen bonding:

In a water molecule attached to the oxygen atom are two hydrogen

atoms. These bonds are covalent because the oxygen and hydrogen atom share

electrons. As a consequence, the protons of the hydrogen atoms pointing away

from the oxygen atom are not shielded efficiently by the electrons. Thus the

proton side of the water molecule becomes positively charged. On the

opposite side of the water molecule, the electrons that fill the outer orbit of the

oxygen provide a negative charge. When a water molecule intermingles with

other water molecules the hydrogen portion of one molecule is attracted to the

oxygen portion of its neighboring molecules, and hydrogen bridges are formed.

28

“Gas” of free electrons


Hydrogen Bonding

Vander Waals Forces:

Normally the electrons of the atoms are distributed equally around the

nucleus and produce an electrostatic field around the atom. However this field

may fluctuate so that its charge becomes momentarily positive and negative. A

fluctuating dipole is thus created that will attract other similar dipoles. Such

interatomic forces are quite weak.

FACTORS ASSOCIATED WITH ADHESION:

Surface energy :

For adhesion to exist, the surfaces must be attracted to one another at

their interface. Such a condition may exist regardless of the phases-solid, liquid

(or) gases of the two surfaces, with the exception that adhesion between two

gases is not be expected because of the lack of an interface6.

The energy at the surface of a solid is greater than in its interior e.g.:

space lattice. Inside the lattice, all of the atoms are equally attracted to each

other. The interatomic distances are equal and the energy is minimal. At the

29


surface of the lattice, the energy is greater because the outmost atoms are not

equally attracted in all directions. The increase energy per unit area of surface

is referred to as the surface energy (or) surface tension.

The tendency of a soap film to contract and drops of a liquid to form

spherical shapes due to surface tension can be understood on the principle of a

system achieving a state of lowest energy by minimizing its surface area. The

surface atoms of a solid tend to form bonds to other atoms that come onto close

proximity to the surface in order to reduce the surface energy of the solid. This

attraction across the interface for unlike molecules is called adhesion.

E.g.: Molecules in the air may be attracted to the surface and to be

absorbed by the material. Silver, platinum and gold absorb oxygen readily.

With gold, the bonding forces are of the secondary type but in case of silver,

the attraction may be by chemical or primary bonding and silver oxide may

form.

The surface energy and there fore adhesive qualities of a given solid can

be reduced by any surface impurity such as gas adsorption or oxidation. The

functional chemical groups available or even the type of crystal plane of a

space lattice present at the surface may affect the surface energy.

Wetting :

It is very difficult to force two solid surfaces to adhere. Regardless of

how smooth their surfaces may appear they are likely to be very rough when

they are viewed at the atomic or molecular dimensions. Consequently, when

they are placed in apposition, only the “ peaks” or asperities are in contact.

Since these areas usually constitute only a small percentage of total surfaces,

no perceptible adhesion takes place. The attraction is negligible when the

30


surface molecules of the attracting substances are separated by distances

greater than 0.0007 m or (0.7nm)6.

One method of overcoming this difficulty is to use a fluid that will flow

into these irregularities and this provides contact over a great surface of the

solid.

E.g.: when two polished glass plates are placed one on top of other and

are pressed together, they exhibit little tendency to adhere. However if a film

of water is introduced between them considerable difficulty is encountered in

separating the two plates. The surface energy of the glass is sufficiently great

to attract the molecules of water.

To produce adhesion in this manner, the liquid must flow easily over the

entire surface and adhere to the solid. This characteristic is referred to as

“wetting.” If the liquid does not wet the surface of the adherend, the adhesion

between the liquid and the adherend will be negligible or non-existent. If there

is a true wetting of the surface, adhesion failure should not occur. Failure in

such cases actually occurs cohesively in the solid or in the adhesive itself, not

in the interface where the solid and adhesive are in contact .The ability of an

adhesive to wet the surface of the adherend is influenced by a number of

factors. Cleanliness of the surface is of particular importance, a film of water,

only one molecular thick on the surface of the solid may lower the surface

energy of the adherend and prevent any wetting by the adhesive. Like wise, an

oxide film on a metallic surface may inhibit the contact of an adhesive.

The surface energy of some substances is so low that, few if any liquids

will wet their surfaces. E.g. some organic substances are of this type (dental

waxes). Close packing of the structural organic groups and the presence of

31


halogens may prevent wetting. Teflon (poly tetra fluoroethylene) is often used

in situations in which it is desirable to prevent the adhesion of film to surface.

Metals on the other hand, interact vigorously with liquid adhesives because of

their high surface energy.

In general, the comparatively low surface energies of organic and most

inorganic liquids permit them to spread freely on solids of high surface energy.

Thus formation of a strong adhesive joint requires good wetting.

Contact Angle:

The extent to which an adhesive will wet the surface of an adherend

may be determined by measuring the ‘ contact angle’ between the adhesive and

the adherend. The contact angle is the angle formed at the interface of the

adhesive and the adherend. If the molecules of the adhesive are attracted to the

molecules of the adherend as much as, or more than, they are attracted to

themselves, the liquid adhesive will spread completely over the surface of the

solid, and no contact angle will be formed.

32


A. When the contact angle is 00, the liquid contact the surface completely

and spreads freely.

B. Small contact angle on slightly contaminated surface.

C. Large angle formed by poor wetting

Thus the forces of adhesion are stronger than the cohesive forces

holding the molecules of the adhesive together.

However, if the energy of the adherent surface is reduced slightly by

contamination or other means, the surface tension of solid (rsv) decreases and a

slight increase in contact angle. If a monolayer film of a contaminant is

present over the entire surface, a medium angle must be obtained. Where as

very high angle would result on solid of low surface such as Teflon. Since

the tendency for the liquid as the wetting angle decreases contact angle is a

useful measure of spreadability or wettability.

Complete wetting occurs at a contact angle of 00, and no wetting occur

at an angle of 1800, Thus the smaller the contact angle between an

adhesive and an adherend, the better the ability of the adhesive to flow into and

33


fill in irregularities with in the surface of the adherend. Also the fluidity of

adhesive influences the extent to which these voids or irregularities are filled.

Solid “flat” surfaces are not actually planar. Surface imperfections

represent potential impediment to the achievement of an adhesive bond. Air

pockets may be created during the spreading of the adhesive that prevent

complete wetting of the entire surface.

When the adhesive interfacial region is subjected to the thermal changes

and mechanical stress, stress concentrations develop around these voids. The

stress may become so great that it initiates a separation in the adhesive bond

adjacent to the void. This crack may propagate from one void to the next, and

the joint may separate under stress.

Requirements for long lasting adhesion :

The most important requirement for adhesion is that the two materials to

be bonded to each other must be in sufficiently close and intimate contact. To

achieve this requirement for solid bodies, liquids or flowable materials can be

used6. The intimate contact with the substrate depends on:

1. Wettability of the substrate

2. Viscosity of the adhesive

3. Morphology and roughness of substrate

34


FACTORS AFFECTING ADHESION

The effective adhesive of restorative resins to mineralized tissues has

been a topic of active research. Bonding is the attachment of one substance to

another. A bonding agent is a material that when applied to the surface of

substances can join them together and resist separation. The extent of adhesive

forces operating across an interface depends on several factors.

Clinical factors affecting adhesion

Factors affecting adhesion to mineralized tissue.

Clinical factors affecting adhesion:

Salivary and or blood contamination

Moisture contamination from hand piece or air water syringe.

Oil contamination of hand pieces or air water syringe

Surface roughness of tooth surface.

Mechanical undercuts in tooth preparation.

Fluoride content of teeth

Presence of plaque, debris, calculus, extrinsic strains or debris.

Tooth dehydration

Presence of bases or liners on prepared teeth.

Salivary and Blood Contamination:

Difficulty in controlling saliva or blood while accomplishing restorative

dental therapy is a significant challenge7. These contaminants can influence

some dental adhesion concepts in a negative manner. Although dentin is a wet

substance, the constituents of saliva and blood create an environment that can

destroy dentin bonding. As an example, consider the following common

clinical situation. A clinician has placed the first component of one of the

35


currently popular dentin bonding agents such as Universal Bond 3. At the

clinical moment salivary or blood contamination becomes present, flooding the

tooth preparation. The impulse is to wash the tooth preparation and place

component once again. However, one of this example product is an acidic

compound of pH 2-3, and washing it off creates essentially an etch or

“conditioning” of the dentin, with removal of the smear or debris layer. Since

Universal Bond 3 depends on smear layer retention of for its bond, what would

be the actual bond to dentin in such a situation if the smear layer is etched

away? A logical approach to this problem would be.

a) Wash the tooth preparation

b). Roughen the tooth preparation surface to make a new smear layer.

c) Re-Do the dentin bonding steps, hoping to avoid further saliva

and/or

blood contamination.

Another common problem is contamination of the enamel and/or

dentinal surfaces after the conditioning or etching solutions have been placed

and a bonding agent has been cured over these surfaces. This is not a

significant problem if the clinician understands the concept of dentin and

enamel bonding. The bonded tooth surface needs only 10 seconds of 37%

phosphoric acid placement, followed by washing with water, drying and

application of another thin layer of uncured bonding agent.

Use of rubber dam or other dry field aids are necessary to avoid salivary

or blood contamination during placement of tooth adhesion materials.

36


Moisture Contamination from hand pieces or air-water syringes :

An unrecognized problem in most dental offices is water leakage from

air rotor hand pieces or air-water syringes. The source of leakage can be

caused by several situations. Among them are

Lack of drying devices on air lines leading from the compressor,

allowing wet air to be carried to the syringe or hand piece.

Condensation of water in air lines after the compressed air has been

dried, but before the hand piece or syringe location.

Leakage of water through gaskets in plumbing at the dental chair unit.

Heat sterilization of hand pieces and air-water syringes, stimulated

recently by an increased emphasis on infection control, has decreased the

microorganisms present, but has increased water leakage in syringes and water

contamination during adhesive dental procedures.

The mixture of water with restorative or bonding resin is a known

problem, but recognition by clinician that this is happening during dental

bonding procedures is less well known.

Blowing air from the hand piece or air syringe on to a dry surface as a

test procedure will demonstrate easily if water contamination is present.

Oil contamination of hand pieces or /Air water syringes :

Oil combined inadvertently with resins used for bonding is a major

problem, and it is estimated that many dental offices have oil contamination in

their air lines. The oil comes from air compressors, most of which are not

maintained well in dental offices. Effective oil filter on air lines are not used

in most dental offices. Any of the current dentin bonding agents combined

with oil contamination provides an unpredictable clinical result and potential

37


clinical failure. Additionally, combination of oil with the liners, including

glass ionomer, resin, calcium hydroxide, and others have unknown results.

Observation of oil present in air lines is not difficult. A simple test may

be conducted by blowing air from an air syringe or hand piece on to a dry

impermeable surface, such as a glass mixing slab or dry rubber glove and

observing any residue that is present. As described previously, water will be

present frequently. Water will evaporate from the test surface. Oil appears

similar water on dry surface, but it will not evaporate.

Removing all oil from dental air lines should be an immediate objective.

There are several brands of oil filters available from dental dealers. These

devices are placed on the air lines after the air compressor and before the air

syringe or hand piece. Filters must be changed frequently, as suggested by

their respective manufactures.

Surface Roughness of Tooth surface :

Most dentists use tungsten carbide steel burs to make tooth preparation.

Those burs make scratches and irregularities in tooth surfaces that are retentive

for subsequently placed restorative materials. Use of diamonds for tooth

preparation is most common in fixed prosthodontics, and there is increasing

use of diamonds in operative dentistry. Diamonds cut irregularities in tooth

structure that are related directly to the size of diamond particles used on the

diamond abrasive instrument. These range from less than 10m to about

100m. Various investigations have reported the influence on adhesion

created by rough tooth surface. Increased surface area created by surface

roughness may explain the slightly better bonds to dentin shown by some

investigations. It is possible that mechanical retention may be increased

38


slightly by the microscopic roughness produced on dentin or enamel by rotary

cutting instruments.

Mechanical Undercuts in Tooth preparation :

Since the beginning of dentistry, mechanical undercuts have been

placed in tooth preparation to provide retention for subsequently placed

restorative materials. If such undercuts are present in tooth structure, and they

hold restorative materials from bodily dislodgment from the preparation, they

may also resist some microscopic movement of the restorative material caused

by thermal or polymerization influences. Therefore, restorations with

traditional dentin-placed undercuts, as well as chemically produced bonding

may produce better clinical results, such as less leakage and less sensitivity,

than those depending on adhesion alone. If the restoration cannot move due to

large undercuts, the adhesive intensity and longevity may be enhanced.

Fluoride content of Teeth:

Increased fluoride content of enamel has been shown to resist acid

etching. This reduction in enamel acid- etch effectiveness is not significant

clinically if the etching time is increased to allow more time for the acid to

degenerate the enamel surface and produce more roughness. Clinicians are

now etching apparently normal enamel for about 15 seconds and enamel that

shows signs of fluoridation for double that time or more7.

Fluoride presence in dentin and its relationship to adhesion of dentin

bonding agents is also a matter of concern, since most persons use fluoride so

commonly. Fluoride presence in dentin appears to influence bonding dentin

adhesion agents negatively. Many dental patients use fluoride gels and rinses

and/or fluoride in trays daily for caries-preventive reasons or for

desensitization of dentin surfaces. Most of the stannous fluoride gels and more

39


concentrated Sodium fluoride have acidic pH (3-6). Research (Christensen &

others, 1991) has shown degeneration of zinc phosphate and glass ionomer

cements caused by low pH bleach gels. Other investigators have shown

fluoride gels to degenerate metal containing glass-ionomer cements

significantly but other routinely used cements to a lesser degree. The influence

of fluoride on bond of adhesive agents to dentin and enamel surfaces is a factor

that needs additional research.

Dentinal canal characteristics:

Dentinal canals at the extreme surface of tooth roots or near the

dentinoenamel junction have small diameters. As dentinal canals are observed

closer to the dental pulp, they become larger. Older dentin has small dentinal

canals, while younger dentin has larger dentinal canals. Superficial abraded

dentin may have occluded canals. When bonding to dentin, most of the current

brands of dentinal bonding agents use some form of mechanical attachment

into dentinal canals, as well as other alleged chemical bonds. If the canals are

small, attachment should be less, and if canals are large, attachment might be

enhanced.

Some research has shown that specific teeth in a given mouth have more

or less bonding strength than others. Clinicians should be aware of the

differences in potential dentin bond related to size of dentinal canals or the

resistance to bonding offered by specific teeth.

Presence of Plaque, Calculus, Extrinsic stains or debris:

Every experienced clinician has seen the effect of leaving dental plaque

on a tooth surface and trying to etch the surface. After etching, the plaque

covered surface remains shiny. Plaque prevents an etch with 37%phosphoric

40


acid. Penetration of plaque by the less-aggressive acids used in dentin bonding

agents is not possible, and clinical adhesive failure will result. Tooth surface

stains and dental calculus are easier to see and are removed usually. If they are

not removed, the bonding agents will not work.

Enamel or dentin tooth surfaces that are expected to bond to resin or

other materials should be cleaned thoroughly before attempting bonding.

Occasionally, this cleaning may require the use of sealers, abrasive

prophylactic pastes or rubber cups, and even the use of abrasive rotary

instruments. Any enamel or dentin surface that requires bonding must be clean

before the bonding procedure begins

Presence of Bases or liners on prepared teeth :

The multitude of bases and liners present today are confusing to

clinicians, and their influence on the bond of subsequently placed restorations

is not understood well in the profession.

Bases and liners can be classified in several groups.

Varnish :

Copal, cellulose or polyamide varnishes are widely used and eliminates

the potential to bond restorative materials to the tooth surface. Although these

varnishes may reduce tooth sensitivity, they should not be used if bonding of

subsequent materials to tooth surface is expected.

Glass ionomer liners:

Placed directly on tooth surfaces, these liners create a moderate bond to

dentin, but it is significantly lower than the bond created by placing resin on

acid- etched enamel surface or the bonds reported for the current generation of

41


dentin bonding agents to dentin. If resin is placed over glass ionomer liner, the

bond of the resin to the tooth can be no stronger than the bond of the glass

ionomer to dentin or the bond of the resin to the glass ionomer.

Resin Liners :

Numerous companies have marketed filled resins of various types for

lining tooth structure. If the chemicals (fluoride, calcium etc) in the resin

liners are used effectively, the liners should be placed directly on the dentin

surface. If this is done, the liners have little or no bond to dentin, and

subsequent restoration placed over the resin liners will not bond to dentin.

If the dentinal surface does not appear to be pink, it generally means

that they are more than one-half millimeter from the dental pulp. In such

cases, use of liners may not be necessary, and bonding directly to dentin is

often the treatment of choice.

An additional unknown factor is the influence of the chemicals in

varnishes or liners on dentin immediately surrounding them, but not covered

by the liner or varnish. Constituents of these materials could have a positive or

negative influence on dentin bonding in other portions of tooth preparations.

Clinicians must make the choice between.

Using the desired chemical effect or desensitization effect of the liner or

vanish or

The reduced microleakage, desensitization and retention of the dentin

bonding agents.

Tooth dehydration:

Dentin is a wet tissue. Bond strength could be related to wetness of

dentin. It may be that over drying could be damaging as placement of the

42


bonding agents in a wet field. Clinical observation has shown that over drying

tooth preparations on to which crowns are to be cemented certainly increases

tooth sensitivity. Until more conclusive research is available, over drying

tooth preparations before placing bonding agents should be considered to be a

negative factor. Drying only until the obvious shine of moisture is gone is a

good clinical guide.

Constituents of temporary cements :

Dentin or enamel that has been on contact with eugenol- containing

temporary cements or stearate- containing non-eugenol temporary cements

may have different bonding characteristics to resin than virgin tooth structure.

Research is mixed on this subject, From research & clinical experiences, it has

been concluded that if temporary cements have been in place on the tooth for

several days, the liquid portions of the cements have been completely absorbed

by the zinc oxide and are rendered relatively inert. No differences were noted

in bonds of dentin bonding agents or resin cements to dentin or enamel

surfaces that have had eugenol or noneugenol cements on them for two weeks

when compared to virgin tooth surfaces. However, more research is certainly

needed in this subject. Fresh liquid eugenol placed on dentin or enamel just

before attempted bonding could be a negative factor in adhesion

43


FACTORS AFFECTING ADHESION TO

MINERALIZED TISSUES

For adhesion to take place there must be intimate contact between the

adhesive and adherend. The ideal interface between dental restorative materials

would be one that stimulates the natural attachment of enamel and dentin at the

dentinoenamel junction. Intimate molecular contact between the 2 parts is a

prerequisite for developing strong adhesive joints8.

This means that the adhesive system must sufficiently wet the solid

surface. The factors that affect this adhesion to mineralized tissues can be

broadly classified as follows.

I. Factors related to the adherent :

Physicochemical properties of dentin that complicate dentin adhesion

The dentin smear layer and dentin permeability.

Transformed dentin structure due to physiological and pathological

processes.

II. Factors related to restorative resins :

Physical properties of adhesives

Polymerization contraction of restorative resins

Contraction stress relaxation by flow

Young’s modulus of elasticity

Initial polymerization site

The relaxation of contraction stress by hygroscopic expansion

Thermal expansion co-efficient and thermal conductivity.

Transmission of stress across the composite dentin interface

Physicochemical Properties of dentin that complicate, dentinal adhesion :

44


Mineralized dentin is relatively stiff (Modulus of elasticity of 14 to 19

GPa and has an ultimate strength of 230 to 370Mpa (compressive) or 45 to 138

Mpa (shear) which varies with dentinal depth and tubule orientation5.

Following acid etching the mineral phase of the dentinal surface and

some non-collagenous proteins are solubilized and some of the proteins are

extracted, exposing the collagen fibrils of the deminralized dentinal matrix.

The demineralized dentinal matrix becomes very soft and elastic. Infact, the

modulus of elasticity of wet demineralized dentinal matrix is only about 5

MPa, which is more than 1,000 times lower than that of mineralized dentin.

The clinical implication of this low stiffness is that the fibril network can easily

collapse when air dried, there by interfering with the up take of adhesive

monomers.

The permeability of bonding substrates to monomer and the monomer

diffusivity into the substrates are essential factor for the hybridization of resin

in dental substrates. Mineralized dentinal matrix is relatively impermeable to

resin monomers in the lengths of time that are required (clinically for bonding

(30 to 60 seconds).

Permeability refers to the ease with which a substance can move into

across a diffusion barrier (i.e. substrate). Two types of dentinal permeability

must be considered. The diffusion of substances through tubules filled with

dentinal fluid to reach the pulp intratubular dentinal permeability . The second

important type of dentinal permeability is the diffusion of monomer into

demineralized intertubular dentin, the dentin between the tubules. This is

referred to as intertubular dentinal permeability.

After the surface is acid etched and rinsed with water, between the

collagen fibers the spaces, are filled with water and are presumed to remain

45


about 15 to 20m wide. It is through these spaces that adhesive monomer

must diffuse if it is to infiltrate the demineralized dentinal matrix. Both

intratubular and intertubular dentinal permeability is important in dentin

bonding.

Dentinal tubules permit adhesive monomer to flow down the tubules for

varying distances. Most tubules contain multiple lateral branches that radiate 2

to 6 m from the lumen and they provide another route for monomer

infiltration of hybrid layers.

Further experimental studies conducted on collagen fibers in dentin

indicated that there is space between the collagen fibers for tissue fluid (i.e.

water) During dehydration procedure this water may be lost and it could result

in shrinkage of collagen fibers.

Nakabaysashi’s original, innovative ideas about monomer infiltration

into demineralized dentinal matrix, and the importance of maintaining the

permeability of the collagen fibril network to monomers, resulted in a major

advance in the understanding of how resin dentin bonding is the result of

molecular intertwining of the resin within the collagen fibers. The resin

monomers penetrate acid- etched (i.e. partially denatured) collagen fibrils via

spaces that can swell or shrink depending on bonding condition. Under some

conditions (high water concentration, acidic pH), the collagen fibrils might

swell slightly and reduce the width of the perifibrillar spaces, making it more

difficult for primer monomers to infiltrate the collagen fibril network. Under

other conditions (air drying, dehydration by water-miscible organic solvents)

the collagen fibrils may shrink (decreasing their diameter) there by increasing

the width of the spaces. But air-drying causes collapsing of the collagen fibril

network bringing the adjacent fibrils into intimate contact with each other. As

46


a result the collagen peptides may form intermolecular hydrogen bonds with

the nearest neighboring collagen peptides, which may contribute to further

collapse of the network by causing shortening of the fibrils and an increase in

stiffness. So overdrying of collagen fibrils should be avoided8.

The dentin smear layer and dentin permeability :

When the tooth surface is instrumented with rotary and manual

instruments during cavity preparation, cutting debris is smeared over the

enamel and dentinal surface forming what is termed the smear layer. The

smear layer has been defined as any debris, calcific in nature, produced by

reduction or instrumentation of enamel, dentin/ cementum. The burnishing

action of cutting instruments generates considerable amounts of frictional heat

locally and shear forces, so that the smear layer becomes attached to the

underlying surface in a manner that prevents it from being rinsed off or

scrubbed away.

The composition reflects the structure of the underling dentin. It mainly

contains pulverized hydroxyapatite and altered collagen, mixed with saliva,

bacteria and other grinding surface debris. The smear layer thickness may vary

from 0.5 to 5m. Smear debris occludes the dentinal tubules with the

formation of smear plugs .The smear layer is porous and penetrated by sub

micron channels, and allows for a small amount of dentinal fluid to pass

through. The smear layer is reported to reduce dentinal permeability by 86%.

In an in vivo study ethylene diamine tetracetic acid (EDTA) was found

to be the most potent conditioner for removing the smear layer and opening up

the orifices of the dentinal tubules. Acidic conditioner inorder of increasing

potential to remove smear layer include citric, polyacrylic, lactic and

47


phosphoric acids. Cavity cleansers, such as Tubulicid and hydrogen peroxide,

were found to have only a slight effect.

The dentinal permeability and, consequently, the internal dentinal

wetness depend on several factors like the diameter and length of the tubules,

the viscosity of dentinal fluid and the molecular size of substances dissolved in

it, the pressure gradient, the surface area available for diffusion, the patency of

the tubules, and the rate of removal of substances by pulpal circulation

The permeability of dentin is not uniform through out teeth, because the

number of tubules/mm2 is not uniform. Dentin located just beneath the

dentinoenamel junction has approximately 1500 to 1900 tubules/m2 that are

about 0.8m in diameter, where as the dentin near the pulp contains 4500

tubules / mm2 that are about 2.5m in diameter9.

Schematic Diagram showing that there are fewer tubules/mm2 in

superficial dentin than in deep dentin, and still fewer tubules per unit area

in root dentin.

48


Dentin near pulp horns more permeable than dentin further away

because the density and diameter of tubules are highest near pulp horns. Axial

dentin is more permeable than the pulpal floors of class II cavities Root dentin

is less permeable than coronal dentin because there are fewer tubules per

square millimeter. The dentin beneath carious lesion is much less permeable

than normal dentin because the tubule of caries affected dentin is filled with

mineral crystals.

The variability in dentinal permeability makes it a more difficult a more

difficult substrate for bonding. Earlier bonding was difficult as the resins were

hydrophobic but recent adhesive systems having a hydrophilic part and are not

affected by increase in depth.

Transformed dentin structure due to physiological and pathological

processes :

Structural changes can occur in the dentinal tubule due to pathologic

carious, erosive and abrasive processes and physiological aging. In carious

instances the lumina of the dentinal tubules are very narrow or may even

obliterated by deposition of intratubular crystals and apposition of irregular

sclerotic dentin.

Dentin undergoes physiologic dentinal sclerosis as part of the aging

process and reactive sclerosis in response to slowly progressive or mild

irritation, such as mechanical abrasion or chemical erosion. Tertiary or

reparative dentin is produced in the pulp chamber at the lesion site in response

to insults such as caries, dental procedure or attrition.

49


Hypermineralization, obstruction of tubules by Whitlockite crystalline

deposits and apposition of reparative dentin adjacent to the pulp are well-

documented responses to caries.

Sclerotic dentin usually contains few patent tubules and therefore has

low permeability. Heavily sclerotic dentin has areas of complete

hypermineralization without tubule exposure, even when etched with an acid.

All of these morphologic and structural transformations of dentin,

induced by physiologic and pathologic processed result in a dentinal substrate

that is less receptive to adhesive treatments than in normal dentin.

Obstruction of the dentinal tubles by “whitlockite” or caries crystals.

50


CHEMISTRY OF ADHESION

There are two main types of chemical adhesion.

By primary valence forces

By secondary valence forces.

The strongest and most stable primary valence bonds are the covalent

and coordinative bonds, which are both electron pair bonds. Ionic bonds may

also give strong adhesion. Secondary valence bonds or intermolecular bonds

are classified as Vanderwaal’s forces and hydrogen bonds.

The chemistry of the adhesive agents can be explained based on the type

of adhesion.

Adhesion based on ionic polymers.

Adhesion by coupling agents

Grafting to collagen.

Adhesion based on ionic polymer :

There are two types of dental materials that are classified as

polyelectrolytes. These are zinc carboxylate cements and glass ionomers or

glass-poly (alkenoates).

The glass-poly (alkenoates) is based on poly (acrylic acid) and

copolymers of, for example, acrylic acid-maleic acid or acrylic acid- itaconic

acid.

51


Structure of poly (alkenoid acid). The drawing shows two copolymers with

the carboxylic acid units.

Investigators have shown that these materials can bond to both enamel

and dentin with out acid etching.

Adhesion of the poly (alkenoic acid)-based materials to apatite can be

achieved by ionic bonding with calcium ions acting as bridges. Hydrogen

bond formation may occur, although to a lesser extent. Dentin is a composite

material with approximately equal quantities by volume of hydroxyapatite and

organic materials. The organic material is mainly collagen with both free

carboxylic groups and amino groups. Hydrogen bonds can be formed between

the carboxylic groups of the poly (alkenoic acid) and amino groups of the

collagen.

Mechanism of adhesion of poly (alkenoic acids) to dentin collagen

52


Ions diffusing from the cement particles or from dentin apatite allow cat

ion bridges to be formed between carboxylic groups of poly (alkenoic acid)

and collagen.

The poly (alkenoic) materials showed good adhesion to enamel and

somewhat poorer adhesion to dentin. Dentin etched with 50% citric acid

showed the lowest strength values. During acid etching the calcium ions are

removed from the apatite of the dentin, and the possibility for formation of

calcium bridges between the carboxylic groups of the poly (alkenoic acid) and

acid groups of both apatite and collagen is greatly reduced. Further more,

there is an enrichment of organic material (collagen) at the surface of dentin

during acid etching, so the bonding to dentin is weakened due to decreased

bridge formation by calcium ions and reduced quantities of apatite at the dentin

surface.

Adhesion based on coupling agents :

This type of adhesion is seen to occur with the non-polyelectrolyte

adhesives. Bonding can be accomplished to the inorganic part of dentin,

hydroxyapatite or to the organic part consisting mainly of collagen bonding

can also be obtained to inorganic part of the dentin.

Treatment of acid-etched enamel with different coupling agents leads to

only minor improvement of the bond strength. One coupling agent was the

silane usually used for silanization of the filler particles in composites, 3-

methacryloyloxypropyl- trimethoxysilane. Another coupling agent was a

butylacrylate-acrylic acid copolymer with free carboxylic acid groups.

53


N-2 hydroxy-3-methacryloyloxy-propyl (NPG-GMA) can co-ordinate

to metal ions (e.g. ca++) by a chelating effect of the carboxylate group, the

amine group, and the hydroxyl group.

The binding of organic coupling agent NPG-GMA to hydroxyapatite via a

metal ion (M)

The coupling agents utilize the concept of hydrophilic and hydrophobic

groups i.e. it consist of a difunctional molecule one part of which enters into a

chemical union with the tooth surface while the other attaches to resin10.

The coupling agents have basically the formula

M-R-X

M- Methacrylate group, which eventually becomes bound tooth resin by

copolymerzation.

X- represents a reactive group, which interacts with the tooth surface.

The reactive groups are end groups.

R-is the linking and spacing group. Spacing group must be able to

provide the necessary flexibility to the coupling agent to enhance the potential

for bonding of the reactive group. If the molecule is excessively rigid the

54


ability of the reactive group to find a satisfactory conformational arrangement

is jeopardized e.g.: Ethyl/oxypropyl

In N- phenyl, glycine glycidyl methacrylate a chelate bond is found

between the N-phenylglycine group and the calcium of the tooth, while the

methacrylate group becomes incorporated into the resin during polymerization.

Another coupling agent which works by chelating with calcium is (4-META).

The monomer 4 – methacryloyloxyethyl trimellitic anhydride (4-META)

Bond strength of these coupling agents can be increased by pretreatment

with certain mordant ions such as ferric and aluminum ions in the form of

aqueous solutions of their chlorides/oxalate salts. A strongly bound surface

layer concentrated in ions capable of reacting with the chelating species is

formed. Systems based on the combined use of mordant ions and coupling

agents are now becoming available .The exact mechanism of role of these

mordant ions is not known. But it is possible that the ionic solution is simply

acting as weak acid, which solubilize and reprecipitate the dentin smear layer.

In some case the acid may etch the dentin, opening up the dentinal tubules and

encouraging mechanical attachment10.

A procedure, which can be classified as the multilayer system has been

suggested. This system entails the treatment of the mechanically prepared

cavity with a ferric oxalate solution and an acetone solution of NPG-GMA or

55


NTG- GMA. An acetone solution of PMDM (the reaction product of

promellitic dianhydride and 2- hydroxy ethylmethacrylate) is placed and

surface is air blown. Finally the composite restorative materials is inserted and

polymerized.

The chemistry of such a treatment is based on the assumption that the

treatment with ferric oxalate solution initiates several reactions with the smear

layer, resulting in a porous layer cross-linked with metal ions. The layer

constitutes insoluble iron phosphate and calcium oxalate attached to a

continuous structure.

During treatment with NPG-GMA these monomer are bonded to iron

ions by co-ordinative bonds. A continuos film is formed by polymerization of

the methacrylate groups. NPG-GMA contains benzene ring rich in (pie)

electrons. During treatment with PMDM monomer, this monomer is bonded to

the NPG-GMA by complex or charge transfer complex formation.

The disadvantage of this system is discoloration due to reaction

products of ferric oxalate. In “tenure” ferric oxalate has been replaced with

aluminum oxalate.

Other coupling agents which primarily bond to the inorganic component

of dentin contain reactive phosphate groups. The interfacial bond is

established through attractions between the negative charges of oxygen on the

phosphate and the positively charged calcium at the dentin surface.

The bond strength to dentin produced by this type of adhesive is

typically around 5MPa although it is not certain how durable this bond is in

56


moist environment. This R-O-P bond is thought to become hydrolyzed leading

to a gradual reduction in strength.

M-R-X here X=O-P.

Coupling agents utilizing this concept of hydrophobic and hydrophilic

groups are the monomers based on phosphates or phosphonates. The

hydrophilic phosphate group is thought to interact with the calcium ions of

dentin.

An adhesive which is closely related to that mentioned before is a

chloro substituted phosphate ester of BISGMA. Compound of this type can be

formed by reaction between BIS-GMA and phosphorous oxychloride

(POCL3). Bonding to tooth calcium may occur through chlorines having

partial negative charges. A more likely explanation of the mode of action is

that the chlorophosphorus ester becomes rapidly hydrolyzed on contact with

moisture on the dentin surface. Due to hydrolysis, HCL is liberated. Bond

formation to calcium takes place as mentioned.

HCl -liberated may also play some part in bond formation by altering

the structure of dentin including smear layer. Bond strength resulting from this

type of coupling agent is about 3-5 MPa. But durability is adversely affected

by hydrolysis.

A number of so called second generation adhesives in the market are

based on monomers containing phosphate groups including Scotch bond (3M),

Clearfil new bond (Kuraray) and Prisma Universal bond.

Clearfil new bond contains 2-methacryloxyethyl-phenyl phosphoric acid

(MEP-P) reported to give adhesive strength of 5-6MPA.

57


A product recently becoming commercially available depends on 2-

stage dentin treatment inorder to achieve adhesion. Two liquids are supplied.

The first is an aqueous solution of HEMA and maleic acid. Both are

hydrophilic monomers which are able to make intimate contact with moist

dentin.

The acid solubilizes the dentin smear layer and the soup of solubilized

dentin, HEMA and maleic acid becomes firmly attached to the underlying

dentin, helped by ability of maleic acid to interact with calcium. Second liquid

consists of application of light activated resin, which consists of HEMA, and

BIsGMA along with polymerization activators .The HEMA imparts some

hydrophilic characters to the resin to ensure more intimate contact-than, which

would be achieved with BIsGMA alone.

The adhesive system described so far work mainly through affinity for

calcium ions.

All the above-mentioned adhesive systems form a more tenacious bond

to enamel.

Some direct bonding between reactive groups in dentinal collagen and

reactive groups in adhesive is possible. However the contribution from this

type of bond is negligible compared to the bond formed with calcium.

The first bonding system for dentin that were reproducible enough to

eliminate the need for mechanical retentive cavities began to be reported in the

late 1970’s. Nakabayashi et al reported the first system based on

58


methymethacrylate, tributyl borane as initiator and 4 META as bonding co-

monomer.

4-META/MMA- TBB resin system E.g.: Amalgabond and super bond

D liner.

This system has a water-triggered polymerization. Methyl methacrylate

is placed on the cut dentin surface with its smear layer intact. The monomer

diffuses through the smear layer and into the dentin. The tributyl borane in

presence of water (that is present on dentin surface) splits to butyl radicals,

which graft on to the collagen molecules and initiate the polymerization

reaction of the methyl methacrylate (chemical cure). The 4- META is a

methacryl-substituted mellitic anhydride, which is hydrolyzed to mellitic acid

and chelates calcium.

The chelation adds to binding between the growing methyl methacrylate

chains, increasing both grafting and cross linking density of the final acrylic

dentin composite layer.

The dentin and its smear layer are embedded in hydrophobic resin and

can be bonded to by the curing composite restoratives materials by

copolymerization. The bond is strong and resistant to hydrolysis.

All these systems described are basically adhesive molecules with a

potential for calcium bonding.

It can be divided into 3 groups

1. Phosphate based adhesive

M-R1-POYZ

2. Adhesive based on amino acid.

M-R2-N2-R 3-COOH

3. Adhesives based on dicarboxylic acid

59


M-R4- COOH

COOH

All these case involve attraction between negative changes on the

adhesive and positive changes on the tooth calcium ions.

Collagen bonding adhesive :

Grafting to collagen :

Some adhesive systems have been developed specifically with the aim

of grafting to the organic collagenous component of dentin. Possible bonding

sites of the collagen molecule include the hydroxyl, carboxyl and amino and

amido groups. Removal of hydrogen from any of these groups allows

combination with chemicals present in denting bonding agents. Compounds

that have a capacity to react with one or more groups of collagen are

isocyanates, carboxylic acid chlorides, carboxylic acid anhydrides and

aldehydes.

One product relies on the addition reaction between the isocyanate

groups and both the hydroxyl and the amine groups of collagen.

The adhesive is a low molecular weight polyurethane having excess of

isocyanate groups. Bond strength to dentin about 4 MPA achieved through

this is variable and depends on the presence of moisture on the dentin surface.

Isocyanate groups undergo a rapid reaction with water.

Another commercial product depends on the reaction, which readily

occurs between aldehyde groups and amine groups. The active components

are glutaraldehyde and HEMA. Bonding involves a complex reaction in which

aldehyde and amine groups react to from an adhesive link and the HEMA react

60


with glutaraldehyde at dentin surface to give a polymerizable methacrylate

group, which is attached to dentin and is capable of completing the adhesive

link with restorative resin by co-polymerization. In order to produce optimal

result it is necessary to remove the smear layer.

GLUMA system has been introduced based on this. Here an equimolar

mixture of gluteraldehyde \HEMA is placed on dentin that has been cleansed

of its smear layer by EDTA solution. The Gluteraldehyde\HEMA penetrates

the tubules to depth greater than 300, m. There is some reaction between the

hydroxyl groups and HEMA/ gluteraldehyde. The result is a dentin surface

well wetted by a hydrophilic monomer. An intermediate unfilled resin is then

placed on the treated surface, which forms a graded bridge between the

hydrophilic HEMA and the hydrophobic composite resin. The reaction

basically as suggested by Munnksgaard is that of an amino group of EDTA-

demineralised dentin collagen reacts forming covalent bonds. Other systems

infiltrate the intact smear layer cross-linking it by reaction of the isocyanate

groups with collagen. The smear layer is first deflated and dehydrated with

acetone to maximize this reaction. The cross-linking extends to the very outer

most part of the intact dentin but no further.

The isocyanate also bears a methacrylate group, which is capable of

copolymerizing with composite resin. This is a very quick technique marred

by the very rapid reaction of the isocyanate group which can cause the

applicator brush to drag in the cavity. This system seals the dentin well

provided the cut dentin is covered in an intact smear layer.

If the layer has been removed for any reason protection from acid attack

is less in that area.

61


PARAMETERS AFFECTING THE CLINICAL

PERFORMANCE OF ADHESIVES

Dentine factors

Tooth

Patient

Material

Dentine factors:

Includes micro structural features of the dentine involved with local

adhesion, smear layer, dentinal tubule density, size and length, dentin sclerosis.

Smear layer is partially porous and it dramatically reduces the fluid flow from

the underlying dentinal tubules. It acts as a biological band, aid in reducing

postoperative sensitivity4.

Adhesion is affected by wetness of the dentine; this in turn is related to

the density and size of dentinal tubules. Tubules density is greater near the pulp

and tubules represent a much larger portion of the dentinal volume (or) around

28-volume% along the pulpal wall Vs 4 volume % at the DEJ. So this area has

the greatest potential to immediately wet the cut dentinal surfaces. Bond

strengths in deep dentine generally are lower because of the interference of

moisture from tubules. Newer dentine bonding system including hydrophilic

monomers that penetrate surface moisture and circumvent this problem.

Dentine Sclerosis :

In response to caries, trauma (or) other stimuli, odontoblasts attempt to

seal dentin by laying sown a bridge of peritubular hydroxyapatite crystals.

62


These sclerotic changes associated with again may have an adverse effect o

dentin bonding.

Tooth factors:

a. Lesion size and shape.

b. Enamel and dentine structure.

c. Tooth flexure.

d. Tooth location.

Shallow, saucer shaped lesions lack insufficient surface area for

adequate retention, precludes sufficient bulk of restorative material to resist

deflection. This type of restoration appears to be particularly vulnerable to

dislodgement during tooth flexure. Eccentric forces on occlusal surface

generate a critical flexure resulting in stress concentration in bonded areas.

These flexural forces appear capable of debonding cervical restorations,

especially those without macro-mechanical retention4.

Tooth location:

Created cervical restorations failure in mandibular teeth related to

difficulties with moisture control; (or) due to greater propensity for tooth

flexure to occur in mandibular teeth, this again could occur as the result of

lingual inclination of the crown and the smaller cross sectional area of

mandibular teeth in the cervical area.

Patient factors:

History of bruxism(or) traumatic occlusion produces greater occlusal

stresses on their teeth. Clinical studies observed that, there is a link between

the presence of occlusal stress and loss of cervical restoration retention.

63


Material Factors :

Early improvements in dentin bonding agents had focused on

developing chemical bonds to tooth structure. But currently micro-mechanical

bonding is emphasized.

First generation DBA was designed for ionic bonding to hydroxyapatite

(or) for covalent bonding to collagen. These materials were hydrophobic and

were limited by the relative attachment strength of the smear layer to the

underlying dentin. Bonding strength was about 2-6Mpa. New generation

bonding agents procedures attempt to remove penetrate (or) solublize the

smear layer and then wear the underlying dentin with resin monomers that are

more hydrophilic. Bond strengths are decidedly improved by eliminating (or)

penetrating the smear layer with mild organic acids. However the dentin may

be extensively demineralized and weakened depending upon the concentration

of acid and exposure time. Strong acids removed smear plugs and

demineralized the intertubular dentin near the surface. After dentin-

conditioning application of hydrophilic monomers penetrates the decalcified

inter tubular dentine and embed 1-5 m of superficial dentine. This

transitional zone called Hybrid layer, interpenetration zone (or) interdiffusion

zone, appears to be the primary site for dentinal adhesion4.

Bonding strength ranged from 12-22 MPa. Hydrophilic systems seem

to keep the collagen network open while penetrating it. Also polymerization

shrinkage, water absorption of the overlying composite restoration also

influence bond strength. More cervical retention failures are associated with

higher modules composite that include macro fillers and higher filler content.

Where as macrofil composites with lower elastic modulus appear to flex in

response to cervical deformation rather than debonding.

64


STRUCTURE AND COMPOSITION OF ENAMEL

AND DENTIN

Enamel :

Enamel is the hardest of the mineralized tissues of the body. Enamel is

formed by cells called ameloblasts, which originate from the embryonic germ

layer known as ectoderm. Enamel covers the anatomical crown of the tooth. It

is thickest over the cusp and thinnest at the base of the pits, fissures and the

cervical region of the crown12.

Composition:

Enamel composed of both inorganic and organic substances. 95% to

98% inorganic matter by weight. Hydroxyapatite, in the form of a crystalline

lattice, is the largest mineral constituent and is present 90% to 92% by volume.

Other minerals and trace elements are contained in smaller amounts. The

remaining constituents of tooth enamel are an organic content of about 1% to

2% and a water contents of about 4% by weight, these total approximately 6%

by volume. Various ions-strontium, magnesium, lead and fluoride, if present

during enamel formation, may be incorporated into or adsorbed by the

hydroxyapatite crystals. The bulk of organic material consists of tyrosine-rich

amelogenin polypeptide (TRAP) peptite sequence lightly bound to the

hydroxyapatite crystals as well as non-amelogenin protein. The organic

component of enamel is the protein enamelin. The distribution of enamelin

between and on the crystals aids enamel permeability.

65


Physical properties :

The hardest substance of human body is enamel. Hardness may vary

over the external tooth surface according to the location; also, it decreases

inward, with hardness lowest at the DEJ. The density of enamel decreases

from the surface to the DEJ. Enamel is a very brittle structure with a high

elastic modulus and low tensile strength, which indicates a rigid structure.

The high inorganic content confers a translucent quality to the enamel

with color being imparted by the dentin especially where enamel is thinnest at

the cervical region. Developmental anomalies of maturation and consequences

of carious attack produce localized changes in opacity,

Specific gravity is 2.8.

Hardness-200-500 Knoop hardness range.

Enamel is selectively permeable to certain ions and molecules,

permitting both partial and complete penetration. Enamel permeability

decreases with age because of changes in the enamel matrix.

Enamel is soluble when exposed to an acid medium, but the dissolution

is not uniform. Solubility of enamel increases from enamel surface to DEJ.

Acid etching of enamel surface produces an irregular and pitted surface

with numerous microscopic undercuts by an uneven dissolution of enamel rod

heads and tails. Composite or pit-and-fissure sealant is bonded to the enamel

surface by resin tags formed in the acid- etched enamel rod structures.

Therefore the structure of enamel can be an asset when it is subjected to

purposeful and controlled acid dissolution of the enamel rods to provide this

micro retention for composite or sealant.

66


Microscopic structure of enamel :

Human enamel is composed of rods that in transverse selection are

shaped with a rounded head or body section and a tail section, which forms a

repetitive series of interlocking prisms. The rounded head portion of each

prism (5 m wide ) lies between the narrow tail portions (5 m long) of two

adjacent prisms. The rounded head portion is oriented in the incisal or occlusal

direction; the tail section is oriented cervical.

Enamel rods follow a wavy, spiraling course, producing an alternating

arrangement for each group or layer or rods as they change direction in

progressing from the dentin toward the enamel surface where they end a few

micrometers short of tooth surface.

Rods follow a curving path through one third of the enamel next to the

dentinoenamel junction. After that, the rods usually follow a more direct path

through the remaining two third of enamel to the enamel surface. Other

microscopic structures also appear in enamel these include lamellae, which

represent a localized increase in the size of rod sheath and may run both a short

and long course.

Enamel tufts are hypomineralized structures of enamel rods and inter-

rod substance that projects between adjacent groups of enamel rods from the

dentinoenamel junction. Enamel Spindles are odontoblastic processes, which

cross dentinoenamel junction into the enamel.

Enamel lamellae are thin, leaf like faults between enamel rod groups

that extend from the enamel surface toward the dentinoenamel junction.

67


The enamel surface itself is a micro morphologically and chemically

complex region. An understanding of the micro morphological characteristics

of the enamel and its biophysical and physiological properties has been

significant in achieving interactions between it and dental biomaterials.

68


DENTIN

Dentin forms the largest portion of the tooth structure extending almost

the full length of the tooth. Externally dentin is covered by enamel on the

anatomic crown and cementum on the anatomic root. Internally dentin forms

the walls of the pulp cavity.

The dentin is laid down by Odontoblasts. The most recently formed

layer of dentin is always on the pulpal surface. This unmineralized zone of

dentin is immediately next to the cell bodies of the odontoblasts and is called

predentin. The dentin forming the initial shape of the tooth is called primary

dentin.

After the primary dentin is formed and the tooth has erupted dentin

deposition continues at a reduced rate even without obvious external stimuli

and the dentin is called as secondary dentin. In secondary dentin the tubules

take a different directional pattern in contrast to primary dentin.

Reparative dentin (tertiary dentin) is formed by replacement

odontoblasts (termed secondary odontoblasts) in response to moderate level

irritants, such as attrition, abrasion, and erosion, trauma, moderate rate dentinal

caries, and some operative procedures. It usually appears as a localized dentin

deposit on the wall of the pulp cavity immediately sub adjacent to the area on

the tooth that has received the injury.

When a moderate level of stimuli are applied to dentin the affected

odontoblastic processes may die with associated odontoblasts. These areas of

69


dentin are called dead tracts and extend from the external dentin surface to the

pulp.

Sclerotic dentin results from aging or mild irritation and causes a change

in the composition of the primary dentin. The peritubular dentin becomes

wider, gradually filling the tubules with calcified material, progressing from

the dentinoenamel junction pulpally. These areas are harder, denser, less

sensitive, and more protective to the pulp against subsequent irritations.

Sclerosis resulting from aging is “physiological dentin sclerosis” and that

resulting from a mild irritation is “ reactive dentin sclerosis”. Reactive dentin

sclerosis often can be seen radiographically in the form of more radiopaque

area in the S-shape of the tubules. Eburnated dentin is a term referring to the

outward portion of reactive sclerotic dentin where slow caries has destroyed

formerly overlying tooth structure, leaving a hard, darkened, cleanable surface.

Structure :

The dentin comprises of dentinal tubules, which are small canals that

extend across the entire width of dentin, from dentinoenamel junction or

dentinocemental junction to the pulp. Each tubule contains the cytoplasmic cell

process (Tome’s fiber) of an odontoblast. Each dentinal tubule lined with a

layer of peritubular dentin, which is more mineralized than the surrounding

intertubular dentin12.

The surface area of dentin is much larger at the dentinoenamel or

dentinocemental junctions than it is on the pulp cavity side. Since the

odontoblasts form dentin progressing inward toward the pulp, the tubules are

forced closed together. The number of tubules increases from 15,000 to

20,000/mm2 at the dentinoenamal junctions to 45000 to 65,000/mm2 at the

70


pulp. The lumen of the tubules varies from the dentinoenamel junction to the

pulp surface as well. In coronal dentin, the average diameter of tubules at the

dentinoenamal junction is 0.5 to 0.9m, but increase to 2 to 3m at the pulp.

The course of dentinal tubules is in a slight S-curve in the tooth crown,

but the tubules are straighter in the incisal ridges, cusp and root areas. The

ends of the tubules are perpendicular to the dentinoenamel junction and

dentinocemental junctions. Along the tubule walls are small lateral openings

called canaliculi. As the odontoblastic process proceeds from the cell in the

pulp to the dentinoenamel junction lateral secondary branches extend into the

canaliculi and appear to communicate with lateral extensions of adjacent

odontoblastic processes. Near the dentinoenamel junction the tubules divide

into several terminal branches, thus forming an inter communicating and

anastomosing network.

Chemical composition :

Composition of human dentin is approximately 75% inorganic material,

20% organic material, and 5% water and other materials. Dentin is less

mineralized than enamel but more mineralized than cementum or bone. The

mineral content of dentin increases with age. The mineral phase is composed

primarily of hydroxyapatite crystallites. The organic phase of dentin consists

primarily of collagen.

The dentinal tubules are normally filled with odontoblastic processes

and dentinal fluid, which makes it a difficult surface to bond to. Further the

collagen fibers are usually type I collagen with traces of type IV collagen.

They consist of carboxyl, amino and hydroxyl surface groups. The other non-

collagenous constituents that can be found are dentin phosphoprotiens,

sialoproteins and osteocalcins.

71


Physical properties :

Thickness of dentin varies with the age of the tooth. As age advances,

the thickness is more than the younger age groups. Amount of dentin in

primary teeth is half of that in corresponding permanent successor.

Depending on the depth of the preparation, the substrate surface can

consist of widely varying proportion of intertubular dentin, peritubular dentin,

secondary dentin and sclerotic dentin. Dentin is saturated with water and

oxygen and water content again varies according to the type of dentin.

Resistance to fatigue :

Collagen fibrils are generally distributed randomly in intertubular dentin

but are oriented circumfererentially around tubules5. The more randomly the

fibrils are distributed, the higher will be the probability that the growth of

micro cracks will be retarded during function. If there is an intimate

association between resin and collagen fibrils, then that bond will undergo

stress and strain under function and may exhibit fatigue over time. If there is

no true bond, then both the resin and the collagen fibrils may experience

fatigue separately over time.

Micro hardness:

Pashley et al reported that the micro hardness of dentin fell when dentin

was tested from superficial to deep regions. Using a modified atomic force

microscope (AFM) Kinney et al demonstrated that the decrease in hardness

with dentinal depth, reported by Pashley et al caused by a decrease in the

stiffness of intertubular dentinal matrix14.

72


Elasticity:

Mineralized dentin is relatively stiff (modulus of elasticity of 14 to 19

GPa) and has an ultimate strength of 230 to 370 MPa (compressive) or 45 to

138 MPa (shear).

Following acid etching, the mineral phase of the dentinal surface and

some noncollagenous proteins are solubilized and some of the proteins are

extracted, exposing the collagen fibrils of the demineralized dentinal matrix.

This produces a profound change in the physical properties of dentin

The demineralized dentinal matrix becomes very soft and elastic. The

modulus of elasticity of wet demineralized dentinal matrix is only about 5MPa,

which is more than 1,000 times lower than that of mineralized dentin. The

clinical implication of this low stiffness is that the fibril network can easily

collapse when air-dried, there by interfering with the uptake of adhesive

monomers.

Permeability :

Permeability refers to the ease with which a substance can move into or

across a diffusion barrier. Two types of dentinal permeability must be

considered. The movement of fluid with in dentinal tubules intratubular

permeability is responsible for dentinal sensitivity or pain.

The diffusion of substances through tubules filled, with dentinal fluid to

reach the pulp is another example of intratubular dentinal permeability.

The second important type of dentinal permeability is the diffusion of

monomer into demineralized intertubular dentin. This is referred to as

intertubular dentinal permeability.

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For hybrid layer formation, intertubular dentin must be demineralized to

expose the collagen fibrils of the dentinal matrix and to create diffusion

pathway for monomer infiltration. These fibrils are separated by spaces about

15 to 20m wide that was previously occupied by apatite crystallites. After the

surface is acid etched and rinsed with water, these spaces are filled with water

and are presumed to remain about 15 to 20m wide. It is through these spaces

that adhesive monomer must diffuse if it is to infiltrate the demineralized

dentinal matrix.

The movement of resin monomer into these long, continuous,

interconnected, narrow channels, or pores is an example of intertubular

permeability into demineralized dentin. The permeability of the substrate must

be maintained as high as possible to obtain good monomer infiltration for

hybridization of demineralized enamel and dentin.

The penetration of resin monomer into dentinal tubules to form

hybridized resin tags to intratubular dentin is an example of intratubular

dentinal permeability. Both types of dentinal permeability are important in

dentin bonding

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ENAMEL BONDING SYSTEMS

Enamel bonding systems most often consist of an an unfilled or lightly

filled liquid acrylic monomer mixture placed onto acid etched enamel.The

monomer flows into the interstices between and within enamel rods14.

The most significant discovery in dentistry during the last three decades

is that by Dr. Michael Buonocore in 1955, working in New York. He

discovered that the bond strength between human enamel and acrylic resin

could be tremendously enhanced by exposing the tooth to a mild acidic

solution before applying resin to enamel surface.The effective etching was

possible only due to the morphological characteristics of enamel. It is

composed of bundles of rods, prisms, seeming to radiate from the center of the

tooth towards the periphery. The area that surrounds these individual prisms

and serves as mortar for them is known as the interprismatic enamel. It is a

fortunate accident of nature that normally there is a difference between the

resistance of enamel prisms and interprismatic enamel to acidic attack. Thus

Dr. Buonocore discovered placing a weak acidic solution on the enamel

surface causes a differential etch rate between the two areas. This results in an

irregular and pitted surface. In addition to the presence of enamel prisms it has

been discovered that the enamel prisms it has been discovered that the enamel

contains approximately l%-2% space by volume. Although this means that the

enamel is only minutely porous. These porosity also play a role in the bonding

process. This results in augmentation of the bond strength achieved by

differential etching.

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Etching Agents:

1. Phosphoric Acid: A concentration between 30%-50% with 37% being the

concentration most commonly provided.

2. Pvruvic acid: This may be a suitable alternative to phosphoric acid. But the

stability of pyruvic acid solutions are not consistent.

3. An Alpha- ketocarboxvlic acid

Etching Pattern:

Exposure of human enamel to conditioning solutions produces three

basic etching patterns:

TYPE-I(Core Etching):

This pattern is created when the center of the prisms rather than the

interprismatic enamel (i.e.) prism core material is preferentially removed

leaving the prism peripheries relatively intact resulting in a honeycomb

appearance. The average width of the craters usually found in this type of

etching is 5 microns. This fact is of particular significance when selecting the

luting agent for the bonding and fusing techniques. Any filler particle of

greater diameter would simply not penetrate the enamel surface.

TYPE-H (Peripheral Etching):

This type of etching results when the interprismatic enamel erodes more

rapidly than the prism core i.e. the peripheral regions of the prisms are

dissolved preferentially leaving the prism core relatively intact resulting in a

cobblestone appearance15.

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TYPE-III ( Mixed patterns):

This type of etching pattern results when the enamel being etched is

composed of a homogenous mass instead of the more commonly found

prismed structure.

Deciduous teeth often exhibit just a stratum in their outermost layer.

Since the outer layer is homogenous in stiucture applying an acid etchant

results only in a reduction of enamel bulk not the differential etch necessary for

bonding. This type HI pattern can be troublesome for bonding because it does

not allow the resin to grip the enamel. This area of prism less enamel are not

confined to the deciduous teeth but also in the cervical two thirds of the crowns

of molars and premolars. These zones are areas where the dentist hopes to

achieve most of his bond strength , when using direct bonded retainers. This

prism less enamel usually comprises only the outer 13-20 microns of the

enamel. Applying the etchant not only roughens the outer surface but actually

dissolves it, it is possible to etch past this prism less layer using the etchant

itself. A 60 seconds application of 30% orthophosphoric acid results in a loss

of 20microns in depth of histologic change. Once 20microns of enamel have

been D removed from the surface the underlying structure usually exhibits one

of the other three etching patterns. Thus the time needed to etch an area of

enamel displaying prism less outer structure is considerably greater than an

area of normal enamel. Etching pattern is not of clinical significance because

the clinician cannot define the etching pattern by visual examination. They are

not important to the resulting bond strength.

Advantages of etching:

Etching results in tremendous increase in the surface energy which

increases the wettability of the surface. Etching increases the surface area

available for bonding. The improved mechanical bonding is responsible for the

77


high bond strength of 18 22MPa.This high bond strength is of simple micro

mechanical retention. This can be explained by the fact once the enamel

surface has been roughened by the etchant the enamel pores also become

enlarged. Since these pores often interconnect their increase in size not only

allows relatively larger resin molecules to penetrate the subsurface of the

enamel but also allows these resin tags to interconnect. Stronger enamel

bonding depends upon resin tags becoming interlocked with the surface

irregularities created by etching. Resin tags which form between enamel

peripheries are called MACROTAGS.

A much finer network of thousands of smaller tags from across the end

of each rod where individual hydroxyapatite crystals have been dissolved

leaving crypts outlined by residual organic material. These fine tags are called

MICROTAGS. Microtags and macrotags are the basis of micro mechanical

bonding. Micro tags are important because of their larger number and great

surface of contact. The length of the macro tags are unimportant because the

fracture occurs in the neck of the tags. Most macro tags are only 2-5

micrometer in length. Etching improves mechanical bonding between resin and

enamel. This forms the basis of many innovative dental procedure such as resin

bonded metal retainers porcelain laminate veneers and orthodontic brackets

The etching improves marginal seal, which prevents marginal staining caused

by interfacial leakage to a large extent. The improved mechanical bonding

between resin and enamel. This forms the basis of many innovative dental

procedure such as resin bonded metal retainers porcelain laminate veneers and

orthodontic brackets. Thus etching improves marginal seal, which prevents

marginal staining caused by interfacial leakage to a large extent.

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Enamel bonding agents :

Enamel bonding systems most often consist of an an unfilled or lightly

filled) liquid acrylic monomer mixture placed onto acid etched enamel12. The

monomer flows into the interstices between and within enamel rods.

Traditionally enamel bonding agents have been made by combining different

methacrylates such as bis-GMA and TEGDMA to control viscosity. Because

enamel can be kept fairly dry, these rather hydrophobic resin work well as long

as they are restricted to enamel.

APPLICATION OF THE ACID ETCH TECHNIQUE:

It is widely used for composite filling as a means of aiding retention and

reducing or preventing micro leakage.

For class IV cavities the acid etch technique has replaced the gold inlay

as the treatment of choice for restoring the tooth contours and function. In this

example the use of an adhesive system allows the conservation of considerable

quantities of tooth substance which would otherwise be lost in cavity

preparation.

Bonding of resins using the acid etch technique has also been used as a

means of strengthening or splinting teeth which have been weakened by cavity

preparation. The teeth having a prepared cavity is weakened relative to an

unprepared tooth. Under stress fracture being the most likely occurrence.

Restoring with a non adhesive restoration has little beneficial effect on the

strength of the tooth whereas the use of an adhesive material will strengthen

the tooth and help to prevent cusp fracture.

PIT AND FISSURE SEALANTS: are now widely used for preventing pit and

fissure caries. The success of fissure sealants depends on initial placement

79


condition and techniques. In order to get good resin tag formation the enamel

must be properly etched and washed and thoroughly dried before the sealant is

applied.

With the advent of acid etch technique resins are widely used for

attaching orthodontic brackets. With the acid etch techniques composites are

gaining popularity for attachment of bridges .e.g. Rochette bridge, Maryland

bridge. The attachment of acrylic or porcelain labial veneers in order to

improve the appearance of stained, discoloured misshapen.

BIOCOMPATABILITY;

Pulpal tissue:

No danger of pulpal irritation when it is placed over enamel. When they

are placed over dentin or cemental tissues however there is danger of pulpal

inflammation. The danger increases with the proximity of the acid to the pulp ,

the concentration of acid used and the duration of its application. Hence the

etchant must be carefully placed when dentine or cementum may come into

contact with the acid.

Gingival tissues :

Damage to the gingival tissue is not a problem within the range of

normal clinical technique. However gingival irritation occurs when gingival

tissue is exposed to up to 50% orthophosphoric acid. Appearances are similar

to that of aspirin bum.

To the tooth :

The loss of fluoride rich surface enamel during prolonged etching may

make the adjacent enamel more' usceptible to enamel decalcification as in

orthodontics.

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Clinically bonding to enamel should present a problem. However this

does not mean that failure of enamel bonded restoration will not occur, since

cohesive failure of the adhesive of the restoration can still take place. Equally,

metallic or ceramic restorations can fail adhesion due to a lack of bonding

between the resin and these restorative materials.

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SMEAR LAYERS

The observation that smear layers could occlude the tubular structure of

dentin and bone was first made by Van Leeuwenhoek in 1677, although he did

not call them smear layer. More recently dentinal smear layer was described

by Boyde et al. The composition of the smear layer was demonstrated by Eick

et al to consist of calcium and phosphate plus organic material containing

sulfur, nitrogen and carbon. When observed under a SEM, it has a rough

smeared appearance with obliterated tubule orifices. It is composed of

varying amounts of blood, saliva, bacteria, denatured collagen, and enamel and

dentine particles.

The composition of the smear layer reflects the composition of the

dentin from which it is formed. Thus the smear layer in] superficial normal

dentin may have a composition close to that of intertubular dentin whereas the

composition of the smear layer in deep dentin would reflect its lesser degree of

mineralization. Similarly smear layers created on caries affected and sclerotic

cervical dentin has more Whitlockite just like this type of dentin where more

Whitlock is present than normal dentin.

The smear layer acts like a natural bandage over the cut surface since it

occludes many of the dentinal tubules with debris called smear plugs covered}

by the smear layer. The thickness of the smear layer varies as a function of

whether the dentin is dry or wet during rotary instrumentation. The thickness is

approximately 1-5 m. The morphology, thickness and composition of the

smear layer vary with the method used for cutting the surface, with coarse

diamond abrasives used dry producing the thickest deposits.

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Smear layer (SEM 3, 950 x)

Smear layer has 2 phases :

A solid phase - Made up of cutting debris.

A liquid phase - Made up of tortuous fluid filled channels around the

cutting debris.

There are two different opinions regarding smear layer treatment. Some

believe that the smear layer acts as an affective, natural cavity liner that seals

dentinal tubules and reduces permeability making the smear layer a clinical

asset. Others argue that the smear layer interferes with the adhesion of

restorative materials, serving as a focus for bacteria and bacterial toxins and

therefore it should be removed. One study reported that the smear layer, which

was firmly attached to the dentin initially, became loose and was largely

replaced by bacteria and fluid within a few weeks.

In order to chemically attach a restorative system to tooth structure, one

of the several options must be considered for the smear layer. For the currently

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available dentine bonding agents, the smear layer is managed in one of the five

ways;

No treatment at all: The smear layer is left in place without

modification, and the dentin-bonding agent is applied directly to it.

Dissolution of the smear layer: The dissolved smear layer plays a part in

the chemical attachment of the dentin-bonding agent to dentin.

The smear layer is removed: the dentine-bonding agent develops

chemical attachment directly to intact dentin.

It involves the modification of the smear layer. This process

theoretically improves the attachment of the smear layer to dentin.

This means of smear layer treatment involves its removal and

replacement with another mediating agents.

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DENTIN BONDING SYSTEMS

Dental Bonding System:

The dental adhesive system consists of a conditioner (etchant), primer

and bonding agent (adhesive).

Dentin bonding systems involve an unfilled (or lightly filled), liquid

acrylic monomer mixture placed onto an acid-etched and primed dentin

surface. The bonding primer depends on hydrophilic monomers, such as

2-hydroxyethy! methacrylate (2-HEMA or HEMA), to easily wet hydrophilic

dentin surfaces that contain some moisture. Although primer and/or bonding

agent may flow into dentinal tubules, the bond strength is primarily achieved

by micromechanical bonding to the intertubular dentin (between tubules) along

the cut dentin surface. Despite the fact that many dentin-bonding systems have

been formulated to allow chemical reactions to take place with dentin, this has

had little or no apparent contribution on the final bond strength. Generally,

90% or more of dentin bond strength is presumed to be due to mechanical

bonding12.

Mechanical preparation of dentin leaves behind a highly distorted debris

layer (smear layer) that coves the surface and conceals the underlying

structures. Early dentin bonding systems were hydrophobic and were bonded

directly to the dentin smear layer. Therefore macro shear bond strengths were

found to be less than 6 MPa, because that is the strength of the bond of the

smear layer to sound dentin. Initial dentin etching process removed the smear

layer, but tended to over etch dentin. Bond strengths of 10 to 12 MPa were

produced, and were not significantly increased until bonding systems were

chemically modified to become more hydrophilic (18 to 20 MPa). Careful

85


dentin etching produced micromechanical relief for bonding between tubules

(intertubular dentin) without excessive demineralization of peritubular dentin.

Coupled with hydrophilic primers, bond strengths increased to 22 to 35 MPa.

The theoretic limit for dentin bonding system strength may actually be higher

(80 to 100 Mpa) than that for enamel, because dentin is more resistant to shear

fracture. The clinically important limit for dentin bonding is not yet known.

However, because of the presence of more water in dentin than enamel, the

clinical longevity of dentin bonding may not be as long as that of enamel. As

portrayed in the priming action in dentin bonding systems is designed to

penetrate through any remnant smear layer and into the intertubular dentin and

to fill the spaces left by dissolved hydroxyapatite crystals. This allows acrylic

monomers to form an interpenetrating network around dentin collagen. Once

polymerized, this layer produces what Nakabayashi referred to as the hybrid

zone (interdiffusion zone or interpenetration zone). Depending on the

particular chemistry of a bonding system, the hybrid layer may vary from 0.1

to 5 m deep. If this decalcified dentin zone is not filled (bonded) by bonding

system, it may as a weakened layer or zone contributing to fracture, in

addition, the extent of the etching effect on the strength of the collagen fibers is

not yet known, however these systems demonstrate that stronger dentin

bonding is possible and portend a bright future for bonding systems.

The key ingredient for priming in many dentin-bonding systems is

hydroxyethyl methacrylate (HEMA). This, molecule is an analog to methyl

methacrylate, except that an ethoxy ester group to make it hydrophilic replaces

the pendant methyl ester. Importantly, it is relatively volatile and has some

tendency to produce mild sensitivity. Dentists and assistants should be aware

that it is very mobile. , can diffuse through rubber gloves, and will cause skin

dryness and cracking in many individuals. Therefore during the use of

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primers and bonding agents high-volume evacuation should be used to

minimize HEMA vapor contact.

Bonding normally has been conducted in three steps (three-component

systems). During the late 1990s,the number of stages (etching, priming,

bonding) was reduced by combining the actions of various steps. Two

component systems were devised that either employed etching with

priming/bonding or etching/priming with bonding. In latter case, the term self-

etching primer was used to describe the first component of the system. This is

most often achieved by employing acidic monomers that dissolve or disrupt the

smear layer, dissolve hydroxyapatite in the intertubular zone and tubules, and

then polymerize to generate a hybrid zone. Despite the approach to designing

two-component system, they generally required significant solvent to

cosolubilize the modifying material. Solvent levels among systems vary

considerably but are generally in the range of 65% to 90% solvent. Choices for

solvent systems, base on acetone or ethanol with water, do affect the wetting

efficiency.

For bonding systems to efficiently produce a hybrid layer, it is

extremely important to keep the dentin hydrated. Quite often, the rinsing and

drying of dentin that follows tooth preparation or specific etching steps, results

in dehydrated superficial layers of dentin. Etched dentin no longer contains

hydroxyapatite crystals between collagen fibers. It consists only of the

remaining collagen and water. Dehydration, whether intentional or not, causes

the remaining collagen sponge to collapse with collagen molecules forming a

mat and excluding monomers necessary for hybrid layer formation. Therefore

etched dentin either must be kept moist or be intentionally rehydrated.

Rehydration can be accomplished with a moist cotton pledget or applicator tip

in contact with the surfaces for approximately 10 seconds or by the use of

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rewetting agents. If dentin moisture is inadequate, then the hybrid layer will

not form, and the bonding system will fail to seal and bond. It is suspected that

in adequate precautions in this regard in many bonding instructions during the

early 1990s may have contributed to the premature failure of many dentin-

bonding systems.

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CRITERIA FOR IDEAL DENTIN BONDING

SYSTEM

Should provide an immediate permanent, high- strength bond to

dentine3.

Should have a bond strength to dentin similar to that to enamel

Should be compatible with dental tissues

Should minimize microleakage at the margins of restorations

Should prevent, recurrent caries and marginal staining

Should be easy to use and minimally technique sensitive

Should a reasonable shelf life

Should be compatible with a wide range of resins

Use a resin of low film thickness (> 20mm) if the system is to be

suitable for use with indirect restorations.

Show no reduction in bond strength when applied to a moist surface,

and

Have no potential for sensitization of patients or operators

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CONDITIONING OF THE DENTIN SUBSTRATE

Conditioning of the dentin will be defined as any alteration of the dentin

done after the creation of dentin cutting debris, termed the smear layer. The

objective of dentin conditioning is to create a surface capable of micro

mechanical and possible chemical bonding to a dentin-bonding agent.

The principle effects of conditioning of dentin may be classified as

a. Physical changes

b. Chemical changes

Physical changes are principally :

Increases or decreases in the thickness and morphology of the smear

layer.

Changes in the shape of the dentinal tubules.

Chemical changes are principally :

Modifications of the fraction of organic matter

Decalcification of the inorganic portion.

Removal of the smear layer generally results in increase permeability of

the dentin. The small particles comprising the smear layer have a large surface-

to volume ratio. The particles dissolve more easily than the intact dentin. If

the smear layer and smear plugs within the tubules are lost, the exposed dentin

becomes more permeable and sensitive. For clinical success, the conditioned

dentin must be sealed to prevent sensitivity and to prevent the pathology

associated with the increased permeability of the dentinal tubules16.

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Conditioning of dentin may be done by several means.

Chemicals

Acids.

Calcium chelalors

Thermal

Lasers

Mechanical

Abrasion.

Acid conditioners :

Mode of action of chemical conditioners :

It has been suggested that mineralized collagen matrices have apatite

crystallites arranged not only around collagen fibrils but also with in them, in

the whole regions. Most of the apatites consist of Ca 10 (Po4) X2 where X can

be carbonates, fluoride or hydroxyl ions. The major phosphate ion species is

the non-protonated, trivalent form. This makes the apatite an excellent buffer

for hydrogen ions. One can argue that intertubular dentin is solid buffer

material, because both apatite and collagen can take up hydrogen ions from

acidic solutions, either as product of bacterial metabolism or therapeutically

applied acidic conditions. As hydrogen ions are taken up by trivalent

phosphate the resulting protonated phosphate species no longer fit into the

crystalline apatite lattice and hence the lattices disintegrate and dissolve into

adjacent fluids. As the crystallites dissolve the underlying collagen fibrils

become accessible, these fibrils may also take up hydrogen ions. As acid

conditioning proceeds into intertubular dentin the perifibril porosities

previously occupied by apatite crystallites become filled with the liquid phase

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of the conditioner. The acidic conditioners demineralize dentin to a depth of at

least 2-5 m16.

The factors that limit the depth of demineralization are:

Type of acid

Etching time

Strength of the acid

Buffering capacity of the dentin.

The depth of demineralization is limited in sclerotic cervical dentin

because of either hypermineralization or formation of more acid resistant forms

of calcium phosphate.

Effect of chemical conditioners :

They remove the smear layer and expose a microporous scaffold of

collagen fibrils thus increasing the microporosites of intertubular dentin.

Because this collagen matrix is normally supported by the inorganic dentinal

fraction, demineralization causes it to collapse. On intertubular dentin the

exposed collagen fibrils are randomly oriented and are often covered by an

amorphous phase with relatively few microporosities and variable thickness.

Etchants thickened with silica leave residual silica particles deposited on the

surface, but the silica does not appear to plug the intertubular micro porosities.

Sometimes fibrous structures probably remnants of odontoblastic processes are

pulled out of the tubules and smeared over the surface. With aggressive acid

etchants/ hypertonic acids the acid may tend to pull the collagen fibers away

from the intact dentin/unaffected dentin leaving a sub micron space termed as

hiatus. With increasing aggressiveness of the conditioning agent a

circumferential groove may be formed at the tubule orifice separating a cuff of

mineralized peritubular dentin from the surrounding intertubular dentin.

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Alternatively the mineralized peritubular dentin may be completely dissolved

to form a funnel shape.

Historically several acids have been researched as dentin conditioners.

These include hydrochloric, oxalic, pyruvic acid, phosphoric acid, and citric

and nitric acids.

The hydrogen ions from these acids diffuse into the dentin while

etching. If one assumes that the self-diffusion co-efficient of hydrogen ions in

free solution at room temperature is 1x106cm2/sec. One can calculate the

distance that the hydrogen ions can diffuse into dentin as the square root of the

product of the diffusion coefficient of hydrogen and time. Moreover the

hydrogen ions don’t diffuse as much as calculated as their diffusion is

restricted by dentin. The surface reactions are violent as carbonate is

converted to carbon dioxide and as calcium and phosphates are liberated.

These products may be liberated faster than they can diffuse from the site

leading to formation of reaction products, that may limit further penetration of

protons. Further the hypertonic solutions when osmotically draw the fluid

from the dentin towards the surface could restrict the inward protein diffusion.

The removal of the smear layer and demineralization of the dentin

matrix may facilitate bonding through a number of mechanisms.

They are

Removal of loose smear layer debris and exposure of dentin matrix

Exposure of collagen fibrils and their Epsilon-Amino groups which may

catalyze HEMA polymerization.

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Exposure of intact collagen that serves as a scaffold for the creation of

resin collagen hybrid layer

Phosphoric acid :

It was the first dentin conditioner that was successfully used to remove

the smear layer, etch the dentin and restore with adhesive composite resin by

Fusayama and others. This helps in removing the surface dentin leaving a

clean well defined etching pattern where the tubules are enlarged into funnel

shape, phosphoric acid is the acid of choice currently for etching purpose.

However controversy remains about the optimal concentration of H3 POH.

The most widely used concentrations used in clinical practice exceed 30% H3

PO4. Chow and Brown demonstrated that the application of H3 PO4solutions

greater than 27% resulted in the formation of monocalcium phosphate

monohydrate, which is readily soluble and would be completely, washed away

in the clinical situation. This is the product preferred because; if the reaction

product is not completely removed after the etching procedure it may interfere

with the bonding of composite resins to etched enamel surface. When H3 Po4,

was used in concentration less than 27% dicalcium phosphate dihydrate was

formed which is less stable. So it is not the desired concentration

Total etching with phosphoric acid :

Phosphoric acid is generally acknowledged to be the preferred enamel

etchant, especially in the presence of salivary pellicle or plaque. Fusayam’s

pioneering research of total etching established the protocol for simultaneous

etchings of dentin and enamel with phosphoric acid, followed by washing,

drying, and application of an adhesive resin. This technique is being

successfully used by an ever-increasing number of clinicians worldwide.

Perhaps this popularity has resulted from the realization that inadvertent

94


exposure of dentin to phosphoric acid is unavoidable. Use of dentin bonding

agents that are successful with accidental or purposeful phosphoric acid

etchings appear to be prudent.

Kurary’s original Clearfil new bond system accomplishes the total etch

using 37% phosphoric acid for 60 seconds. Bisco system uses 10% phosphoric

acid for 15 seconds in all etch techniques. A 10% solution appears to result in

a slightly better bond strength than higher concentrations.

Other acid conditioners :

Historically several acids have been researched as dentin etchants.

These include hydrochloric, oxalic and pyruvic acid in addition to the better-

known acids such as phosphoric, citric and nitric. To put acids in perspective,

it is perhaps best to compare their dissociation constants.

When an etchant is required dilution of a stronger than necessary acid

may result in a better etching solution. The concentrated acid will uniformly

strip a surface, while the dilution results in selective dissolution, termed “

etching”. Acids with the lower Pka’s tend to be used in a more dilute solution

than those with higher Pka’s.

Nitric acid :

It is stronger than phosphoric acid

Easily removes the smear layer

Used in concentration of 2.5% causes funneling of the orifice of dentin

to a depth of 5mm in 40 seconds. Nitric acid conditioners are highly adhesive

and provide good tubule seals.

e.g. Tenure, Mirage Bond, Restobond 3.

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Citric acid :

10% citric acid is used for the purpose of removing the smear layer. It

has been reported by Nakabayashi (1989) that such treatment tends to lower

the porosity or permeability of the demineralised surface, possibly by

denaturing the collagen. 10% citric acid and 3% ferric chloride combination

was developed by Nakabayashi, found to be effective smear layer remover.

This combination was found to be particularly effective for methacrylate based

adhesives containing 4-META (4- methacryloxyethyl trimellitate anhydride)

Ferric ions appear to be necessary since the citric acid alone yields poor

results with this system.

e.g. Super-bond

The higher bond strength of 4 methacryloxyethyl trimellitic anhydride/

methyl methacrylate- tetra butyl borane oxidized ( 4 META/ MMA- TBB)

products conditioned by 10% citric acid and 3% ferric chlorides solution can

also be achieved by substituting cupric chloride for ferric ions Another

combination etchant is 10% citric acid with 20% calcium chloride. This

combination result in improved bond strength. This high concentrate of

calcium may stabilize collagen during surface etching. It also decreases the

extent of the demineralization of hydroxyapatite by a common ion effect. The

depth of decalcification is about 8 microns compared to the phosphoric acid

etching, which results in 16-micron depth of decalcification. . Eg. Clearfil

Liner Bond.

The tubules do not open into a funnel shape. Hydroxyapatite is

removed from intertubular and peritubular dentin, resulting in exposed

collagenous structure in the intertubular dentin.

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Pyruvic acid :

Pyruvic acid and pyruvic acid buffered with glycine have been reported

to satisfactorily acid etch both enamel and dentin (Asmussen and Munksgaard,

1988). When using the gluma bonding system Glycine was used to adjust the

pH and perhaps to facilitate polymerization reactions.

Dissociation constants of some acids used on tooth etching and

conditioning :

Acid PKa

Hydrochloric 1.4

Nitric 1.4

Maleic 1.8

Phosphoric 2.1

Citric 3.1

Oxalic 4.1

CHELATORS :

Chelators are used to remove the smear layer with out decalcification or

significant physical changes to the underlying substrate as opposed to the

strong acid etchants.

EDTA :

The best-known chelating conditioner is ethylene diamine tetracetic acid

(EDTA) adjusted to a pH of about 7.4. It was developed for use in the Gluma

system.

While the smear layer is removed, no significant concavity is formed,

and the funnel shape change associated with phosphoric acid not evident.

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The smear plugs in the dentinal tubules are not fully removed by 30 seconds

application of the conditioner. Inokoshi and other’s data indicate that the

Gluma system also results in a significant hybrid layer. The system uses both

glutraldehyde and HEMA in a primer that is applied after the EDTA

conditioner removes the smear layer.

Maleic acid (e.g. Scotch bond 2); Denthesive ( Heraeus Kulzer Inc)

Irvine, CA 92718) also results in removal of the smear layer when used as a

primer in combination with HEMA in a scrubbing action on the dentin. The

generally reported bond strengths with this system compare favorably with

other bonding system that have thicker hybrid layers. This observation

suggests that the thickness of the hybrid layer may not have much effect on

dentin bond strength.

Lasers :

Hard tissues lasers in dentistry are an emerging technology. A pulsed

Nd: YAG laser will not disturbs the pulp, even when the approach is a close as

1mm. Heat is dissipated between the 10 to 30 pulses per second. The

mechanism of dentin removal is microscopic explosions caused by the thermal

transients while most research has been conducted on dry dentin, the laser will

operate on dentin immersed in saliva or water. The carbonized, black sort that

results is easily washed off with water. The lased surface results in

desensitized dentin, presumably by occlusion of the open and permeable

dentinal tubules. Microorganisms and organic debris are eliminated from the

lased surfaces. The laser decreases the organic fraction and increases the

inorganic fraction of the dentin surface.

Lasing of the dentin has the potential to increase the bond strength of

the current dentin bonding agents. Its effect on the bond strength of Scotch

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bond 2 was recently presented by white and others . The bond strength

increased about 60% compared to the control smear-layered dentin,

presumably by increasing the bondable inorganic fraction of the dentin surface.

The laser may create micromechanical retention, which is an analogue to the

effect seen on laser-etched enamel.

Micro abrasion :

Modification of dentin by micro abrasion with aluminum oxide removes

healthy as well as diseased dentin and results in a smear layer. The abrasion

action, of aluminum oxide depends on the particle size as well as on the

velocity. Particle 0.5 microns or less in diameter do not affect the enamel

except to cleanse it. The 0.5-micron or larger particles create a smear on the

dentin and increase the surface area. The smear layer might be used to

enhance the bond strengths of smear-mediated dentin bonding agents.

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PRIMERS

Major advances have been achieved by the introduction of primers,

which promote wetting of the dentin with the bonding agent, and penetration of

the bonding agent into the dentin. Primer monomers are amphiphilic i.e. they

contain hydrophilic groups (e.g. -OH, -COOH) for better compatibility of the

resin monomers with the moist dentin, and hydrophobic methacrylate groups

for the co-polymerization with the bonding resin. Nakabayashi and Pashley

summarized the function of dentin primers to be "to maintain or recover the

porosity of the demineralized dentin".

Primers are monomers dissolved in solvents such as water,

acetone/alcohol and are applied to the etched/conditioned dentin substrate but

are not rinsed off. Organic solvents aid in displacing water, expanding or

reexpanding the collagen network and thus promoting the infiltration of the

monomer into the submicron or nanometer sized spaces within the collagen

fiber network12.

The first dentin bonding mechanism that gave reliable, high bond

strengths, reported by Nakabayashi et al was based on the use of

4-META/Methyl Methacrylate-tri-n-butyl borane (MMA-TBB) resin and 3%

ferric chloride in 10% citric acid as a conditioner.

Effective primers contain monomers with hydrophilic properties that

have an affinity for the exposed collagen fibril arrangement and hydrophobic

properties for copolymerization with adhesive resins. The objective of this step

is to transform the hydrophilic dentin surface into a hydrophobic and spongy

state. Besides 2-hydroethyl methacrylate HEMA, primers contain other

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monomers, such as NTG-GMA, PMDM, BPDM and PENTA. More recent

primers also include a chemical/photopolymerization initiator so that these

monomers can be polymerized in situ. In prime and bond and Bisco one step

dental adhesive they combine the priming and bonding step.

Bonding can be carried out by applying primer to a collapsed matrix

followed by application of bonding agent or else a bonding agent may be

directly applied to a noncollapsed demineralised dentin as these substrates have

high permeability to monomers, thereby permitting hybrid layer formation

without the intermediary step of primer application. In bonding systems in

which the acidic conditioner permits the demineralized dentin to collapse when

air dried, a primer is required to reexpand the collagen fibril network and

restore the permeability of the demineralized intertubular dentinal matrix.

There are at least 2 possible explanations for the major shrinkage of the

demineralized dentinal meshwork when it is air dried.

Collagen of etched dentin by air – drying

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The passive theory assumes that the demineralized collagen fibril

network is floating/suspended in water. Each fibril is separated from the other

by a water filled space which occupies the space that was previously occupied

by apatite crystallites. As the water supported collagen network is air dried, the

amount of water separating the fibrils disappears as the water evaporates and

the collagen fibrils come closer together in all three dimensions. This results in

a passive collapse of the collagen network. . The result is a loss of space

between the fibrils. The addition of water rapidly reverses these events causing

passive reexpansion (i.e. floating) of the collapsed network. Gwinett also

suggested that the surface tension forces operating at the air collagen network

interface might be responsible for the collapse. As the collagen molecules

come closer together, they may interact by forming hydrogen bonds as well as

interacting electrostatically and hydrophobically.

Reexpansion of the Collagen Network:

If water or an aqueous primer is added to dried dentin, the water

reverses all of these events, water molecules would hydrogen bond with

collagen peptides, breaking intermolecular hydrogen bonds. Sugizaki’s SEM

and TEM observations showed that the collagen fibrils are closer together in

collapsed dentin than when the matrix reexpands. He thought that the

reexpansion of the collagen meshwork was the result of HEMA/hydrophilic

primers, although more recent work indicates that it might have been the water

content of the primers that was responsible for reexpansion.

Kanca and Gwinnett recommended that etched dentin should not be

dried before application of the bonding primer.

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Moist Bonding:

When the etched dentin is excessively dried after rinsing off the etchant,

the collagen network will collapse and the microchannels opened by the

removal of the apatite crystal will be closed. In order to avoid the collapse of

the collagen network, a moist (wet) bonding procedure has been proposed in

which the primer is applied to the moist or even wet dentin where the

perifibrillar spaces are kept open with water.

A review of literature has shown that moist bonding is only essential for

particular bonding systems with a low water content of primer such as All-

Bond 2. The primer of All Bond 2 contains acetone as solvent with only 5% of

water, In contrast primers with water content of 20% or more (eg. Optibond

FL, Scotchbond Multipurpose) are able to reexpand the collapsed collagen due

to their intrinsic rewetting capacity. Acetone based primer adhesives (eg. Prime

and Bond 2.1, One-step) have shown higher bond strengths and reduced

microleakage when a moist bonding protocol is followed.

In conclusion moist bonding is only mandatory in bonding systems with

minimal water content of the primer/primer-adhesives, while water based

primers/primer adhesives have shown to be less sensitive to variations in the

moisture of the etched dentin surface. Tay et al concluded that the term

bonding to moist or wet dentin should not be loosely interpreted and must be

clearly defined and the presence of water in acetone-based primers may be

sufficient to rewet briefly desiccated dentin.

Research has demonstrated that moist bonding increases the bond

strengths of many bonding systems. However the water present in between the

fibrils should be displaced completely as if too much water is present, the resin

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monomers may not be able to successfully compete for the collagen fibril

surface thereby leaving voids.

Water Based Primers :

The first approach to creating a hybrid layer in wet dentin is the use of

water-soluble primers containing HEMA. Examples of this type of primer are

Scotchbond 2 nd Scotchbond Multi-purpose. After application of the water-

HEMA mixture,the surface is air dried to evaporate the water. As the water

concentration falls, the HEMA concentration rises, until theoretically there

should be near zero water and 100% HEMA on the surface. Water has a much

higher vapor pressure than does HEMA. In fact at atmospheric pressure

HEMA can be regarded as almost volatile. This permits its retention as its

solvent, water is evaporated during air drying.

Use of Water Miscible Primer Solvents :

The second method of creating hybrid layers in this category of bonding

is to sequentially acid etch, rinse; leave moist or dry, prime and then bond. The

HEMA will be in 2 types ; 1) 35% HEMA in water, 2) 13% Polyalkonic acid

copolymer in 50% HEMA. The problems with moist bonding is to determine

how moist is moist. The dry condition is easily recognized and achieved but

when does a moist condition become overwet. This is complicated by the fact

that the intrinsic wetness of dentin varies from about 1% in superficial to about

22% in deep dentin. The consequences of applying acetone-based primers to

overwet dentin have been described by Tay et al using All Bond 2, BISCO;

those authors found that small globules formed within dentinal tubules. These

were formed when the first one or 2 layers of primer were applied. That is in

the tubules filled with dentinal fluid there was too much waters available to

dilute the acetone with the result that the monomer came out of the solution.

As more globules formed, they accumulated on the walls of the tubules,

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reducing the permeability of the tubules, permitting successive primer

applications to dehydrate the tubules enough to from normal resin tags.

If excessive extrinsic water is left on the surface prior to application of

the All Bond 2 primer, the primers tend to bridge the excess water droplets to

from a tiny blister. This prevents resin tag formation in those tubules beneath

the water droplet, clinically if the clinician sees a rough texture on the primed

surface that might be caused by this phenomenon, he or she can destroy those

droplets with the tip of a brush, which can be used to add more primer. The

danger is that this may occur somewhere in a complex cavity design that is not

easily visualized. This may result in an unbonded region, which could change

its dimensions under thermal/occlusal stress and produce sufficient fluid shifts

to cause dentinal sensitivity . It may also permit the concentration of stresses

that may lead to bond failure in that portion of the restoration. Thus

overdrying/overwetting of dentin can have undesirable effects.

The goal of priming is to replace all of the water/acetone monomer

mixtures in the interfibrillar spaces with polymerizable monomers. Maciel et al

demonstrated that 100% acetone, ethanol and HEMA all cause a time

dependent stiffening of demineralized dentinal matrix. Once stiffened the

matrix cannot collapse thus allowing efficient hybrid layer formation.

The primer should be either water or water miscible agent. The

commonly used solvents are;

Acetone

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Highly volatile evaporates quickly

Excellent water-Chaser

Strong drying agent (risk of overdrying dentin)

Storage and dispense problems

Ethanol (water)

Excellent penetration capability

Good compromise in respect of evaporation

Good surface energy for wetting exposed collagen fibril network

Water

Good penetration capability

Enables self-etching capability of acid monomers

Evaporates slowly consequently more difficult to remove

Remaining water may hamper resin penetration/polymerization

Application of primer to Smear Layer covered Dentin followed by

bonding Agent:

Bonding to the smear layer covered dentin was not very successful

before 1990 as the resins did not penetrate through the smear layer and the

smear layer was very weak. This led most manufacturers to use acidic

conditioners. However the resulting soft collagen rich surface can collapse and

interfere with monomer infiltration. So in order to prevent this and to simplify

the number of bonding steps Watanabe developed a new bonding system

which was an aqueous solution of 20% Phenyl-P in 30% HEMA. This self

etching and self priming system provided important new information on smear

layer as bonding substrates. The ideal self-etching, self priming bonding

system is one that can penetrate 2.0 m of smear layer and engage underlying

dentin to a depth of 1 mm. However as smear layers are made up of dentin they

have a significant buffer capacity and tend to buffer the acidity of the acidic

monomer used as a self etching agent. This property in addition to the tight

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packing of smear layer particles limit the penetration of monomer to about 2.0

m.So Toida et al advised the removal of smear by a separate etching step to

produce more reliable and durable bonds.

Steps for effective priming :

Microscopic examination of attachments produced by primer has shown

deficiencies like ;

1) Incomplete surface coverage

2) Incomplete interfibrillar saturation within the hybrid zone

3) Incomplete penetration to the full depth of demineralized dentin.

One method of improving surface coverage and diffusion of the primer

is by the application of multiple coats. A 2nd coat of primer has shown to

increase the shear bond strength significantly.

The surface of dentin should not be overdryed or overwet.

The etching time should not exceed the time recommended by the

manufacturers.

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HYBRID LAYER

Dentin hybrid layer is a “transitional zone of resin reinforced dentin

sandwiched between cured resin and the unaltered substrate” (Nakabayashi).

The essential mechanism of adhesion for current dentin bonding systems to the

dentin substrate is described as micro mechanical and is generated by

monomer impregnation of the exposed collagen of demineralised superficial

dentin. The hybrid layer thus formed is a mixture of dentinal components and

cured resin at the molecular level. The synonyms are “ adhesion interface”,

“resin-dentin “interdiffusion zone”, and interpenetration zone5.

Hybrid layer

The formation of hybrid zone depends on several factors in general they

are

i. Type of the conditioners

ii. Depth of the cavity- hybrid layer appeared to be thinner at the deeper

part of the dentin compared with the middle and the superficial parts.In

the superficial dentin most of the hybrid layer is composed of

hybridized intertubular dentin with only occasional resin tag penetrating

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into the tubules. In deep dentin the tubules are so numerous and so

large that there is little intertubular dentinal matrix so these is less

amount of hybridized intertubular dentin and large resin tags are seen.

iii. Permeability of the dentin surface

iv It depends on the conditioning priming pretreatment

v. Diffusability and wettability of the monomer resins.

In order to obtain an intimate association between the resin monomers

and collagen fibrils the primer and bonding agents must be able to wet the

collagen fibrils. If the fibril is enveloped by water, the monomer must be able

to successfully compete with water for the fibril surface. But monomer

penetrating is just one part, as after penetration the monomer must polymerize

right there in situ. An adhesive system that has been demonstrated to have

good bonds is 4-META in methylmethacrylate (MMA-TBB). The HEMA

bonds to either the calcium or iron precipitates. Further the polymerization

takes place by the unique initiator in a butyl borane in conjunction with O2 and

H2O as co catalysts. So the polymerization is initiated once polymerized the

resin formed not only entangles and envelops collagen but also encapsulates

hydroxyapatite.

The characteristics necessary for the formation of hybrid layer

Substrate must be suitably prepared by smear layer and smear plug

removal.

The dentinal peptides including collagen must not be denatured when

the dentin is decalcified because the denatured collagen shrinks or

collapses quite easily, decreasing the porosity and penetrability of

protein molecule.

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The bonding resin must include monomer with both hydrophilic and

hydrophobic groups that can penetrate the dentin and combine with it.

One of the critical factors is a suitable monomer mixture which diffuses

and impregnates into the demineralised dentin, thus stabilizing the dentin

matrix. Once the adhesive monomer has penetrated into the demineralized

substrate to its full extent, it must be made to polymerize in situ at the full

penetration depth it has achieved, with minimal shrink back.

The catalyst must allow polymerization in the presence of oxygen and

water. This is accomplished by the unique initiator tri-n-butyl borane in

conjunction with two co-catalysts, viz., oxygen and water. These co-catalysts

are abundantly available on dentinal surfaces and within its subsurface and

tubules and comprise a significant portion of dentin. The polymerization

reaction is initiated once the catalyst comes in contact with water and oxygen.

Polymerization shrinkage of dental monomers is always towards the initiation

points of the reaction. Therefore, the shrinkage of the forming resin is in the

optimal direction towards the substrate .

SEM and TEM Examination of the ultra structure of resin dentin

interdiffusion zone :

By Van Meerbeck et al, both SEM and TEM confirmed the presence of

the resin-dentin interdiffusion zone as the junction between the deep unaltered

dentin structure and the restorative resin.

Within the interdifussion zone, three sub layers were identified by TEM

with characteristic ultra structure and staining they are,

An upper layer, with diffuse black staining containing few structural

features. No separation between the interdiffusion zone and the adhesive

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resin is apparent. Small inorganic microfiller particles were deposited

on top of the interdiffusion zone, and only the smaller sized particles

could be found in deeper layer.

Underneath this zone, partially altered collagen fibrils were closely

packed, mostly running parallel with the interface and perpendicular to

the dentinal tubules. Their outline was electron dense forming tunnel

like structures. At the base of the upper layer, several stained

projections were found to interdiffuse between sectioned collagen

fibrils.

Finally, the third dense layer, containing hydroxyapatite crystals,

demarcating the superficially demineralised dentin layer from the

deeper unaltered dentin. Resin diffusion into the decalcified dentin

surface layer was evident, but diminished with depth, presumably

reducing deeper resin impregnation into the interfibrillar spaces.

The hybrid layer, as a microscopic structure, is very difficult to

evaluate, as has been described earlier. Under some bonding conditions, the

demineralized layer is not completely infiltrated by resin. Micro leakage might

take place.

Micro leakage is the diffusion of a substance into a fluid filled gap or

defect between filling materials and tooth structure. This is usually seen to

occur via 3 routes.

With in or via the smear layer

Between the smear layer and cavity varnish or cement.

Between the cavity varnish or cement and the restorative material. This

occurs when the forces of polymerization contraction exceed dentin

bond strength leading to the formation of a gap.

Leakage from the margin of the restoration deep into the hybrid layer

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via interconnected defects, porosities and flaws that exist is termed

nanoleakage. The clinical significance of nanoleakage is unclear.

Reverse Hybrid Layer :

The acid etched surface of dentin is further subjected to treatment with

NaOCl. This results in dissolution of the collagen fibrils, which are exposed.

Further the use of self-etching primers results in superficial etching of the

surface. Here the hybrid layer is surrounded by more of inorganic material

unlike the normal hybrid layer where the collagen fibers are encapsulated by

resin, and so this layer thus formed is termed reverse hybrid layer or soft tissue

hybrid layer). Dentin bonding agent when comes in contact with pulp forms

this.

Three types of ultra morphological features have been described as

resulting from this hybridization process:

1. Shag carpet appearance:

Here there's loose organization of collagen fibrils that are directed

towards the adhesive resin and often unraveled into their microfibrils1.

This feature is seen when the dentin surface after being acid etched is

actively scrubbed with an acidic primer solution.

Because of the combined mechanical / chemical action of rubbing the

acid etched dentin with an acidic primer (or P/A combination) which probably

dissolves additional mineral while fluffing and separating the entangled

collagen at the surface. This promotes infiltration of monomers into the

loosened collagen scaffold by a kind of massaging effect.

2. Tubule wall hybridization:

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Here there is extension of hybrid layer into the tubule wall area. Resin

tag formation in the opened tubule is surrounded by a hybridized tubule orifice

wall which is thought to favourable in hermetically scaling the pulp dentinal

complex. This may be particularly effective when the bond fails either at the

top or the bottom of the hybrid layer, which are considered weak links in the

micro mechanical attachment.

3. Lateral tubule hybridization:

There is a formation of tiny hybrid layer into the walls of the lateral

tubule branches. This micro version of hybrid layer typically surrounds a

central core of resin called a micro resin tag.

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CLASSIFICATION OF DENTIN BONDING

AGENTS

a) According to composition

b) According to type of primers or combined primer\adhesive resin

According to mode of action

c) According to bond strength

d) According to mode of curing

e) According to number of clinical steps

b) According to generation

f) Adhesive system with stress bearing potential

g) Adhesive system that include fluoride

h) Classification based on adhesion strategies (VanMeebeck)

i) According to smear layer modified/removed/ dissolved

ACCORDING TO CHEMICAL COMPOSITION:

Polyurethanes

Polyacrylic acids

Organic phosphonates

Mellitic anhydride and methyl methacrylate (4- META)

Hydroxyethyl methacrylate+Glutraldehyde(HEMA+GA)

Ferric oxalate +NPG-GMA (N-phenyl glycine and glycidyl

methacrylate)+PMDM(Pyromellitic dianhydride and 2 HEMA)

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According to type of solvent of primers or combined primer\adhesive

resin1 :

Acetone Acetone

water

Acetone

ethanol

Ethanol Ethanol

water

Water

ABC Enhanced

(Chameleon)

AQ Bond

(sun Medical

All-Bond 2

(BISCO)

Excite

(Vivadent)

Gluma

Comfort

Bond

(Kulzer)

Amalgambond

plus (parkerr)

EG Bond (sun

Medical)

Reactmer

(shofu)

Optibond

Solo plus

(kerr)

Optibond FL

(kerr)

ART Bond

(Coltene)

Gluma One

Bond (Kulzer)

Tenure Quik

(Den-Mat)

PQ1

(ultradent)

Permaquik

(ultradent)

Clearfil SE

Bond

(Kuraray)

One step

(BISCO)

Quadrant

Unibond

(cavex)

Denthesive II

(kulzar)

Permagen

(ultradent)

Scotchbond

1 (3M)

EBS (ESPE)

Prime&Bond

NT (Dentsply)

Syntac sprint

(Vivadent)

Fuji Bond LC

(GC)

Solid Bond

(Kulzer)

One-coat Bond

(coltene)

Solist (DMG) Prompt L. Pop

1.2 (ESPE)

Stae (SDI) Scotchbond

multi-purpose

(3M)

Tenure Quik F

(Den-Mat)

Syntac Single

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According to mode of action (Eick et al) :

1. Those that bond with calcium ion-based on phosphate esters of BISGAMA

and its modifications bond with calcium ion in the smear layer and dentin

surface. The smear layer is therefore left intact.

Eg: Scotch bond/and Bondlite.

2. Those that bond with amine or hydroxyl groups-based on isocyanate or

aldehyde. They bond with amine or hydroxyl groups of organic component

of dentin. Hence the smear layer has to be removed and dentin surface

decalcified to expose the collagen fibers.

Eg. Gluma

3. Those that bond with reprecipitated smear layer-Dentin bonding system in

this category require partial removal and modification of smear layer.

Bonding is possibly by mechanical entanglement with collagen fibrils on

dentin surface

Eg: Scotchbond 2 and Tenure.

According to bond strength :

Category I :

Included dentinal adhesives, which produce shear bond strength of 5-7

Mpa

Eg; Dentin Adhesit

Scotch bond dual cure

Gluma

The failures occurred at the interface or in the resin adhesives

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Category II :

Included the experimental and commercial products derived from Bowen’s

work with ferric and aluminum oxalates and have produced shear bond

strength between 8-14 Mpa

eg;Tenure

Mirage Bond

Category III :

Included dentinal adhesives , which produced shear bond strength values

of about 17 –20 Mpa

Eg; Super bond

Scotch bond 2

Scotch bond Multipurpose

All bond

According to their mode of curing:

Chemical cure

Eg;Amalgam bond plus

Light cure

Eg; One bond

Gluma comfort bond

Dual cure

Eg;Clearfil liner bond 2v

Prime and bond NT

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According to number of steps needed to complete the bonding process17:

Three-step’ or conventional’ system

Two step systems

Single bottle systems

Self etching primer

`One-bottle’ or ‘All in one’ systems.

`Three-step’ or conventional systems :

This group represents those materials that have separate etching,

priming and adhesive steps. Still widely used and have been shown to provide

reliable bonding. The greatest problem with this group would seem to be that

three district steps are needed, they are more technique sensitive.

`Two-step’ systems :

This group has two subgroups: The first includes those systems that

have a separate etch and have combined the priming and bonding steps. These

systems are often referred to as `single bottle’ systems. Although one step has

been eliminated, the great problem is ensuring good infiltration of the priming-

bond into demineralized dentin.

The Other subgroup combines the etching and priming steps together

and are referred to as self etching `primers’. Have ability to etch the enamel to

a greater extent to ensure a good seal. The problem of technique sensitivity

have been significantly reduced with these systems compared with

conventional and `single-bottle’ systems.

The self-etching priming agent does not have to be washed off the

dentin, therefore eliminating the need to maintain the dentin in a moist state.

The method of demineralization of these materials is by the use of an acidic

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resin that etches and infiltrates the dentin simultaneously. The dentin is an

excellent buffer, so the acidity of the self-etching primer is rapidly reduced and

after polymerization is neutralized.

`One-bottle’ or `All-in-one’ systems :

This is the simplest of all dentin-bonding systems. They combine all

steps into one process. Their mode of demineralization is identical to that of

the self-etching priming materials, but the bonding resin is also incorporated.

These systems also have the problem of not etching the enamel as effectively

as phosphoric acid. These systems are the newest and have no long-term

clinical data to demonstrate their effectiveness.

ACCORDING TO GENERATIONS :

First Generation Dentin Bonding Agents :

Buoncore et al in 1956 reported that glycerophosphoric acid

dimethacrylate (GPDM) could bond to hydrochloric acid- etched dentinal

surfaces. This bond was believed to be due to the interaction of this

bifunctional resin mole cule with the calcium ions of hydroxyapalete, but

immersion in water would greatly reduce this bond. Nine years lates Bowen

tried using N- phenyl glycine and glycidyl methacrylate (NPG) which is a

bifunctional molecule or coupling agent. This molecule has one end bonding to

the dentin while the other end bonds to the composite resin. The NPG-GMA)

also bonded to the dentin by chelation with calcium on the tooth surface.

Among the first generation of bonding agents used were.

1. Glycerophosphoric acid dimethacrylate

2. Cyanoacrylate

3. NPG- GMA

The First commercial system of this type is Cervident, S.S. white

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Disadvantage :

1. Poor adhesion to dentin

2. Bond strength of 2.87 Mpa

3. Hydrolysis of GPA-DMA in oral environment

4. Difficulty in bulk polymerization of cyanoacrylates

Second Generation :

In the late 1970s, the second generation systems were introduced.

Majority of these incorporated halophosphorous esters of unfilled resins such

as bisphenol –A-glycidyl methacrylate or BIs-GMA or hydroxyl ethyl

methyacrylate( HEMA). The mechanism by which these second generates

systems bonded to dentin was postulated to be through an ionic bond to

calcium by Chlorophosphate group. These were weak bonds but they were a

significant improvement over the first generation systems.

The bonding mechanism involves a surface wetting phenomenon as

well as ionic interaction between the phosphate groups and dentinal calcium.

The second generation bonding system required a smear layer intact to create.

This was to create a ca+ rich layer where the phosphate can combine with ca+.

Limitations :

1. The phosphate bond to dentin was not strong enough to resist the hydrolysis

resulting form water 1mmession. This hydrolysis resulting form either

saliva exposure or moisture form the dentin itself, could result in composite

resin debonding from dentin and causing micro leakage.

The dentin was not etched in these early bonding system, much of the

adhesion was due to bonding to this smear layer and this resulted in bond

strength to dentin that were weak and unreliable.

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Eg: Clearfil, Scotch Bond, Bond Lite (sybron/kerr) J&J Dentin

bonding agent

Invitro bond strength of these materials were reported to be 5 to 6 MPa.

The bond however hydrolyze over time in the oral environment which

attributed & their poor clinical success.

Dentin Adhesit (Vivadent) comprising of isocyanate monomer is also

generally considered a second generation bonding agent.

Third generation adhesives :

The third generation of dentin adhesives was based on the use of an acid

group to react with ca2+ ion and a methacrylate group to co polymerize with

unfilled resin that was applied before placement of the composite restorative

material.

The first and second generation of adhesives achieved low bond

strengths partly because of failures within smear layer or between smear layer

and underlying dentin.

Smear layer had a negative influence on the performance of adhesive

systems. To overcome this, third generation dentin bonding agents were

introduced which differed from early materials in that an additional step was

employed to either modify or remove the smear layer before the application of

actual adhesive.

The third generation adhesive procedures for bonding dentin involved

two approaches.

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Modification of the smear layer to improve its properties or

Removal of smear layer without disturbing the plug that occluded the

dentinal tubules.

Third generation bonding procedure generally involved four steps :

Application of dentin conditioner, which is a type of acid, used to alter

or remove the smear layer.

Application of the primer (dentin bonding agent)

Application of the adhesive, typically an unfilled resin.

Placement of resin based composite.

Dental conditioner is an acidic solution that removes the smear layer

and is rinsed off after application. The primer solution usually contains an

adhesion promoter in a solvent such as water ethanol or acetone. These are

applied to the surface and dried, presumably leaving the adhesion promoter on

the dentin with its hydrophobic groups exposed to create a favorable surface

for the bonding agent.

Removal of the smear layer by the use of acids or chelating agents

reduces the availability of calcium ions for interaction with chelating surface-

active co monomers, such as NPG-GMA. Bowen et al, in 1982, tried to

supplement the calcium ion by applying an acidic solution of 6.8% ferric

oxalate to dentin as an acidic conditioner or cleanser. An insoluble precipitate

of calcium oxalates and ferric phosphates was formed on the surface, the

precipitate was also expected to seal the dentinal tubules and protect the pulp.

The subsequent application of an acetone solution of pyromellitic acid

diethylmethacrylate (PMDM) mixed with NPG-GMA or its alternatives, N-

tolylglycine glycidyl methacrylate. (NTG-GMA) improved bonding level of

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clinical significance. Ferric oxalate sometimes causes black interfacial staining,

and was replaced by aluminum oxalate. This technique gave bond strength of

about 15MPa to both enamel and dentin. Tenure was the first commercial

oxalate bonding system, which utilized phosphoric acid in conjunction with

aluminum oxalate and nitric acid as a dental conditioner.

Extensive research in Japan has demonstrated favorable effect of 4-

META on bonding to dentin. 4-META contains both hydrophobic and

hydrophilic chemical groups. With this system, dentin is etched with an

aqueous solution of 10% citric acid and 3% ferric chloride, followed by the

application of an aqueous solution OF 35% HEMA And a self curing adhesive

resin containing 4-META, methyl methacrylate (MMA) and TBB, the last as

polymerization initiator. Based on this technology, adhesive system, such a

C&B Metabond, Super Bond D-Liner, and Amalgam-bond plus are

commercially available.

Mirage bond: utilized enamel and dentin conditioner of NPG (N- phenyl

glycine )+2.5% nitric acid followed by application of PMDM. Dentin bonding

strength achieved was 10.9 1.2 Mpa.

Gluma Bonding system :

In 1984, a new bonding agent Gluma was developed

It utilizes 0.5 M EDTA (ethylene diamine tetra acetic acid) at an

approximately neutral pH to remove the smear layer and free collagen from

embedding apatite.

The second step is treatment with an aqueous solution of 35% HEMA

and 5% glultraldehyde. The bonding reaction involves attack of the aldehyde

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on the amino groups of collagen. The resulting complex is able to react with

the hydroxy group of methacrylate monomer, which then bonds to the resin.

Gluma could provide 15 MPa bond strength.

Scotch bond 2 dentin bonding system :

The Scotch bond 2 has two components.The primer, Scotch prep (3M)

an aqueous solution of 23% maleic acid and 55%HEMA . Bonding agent

consists of hydrophilic monomer-HEMA(32.5%)hydrophobic monomer-

BISGMA (62.5%) and photoinitiator.

The scotch bond 2 dentin bonding system to receive “ provisional “ and

later, “full acceptance” from the American dental Association in 1987. The

result was preservation of a modified smear layer with slight demineralization

of the underlying intertubular dentin surface.

Prisma Universal Bond 2 :

The main material has two components: Dentin primer

ethanol, HEMA, PENTA

Adhesive TEGDMA, Urethane dimethacrylate,

PENTA, Gluteraldehyde.

The phosphate group containing monomer (PENTA) differs in

functionality of acrylate groups as well as in the balance of hydrophilic and

hydrophobic parts of the molecule.

In this system the smear layer is intact and the dentin primer applied

helps in saturating the smear layer with monomer. As a result these is no

thorough penetration of the adhesive resin only a few resin tag are seen in areas

initially covered by a locally very them or permeable smear layer.

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In the adhesive, urethane dimethacrylate helps in generating better

hydrogen bonds than BISGMA.

Prisma Universal Bond 3 :

The only difference between the Prsima universal bond 2 and this is that

there is an increased amount of gluteraldehyde in the adhesive.

Disadvantage of third generation bonding systems :

Time consuming

Technique sensitive

Fourth Generation dentin bonding agents :

Although the smear layer acts as a “diffusion barrier” that decreases the

permeability of dentin, it must be removed so that resin can be bonded to the

underlying dentin substrate. Based on that consideration, fourth generation

dentin adhesives were introduced for use on acid-etched dentin. Recently

removal of the smear layer via acid etching has led to significant improvement

in bond strengths.

In 1982 Nakabayashi and his colleagues reported the formation of

hybrid layer resulting from the polymerized methacrylate and dentin.

The use of total etch is one of the main characteristics of the fourth

generation bonding. The total etch technique permits the etching of enamel and

dentin simultaneously using phosphoric acid for 15 to 20 seconds. The surface

must be left moist to inorder to avoid collagen collapse. The application of

hydrophilic primer can infiltrate the exposed collagen network forming the

hybrid layer. Unfortunately “ moist dentin” is not easily defined clinically and

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hence the bonds may not be ideal if the dentin is excessively wet /dried. The

formation of resin tags and adhesive lateral branches complete the bonding

mechanism between the adhesive material and etched dentin substrate.

Fourth generation adhesives are basically composed of

An acid etching gel that is rinsed off

A solution of primers that are reactive hydrophilic monomers in ethanol,

acetone, and/or water; and

An unfilled or filled fluid-bonding agent

The latter generally contains hydrophobic monomers such as bisphenol

glycidyl methacrylate (BIS-GMA), frequently combined with hydrophilic

molecules such as HEMA12.

The application of acid to dentin results in partial or total removal of

smear layer and demineralization of the underlying dentin. Besides

demineralizing intertubular and peritubular dentin, acids open the dentin

tubules and exposes dense filigree of collagen fibers.

Thus increasing the micro porosity of the intertubular dentin. Dentin is

demineralized up to 7.5m. depending on the type of acid, application time and

concentration.

Alteration in the mineral content of the substrate also change the surface

free tension and the substrate must have a high energy of dentin. The adhesive

system must have a low surface free energy for adequate interfacial contact.

Substrates are characterized as having low or high surface energy. Of those

materials used in dentistry, hydroxyapatite and glass-ionmer cement filler

particles are high-energy substrates. Collagen and composite have low energy

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surfaces. Consequently, dentin consists of two distinct substrates, one of high-

surface energy (hydroxyapatite) and one of low surface energy (collagen).

Thus, after etching with acidic agents, the dense web of exposed collagen is a

low-surface energy substrate. Infact, there is a correlation between the ability

of an adhesive to spread on the dentin surface and the concentration of calcium

on that same surface. An increase in the critical surface tension of dentin by

surface-active components (primers) is highly desirable in this case, since a

direct correlation between surface energy of dentin and shear bond strengths

has been demonstrated.

When primer and bonding resin are applied to etched dentin, they

penetrate the intertubular dentin, forming a resin-dentin intertubular dentin,

forming a resin-dentin interdiffusion zone or”hybrid layer”. They also

penetrate and polymerize in the open dentinal tubules, forming resin tags.

Examples:

All bond 2 (Bisco)

Scotch Bond multipurpose (3M)

Prime and Bond (Probond, dentsply)

Solid Bond (kulzer)

Optibond (sybron/kerr)

Permaquick (ultradent)

Imperiva bond (Shofu).

All Bond-2 :

Uses an etchant of 35% phosphoric acid on dentin and enamel followed

by the application of hydrophilic primer (primer A) containing 2% NTG GMA

(N TOLYGLYcine- glycidyl methacrylate) and primer B- 16% BPDM

(biphenyl dimethacrylate) in ethanol or acetone. Subsequently, an unfilled

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resin containing BIS GMA and HEMA is applied. Mean bond strength for

thus system is seen to be 21.47.8MPa

Scotch bond multipurpose:

Uses 10% maleic acid to etch both enamel and dentin.

Primer is an aqueous solution of HEMA and poly alkenoate

copolymers. The adhesive resin is a BIS GMA containing HEMA and photo

initiators.

The bond strength achieved was 21.0 MPa with wet dentin and 18.0

MPa with dry dentin.

Panavia 21 (kuraray) also utilizes a primer containing MDP, HEMA and

5 NMSA. It does not require a separate conditioning step. Adhesive monomer

is the phosphoric acid ester of MDP. MDP has a potential towards providing

long-term bond strength to metal and silanated porcelain. The material is

strongly oxygen inhibiting so the manufacturer provides a gel to prevent

oxygen coming in contact with it. Bond strengths with the system have been

observed to be 211.5 Mpa

Amalgam Bond :

Conditioner 10% citric acid

3% ferric chloride

Primer HEMA with water

Adhesive 4 META

MMA TBB

Other fourth generation bonding system include Imperva Bond (Shofu),

solid Bond (Kulzer), Opti Bond c & B, Metabond, etc. Mean shear bond

strength achieved with this generation of agents is 17-24 MPa.

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Advantages of this concept of bonding agent :

Reduced technique sensitivity

Similar bond strengths to enamel and dentin

No reduction in bond strength when applied to moist surface or under

conditions of high humidity.

Some systems can bond to mineralized tissue as well as metal,

amalgam, porcelain and indirect composite restorations.

Fifth generation dentin bonding agents :

Because of the complexity and number of steps or compounds involved

with the fourth-generation systems, researches and manufacturers have worked

to develop simpler adhesive systems. The objective has been to achieve

similar or improved bonding and sealing to that provided by the fourth

generation materials, but to do it with fewer “bottles” and/or in less time18.

Uses a one-component resin is, after conditioning of enamel and dentin

the steps of priming and bonding are combined so that bonding is achieved

with a one-component formula.

These systems have generally been reported to as “One component

systems”. This technique also referred to as “One coat, one bond and one cure

technology”.

These materials consist of hydrophilic and hydrophobic resin

simultaneously dissolved in solvents like alcohol or acetone, displacing water

and achieving an intimate contact to dentinal structures.

These materials also generally rely on residual moisture in the dentin

and hydrophilic water chasing compositions to effect resin penetration into the

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dentin. Given the relatively high percentage of solvent, these formulations may

be less forgiving to small changes in the dentin moisture content and may also

require multiple application of primer/adhesive combination for successful

bonding.

The fifth generation consists of two different types of adhesive

materials.

The so called “one bottle systems”

Self etching primer bonding systems

One bottle system :

These systems combined the primer and adhesives into one solution to

be applied after etching enamel and dentin simultaneously with 35 to 37

percent phosphoric acid for 15 to 20 sec. These bonding systems create a

mechanical interlocking with etched dentin by means of resin tags, adhesive

lateral branches and hybrid layer formation and show high bond strength

values both to etched enamel and dentin18.

The three step bonding procedures usually take up to 2 minutes. Hence

the so-called one bottle systems. (Eg. Excite, Gluma one bond, one coat bond,

Optibond Solo, Prime and Bond NT, Single bond, Solobond M, Syntac Sprint).

It has been further seen that primer adhesive with incorporated filler particles

(eg Optibond Solo) have higher bond strengths than unfilled products. When

evaluating the marginal adaptation of class V restoration invitro most three-

step systems showed more gap formation. This could be attributed to amore

complete hybridization of the dentin in three-step smear layer removing

bonding systems.

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Self Etching primer :

Watanabe and Nakabayashi developed a self etching primer that was an

aqueous solution of 20 percent Phenyl-P in 30 percent HEMA for bonding to

enamel and dentin simultaneously. The combination of etching and priming

steps reduce the working time, eliminate the washing out of the acidic gel and

also eliminate the risk of collagen collapse. However, the self-etching primer

solution also has some disadvantages. Like the solution must be refreshed

continuously because its liquid formulation cannot be controlled where it is

placed and often residual smear layer remained in between adhesive material

and dentin. Also the effectiveness of self etching primer systems on properly

etching the enamel was less predictable than the result obtained with

phosphoric acid gel. Toida advised the removal of the smear layer by a

separate etching step before bonding would produce a more reliable and

durable bond to dentin.

Bond strength test did not demonstrate significant differences between

one bottle systems and self etching primer bonding systems. Leakage tests

showed that the seal achieved at the enamel margins with one bottle system is

superior to that resulting from self etching primer.

Sixth Generation dentin bonding agents:

To improve bond strength and to make manipulation easy this

generation of adhesives has been tried.The sixth generation bonding systems

are characterized by the possibility to achieve a proper bond to enamel and

dentin using only one solution. The first evaluation of these systems showed

sufficient bond to conditioned dentin while bond to enamel was less effective.

This may be due to the fact that the sixth generation systems are composed of

an acidic solution that cannot be kept in place, must be refreshed continuously

and have a PK that is not enough to properly etch enamel.

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Self conditioning primer :

(Eg. Clearfil liner bond 2, Resulcin Aqua Prime+ Monobond) when

used there is no need of etching, rinsing and drying. In vitro studies have

shown that the efficacy of clearfil liner bond 2 when used on unaltered dentin

is comparable to the 3 step systems.

Recently a water based agent has been introduced which combines the

functions of the conditioner, the primer and the adhesive in a so called self-

conditioning primer-adhesive/condiprimer-adhesive (Etchand Prime 3.0). The

active solution is mixed from two components resulting in the formation of

an acidic (self conditioning) monomer which superficially etches dentin and

enamel. The dentin bond medicated by this bonding agent seems to be

adequate. However the etching pattern of enamel appears to be less retentive

than that produced by phosphoric acid etching.

Eg. Prompt L Pop: This has 3 compartments:

Compartment 1 : Containing methacrylated phosphoric acid esters,

photointiators and stabilizers.

Compartment 2 : Contains water, complex fluoride and stabilizers.

Compartment 3 : has a microbrush.

The blister is activated by squeezing compartment 1, thereby releasing

its content into compartment 2. The mixing ratio is 4:1 and the freshly mixed

solution is released on the microbrush into compartment 3.

On applying this on dentin the smear layer will be dissolved. Then the

dimineralized dentin is loaded with prompt L pop monomers leading to the

formation of a hybrid layer.

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Dentin might trigger inflammatory pulpal responses. Based on these

concerns, acids were believed to be contraindicated for direct application of

dentin and the total etch technique did not gain acceptance in Europe or the

United states. However, newer adhesive systems) the fourth and fifth

generation materials described in the previous section) based on the total etch

philosophy have proved successful in vitro and vivo. Clinical retention rates

have been reported to be very close to 100% compared with a second

generation-adhesive system having retention rates in the 50% rates in 50%

range. Laboratory bond strength usually vary from 17 MPa to 30 MPa, which

are very close to the values obtained on enamel.

Seventh Generation:

A new simplified adhesive system has been introduced that is the first

representative of the 7th generation of adhesive materials. The 7th “generation’

simplifies the multitude of 6th “generation” materials into a single component

single bottle system19.

i bond (Heraeus Kulzer), the first no-mix, self etching, self priming,

single bottle adhesive represents the most current formulation of dentinal

adhesives on the market. It eliminates the uncertainty of mixing, and thus, any

resulting technique sensitivity. It also eliminates the etching step, and by

accomplishing the priming and the bonding of dental surfaces simultaneously,

simplifies the adhesive procedure tremendously. This is a true, one-step, one

bottle system for the complete etching and bonding of both enamel and dentin

surfaces.

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Advantages:

Excellent bonding strength to dentin (18-25Mpa)

Similar adhesion to both prepared and unprepared enamel.

Contains a desensitizing agent based up on Gluma.

Can be used effectively for both direct and indirect composite

restorations.

Adheres well to ceramic and metal.

Single bottle product.

Insensitive to amount of residual moisture on surface of preparation.

The bond strength to both dentin and enamel are essentially the same,

regardless of the moisture or lack of moisture on the prepared surfaces.

The shear bond strength of i Bond to dentin is relatively unaffected by

the type of curing light used to polymerize the material, whether halogen, LED

or plasma Arc.

Adhesive systems with stress-absorbing potential4 :

Product name Manufacturer

Systems that provide a practical-filled adhesive resin

Clearfil liner bond Kuraray, Osaka, Japan

Clearfil liner bond 2 Kuraray

Fuji bond LC GC, Tokyo, Japan

Imperva FL-Bond (Fluorobond) Shofu, Kyoto, Japan

Optibond Kerr, Glendora, CA, USA

Optibond FL Kerr

Optibond solo Kerr

Permaquik Ultradent, South Jordan, UT, USA

Solid Bond Heraeus Kulzer, Wehrheim, Germany

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Adhesive systems that include fluoride with caries –protective and

remineralization potential4 :

Product Name Manufacturer

Clearfil liner Bond2 Kuraray

Fuji bond LC GC, Tokyo; Japan

Imperva Fl-Bond (Fluorobond) Shofu, Kyoto, Japan

Opti Bond Kerr, Glendora, Ca, USA

OptiBond FL Kerr

Optibond solo Kerr

Permaquik Ultradent, south jordan, UT, USA

Prime&Bond 2.1 Detrey-Dentsply, Konstanz, Germany

Solid Bond Heraeus Kulzer, Wehrheim, Germany

Syntax Single component Vivadent, Schaan, Lictenstein

Syntax Sprint Vivadent,

Tenure Quik Den-mat, Santa Maria, CA, USA

Classification based on adhesion strategies (VanMeerbeck and others)20

Total etch adhesives.

3 step

2 step

Self etch adhesives

2 step

1 step

Resin modified glass ionomer adhesives

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Total etch adhesive systems:

Total etch adhesives involve a separate etch and rinse phase.

Simultaneous application of an acid to enamel and dentin, known as the total-

etch technique, is the most common strategy of dentin bonding. The total-etch

technique was initiated in Japan by phosphoric acid etching of dentin before

the application of a phosphate ester type of bonding agent. In spite of the

obvious penetration of this early adhesive into the dentinal tubules, the

application of phosphoric acid on dentin did not result in a significant

improvement in bond strength, possibly because of the hydrophobic nature of

phosphonated resin. In addition, in the mid-1970, some researches had

hypothesized that the application of acids to dentin might trigger inflammatoy

pulpal response.

Two step total etch adhesives combine the primer and adhesive resin in

to one application. The underlying mechanism of adhesion of dentin is alike

for the three and two step total etch adhesives. The dentin smear layer

produced during cavity preparation is removed by the etch-and-rinse phase,

which concurrently results in a 3-5m deep demineralization of dentin surface

collagen fibrils are nearly completely uncovered from hydroxyapatite and form

a micro retentive network for micro-mechanical interlocking, of monomer

The etch and rinse technique is still the most effective approach to

achieving efficient and stable bonding to enamel and basically requires two

steps. Selective dissolution of hydroxyapatite crystals through etching is

followed by insitu polymerization of resin that is readily absorbed capillary

attraction within the created etch pits, there by enveloping individually

exposed hydroxyapatite crystals. Two types of resin tags interlock with in the

etch pits. “Macro-tags” fill the space surrounded the enamel prism while

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numerous “micro tags” result from resin infiltration polymerization with in the

tiny etch pits at the cores of the etched enamel prisms.

At dentin, this phosphoric acid treatment exposes a microporous

network of collagen that is nearly totally deprived of hydroxyapatite.

TEM and chemical surface analysis by energy dispersive X-ray

spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS) have

conformed that nearly all calcium phosphates were removed at least became

under detection limit. As a result, the primary bonding mechanism of etch and

rinse adhesives to dentin is primarily diffusion based and depends on

hybridization or infiltration of resin with in the exposed collagen fibril

scaffold. True chemical bonding is rather unlikely, because the functional

groups of monomers may have only weak affinity to the “ hydroxyapatite

depleted” collagen.

Bonding of resin to dentin, using a “total etch” technique

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Three –Step Total-Etch Adhesives

Product

ABC Enhanced

Aelitebond

All bond 2

Amalgambond plus

Clearfil liner bond2-4

Dentastic

Denthesive

EBS

EBS Multi

Gluma Bonding System

Gluma CPS

Imperva Bond (total-etch)

Mirage Bond

OptiBond (total-etch)

OptiBond FL (total-etch)

PAAMA2

Permagen

Permaquik

Quadrant UniBond

Restobond 3

Scotchbond Multi-Purpose

Sctochbond Multi-Purpose Plus

Solid Bond

Super-Bond D Liner

Tenure S

Manufacturer

Chameleon, Kansas city, KA, USA

BISCO

Bisco

Parkell

Kurary

Pulpendt

Hereaus-Kulzer

ESPE

ESPE

Bayer

Bayer

Shofu

Chameleon

Kerr

Kerr

Southern Dental industries

Ultradent

Ultradent

Canvex Holland, Haarlem, Netherlands,

Lee Pharmaceuticals, South El Monte,

CA,VS

3M

3M

Heraeus-Kulzer

Sun Medical

Den- Mat

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Plus- minus balance of three-step total etch adhesives1.

Plus Minus

Separate application of conditioner ,

primer and adhesive resin

Risk of “over” - etching dentin (highly

concentrated phosphoric – acid etchants )

“Lower” technique – sensitivity Time – consuming three step application

procedure

In – vitro and in-vivo proven

effectiveness of adhesion to enamel

and dentin

Post – conditioning rinse phase required

(time consuming and risk on surface

contamination when not using rubber

dam )

Best bond to enamel Sensitive to “overwet ” or “overdry” dentin

surface conditions

Most effective and consistent results Weak monomer – collagen interaction

(which may lead to nano – leakage and

early bond degradation

Possibility for practice – filled adhesive

(“shock – absorber”)

Two step total etch1 :

One concern in two step total etch is a risk of getting a thin hybrid layer.

Monomers should be sufficiently supplied not only to saturate the exposed

collagen fibril network, but also to establish a satisfactorily thick resin layer on

top of the hybrid layer. Such a distinct resin layer must be regarded as a

flexible, intermediate shock absorber. In light of an elastic bonding concept, it

is expected that this shock absorber may help to protect the adhesive joint

against early failure caused by the shrinking composite cured on top.

Therefore when using one – bottle adhesives, it is recommended to apply

multiple layers to ensure a sufficiently, think resin film on top of the hybrid

layer. They are particularly necessary when using primer / adhesive resin

139


combination with high acetone content. The so called nanofiller added is

certain one bottle adhesives (Prime & Bond NT) may also help to establish a

uniform resin film that stabilizes the hybrid layer . After priming the surface

should appear glossy with out dryspot, the clinical indication that resin was

adequately and sufficiently applied.

Brand name ManufactureTwo Step Total Etch Adhesives -One Bottle AdhesivesBond 1Dentastic UnoDentastic DuoEasy BondExcite2

Gluma 2000Gluma One BondGluma Comfort BondOne Coat BondOne StepOptibond SOLOOptibond solo plusPrime & Bond 2.1Prime &Bond 2.1 Dual CurePrime & Bond NT2

Prime & Bond NT Dual CurePQ1Scotchbond 1 (single Bond)SnapbondSolistSolobond MStaeSyntac Single-ComponentSyntac SprintTenure Quik with Fluoride

Jeneric/Pentron, Wallingford, CT, USAPulpdent, Watertown, MA, USAPulpdentParkell, Farmingadale, NY, USAVivadentBayer, Leverkusen, GermanyHereaus-KulzerHereaus-KulzerColteneBisco, Schaumburg, IL, USAKerrKerrDentsplyDentsplyDentsplyDentsplyUltradent, South Jordan, UT, USACooley& Cooley, Houston, TX, USADMGVoco, Cuxhaven, GermanySouthern Dental Industries, Victoria,AustraiaVivadentVivadentDent-Mat, Santa Maria, CA, USA.

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Plus Minus Balance of Two Step Total Etch Adhesives1

Plus Minus

Basic features of three – steps

systems

Not substantially “faster”

application (multiple layers)

“simpler” application procedure by

reduction with 1 step

More technique- sensitive

(multiple layers)

Possibility for “ single-dose”

Packaging

Consistent and stable composition

Controlled solvent evaporation

Hygienic application

Risk of too thin bonding layer (no

glossy film, no “shock” absorber,

insufficiently polymerizable due to

oxygen inhibition)

Possibility for particle-filled adhesive

(“shock-absorber”)

Effects of total-etch technique

Risk of “over” –etching dentin

Post-conditioning rinse phase

required sensitive to degree of

dentin wetness

Weak monomer-collagen

interaction

Insufficient long-term clinical

results

Self etching primers :

The first system based on this philosophy included acidic etchants with

low concentration than the traditional 30-40%. Phosphoric acid. Some studies

have indicated that low concentration etchants (such as 2.5% nitric, 10%

citric), 10% phosphoric, or 10% maleic) are as effective as 30% to 40%

phosphoric acid when applied to enamel for 15 seconds. However other studies

have shown that such low concentration acids have lower enamel bond

141


strengths than conventional 30% to 40% phosphoric acid, when the traditional

frosted enamel surface often is not apparent after the application of weaker

acids. Under SEM enamel etched with 10% maleic acid or with 10%

phosphoric acid for 15 seconds does not acquire the etching pattern

characteristic of enamel etched with 30-40% phosphoric acid for 15 to 30

seconds.

More recently another type of acidic conditions, the self-etching primers

(SEPs), was introduced in Japan. These acidic primers include a phosphonated

resin molecule that performs two functions simultaneously-etching and

priming of dentin and enamel. Unlike conventional etchants, self-etching

primers are not rinsed off. The bonding mechanisms of self etching primers is

based on the simultaneous etching and priming of enamel and dentin without

rinsing, forming a continuum in the substrate and incorporating smear plug into

the resin tags.

In addition to simplifying the bonding technique, the elimination of

rinsing and drying steps reduces the possibility of over wetting or over drying,

which can have a negative influence in adhesion. However, the sealing of

enamel margins in vivo may be compromised because a perfect marginal

integrity is not achieved.

Based on the use of non- rinse acidic monomers that simultaneously

condition and prime dentin and enamel. The concept of self- etch primers was

introduced with Scotch bond 2 in the early 90.s.. However this system was

advocated only to be applied on dentin alone, and therefore required a selective

enamel etching step.

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The current self etch adhesive provide monomer formulations for

simultaneous conditioning and priming of both enamel and dentin.

Bonding to dentin using a self – etching primer

Two – step self etch adhesive1

143


Product Manufacturer

Clearfill Liner Bond 2

Clearfill Liner Bond 2v

Clearfill SE

Kuraray

Kuraray

Kuraray

Imperva FL-Bond

NRC & Prime&Bond NT

OptiBond (no-etch)

OptiBond FL (no-etch)

Sustel (F2000)

Unifil BOND

Coltene ART bond

Denthesive 11

Ecusit Primer-Mono

Imperva bond (no etch)

Scotchbond 2

Solid Bond3

Superlux Universalbond 2

Syntac

XR-Bond

Shofu

Dentsply

Kerr, Orange, CA, USA

Kerr

3M

GC

Coltene, Alstatten, Switserland

Hereaus-kulzer, Wehrheim, Germany

DMG

Shofu

3M

Hereaus-Kulzer

DMG

Vivadent

Kerr

One step self etch (all – in- one adhesives)1

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Product Manufacture

AQ Bond-Touch & Bond

Etch&Prime 3.0

One-up Bond F

Prompt L-Pop

Xeno CF Bond

Sun Medical, Kyoto, Japan

Degussa, Hanau, Germany

Tokuyama, Tokyo, Japan

ESPE

Sankin, Otahara, Japan

Self etch adhesives subdivided depending on their pH and etching

potential1

Mild (pH=2) Strong (pH1)

Clearfil Liner Bond 2V (Kuraray)

Clearfil SE Bond (Kuraray)

F2000 Primer/adhesive (3M)

Imperva FL-Bond (Shofu)

Mac-Bond II (Tokuyama)

One-up Bond F (Tokuyama)

Experimental PQ/Universal (Uttradent)

Unifil Bond (GC)

Non-Rinse Conditioner & Prime &

Bond NT (Dentsply)

Prompt L- Pop (ESPE)

Vivadent experiment self-etch

adhesive

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Mild self etch adhesives :

“Mild” self etch system has a pH of around 2 and demineralize dentin

only to a depth of 1 m. This superficial demineralization occurs only

partially, keeping residual hydroxyapatite still attached to collagen.

The bonding mechanism of “mild” self etch adhesives to dentin based

on hybridization , with the difference that only submicron hybrid layers are

formed and resin tag formation is less pronounced .

The preservation of hydroxyapatite with in the submicron hybrid layer

may serve as a receptor for additional chemical bonding. Carboxylic acid –

based monomers 4-META (4-methacryloxyethyl trimellitic-acid ) and

phosphate based monomers, such as Phenyl p (2 – methacryloxyethyl phenyl

hydrogen phosphate) and 10 MDP(10-methacryloxydecyl dihydrogen

phosphate) have a chemical bonding to calcium of residual hydroxyapatite .

Thus two - fold bonding mechanism may be advantageous in terms of

restoration longevity. It cornprises a micromechanical bonding component

that may provide resistance to “acute” debonding stress. The additional

monomer \ hydroxyapatite – around – collagen interaction on a molecular

level may result in bonds that better resist hydrolytic degradation

process, and these may help keep the restoration margins sealed for longer

periods.

Weak self – etching effect is mandatory inorder to

1. Deal with smear layers resulting from cavity preparation.

2. Achieve micro mechanical interlocking with in etch pits at enamel

3. Achieve micro mechanical interlocking through hybridization at dentin

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Strong self – etch adhesive :

Have a pH 1 or below. Thus high acidity results in rather deep

demineralization effects. At enamel, the resulting acid etch pattern resembles a

phosphoric acid treatment following an etch & resins approach. At dentin,

collagen is exposed and nearly all hydroxyapatite is dissolved. The bonding

mechanism of “ strong”- self-etch adhesives is primary diffusion-based, similar

to etch & rinse approach.

Advantages:

Simplify the bonding process by eliminating steps

Eliminate some of the technique sensitive of total etch system

Since etch/ rinse phase is eliminated, the issue of wet bonding is of no

relevance.

The risk on incomplete resin infiltration of the exposed collagen fibril

scaffold with resin up to the same depth of demineralization.

“Intermediary strong” two – step self- etch adhesives :

pH is about 1.5

Most typical is the two – fold build up of the dentinal hybrid layer with

a complete demineralized top layer and a partially deminaralized base.

Following a “ Intermediary strong” self- etch approach , the deepest region of

the hybrid layer up to a maximum of 1m still contains hydroxyapatite , by

which the transition of the hybrid layer to the underlying unaffected dentin is

more gradual.

Based on acidity the one step self etch adhesive i-Bond are Xeno III

must also categorized as “ intermediary strong” self-etch adhesives.

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Plus-Minus Balance of Self-Etch Adhesives1

Plus Minus

Simultaneous demineralization and

resin-infiltration

Insufficient long-term clinical

research

No post-conditioning rising Adhesion potential to enamel needs

yet to be clinically proven

Not sensitive to diverse dentin-

wetness conditions

Time-saving application procedure

Low technique-sensitivity

Possibility for “Single-dose”

packaging

Consistent and stable compositon

Controlled stable composition

Hygienic application

Possibility for particle-filled

adhesive (‘shock-absorber’)

Adequate monomer-collagen

interaction

Effective dentin desensitizer

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According to smear layer modified / removed / dissolved :

The most common classification of adhesives is based on the time of

their release on the dental market. Classification in generation lacks scientific

basis and thus does not allow the adhesives to be categorized on objective

criteria. A more logical classification of adhesives would be based on the

number of clinical application steps and, more importantly, on their interaction

with the dentinal substrate.

Three adhesion strategies, distinguished by how they interact with the

smear layer are currently in use with modern dentin adhesive systems.

One strategy aims to modify the smear layer and incorporate it in the

bonding process :

One and two-step smear layer-modifying adhesives can be

distinguished, as they either provide only an adhesive resin or, successively, a

primer and an adhesive resin or successively, a primer and an adhesive resin.

The second strategy completely removes the smear layer and concurrently

demineralizes the underlying dentinal surface :

The system using this strategy can be further subdivided into two- and

three-step smear layer- removing adhesives, depending on whether they have a

combined or separate application of primer and adhesive.

The third adhesion strategy is a combination of these two :

This system dissolves the smear layer rather than removing it and

simultaneously demineralizes the underlying dentinal surface, but only

superficially. This category can also be subdivided into one- and two-step

smear layer-dissolving adhesives.

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Smear layer-Modifying Adhesives :

Dentin adhesives that modify the smear layer are based on the concept

that the smear layer provides a natural barrier to the pulp, protecting it against

bacterial invasion and limiting the outflow of pulpal fluid that might impair

bonding efficiency. Efficient wetting and in situ polymerization of monomer

infiltrated into the smear layer are expected to reinforce the bonding of the

smear layer to the underlying dentinal surface, forming a micro mechanical and

perhaps chemical bonds to underlying dentin. Clinically, these systems require

selective etching of enamel in a separate step. Most typical in this group are

the primers that are applied before the application of polyacid-modified resin

composites or compomers.

The interaction of these adhesion with dentin is very superficial, with

only a limited penetration of resin into the dentinal surface . This shallow

interaction of the adhesive system with dentin, without any collagen fibril

exposure, confirms the weak acidity of these smear layer-modifying primers.

The dentinal tubules commonly remain plugged by smear debris.

One step smear layer modifying system4

Product Name Manufacture

Hytac OSB (in combination with Hytar) ESPE,Seefeld,Germany

Pertac Universal Bond ESPE

Prime & Bond 2.1(no-etch,in

Combination with Dyract)

Caulk, Konstanz, Germany

Solist(in combination with luxat)

Tokuso Light Bond (one step)

DMG, Hamburg, Germany

Tokuyama Soda, Tokuyama,

Japan

150


Two –step smear layer modifying systems4


Optec Universal Bonding System Jeneric/Pentron, Wallingford, CT, USA

Pentra Bond II Jeneric /Pentron

Pro BOND Caulk, Konstanz, Germany

Tokuso Light Bond ( two Step) Tokuyama soda, Tokuyama, Japan

Tripton ICI, Macclesfield, UK

Smear layer-Removing Adhesives :

Most of today’s adhesive systems opt for a complete removal of the

smear layer, using a total-etch concept. Their mechanism is principally based

on the combined effect of hybridization and formation of resin tags . These

systems are applied in three consecutive steps and subsequently categorized as

three steps smear layer-removing adhesives. Even when applied to sclerotic

dentin, the relatively aggressive phosphoric acid etching procedure results in

the formation of a loosely organized hybrid layer.

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Three step smear layer removing systems4

Product name Manufacture

ABC enhanced Chameleon, kansas city, KS, USA.

Aelitebond Bisco, itasca, IL, USA

All-Bond Bisco

Amalgambond plus Parkell, Farmingade, NY, USA

Clearfil liner Bond Kurary, Osaka, Japan

Dentastic Pulpdent, Watertown, MA, USA

Denthesive Heraeus Kulzer, wehrheim, Germany

EBS ESPE, Seefeld, Germany

Gluma Bonding System Bayer, Laverkusen, Germany

Gluma CPS Bayer

Imperva Bond (total-etch) Shofu, Kyoto, Japan

Mirage Bond Chameleon

OptiBond (total-etch) Kerr, Glendora, CA, USA

Opti Bond FL (total-etch) Kerr,

PAAMA2 Southern Dental industries, Victoria,

Australia

Permagen Ultradent, South Jordan, UT, USA

Permaquik Ultradent

Restobond 3 Lee pharmaceuticals,south Ei Monte,

CA, USA

Scotchbond Multi-Purpose 3M. St. Paul, MN, USA

Scotchbond Multi-Purpose Plus 3M, St, Paul, MN, USA

Solid Bond Heraeus Kulzer

Super-Bond D Liner Sun Medical, Kyoto, Japan

Tenure S Den-Mat, Santa Maria, CA. USA

152


Two step smear layer removing systems4


One-step Bisco, Itasca, IL, USA

Fuji Bond LC GC, Tokyo, Japan

Gluma 2000 Bayer, Leverkusen, Germany

Optibond solo Kerr, Glendora, CA, USA

Prime & Bond 2.0 (total etch) Caulk, Konstanz, Germany

Scotchbond 1 (Single bond) 3M, St. Paul, MN, USA

Solist DMG, Hamburg, Germany

Syntac Single-Component Vivadent, Schaan, Liechtenstein

Syntac Sprint Vivadent

Tenure Quik Den-Mat, Santa Maria, CA, USA

Smear layer dissolving adhesives :

A simplified application procedure is also a feature of the smear layer-

dissolving adhesives or “self etching adhesives”, which use slightly acidic

primer or so called self etching primers. These primers practically demineralize

the smear layer and the underlying dentin surface without removing the

dissolved smear layer remnants or unplugging the tubule orifices.

The current two-step smear layer-dissolving adhesives provide self-

etching primers for simultaneous conditioning and priming of both enamel and

dentin. Simplification of the clinical application procedure is obtained not only

by reduction of application steps, but by omission of a post conditioning

rinsing phase. These condiprimers are only air dispersed with out rinsing. As

a supplementary advantage, the controversy of post conditioning drying or

keeping the dentin moist, as in a wet bonding technique is avoided. The actual

rationale behind these systems is to superficially demineralize dentin and so

153


simultaneously penetrate it to the depth of demineralization with monomer that

can be polymerized in situ.

Two step smear layer dissolving systems4


Clearfil Liner Bond 2 Kuraray, Osaka, Japan

Coltene ART bond Coltene, Altstatten, Switzerland

DenthesiveII Heraeus Kulzer, Wehrheim, germany

Etch & Prime 3.0 Degussa, Hanau, Germany

Ecusit Primer-Mono DMG,Hamburg,Germany

Imperva FL-Bond (no etch) Shofo, Kyoto, Japan

Imperva FL-Bond (Fluorobond) Shofo, Kyoto, Japan

Optibond ( no-etch) Kerr, Gledora, CA, USA

OptiBond FL (no-etch) Kerr,

Scotchbond2 3M, St. Paul, MN, USA

Superlux Universalbond 2 DMG, Hamburg, Germany

Syntac Vivadent, Schaan, Liechtensein

XR-Bond Kerr

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Bonding generations table19

Bonding

generation

Characteristics Bond

strength to

dentin

Examples Components

7th Single component

Desensitizing

Self etching

Self priming

No mixing

Moisture independent

Bonds to metal

Little or no sensitivity

18-25MPa iBOND 1

6th Multi component

Multi step

Self etching

Self priming

Hybridization

No mixing

Little sensitivity

18-23MPa Prompt-L-

Pop SE Bond

Liner Bond

II

2-3

5th Single component

Moist bonding

Hybridization

No mixing

Little sensitivity

20-24 MPa Gluma

Comfort

Bond

Prime &

Bond NT

single Bond

Excite

One step

Bond1

1

4th Hydridization 17-25MPa All bond II 2-5

155


Total etch

Little sensitivity Pro Bond

Scotchbond

MP

Tenure

Bond it

Syntac

3rd 2 component primer

and adhesive system

Bonds to metal

Reduced sensitivity

8-15 MPa Prisma

Universal

Bond

Scotchbond

II Tenure

Gluma

X-R Bond

2-3

2nd Weak adhesives

requiring retentive

preparations

Prone to water

degradation

2-8 MPa Bond Lite

Scotch bond

Dentin

Adhesit

2

1st Very Weak Bond to

dentin

2 MPa Cervident

Cosmic

Bond

1

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AMALGAM BONDING SYSTEMS

Amalgam bonding systems may be used to seal underlying tooth

structure and bond amalgam to enamel and dentin. They require dual

characteristics to achieve optimal wetting. Amalgam is strongly hydrophobic,

whereas enamel and dentin are hydrophilic. Therefore the bonding system

must be modified with a wetting agent that has the capacity to wet either

hydrophobic or hydrophilic surfaces. Typical dentin bonding systems may be

used, but special 4-methyloxy ethyl trimellitic anhydride (4-META) based

systems are used frequently. This monomer molecule contains both

hydrophobic and hydrophilic ends12.

Macro shear bond strengths for joining amalgam to dentin are relatively

low (2 to 6 Mpa). Although good bonding occurs to tooth structure,

micromechanical bonding at the interface of the amalgam with bonding system

is poor. Most debonding occurs by fracture along this interface. Since no

chemical bonding occurs at this interface, it is important to develop

micromechanical bonding. To accomplish this, the bonding system is applied

in much thicker layers, so that amalgam being condensed against the resin

adhesive layer will force fluid components of the amalgam to squeeze into the

unset bonding adhesive layer and produce micromechanical laminations of the

two materials. Thicker bonding agent films can be produced by adding

thickening agents to the unset bonding materials or by applying many

applications of bonding material.

The primary advantages for amalgam bonding agents in most clinical

situations are the dentin sealing and improved resistance form, but the increase

in retention form is not significant. Adhesion of amalgam to tooth structure is

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not necessary in clinical circumstances when satisfactory retention and

resistance forms of tooth preparation already exist. Primary indication for

amalgam bonding is when weakened tooth structure remains and bonding may

improve the overall resistance form of the restored tooth.

Sealing amalgam preparations is the sole purpose for bonding, and then

an alternative is the use of dentin sealers. The earliest version of such a system

(Gluma 2, Bayer Dental Products) was actually the primer component of a

dentin bonding system. Since the introduction of that product, several others

have been developed that are essentially primer monomers and/or polymers

dissolved in solvent that penetrate the surfaces of the preparation and dry or are

cured as a polymer film. The action of this film is very similar to that of

varnish, except the film has much better wetting characteristics and produces a

completely impervious layer. The film actually covers enamel as well as dentin

but is still categorized as a dentin sealer. Because the same material may be

used over open dentin tubules on exposed root surfaces to eliminate fluid flow

and desensitize dentin, dentin sealers are also known as dentin desensitizers.

However, an expansive list of other products also may be called dentin

desensitizers, but they are not routinely used to seal dentin under amalgam

restorations.

Bonding systems used below insulating restorations, such as composite,

do not utilize traditional liners and bases except when the tooth excavation is

extremely close to the pulp (RDT<0.5 mm). In that case, a traditional calcium

hydroxide liner is used for pulpal medication, to stimulate reparative dentin.

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PULPAL CONSIDERATIONS OF ADHESIVE

MATERIALS

It has been suggested that conditioning agents (etching agents used on

dentins) should be

Isotonic to avoid osmotic pressure charger in dentinal tubules

Of neutral pH or at least between PH 5.5 and PH. 8.0

Nontoxic to dentin, pulp and gingival tissue,

Compatible with the chemistry of the materials it will contact.

Water soluble and easily removed

Unable to deplete the enamel or dentin chemically

Able to enhance the surface chemically in preparation for bonding.

Many dentin-conditioning agents have pH values much lower than

5.5.Acids can challenge pulp vitality and they can harm the pulp if they contact

it. The smear layer and tubular plug (smear unit) and peritubular dentin

(sclerotic dentin) can be rapidly dissolved by strong acidic conditioning agents

when applied for excessive time intervals20.

The concentration of an acid reaching the pulp tissue is determined by

how much penetrates through dentinal tubules and reacts along the way with

hydroxyapatite and proteins contained with in the tubules. The solute

concentration of an acid is reduced over distance such that at relatively large

thickness (>1.0mm) the concentration of a substance is relatively low by the

time it reaches pulp surface. As the remaining dentin thickness decreases,

there is less reduction of solute concentration, causing a higher concentration at

the pulpal surface as the diffusing solutes reach the end of the tubules.

Cytotoxic effects with in the pulp tissues can be caused by low pH, hypertonic,

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and hypotonic concentrations (abnormal osmolatity) or chemical interferences

with vital biochemical reactions.

The pulp of younger virgin tooth with wide open dentinal tubules to

begin with is more susceptible to the toxic components of dental materials and

responds with a more intense inflammatory response than does an older tooth

which over the years has produced a considerable amount of sclerotic dentin

and reparative dentin that protect the pulp with.

(a) Sclerosis of dentin either as a natural process of aging or induced by the

irritation from caries, attrition, abrasion and erosion, and

(b) Reparative dentin formation, induced by the above factor and also by

tooth cutting and restorative procedures.

Some investigators recommend that the smear layer be removed with

various acids to optimize the bonding of restorative materials to dentin, while

others feel it can be left but modified, since its presence reduces the

permeability of dentin.

Many authors utilizing either phosphoric acid or citric acid as

conditioning agents found them to be too destructive, since they removed the

smear unit, opened and widened (funneled) dentinal tubules, and increased the

severity of the pulpal responses to materials placed subsequently.

Technique factors must be taken into consideration :

When evaluating whether an etching technique is good or bad, one must

remember that subtle changes in techniques and methods can cause important

changes in results, and that the following factor must be taken into

consideration.

160


Type of acid, concentration, time interval; of application.

Active (rubbing, scrubbing) or passive (soaking) application

Whether the etching was applied as a solution or as drops .

Cavity preparations or just exposed superficial dentin

Consideration of remaining dentin thickness (RDT)

Presence or absence of sclerotic dentin and reparative dentin.

Age of the patient and species and age of experimental animal.

Pulpal responses to subsequent type of restoration;

Condensation of amalgam

Self cured composite resin, placed under pressure.

Visible- light cured composite resin placed incrementally, and

Pulpal response to a fresh mix of a restorative material or

to a cured disc of the material in question placed in a leaching solution

to measure the release of H+.

Shortening of application time of conditioning agents :

In 1977 Brannstrom and Nordenvall noted no demonstrable differences

between dentinal surfaces etched for 15 seconds or two minutes and

recommended shorter etching times.

Brannstrom felt that the degree of chemical action depended on the

duration of its application. Removal of the smear layer from both enamel and

dentin was accomplished rapidly in five to ten seconds of exposure to a weak

acid and five seconds of 37% H 3Po4applied to dentin was quite adequate to

produce necessary changes. But the same agent that may remove the smear

layer in five seconds can cause considerable decalcification if left in place for

30 seconds, and produce pulpal damage if left for 60 seconds (Mount, 1990).

Pulpal responses to bonding agents :

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Bonding agents of themselves do not appear to be toxic. As far back as

1975 it appeared that bonding agents helped reduce the expected pulpal

responses induced by the subsequent placement of toxic composite resins.

Gluma bonding technique also provided immediate bactericidal and

long term (90 days) bacteriostatic action.

162


CLINICAL APPLICATIONS OF DENTIN

BONDING AGENTS

Bonding of directly placed resin based restorative materials.

Bonding of ceramic restorations.

Bonding of amalgam restorations.

Re-attachment of fractured tooth fragments.

Pulp capping.

Desensitization of sensitive cervical dentin or cementum.

Adhesive luting of bridgework.

Repair of porcelain and metal ceramic restoration.

Desensitization:

Dentin hypersensitivity is a common clinical condition that is difficult

to treat because the treatment outcome is not consistently successful.

Hydrodynamic theory explains dentin hypersensitivity.

Patients may complain of discomfort when teeth are subjected to

temperature changes, osmotic gradients such as those caused by sweet or salty

foods, or even tactile stimuli. The cervical area of tooth is the most common

site. Cervical hypersensitivity may be caused not only by chemical erosion,

but also by mechanical abrasion or even occlusal stresses.

Theories about the transmission of pain stimuli in dentin sensitivity

suggest that pain be amplified when the dentinal tubules are open to the oral

cavity. The relationship between dentin hypersensitivity and the patency of

dentin tubules in vivo has been established and occlusion of the tubules seems

to decrease that sensitivity. It also has been suggested that the incorrect

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manipulation of some adhesives materials, namely those with acetone, may

actually trigger postoperative sensitivity.

Clinicians have used many materials and techniques to treat dentin

hypersensitivity, including specific dentifrices, co2 laser irradiation, dentin

adhesives, antibacterial agents, aldehydes, resin suspensions, fluoride rinses,

fluoride varnishes, calcium phosphate, potassium nitrate, and oxalates.

The use of dentin adhesives to treat hypersensitive root surface has

gained popularity over the last few years. Reduction in sensitivity may result

from formation of resin tags and a hybrid layer when a dentin adhesive is used.

The precipitation of proteins from the dentinal fluid in the tubules may also

account for the efficacy of desensitizing solutions.

The primers of multibottle adhesive system All-Bond 2 (Bisco) have a

desensitizing effect, even without consistent resin tag formation.

In a clinical study using the primer of the original Gluma adhesive

system (an aqueous solution of 5% gultaraldehyde and 35% HEMA, currently

marked as Gluma Desensitizer), the desensitizing solution was applied to

crown preparations. The author concluded that Gluma primer reduced dentin

sensitivity through a protein denaturation process with concomitant changes in

dentin permeability.

Adhesive Amalgam restoration :

Marginal discoloration, recurrent caries lesions, and postoperative

sensitivity are the most frequent consequences of the penetration of oral fluids

and bacteria through gaps at the dentin resin interface towards the pulp.

164


Delayed interfacial marginal leakage occurs at the amalgam-

preparation interface. Corrosion products from amalgam seal the interface

after a few months, however, this process may take more than 6 months for

copper rich amalgam alloys.

To overcome the inevitable marginal micro leakage, dentin adhesive

systems have been used both under mercury-based amalgam restorations and

under gallium-based amalgam restorations. The use of adhesive systems

beneath amalgam restorations reduces or prevents marginal leakage both in

vivo and in vitro and improves marginal integrity of the restoration when

compared to the use of a copal varnish. Additionally, dentin adhesives

reinforce the amalgam restoration margins, making the cavosurface angle less

susceptible to acidic demineralization in vitro.

Several laboratory and clinical studies have shown that dentin adhesive

systems such as All-Bond 2 (Bisco), Amalgam bond plus (Parkell), Panavia

(kuraray) and Scotch bond Multipurpose plus (3M) can be used to bond

amalgam restorations. The attachment mechanism between the adhesive and

the amalgam is not full understood, but it may be micromechanical

entanglement of the uncured adhesive material with the settings amalgam mix

during condensation of the amalgam.

This bonding mechanism actually may depend on the type of amalgam

used, for example spherical amalgam alloys critically have higher bond

strength than dispersed phase or admixed amalgam alloy.

Recent studies have demonstrated that some current adhesive systems

provide bond strength in range of 10 to 14 MPa. As a safety precaution,

165


primary mechanical retention features are still recommended when an adhesive

system is used with amalgam.

Some studies also suggest that the use of dual- cured filled liners may

be beneficial for bonding amalgam to dentin. The additional adhesive liner

may provide an increased retention to adhesive amalgam restorations, therefore

allowing for preparations with lower demand for additional retention features

such as dove tails, slots, holes or even pins, Moreover marginal leakage has

been shown to decrease when thick dual cured or self cured liners are used.

Another advantage from the use the of dentin adhesives under amalgam

restoration is that the residual tooth structure becomes more resistant to

fracture.

Light curing of resin from the external tooth surface after condensing

the amalgam into the preparation recently has been evaluated in vitro for three

dual-cured adhesive system. The rationale behind the use of light curing

through the tooth walls was that some dual cured adhesives might not be able

to polymerize completely underneath the amalgam restoration.

Dentin adhesive systems also are used to bond fresh amalgam to

existing amalgam restorations in repair procedures. The prognosis of this type

of procedure is unpredictable and can be unsuccessful. The interfacial failure

between fresh amalgam and old amalgam may be result of lack of micro

mechanical retention in the “old” amalgam restoration surface. Therefore

dentin adhesive systems are not recommended for amalgam repair.

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Indirect Adhesive restorations :

Current dentin adhesive systems are considered as universal adhesives

because they bond to various substrates besides dentin. Recent developments

in adhesion technology have led to new indications for bonding to the tooth

structure, such as indirect composite and ceramic restorations (Crowns, inlays,

onlays, and veneers). The use of a universal adhesive system in conjunction

with resin cement provides durable bonding indirect restorations to tooth

structure.

Ceramic restorations (with the exception of aluminous core porcelains

such as In-ceram high strength ceramic) must be etched internally with 6% to

10% hydrofluoric acid (HF) for to 2 minutes to create retentive micro

porosities.

HF must be rinsed off carefully with running water for at least 2

minutes. Some clinicians use sandblasting with aluminum oxide particles in

the internal surface of the restorations. After rinsing off the HF and drying

with an air syringe, a silane-coupling agent is applied on the etched porcelain

surface and air-dried. The coupling agent acts as a primer because it modifies

the surface characteristics of etched porcelain. Because etched porcelain is an

inorganic substrate, the coupling agents make this surface more receptive to

organic materials, the adhesive system and composite resin cement. The use of

silanes may actually increase the bond between the composite and porcelain in

the range of 25%. Indirect composite restorations may be bonded to etched

dental substrates using a universal adhesive system and a resin luting cement.

One of the great advantages of indirect composite restorations is that

polymerization shrinkage occurs outside the mouth.

167


Additionally, the degree of monomer conversion is higher for indirect

resin-based restorations. However, this increased level of double bond

conversion results in only a small amount of monomer double bonds on the

internal surface of the indirect composite restoration therefore decreasing the

potential for bonding with the adhesive system and with the composite luting

cement. To overcome this unsuitable bonding surface, the composite maybe

treated with surface activators to reestablish the surface energy. [Composite

Activator (Bisco), Activator-Art Glass (Heraeus kulzer)]. Another alternative

is sandblasting the bonding surface of indirect restoration to expose an internal

area where more double bonds may be present. HF is contraindicated for

treating indirect composites because it softens some composite materials.

Porcelain and Ceramic Repair systems :

Fractured regions on porcelain-fused-to-metal or all-ceramic

restorations may be repaired by etching the surface with hydrofluoric (HF)

acid, silanating the etched ceramic material, applying bonding agent, and

adding composite to replace the missing material. This is not a long-term

solution to the problem but does provide an immediate alternative rather than

complete replacement of the original restoration. Wetting of ceramic materials

by bonding materials is different than for dentin and may not work well with

all bonding systems. If the substrate being repaired includes exposed metal

alloy on a portion of a porcelain-fused-to-metal restoration, then the metal

should be sandblasted and etched to enhance retention.

168


DENTIN BONDING AGENTS FOR PULP CAPPING :

The direct pulp-capping technique with adhesive system has recently

been advocated with mixed evidences of clinical success from vital pulp

therapy performed in the teeth of animals. The apparent clinical/radiographical

success of pulp therapy and the results from vital pulp capping performed in

animals teeth are also compared to clinical conditions and results obtained

form pulp capping procedures performed in mechanically exposed sound

human pulps.

For vital pulp capping to be successful, the tooth should be

asymptomatic or have minimal symptoms and the bleeding must be controlled.

This control may be achieved by washing the area with sterile saline and

drying it with either paper points or cotton pellets,

For vital pulp capping by total etch procedure, hemostasis must be

obtained. The exposure site is then covered with a non-setting calcium

hydroxide paste (e.g., Pulpdent, Pulpdent Corp. of America, Brookline, Mass.)

and the cavity preparation completed. Following disinfection of the cavity, the

enamel and dentin are etched with 32% phosphoric acid for 15 seconds. The

acid and calcium hydroxide are rinsed off and the preparation is lightly dried.

The entire preparation, including enamel, dentin and pulpal tissue , is treated

with a dentin bonding system. Fourth-generation system with a separate primer

and adhesive is recommended, as little research has been published to date on

the fifth-generation dentin bonding systems. Following placement of several

layers of the hydrophilic primer, a thin layer of the adhesive resin is painted

onto the enamel, dentin and pulpal tissue and light cured. A second layer of

unfilled resin is applied, and a thin layer of resin-modified glass ionomer is

also applied over and around the exposure site to mechanically protect the

perforation from intrusion of the restorative material during packing or

169


condensation. These layers are also light cured. The restoration is subsequently

completed in conventional fashion.

Pulp capping

In a study performed in primate teeth, Akimoto et al. showed that

Clearfil liner bond 2 permitted the differentiation of new pulpal cells that

stratified, polarized (reoriented), and laid down a dentinal bridge. These

histological findings may support the use of those materials for placement on

pulp exposures. It has also been reported that possible failures of pulp capping

therapy with adhesive systems may be due to poor hemorrhage control,

material placement and incomplete polymerization. The results observed with

170

Pulp exposure

Total etch technique

Hemostasis

Disinfect cavity

Etch

PrimersAdhesive

Resin modified glass ionomer

Restoration


animal teeth capped with adhesive systems are different from those in which

similar vital pulp therapy has been performed in human teeth.

Recent studies performed in human teeth have demonstrated that

following application of an adhesive system to pulpal wounds, the materials

delayed pulpal healing, resulting in lack of dentin bridge formation, even 60

days after the pulp capping procedure. The pulp exposure site showed a

persistent inflammatory response evidenced by macrophages and giant cells.

Gwinnett and Tay recently demonstrated the features of the pulpal

responses following application of all bond 2 to acid- conditioned human pulp

tissue. The authors reported an irreversible injury to the odontoblasts closest to

the site of cavity preparations that resulted in a death of these cells. In some

specimens, the presence of these particles appeared to have triggered a foreign

body response, characterized by the presence of a mononuclear infiltrate as

well as the appearance of multinuclear giant cells. The persistence of

unresolved chronic inflammation wan associated with the lack of calcified

bridge formation in these specimens.

Following application of Clearfil Liner bond 2 to mechanically exposed

human pulps a large number of macrophages and giant cells were notable

features of the pulp tissue capped with clearfil liner bond 2. The materials were

evaluated at 4.30, between 90 and 300 days.

In studies performed in human teeth, the histological findings has no

direct correlation with clinical observations. Patients who had their pulps

capped with adhesive systems reported no clinical discomfort during the

experiments. In contrast, the histopathological analysis of the teeth showed

intense inflammatory responses in the short term and persistent inflammatory

171


reactions close to the resin pulp capping in the long-term. Periapical lesions

were not detected even along-term evaluation (360 days in primary teeth or

between 60 and 300 days in permanent teeth. These observations have

confirmed that clinical and radiographic evidence alone cannot support the

introduction of any new pulp therapy.

The results obtained from in vivo animal studies; in which various

adhesive systems were applied to mechanically exposed pulps cannot be

directly extrapolated to human clinical conditions.

Clinical and radiographic evaluations of teeth submitted to various pulp

therapies do not indicate the biocompatibility of dental materials or support

pulp capping techniques.

LIST OF GUIDELINES TO ENSURE CLINICAL

SUCCESS

1. Use proper isolation :

Hydrophilic bonding systems may tolerate saliva contamination to

certain degree but evidence for such tolerance remains minimal so proper

isolation is necessary.

172


2. Bond to enamel :

Whenever a restoration is bond to dentin the adjacent enamel should be

etched. Enamel etching is a very reliable method of bonding resins to tooth

structure.

3. Roughen sclerotic dentin :

Bonded restoration are most likely to fail when bonded to sclerotic

dentin. Light roughening with diamond or carbide bur may provide more

micromechanical locking.

4. Use mechanical retention it supplements retention :

5. Leave dentin moist after etching :

Virtually all present day dentin adhesives bond to dentin that is moist.

Systems containing acetone primers are well suited for bonding to wet

surfaces.

General rule dentin should not be dessicated. If dessicated or if dentin is

dried to check enamel etch. It should be remoistened to improve bond strength.

However pooled moisture should not be allowed to remain on tooth as excess

water can dilute the material and reduce it effectiveness. A glistening hydrated

surface is that referred appearance.

6. Apply and dry primers correctly :

They should be applied in adequate quantity some require multiple coats

or longer application times. Also solvents must be driven off completely with

compressed air before the bonding agent or composite is applied. It is reported

that adhesion may be compromised if acetone is not evaporated properly.

173


7. Do not over thin the bonding resin :

Application of me resin bonding agent is the simplest steps in the 3 step

bonding procedure.

If it is excessively or aggressively air thinned, oxygen inhibition

prevents complete polymerization and result sin low bonding strength.

Thinning of bonding agent by a dry brush is better than thinning with air blast.

8. Use flexible restorative system :

Flexible restorative system (Microfilled composites) or "Stress breaking

liners" (filled bonding relines) may improve the quality of bonded restoration

by compensation for stresses generated by polymerization shrinkage and tooth

flexure.

9. Fill incrementally :

Decrease overall polymerization shrinkage.

10. Delay finishing :

Bond strength is increased after 24 hours so a brief delay in finishing

may help preserve the integrity of delicate margins.

11. Rebond margins :

Because it is assumed that gap may occur in atleast some marginal

areas. The margins are re-etched and sealed with special low viscosity resin.

12. Follow directions :

Reputable manufacturers have specific protocols for application of their

bonding systems.

174


CONCLUSION

Advances in adhesive dental technology have radically changed

restorative dentistry. The acid etch technique for enamel bonding led to the

development of revolutionary restorative, preventive and esthetic treatment

methods. More recently developments in resin/dentin bonding have moved

adhesive dentistry at an even higher level. But it is necessary that these

materials must be used properly to optimize their clinical performance.

Dentine adhesive systems have created a new era in the field of

dentistry. Owing to its property of adherence to the tooth structure by both

micromechanical and chemical means, it finds a wide range of application in

various fields. It has lead to the most desired form of treatment needs, i.e. the

conservation of tooth structure, which is the ultimate goal of conservative

dentistry. Although, it was initially considered as a time consuming procedure,

with the introduction of the sixth and seventh generation dentine adhesive

system, the technique of dentine bonding has reduced to a single step. Finally,

the responsibility lies in the hands of the clinician to make the appropriate use

of its superior qualities. Yet, various clinical studies have to be carried out to

prove its long term efficacy.

175


REFERENCES

1. B. Van Meerbeek, M. Vargas, S Inouse, Y Yoshida, M. Peumans, P.

Lambrechts. G. Vanherle. Adhesives and cements to promote

preservation dentistry. Operative Dentistry Supplement 6, 2001-119-144.

2. Karl F.Leinfelder. Dentin adhesives for the twenty-first century. Dental

clinics of North America vol 45. Number 1. January 2001.

3. F.J.T. Burko, E.C. Combe and W.H. Douglas. Dentine bonding system;

Dental update 2000; 27:85-93.

4. B. Van Meerbeek, J. Perdigao, P-Lambrechts, and G. Vanherle; The

clinical performance of adhesives; Journal of dentistry 1998 volume 26,No

1. 1-20.

5. Nobuo Nakabayashi, David H. Pashley; Hybridization of dental hard

tissues.

6. Kenneth J.Anusavice : Phillip’s science of dental materials, eleventh

edition 21-40,structure of matter and principles of adhesion.

7. Gordon J. Christensen. Clinical factors affecting adhesion; Operative

dentistry supplement 5,1992.24-31.

8. B. Van Meerbeek et al. Factors affecting adhesion to mineralized tissues,

Operative dentistry supplement 5, 1992 111-124.

9. David H Pashley et al: The effects of dentin permeability on restorative

dentistry, DCNA 46; 2002; 211-245.

10. I. Eystein Ruyter: The chemistry of adhesive agents; Operative dentistry

supplement 5, 1992,32-43.

11. Manville G Duncansor, Frank J. Miranda, Robert T. Probst. Resin

dentin bonding agent – rationale and result. Quintessence international vol

17, 10, 1986.

176


12. Sturdevant C.M, Theodore M. Roberson, Herald O.Heymann, Edward

J. Swift; the art science of operative dentistry. Fundamental concepts of

enamel and dental adhesion 235-268.

13. John Gwinnett: Structure and composition of enamel: Operative dentistry

supplement 5,1992. 10-17.

14. Garyson W. Marshall. : Dentin microstructure and characterization,

Quintessence International: 1993(9) 606-617.

15. Edward J. Swift, Jorge Perdigio, Harold 0. Heymann: Bonding to

enamel and dentin: A brief history and state of the art, Quintessence

International 1995, vol 26. No.2.

16. Raymond L Bertolotti: Conditioning of the dentin substrate. Operative

dentistry supplement 5, 1992.

17. M.J. Tyas, M.F Burrow. Adhesive restorative materials: a review;

Australian Dental Journal 2004: 49 (30:112-121.

18. Gerarad Kugel, Marco Ferrari: The science of bonding: From first to

sixth Generation; JADA 2000 vol 131, June 2000.

19. Dr. George Freedman and Dr Karl Leinfelder; 7th generation adhesive

systems: Famdent practical dentistry handbook 2003 vol 3 April-June.

20. B. Van Meer beek, J. De Munck, Y. Yoshida, S. Inoure, P. Lambrechts.

Adhesion to enamel and dentin. Current status and future challenges.

Operative dentistry 2003, 28-3, 215-235.

21. Harold R Stanley; Pulpal consideration of adhesive materials; Operative

dentistry supplement 5,1992.

22. J.R. Holtan, G.P. Nystron, R.A. Phelps, TB Anderson, W.S. Becker,

Influence of different etchants and etching times on shear bond strength;

Operative dentistry, 1995, 20,94-99.

23. Franklin R. Try, David. H.Pashley: Aggressiveness of contemporary self-

etching systems: depth of penetration beyond dentin smear layer layers,

Dental materials 17 (2001) 296-308.

177


24. C.Prati, S. Chersoni, D.H. Pashley, Effect of removal of surface collagen

fibrils on resin- dentin bonding, Dental materials 15 (1999) 323-331.

25. Johan Blomlof et al; Acid conditioning combined with single-component

and two component dentin-bonding agents: Quintessence international

2001; 32:711-715.

26. PT Triolo et al; Shear bond strengths of composite to dentin using six

dental adhesive systems: Operative dentistry 1995,20,46-50.

27. M Miyazaki, J A Platt, H. Onose, B.K. Moore; Influence of dentin

primer application methods on dentin bond strength, Operative dentistry,

1996,21,167-172.

28. Slavoljub Zivkovic: Quality assessment of marginal sealing using seven

dentin adhesive systems: Quintessence international 2000; 31:423-429.

29. Bruno T. Rosa, Jorge Perdigao, Bond Strengths of non-rinsing adhesives,

Quintessence International 2000,31:353-358.

30. Y Shimada et al, Bond strength of two adhesive systems to primary and

permanent enamel: Operative dentistry 2002,27,403-409.

31. Y. Shimada et al; Shear bond strength of current adhesive systems to

enamel, dentin and dentin- enamel junction region; Operative dentistry,

2003, 28-5,585-590.

32. M. Tanumiharja, M.F. Burrow, MJ. Tyas: Microtensile bond strengths

of seven dentin adhesive systems, Dental materials 16 (2000) 180-187.

33. GC Lopes et al; Dentin bonding effect of degree of mineralization and acid

etching time: Operative dentistry, 2003, 28-4, 429-439.

34. Amer Abu-Hanna, Valeria U. Gordan and Ivar Mjor; The effect of

variation in etching times on dentin bonding; General dentistry 2003, 2833.

35. George Eliads, Georgios Palaghias, George Vougiouklakis; Effect of

acidic conditioners on dentin morphology, molecular composition and

collagen conformation in situ, Dental materials 1997,13, 24-33.

178


36. M Hashimoto et al: The effect of hybrid layer thickness on bond strength:

demineralised dentin zone of the hybrid layer, Dental materials 16 (2000)

406-411.

37. Jorge Perdigao, J C. Ramos, Paul Lambrechts, In vitro interfacial

relationship between human dentin and one-bottle dentin adhesives, Dental

materials 1997:13, 218-227.

38. H. Li, M.F. Burrow, M.J. Tyas: Nanoleakage patterns of four dentin

bonding systems, Dental materials 16(2000) 48-56.

39. David H Pashley, Franklin R Tay: Aggressiveness of contemporary self –

etching adhesives: etching effects on unground enamel: dental materials 17

(2001)277-283.

40. Frankenberger, J Perdigao, B T Rosa, M Lopes: No-bottle Vs

multibottle dentin adhesives – a Microtensile bond strength and

morphological study: Dental materials 17 (2001) 373-380.

41. Richard B.T Price, Gordon C. Hall: In vitro comparison of 10-minute

versus 24-hour shear bond strengths of six dentin-bonding systems,

Quintessence Int 1999; 30:122-134.

42. Murat Turkun, Sebnem Turkun, Atakan Kalender: Effect of cavity

disinfectants on the sealing ability of non-rinsing dentin- bonding resins;

Quintessence international 204; 35; 469-476.

43. Hagay Slutzky, Shlono Matalon, Ervin I, Weiss; Antibacterial surface

properties of polymerized single bottle bonding agents: Quintessence

international 2004; 35; 275-279.

44. Esra Can Say et al; In vitro effect of cavity disinfectants or the bond

strengths of dentin bonding systems; Quintessence International 2004; 35;

56-60.

45. Sigurdur O. Eiriksson et al; effects of Saliva contamination on resin-

resin bond strength, Dental materials (2004) 20, 37-44.

179


46. Sigurdur O. Erriksson et al; Effects of blood contamination on resin-

resin bond strength, Dental materials (2004) 20, 184-190.

47. G. Schmalz, Z. Erguca and K-A. Hiller Effect of dentin on the

antibacterial activity of dentin bonding agents: Journal of endodontics vol.

32, No5. 2004.

48. Arlin Kiremitci, Filiz Yalcin, Saadet Gokalp; Bonding to enamel and

dentin using self-etching adhesive systems; Quintessence international

2004, 35: 367-370.

49. Maria Carolina Guilherme, Erhardf et al: In vitro influence of carisolv

on shear bond strengths of dentin bonding agents: Quintessence

international 2004; 35: 801-805.

50. Jorge Perdigao et al; Effect of calcium removal on dentin bond strengths;

Quintessence International 2001; 32: 142-146.

51. Lorenzo Breschi et al; High resolution SEM evaluation of dentin etched

with maleic and citric acid, Dental materials 18 (2002)26-35.

52. Atila Stephan Atac, Zafer C.Chehreli, and Burcin Sener; Antibacterial

activity of fifth-generation dentin bonding system, Journal of endodontics

Vol. 27, No 12, 2001.

53. G. Eliades, G. Vougiouklakis, G. Palaghias: Heterogeneous distributions

of single-bottle adhesive monomers in the resin- dentin interdiffusion zone:

dental materials 17 (2001) 277-283.

54. P.N.R. Pereira et al: Effect of intrinsic wetness and regional difference on

dentin bond strengths, Dental materials 15 (1999) 46-53.

55. K. Miyasaka, N. Nakabayashi; Combination of EDTA conditioner and

phenyl-P/HEMA self-etching primer for bonding to dentin, Dental

materials 15 (1999) 153-157.

56. M. Miyazaki, K Tsubota, H Onose, K. Hinoura: Influence of adhesive

application duration on dentin bond strength of single-application bonding

systems; Operative dentistry 2002, 27,278-283.

180


57. Sofia S.A. Oliveira et al, The influence of the dentin smear layer on

adhesion, a self – etching primer Vs a total-etch system Dental materials 19

(2003) 758-767.

58. Bora Ozturk and Fusun Ozer; Effect of NaOCl on bond strengths of

bonding agents to pulp chamber lateral walls. Journal of endodontics vol.

30, no5, 2004.

181


ABBREVIATIONS USED

bis-GMA Bisphenol glycidyl methacrylate

BPDM Biphenyl dimethacrylate

DMA Dimethacrylate

DMAEMA Dimethylaminoethyl methacrylate

GPDM Glycerophosphoric acid dimethacrylate

HAMA Hydroxyalkyl methacrylate

HEMA 2- Hydroxyethyl methacrylate

HPMA Hydroxypropyl methacrylate

MA Methacrylate

10-MDP 10- Methacryloyloxy decyl dihydrogenphosphate

4-MET 4- Methacryloxyethyl trimellitic acid

4-META 4- Methacryloxyethyl trimellitate anhydride

MMA Methyl methacrylate

MMEM Mono-methacryloyloxyethylmaleate

MPDM Methacryl propane diol monophosphate

NPG N- Phenylglycine

NPG-GMA N- Phenylglycine glycidyl methacrylate

NTG-GMA N- Tolylglycine glycidyl methacrylate

PENTA Dipentaerythritol penta acrylate monophosphate

Phenyl-P 2- Methacryloxy ethyl phenyl hydrogen phosphate

PMDM Pyromellitic acid diethylmethacrylate

TBB Tri-n-butyl borane

TEG-DMA Triethylene glycol dimethacrylate

TEG-GMA Triethylene glycol-glycidyl methacrylate

UDMA Urethane dimethacrylate

182


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adhesion in dentistry

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