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DENTIN BONDING AGENTS

DR.ROHITA ANN THOMAS POST GRADUATE, DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS

CONTENTS INTRODUCTION ROLE OF ADHESIVE DENTISTRY CONCEPT OF ADHESION ENAMEL ADHESION DENTINE ADHESION CHALLENGES IN DENTINE ADHESION ENAMEL BONDING STEPS FOR ENAMEL BONDING MECHANISM INVOLVED

DENTINE BONDING CONDITIONING OF DENTINE PRIMING OF DENTINE

DENTINE BONDING AGENTS CLASSIFICATION GENERATIONS OF BONDING AGENTS FIRST GENERATION SECOND GENERATION THIRD GENERATIONS FOURTH GENERATION FIFTH GENERATION SIXTH GENERATION SEVENTH GENERATION

ROLE OF MICROLEAKAGE BIOCOMPATIBILITY ANTIBACTERIAL PROPERTY CLINICAL FACTORS IN DENTINE ADHESION NEWER CLINICAL INDICATIONS OF DENTINE

ADHESIVES DESENSITISATION ADHESIVE AMALGAM RESTORATIONS INDIRECT ADHESIVE RESTORATIONS

FAILURES IN DENTINE BONDING SUMMARY BIBLIOGRAPHY

INTRODUCTION

There is much interest and activity in dentistry today with dentin bonding agents.

In the modern society, aesthetics has become a major concern for every individual .Thus most of us desire for a perfect set of teeth.

Therefore, teeth that have been deformed or ravaged by dental diseases need to be restored to their natural form and colour.

Moreover, the classic concepts of tooth preparation advocated in the early 1900s have changed dramatically.

Now more focus is laid upon conservative approach to the tooth preparation.

Therefore the introduction of adhesive restorative materials has reduced the need for an extensive tooth preparation.

In order to successfully accomplish this, dentin bonding systems have been introduced which bond the composite resin to the tooth structure.

DEFINITION Adhesion is derived from Latin meaning "a state in which two

surfaces are held together by interfacial forces like valence forces or interlocking forces or both".

(The American Society for Testing and Materials)

Thus for the process of adhesion to occur , we need to understand the role of following components:

ADHESIVE

ADHEREND

ADHESIVE STRENGTH

ADHESIVE is defined as a material , frequently a viscous fluid that

joins two substrates together by solidifying , resisting separation & transferring a load from one surface to the other.

ADHEREND is defined the surface to which an adhesive adheres.

ADHESIVE STRENGTH is the measure of the load-bearing capacity of an adhesive joint.

Therefore the development of resin based restorative material has opened new vistas to a more conservative approach to caries management.

MECHANISM OF ADHESION:

MECHANICAL

ADSORPTION

DIFFUSION

COMBINATION

INDICATIONS FOR ADHESIVE DENTISTRY

Restoration of class 1,2,3,4,5,6 carious lesions Change the shape & colour of anterior teeth(using full or partial

veneer ) Seal pits and fissures Bond orthodontic brackets Desensitize exposed root surfaces Bond amalgam restorations to tooth Bond fractured segments of anterior teeth. Bond pre-fabricated fibre or metal posts and cast posts. Seal root canals during endodontic therapy.

ENAMEL ADHESION In 1955,Michael Buonocore described a clinical technique that used a diluted

phosphoric acid to etch the enamel surface to provide retention of unfilled, self-cured acrylic resins.

The resin would mechanically lock to the microscopically roughened enamel surface, forming small "tags" as it flowed into the 10-µm to 40-µm deep enamel microporosities and then polymerized.

The first clinical use of this technique was the placement of pit and fissure sealants.

The formation of resin micro tags within the enamel surface is the basis of RESIN-ENAMEL ADHESION.

The steps involved are:

Acid etching transforms smooth enamel into an irregular surface & increases its free surface energy

Application of a fluid resin based material to the irregular etched surface , facilitates penetration of the resin into the surface aided by capillary action

Monomers in the material are polymerised and the material becomes interlocked with the enamel surface.

ETCH PATTERN

Enamel etching leads to the following types of micro morphological patterns:

TYPE 1 ETCH PATTERN-dissolution of prism cores without involvement of prism peripheries.

TYPE 2 ETCH PATTERN-PERIPHERAL ENAMEL IS DISSOLVED , but the cores are left intact.

TYPE 3 ETCH PATTERN-it is less distinct than the other two patterns.

ETCHANT CONCENTRATION Buonocore used 30-40% phosphoric acid.

Currently,37% phosphoric acid in gel form is used. Silverstone found that the application of 30-40% phosphoric acid

resulted in a very retentive enamel surface. >40% - Calcium salts are less dissolved - ETCH patterns

with poorer definition.

<27% - Formation of dicalcium phosphate dihydrate -

cannot be easily removed by rinsing.

ETCH TIME Currently, an etching time of 15 seconds is used.

An etching time of 60 seconds originally was recommended for permanent enamel using 30-40% phosphoric acid.

However , studies show that a 15 second etch resulted in a similar surface roughness as that provided by a 60 second etch.

Phosphoric acid is said to be a more aggressive acid,so alternative etchants have been suggested:

EDTA (24%; ph=7) Citric acid Tannic acid Maleic acid Polyacrylic acid

ALTERNATE ETCHANT SYSTEMS: Lasers Air abrasion-Al2O3 particles

LASERS

Adhesion to dental hard tissues after Er:YAG laser etching is inferior to that obtained after conventional acid etching.

Enamel and dentin surfaces prepared by Er:YAG laser etching show extensive subsurface fissuring that is unfavorable to adhesion.

(J Prosthet Dent 2000;84:280-8.)

Adhesion to laser-ablated or laser-etched dentin and enamel was inferior to that of conventional rotary preparation and acid etching.

( Dental Materials (2005) 21, 616–624)

Figure 1 Scanning electron microscopic images of dentin: (A) rotary-prepared and acid-etched (3500!),(B) laser-prepared (9000!), and (C) laser-prepared and then acid-etched (3500!).

(Fig. 1A) revealed a smoothsurface with tubule orifices devoid of smear plugs.The intertubular dentin is undisturbed.

In contrast, SEM of a cross-section oflaser-ablated, laser-etched dentin showed a highly irregular surface and fissuring. Areas of poor hybridization between composite and dentin suggest poor hybridization, or no hybridization.

Laser-prepared dentin revealed surface scaling and flaking, along with peritubular cuffing (Fig. 1B). Acid-etching afterlaser ablation appeared to decrease some of the surface scaling and flaking (Fig. 1C).

Figure 3 Separation of resin adhesive and unaffected subsurface dentin from laser-ablated, then acid-etched dentin.

Laser ablated,acid-etched dentin demonstrated areas of detachmentFrom both the resin adhesive and the unaffected subsurface dentin (Fig. 3).

SEM photographs of 37% orthophosphoric acid, 10% maleic acid, and Er,Cr:YSGG hydrokinetic laser-treated enamel are shown in Figure 4.

The enamel surface etched with 2 acid solutions and a laser system showed different results according to Silverstone’s10 etching patterns.

• The 37% orthophosphoric acid removed the periphery core material but left the prism core relatively unaffected (type II), producing a very rough enamel surface.

• The 10% maleic acid treatment resulted in preferential removal of prism core material and left the periphery intact (type I).

• Er,Cr:YSGG hydrokinetic laser treated enamel showed a more random etching pattern in which adjacent areas of tooth surface correspond to types I and II, mixed with regions where the pattern could not be related to prism structure. There was no recrystallization or melting observed

BOND STRENGTH

Shear bond strength of composite to phosphoric acid etched enamel exceeded 20 Mpa.

According to studies,a minimum of 17-21MPa of bond strength is needed to prevent the disruption of the bond between the tooth and composite.

DENTIN ADHESION

Bonding to dentin is challenging & difficult. Adhesion to dentin occurs by mechanical method,chemical or both.

But the main method is by penetration of adhesive monomers into collagen fibrils which are exposed post acid etching.

Structural differences exist between enamel & dentin.

Therefore the following reasons account for challenges faced in dentin adhesion:

STRUCTURE OF DENTIN SMEAR LAYER STRESSES AT RESIN-DENTIN INTERFACE

STRUCTURE OF DENTIN

Enamel contains 90% of hydroxyapatite crystals whereas dentin has only 50% and the rest is constituted by water(25%) and type I collagen(25% by volume).

Dentinal tubules exert pressure of 25-30mmHg, thus creating decreased stability of bond between composite resin and dentin.

The number of dentinal tubules decreases from about 45000 near the pulp to 20000 near DEJ

Also the tubule diameter decreases from 2.37µm to 0.63µm near DEJ.

Adhesion can also be affected by remaining dentin thickness(RDT) as bond strength is greater for superficial dentin and its lesser for deeper dentin

WHAT IS SMEAR LAYER?

It is the residual organic or inorganic components formed when a tooth is prepared using a bur or other instrument.

(Sturdevant’s Art & Science of operative dentistry,4th edition)

It is 1-10 µm thick .

COMPOSITION OF SMEAR LAYER:

According to SEM studies done by Shulien TM(1988),it consists of: Small particles of mineralized collagen matrix Inorganic tooth preparation Saliva Blood Bacteria

According to branstroem,the organic component consisted of coagulated proteins from collagen denatured by frictional heat of cutting.

Therefore optimal bonding can occur by:

A. Removal of smear layer by using etch and rinse adhesives.

B. Incorporation of smear layer into bonding layer by self-etch adhesives Complete removal of smear layer increases the dentin permeability by 90%.

STRESSES AT THE RESIN-DENTIN INTERFACE:

As composites polymerize,shrinkage occurs leading to stresses upto 7MPa.

When the composite is bonded only to one surface,stresses are relieved by flow from the unbended surface.

Davidson et al. postulated that minimum bond strength of 17-20 MPa to enamel and dentin is needed to resist contraction forces of resin composite materials.

In the present study, both the self-etching adhesives showed optimal bond strength values greater than 20 MPa for both uncontaminated and contaminated dentin.

DENTINE BONDING AGENTS It is defined as ”a thin layer of resin applied between conditioned dentin and

resin matrix of a composite.” The term dentine bonding agents is no longer relevant as current bond

agents bond to enamel and dentine.

Due to acid –etching ,micro leakage or loss of retention is not a hazard at the resin-enamel interface but its encountered at the resin-dentine interface.

Due to the differences in the composition of enamel and dentine,developing agents that will adhere to dentine was challenging due to the following reasons:

The high water content interferes with bonding. Presence of a smear layer on the dentine surface.

Therefore the bonding agent should be hydrophilic to displace the water ,permitting it to penetrate the porosities in dentine and react with the inorganic/organic components.

But, restorative resins are hydrophobic, therefore the bonding agent should contain both hydrophilic and hydrophobic components.

The hydrophilic part bonds with either calcium or collagen whereas the hydrophobic part bonds with the restorative resin.

CONDITIONING OF DENTIN

It is the etching of dentin surface with acids or calcium chelators. So, when acid is applied to it, dissolution of hydroxyapatite crystals

in intertubular dentin and outer surface of peritubular dentin occurs

Ultimately, the smear layer gets removed and collagen fibrils are exposed.

Materials used are: 37% phosphoric acid nitric acid citric acid EDTA(ethylene diamine tetra-acetic acid)

DURATION OF ETCHING ON DENTIN

Ideal duration is 15-20 seconds.

Increased duration: greater collapse of collagen due to

denaturation.Decreased monomer

infiltration.

Decreased duration: insufficient depth of etching.

PRIMING OF DENTIN

It is the process of applying primers to the etched/conditioned dentin surface to improve the diffusion of the adhesive resin into moist and demineralized dentin

Primer solution is a mixture of monomers with hydrophilic and hydrophobic components dissolved in organic solvent

Priming agents are HEMA(hydroxyethyl methacrylate) and 4-META(4-methacryloxyethyl trimellitae anhydride)

Acid washing / rinsingRemoves smear layerDissolves HA

Drying shrinks remainingCollagen polymer molecules

Rehydration / primingSwells collagen

Mechanism of dentine bonding

Monomer penetration

Mechanism of dentine bonding

Monomer polymerisationAnd collagen entanglement

CLASSIFICATION1. HISTORICAL STRATEGIES

FIRST GENERATION(1965) SECOND GENERATION(1978) THIRD GENERATION(1984)

2. CURRENT STRATEGIES ETCH & RINSE ADESIVESi. THREE STEP-ETCH &RINSE ADHESIVE(FOURTH GENERATION)ii. TWO STEP –ETCH & RINSE ADHESIVE(FIFTH GENERATION) SELF ETCH ADHESIVES TWO COMPONENT –SELF ETCH ADHESIVE(SIXTH GENERATION)o TWO STEP-TWO COMPONENT –SELF ETCH ADHESIVEo ONE STEP –TWO COMPONENT - SELF ETCH ADHESIVE SINGLE COMPONENT-ONE STEP-SELF ETCH ADHESIVE(SEVENTH GENERATION)

Current strategies

ETCH & RINSE ADESIVES SELF ETCH ADHESIVES

THREE STEP-ETCH &RINSE ADHESIVE TWO STEP –ETCH & RINSE ADHESIVE (FOURTH GENERATION) (FIFTH GENERATION)

TWO COMPONENT –SELF ETCH ADHESIVE SINGLE COMPONENT-ADHESIVE(SEVENTH

( SIXTH GENERATION ) ( SEVENTH GENERATION)

TWO STEP-TWO COMPONENT –SELF ETCH ADHESIVEONE STEP –TWO COMPONENT - SELF ETCH ADHESIVE

BASED ON MODERN ADHESION STRATEGY: Van Meerbek et al(2001) suggested a classification based on adhesion strategy.

TOTAL ETCH SELF ETCH

TWO STEP MILD THREE STEP ADHESIVES MODERATE INTERMEDIARY STRONG

TYPE OF ADHESIVE STEPS INVOLVED

ETCH AND RINSE ADHESIVES

THREE STEP ADHESIVE:FOURTH GENERATION

TWO STEP ADHESIVE:FIFTH GENERATION

SELF ETCH ADHESIVESTWO STEP ADHESIVE:SIXTH GENERATION

ONE STEP ADHESIVE:SEVENTH GENERATION

BASED ON THE TREATMENT OF SMEAR LAYER:

Smear layer modifying Smear layer removal Smear layer dissolving

DECADE BONDING AGENT FEATURES

1960s1970s

FIRST GENERATIONSECOND GENERATION

• DENTIN ETCHING WAS CONTRAINDICATED• ADHESION WAS TO SMEAR LAYER• WEAK BOND STRENGTH

1980s THIRD GENERATION • ETCHING ENAMEL & DENTIN• PRIMING-A SECOND STEP WAS DONE• BETTER BOND STRENGTH

EARLY 1990s FOURTH GENERATION • TOTAL ETCH CONCEPT WAS INTRODUCED• WET BONDING & HYBRID LAYER CONCEPTS

INTRODUCED• MULTIPLE TECHNIQUE SENSITIVE CLINICAL STEPS

MID 1990s FIFTH GENERATION • PRIMER & ADHESIVE COMBINED IN ONE BOTTLE• HIGHER BOND STRENGTHS

LATE 1990s SIXTH GENERATION • INTRODUCTION OF SELF-ETCHING PRIMERS• POST OPERATIVE SENSITIVITY WAS REDUCED• LOWER BOND STRENGTHS

EARLY 2000s SEVENTH GENERATION • ALL IN ONE/ONE STEP BOND CONCEPT INTRODUCED

• BOND STRENGTH LOWER THAN 4TH & 5TH GENERATIONS

4-META Methacryloxy ethyl trimellitic anhydride

NPG-GMA N-Phenylglycine glycidyl methacrylate

UDMA Urethane dimethacrylateTEGDMA Triethyleneglycol dimethacrylateMDPB 10-Methacryloyl oxydodecyl

pyridinium bromideMDP 10-Methacryloyl oxydecyl

dihydrogen phosphatePENTA Dipentaerythritol pentaacrylate

monophosphate

TYPE OF RESIN EXPANSIONBis-GMA Bisphenol A glycidyl methacrylateHEMA 2-hydroxyethyl methacrylate

Most products use a three-component system consisting of a conditioner, primer, and adhesive.

1. CONDITIONER (CLEANSER, ETCHANT) – weak organic acid (e.g., maleic acid), a low concentration of a stronger inorganic acid (e.g., phosphoric or nitric acid) a chelating agent (e.g., EDTA).

MAIN ACTIONS:

Alters or removes the smear layer.

demineralizes peritubular and intertubular dentin

exposes collagen fibrils --demineralizes up to a depth of 7.5 microns.

peritubular dentin is etched more deeply than the intertubular dentin increases dentin permeability.

PRIMER

bifunctional monomer in a volatile solvent such as acetone or alcohol

examples of HEMA (hydroxyethyl methacrylate), NMSA (N-methacryloyl-5- aminosalicylic acid), NPG (N-phenylglycine), PMDM (pyromellitic diethylmethacrylate), and 4-META (4- methacryloxyethyl trimellitate anhydride).

MAIN ACTIONS:

Links the hydrophilic dentin to the hydrophobic adhesive resin

Promotes infiltration of demineralized peritubular and intertubular dentin

increases wettability of the conditioned dentin surface

ADHESIVE (BONDING RESIN):

It is an unfilled or partially-filled resin; may contain some component of the primer (e.g., HEMA) in an attempt to promote increased bond strength.

MAIN ACTIONS:

Combines with the primer s monomers to form a resin-reinforced hybrid layer ( resin-dentin interdiffusion zone ) 1 to 5 microns thick.

Forms resin tags to seal the dentin tubules

FIRST GENERATION DENTIN BONDING AGENT

It consisted of surface active co-monomer NPG-GMA(N-phenylglycine glycidyl methacrylate)

MECHANISM OF ACTION:

This co-monomer could chelate with calcium on the tooth surface to generate chemical bonds of resin to calcium.

Example: Cervident(S S White burs,Lakewood)

Clinical result:

It had poor bond strength of 2-3MPa. Therefore when used to restore noncarious cervical lesions

without mechanical retention.

SECOND GENERATION DENTIN BONDING AGENT:

Introduced in 1978. They were based on phosphorous esters of methacrylate derivatives. MECHANISM OF ACTION:

Adhesion was by means of ionic interaction between the negatively charged phosphate groups & positively charged calcium in the smear layer.

Advantage: Bond strength was 3 times higher than the earlier ones. Disadvantage: Bond strength was still lower around 5-6 Mpa. Clinical failure due to the bonding instability in the wet oral environment &

their primary bonding to the smear layer and not the dentin.

ADVANTAGE: Bond strength was 3 times higher than the earlier ones.

DISADVANTAGE: Bond strength was still lower around 5-6 Mpa.

Clinical failure due to the bonding instability in the wet oral environment & their primary bonding to the smear layer and not the dentin.

EXAMPLES:

Clearfil Bond System(Kuraray,Japan) Scotchbond(3M ESPE) Bondlite(Kerr Corporation.CA) Prisma Universal Bond(Dentsply)

THIRD GENERATION BONDING AGENT:

It was a phosphate based material containing HEMA and a 10-carbon molecule 10-MDP(10-methacryloyloxy decyl dihydrogen phosphate)

These were introduced with Clearfil New Bond in 1984.


The concept of phosphoric acid etching of dentin before the application of a phosphate ester type of bonding agent was put forward by FUSAYAMA et al in 1979

Most of the other III generation bonding agents were designed not to remove the smear layer but only to modify it and therefore allow the penetration of acidic monomers like pheny-P or PENTA(dipentaerythritol penta-acrylate monophosphate)

EXAMPLES:

Clearfil New Bond(Kuraray) Scotchbond 2(3M ESPE)

COMPOSITION OF SOME III GENERATION DENTIN BONDING AGENTS

Adhesive system

Etchant Primer Adhesive Bond strength

Scotch Bond 2

2.5% maleic acid + 55% HEMA

HEMA Bis GMA 8.8 Mpa

TenureOxalate bonding system

aluminium oxalate in 2.5% nitric acid

NPG-GMA. BisGMA, TEGDMA

15 Mpa

This generation attempted to deal with both the smear layer and dentinal fluid, with following 2 approaches:i. Smear layer modification to improve its properties.ii. Remove s.layer without disturbing the smear plugs that occlude dentinal tubules.




CURRENT STRATEGIES FOR RESIN-DENTIN BONDING

1. ETCH AND RINSE ADHESIVE: The smear layer is considered to be an obstacle that must be removed to permit resin bonding to dentin.The next generation of dentin adhesives was introduced for use on acid –etched dentin.

The clinical technique involves simultaneous application of an acid to enamel & dentin.This was called as total-etch technique.

MECHANISM OF ACTION: application of acid to dentin results in complete or partial removal of smear layer and demineralization of dentin

Intertubular & peritubular dentin are demineralised,thus exposing collagen fibres & increasing microporosity of intertubular dentin

7.5µm of dentin is demineralised

Primer increases the free surface energy of dentin

Formation of resin tags and hybrid layer.

MOIST BONDING TECHNIQUE WITH ETCH AND RINSE ADHESIVE

• This was given by Kanca & Gwinett in 1990.• Excess water on the substrate that is the tooth surface is not indicated due to

the following reasons:

• Swelling of collagen occurs leading to the decrease in the space available for resin penetration

• Secondly, it dilutes the primer.• Thirdly, when priming is done in such conditions, phase separation of

hydrophobic and hydrophilic components occur leading to blister & globule formation at the resin-dentin interface.

• Thus these water blisters may compress when the restoration is under,forcing dentinal fluid towards pulp and causing post-operative sensitivity.

How wet or dry should the dentin be?

It should be hydrated that is clinically glistening and moist.

How to achieve it?

After etching and rinsingblot the excess water dry with a sponge & which shoulbe touched to the surface of water and not pressed against dentin.

Why is complete drying of dentinal surface contraindicated?

Vital dentin is moist.Therefore drying the dentin with air would cause collapse of dentinal collagen fibrils and thus leading to its shrinkage.

The interfibrillar space should be left open and hydrated for effective resin infiltration.

SEM of dentin that was acid etched with 37% phosphoric acid for 15s & rinsed with water and then briefly air dried.there is disappearance of spaces between collagen fibrils in top 1µm of demineralized zone that extends 5µm.although liquid monomers can permeate the tubules,it cannot pass through the spaces between collagen fibrils in intertubular dentin. TL-dentinal tubule.

SEM of dentin that was kept moist after rinsing off etchant.

The abundant intertubular porosity serves as a pathway for the penetration of the dentin adhesive . T, dentinal tubule.

Scanning electron micrograph of dentin collagen after acid etching with 35% phosphoric acid.Dentin was air dried.

The intertubular porosity disappeared due to collapse of collagen secondary to the evaporation of water.

THREE STEP:ETCH&RINSE ADHESIVES(FOURTH GENERATION)

IT CONSISTS OF

ETCHANT PRIMER ADHESIVE

Here three components came into being:

Phosphoric acid etchant(in gel form) Primer –it consisted of hydrophilic monomers in ethanol , acetone

or water. Primer is a bifunctional molecule having a hydrophilic and a

hydrophobic part.the former attaches to tooth whereas the latter attaches to composite resin.

Examples:HEMA NTG-GMA PENTA

Bonding agent:

It consists of unfilled or filled resin which may be BisGMA(Bisphenol glycidyl methacrylate),UDMA(urethane dimethacrylate) with TEGDMA & HEMA(2-hydroxyethyl methacrylate).

Thus after the application of primer and bonding agent to etched surface aids in their penetration into intertubular dentin to form a resin-dentin inter diffusion zone called HYBRID LAYER which was introduced by Nakabayashi in 1982.

ADVANTAGES:

Higher bond strength of 17-24MPa. They show reliable and consistent results. DISADVANTAGES:

Technique sensitive Time consuming procedure Over wetting or over drying of dentin may occur

• BRAND NAMES-

• All Bond 2 & All Bond 3• Optibond FL(Kerr Corporation)• Adper Scotchbond Multi-purpose(3M ESPE)

• BOND STRENGTH-• 17-30 Mpa.

CLINICAL STEPS INVOLVED:

STEP1:application of etchant gel(37% phosphoric acid) for 15 seconds .

STEP2:rinse the etchant thoroughly and blot dry the substrate(moist bonding technique)

STEP3:application of primer (bottle 1) on the substrate. STEP4:application of adhesive(bottle 2)on the tooth substrate. STEP5: light cure .

IV GENERATION DENTIN BONDING AGENT:

1st step: -Total etching(removal of smear layer)Leaving free minerals on surface-Rinse surface-Without drying of surface (residual water left)

2nd step : adding primer

3rd step:Adding adhesive resin & then composite

4th generation

Composite

Smear layer

Residual water Primer

Adhesive resin

WHAT IS HYBRID LAYER?

DEFINITION “The structure formed in the dental hard tissue by

demineralization of the surface and the sub-surface followed by infiltration of monomers & subsequent polymerization.”

( Nakabayashi,1982)

It is a hybrid combination of the above two. It is a process which creates a molecular level interfacebetween dentin and composite resin.

ZONES

TOP LAYER MIDDLE LAYER BASE

TOP LAYER :loosely arranged collagen fibrils directed towards adhesive resin.MIDDLE LAYER: collagen fibrils separated by electron lucent spaces(10-20nm) represent areas in which HA crystals have been replaced by resin due to hybridization.BASE : partially demineralized dentin.

TWO STEP :ETCH & RINSE ADHESIVES (FIFTH GENERATION)

This was developed to simplify the procedures involved in bonding.

Therefore , the primer and the bonding agent is present in a single bottle.

COMPONENTS:

ETCHANT GEL + PRIMER & ADHESIVE

It consists of

BOTTLE I BOTTLE II(Etchant+Primer) (Adhesive)

BONDING TO DENTIN USING A SELF-ETCH PRIMER

STEPS INVOLED ARE:

STEP1:application of etchant gel. STEP2:rinse the etchant thoroughly and blot dry the substrate

(moist bonding technique) STEP3:application of primer and adhesive (single bottle) STEP4:light cure .

BRAND NAMES: Prime & Bond NT(Dentsply) Adper single bond2 ExciTE(Ivoclar,Vivadent) One coat Bond XP Bond




SELF-ETCH ADHESIVES They are defined as “bonding systems which dissolve the smear

layer and create porosities in the underlying dental substrates without needing an extra conditioning agent(eg:phosphoric acid) to be applied in a single step.

(Quintessence International,vol(8), nov-dec2013) No separate etching step is needed.

ADVANTAGES:

Decrease in the number of steps Less technique sensitive.

The self-etching approach has been proposed in an effort to simplify the dentin/enamel bonding systems.

These materials combine tooth surface etching and priming steps into one single procedure.

The elimination of separate etching and rinsing steps simplified the bonding technique and has been responsible for the increased popularity of these systems in daily practice33

Based on the acidity of self-etch primers & adhesives, they are classified as:

Weak- pH-2 Medium pH-1.5 Strong pH≤1

Most commonly pH ranges from1.3-2.7

SELF-ETCH ADHESIVES

2 COMPONENT SELF-ETCH ADHESIVES 1 COMPONENT SELF-ETCH ADHESIVES(VI GENERATION) (VII GENERATION)

2 STEP & 2 COMPONENT I STEP BUT 2 COMPONENT

VI GENERATION BONDING AGENT1. 2 STEP : 2 COMPONENT SELF-ETCHING ADHESIVES: (NONRINSING CONDITIONERS OR SELF PRIMING ETCHANTS)


These acidic primers contain phosphonated resin molecule that performs two function:

Etching and priming of enamel Incorporating smear plugs into resin tags.

Steps involved are:

Application of bottle I(etchant +primer) After 10 s, application of bottle2 on tooth surface Light cure

BRAND NAMES:

Clearfil SE Bond(Kuraray,Japan) AdheSE(Ivoclar-Vivadent) Optibond Solo Plus Self-etch(Kerr Corp)

2. ONE STEP:TWO COMPONENT-SELF-ETCH ADHESIVE:

consists of- BottleI +Bottle II

Bottle I:conditioner +primer

Bottle II: adhesive resin Both have to be mixed prior to application on tooth surface.

BRAND NAMES: Xeno III(Dentsply) One up bond(Tokuyama) Prompt L bond(3M ESPE)

Self etching primers are acidic in nature, leading to its penetration along the aqueous channels found in the smear layer and widening them.

These offer a simpler clinical step when compared to the tota;l etch adhesive systems.

self etching primers contain acidic esters like HEMA,TEGDMA,MDP.

These primers are similar to those found in third generation dentin bonding systems, the only difference being that in the latter ones only milder acids were used leading to inability to etch beyond the smear layer.

In the sixth generation dentin bonding systems, acidic monomers like 4-MET and 10-MDP are used ,thus dissolving the smear layer.

When the concentration of acidic monomers increasd from 5-10% wt %(III generation dentin bonding agent) to 30-40% (VI generation dentin bonding agent) and dissolved in 30-40% HEMA, pH-1-2 was developed which aided in etching through smear layer.

ADVANTAGES

No etching needed, therefore possibility of over-etching or over-drying is removed Less technique sensitive. Self-etch adhesives are less likely to result in discrepancy between depth of

demineralization and depth of resin infiltration as both the processes are done simultaneously.

Less time consuming

DISADVANTAGES

Decreased shelf life Incompatible with chemical cure composites. Self-etch adhesives that are currently available do not etch as efficiently as

phosphoric acid, especially if the enamel has not been instrumented.

TYPE 2 ( TWO BOTTLE 1 STEP SYSTEM):

Liquid A contains primer. Liquid b contains a phosphoric acid modified resin. Both are mixed before application. Eg:Xeno 3(Dentsply),Adper-prompt L-pop(3M).

SEVENTH GENERATION(early 2000s): (SELF-ETCHING ADHESIVES)

Here the etchant, primer and the adhesive resin are combined into one bottle .

In vitro studies have shown that tooth-restoration interface created when using self etching adhesives do not eliminate the micro leakage and bacterial penetration, which can lead to secondary caries.

(Kakar S,Goswami M,nagar R.Dentin bonding agents-2 Recent trials. World J Dent2012;3(1);115-118.

ADVANTAGES OF VII GENERATION DENTIN BONDING AGENTS:

Lesser application time Decrease in errors with each step.

Examples are:

iBond(Heraeus kulzer) G bond(GC) XenoIV(Dentsply) Clearfil S3(Curare) XenoV+

XenoV+

iBond COMPONENT FUNCTION

UDMA(urethane dimethacrylate)

MATRIX COMPONENTETCHING & CONDITIONING OF ENAMEL & DENTINBONDING TO COLLAGEN VIA HYDROGEN BONDINGBONDING TO CALCIUM IONS VIA CHELATION COMPLEXES

4-META(4-methyloxyethyl trimellitic acid)

MATRIX COMPONENTCROSS-LINKING

WATER SOLVENT FOR MONOMERSPROVIDES WATER FOR ETCHING

CAMPHORQUINONE PHOTOINITIATORS

GLUTARALDEHYDE DISINFECTANT/DESENSITIZER

STABILIZERS

How is iBond applied?

1. Isolate tooth from saliva contamination during adhesive procedure

2. Clean the tooth prepation,removing all debris with water.3. Saturate the microbrush with iBond liquidfrom the bottle or

single dose vial.4. Apply 3 consecutive coats of iBond to enamel & dentin 5. Use gentle air pressure to remove excess solvent6. Cure for 20s with curing light7. Place the composite resin.

Both the hydrophilic and the hydrophobic components are mixed in this system.

Though this simplifies the clinical steps,it has following shortcomings:

Due to the complex nature of this solution,they are more prone to phase separation.

It forms droplets within the adhesive layer. This adhesive layer acts as a semi-permeable membrane permitting bi-

directional water currents.

Thus these bonding agents show much reduced bond strength when compared to the fourth,fifth,and sixth generation of bonding agents.

Advantages:

Most time efficient application procedure. Unidose application,which prevents cross-contamination. Simultaneous demineralisation & resin penetration. Less sensitivity to dentin wetness conditions.

Disadvantages:

Reduced shelf life. Less sealing capacity. Least bond strength. Incompatibility with auto/chemical curing composites.

ONE COAT 7 BOND. 7TH generation ,one component. Light cured self etching resin. High performance on any surface. Has a fast application in 35 seconds. On wet surfaces maintains uniform composition, producing

an effective bond.

DECADE BONDING AGENT FEATURES

1960s1970s

FIRST GENERATIONSECOND GENERATION

• DENTIN ETCHING WAS CONTRAINDICATED• ADHESION WAS TO SMEAR LAYER• WEAK BOND STRENGTH

1980s THIRD GENERATION • ETCHING ENAMEL & DENTIN• PRIMING-A SECOND STEP WAS DONE• BETTER BOND STRENGTH

EARLY 1990s FOURTH GENERATION • TOTAL ETCH CONCEPT WAS INTRODUCED• WET BONDING & HYBRID LAYER CONCEPTS

INTRODUCED• MULTIPLE TECHNIQUE SENSITIVE CLINICAL STEPS

MID 1990s FIFTH GENERATION • PRIMER & ADHESIVE COMBINED IN ONE BOTTLE• HIGHER BOND STRENGTHS

LATE 1990s SIXTH GENERATION • INTRODUCTION OF SELF-ETCHING PRIMERS• POST OPERATIVE SENSITIVITY WAS REDUCED• LOWER BOND STRENGTHS

EARLY 2000s SEVENTH GENERATION • ALL IN ONE/ONE STEP BOND CONCEPT INTRODUCED

• BOND STRENGTH LOWER THAN 4TH & 5TH GENERATIONS

RECENT ADVANCES : UNIVERSAL ADHESIVE

In 2012, the term “universal adhesive” has been given several definitions which are:

a)Can be used in total-etch, self-etch, and selective etch techniques;

b)Can be used with light-cure, self-cure, and dual-cure materials (without the separate activators);

c)Can be used for both direct and indirect substrates;d)Can bond to all dental substrates, such as dentin, enamel, metal,

ceramic, porcelain, and zirconia.

In November 2011, a new “ScotchBond Universal” was discovered.

Which needs a separate self-cure activator or a special amine-free dual-cure cement when in use with dual-cure or self-cure materials, hence not a truly “universal” adhesive.

In March 2012, a “All-Bond Universal” was discovered, which can be used in:

i.total-etch, self-etch and selective etch techniques, ii.can be used with any dual-cure, self-cure and light-

cure materials without the need of a separate activator, iii.can also be used for both direct and indirect

substrates, and can bond with any dental substrates.

All-Bond Universal is the first truly “universal adhesive”.

IS FUTURABOND DC-THE EIGTH GENERATION BONDING AGENT?

BASED ON THE TREATMENT OF SMEAR LAYER

SMEAR LAYER SMEAR LAYER SMEAR LAYER MODIFYING REMOVAL DISSOLVING

SMEAR LAYER

It was first suggested by Skinner in 1961.

Coined by Boyde in 1963.

0.5-2µm thick, granular

Smear plugs…1-10µm

WHY IS THE PRESENCE OF SMEAR LAYER DETRIMENTAL TO BONDING?

It is a weak attachment to dentin and is brittle

so it can be easily dislodged & prone to cohesive failure.

Therefore to overcome this, etch & rinse adhesive was developed.

SMEAR LAYER REMOVAL

DRAWBACK OF COMPLETE REMOVAL OF SMEAR LAYER:

Increases dentin permeability and flow of the dentinal fluid

Thus diluting the bonding agent Examples:

IV & V generation dentin bonding agents.

SMEAR LAYER MODIFYING

Examples:

II & III generation dentin bonding agents.

Incorporation of smear layer inhibited proper bonding and resulted in loss of bond strength.

SMEAR LAYER DISSOLVING

Self-etching adhesives dissolve and include the smear layer in the hybridization process.

BASED ON Ph

STRONG INTERMEDIARY MILD (<1) (1-2) (

Suresh Chandra et al.Comparative evaluation of self-etching primers sixth, fourth& fifth generation dentin bonding systems on carious and normal dentin.J Conser Dent2008;11(4):154-158

Study comparing bond strengths of total etch and self etch primer to carious affected and normal dentin.

Result- higher bond strength with normal dentin than caries affected dentin

Discussion: self etching primers needed highest mean shear load to fracture followed by V, IV generation bonding agents

Self etching primers superficially demineralize normal dentin by dissolving fibrils

Thus aiding in monomer infiltration.

Later the dentin is not washed therefore shrinkage of collagen is avoided.

According to the study the bond strength of self etching primers > fourth & fifth .

BONDING EFFICACY OF VI AND VII GENERATION BONDING AGENTS Manjula Nair, Joseph Paul et al. comparative evaluation of

bonding efficacy of VI and VII generation dentin bonding agents: an invitro study. J Conserv Dent 2014; 17(1):27-30.

Aim: to compare shear bond strength of VIth and VII dentin bonding agents.

Result: VII>VI DBA

Discussion:

VI generation bonding agents have less bond strength to dentin due to high acidity resulting in higher amount of demineralization.

But the VII generation dentin bonding agents (mild self etch adhesives) demineralise upto one µm only keeping residual hydroxyapatite still attached to collagen.

This 1µm is enough for micromechanical retention .

The retention of hydroxyapatite within the hybrid layer acts as receptor for chemical bonding.

Therefore this leads to higher bond strength with mild self etch adhesives.

So this is the cause for low bond strength with Adper SE Plus and Xeno III.

Though according to this study VII generation has higher adhesive property than VI, some studies contradict this.

Comparative evaluation of bonding efficacy of sixth,seventh and eighth generation bonding agents:an in vitro study. Paul Joseph et al.Int .Res. J Pharm.2013,4(9)

The aim of the study was to compare In-vitro the micro tensile bond strength of sixth generation (Clearfil SE Bond, Kuraray, Japan), seventh generation (Adper Easy One, 3 M ESPE, Germany) and eighth generation ((Futurabond DC, Voco, Germany) dentin bonding agents.

Results:

Futurabond DC, Voco, Germany>Clearfil SE Bond, Kuraray, Japan>Adper Easy One, 3 M ESPE, Germany)

Figure 3: Specimens obtained after hard tis sue microtome sectioning

Figure 4: Universal Testing Machine

CLINICAL APPLICATION OF SELF-ETCH BONDING SYSTEMS

Class V composite resin restoration using a self-etch two step system

a) Application of self-etch primer.

b) Application of adhesive.

c) Completed Class V composite resin restoration.

ANTERIOR COMPOSITE RESTORATIONS(CLASS III,IV)

POSTERIOR COMPOSITE RESIN RESTORATIONS

Core build up restoration with light cured composite resin using two-step self-etch bonding system.

a) After removal of defective amalgam restorationb) Application of self-etching primerc) Application of adhesived) Completed composite restoration in molars and the premolar

RESTORATION OF PRIMARY TEETH

Self-etch adhesives are an alternative to total etch systems. But ,the all in one adhesives should be used in combination with

compomers(polyalkenoic acid modified composite resins) & only in small to medium sized cavities with adequate macroretention.

(Quintessence International, vol(8),nov-dec2013)

CORE BUILD-UP WITH LIGHT-CURED COMPOSITE RESIN:

CORE BUILD UP WITH FLOWABLE COMPOSITE….DEFECTIVE AMALGAM RESTORATION…..TWO STEP SEA….FULL CERAMIC PARTIAL CROWN

EXAMPLE OF A SELF-ETCH TWO STEP BONDING SYSTEM INCLUDING ACTIVATOR(ADHESE/ADHESE DC ACTIVATOR) FOR COMBINATION WITH DUAL-CURED RESIN CEMENTS & CORE BUILD-UP COMPOSITES

In the combined post & core technique,the same dual cured composite resin is used for adhesive post cementation & as core material.a. try in of FRC post.b. application of self-etch primer-adhesive into root canal using endo-microbrush.c.adhesively cemented FRC post with composite core build-up.

a

A.

TREATMENT OF CERVICAL DENTIN HYPERSENSITIVITY

PREVENTION OF ROOT SURFACE CARIES

ADHESIVE CEMENTATION OF INDIRECT RESTORATION

MICROLEAKAGE

DEFINITION It is the passage of bacteria and their toxins between

restoration margins and tooth preparation walls


The presence of gaps at the resin-dentin interface leads to ingress of bacteria.

Therefore bonding the resin to a preparation with cavosurface margins in enamel is the best way to prevent microleakage.

Bacteria are able to survive & proliferate within the fluid filled marginal gaps, thus leading to secondary caries.

NANOLEAKAGE

It is the small porosities in the hybrid layer or at the transition between the hybrid layer and the dentin that allow the passage of particles of silver nitrate dye.

Penetration of ammoniacal silver nitrate results in two patterns:

Spotted pattern-in the hybrid layer of self-etch adhesives due to incomplete resin infiltration.

Reticular pattern-that occurs in the adhesive layer due to incomplete removal of water from the bonding area.

NANOLEAKAGE UNDER ELECTRON MICROSCOPE.

Spotted pattern in the hybrid layer formed by one-step self-etch adhesive Reticular pattern and water trees in adhesive layer formed by self etch adhesive

ANTIBACTERIAL PROPERTY OF DENTIN BONDING AGENTS

The development of adhesive systems have enabled variable cavity designs to preserve tooth structure and treatment of dental caries has shifted from the traditional method to that with downsized cavities.

Inspite of considerable improvement in the recent years , polymerization shrinkage & the resultant contraction gaps in tooth restoration interface continue to be a significant problem associated with composite resin restorations.

Thus cariogenic bacteria like Streptococcus mutans,Lactobacillus acidophilus,Lactobacillus casei and Streptococcus salivarius can invade along the microgaps and lead to secondary caries.

Therefore it is imperial to provide resin based materials with antibacterial activity.

Imazato et al have reported the antibacterial property of MDPB((methacryloyldodecylpyridinium bromide) which is monomer present in the bonding agent.

Also, acidic monomers like 10-MDP(10-methacryloyloxy decyl dihydrogen phosphate) due to its inherent acidity has antibacterial property.

Amin S,Shetty HK,Varma RK,Amin V,Nair PM.Comparative evaluation of antibacterial activity of total etch and self etch adhesive systems:An ex vitro study.J Conser Dent 2014 ;17:266-70

The purpose of the study was to compare the antibacterial activity of total-etch and self-etch adhesive systems against Sreptococcus mutans , Lactobacillus acidophilus , and Actinomyces viscosus through disk diffusion method .Of all the materials tested, the antibacterial effects may be related to the acidic nature of the adhesive systems.

Sampath PB, Hegde MN, Hegde P.Assessment of the antibacterial properties of newer dentin bonding agents. An in vitro study.Contemp Clin Dent 2011;2:165-9. The aim of this study was to evaluate and compare the

antibacterial activity on Streptococcus mutans using direct control test.The incorporation of antibacterial agents into dentin bonding agents may become an essential factor in inhibiting residual bacteria in the cavity.

Amin S,Shetty, HK,Varma et al. Comparative evaluation of antibacterial activity of total etch and self etch adhesive systems:An ex vitro study.J Conser Dent 2014 ;17:266-70

Aim: The aim of this ex vivo study was to compare the antibacterial activity of total-etch and self-etch adhesive systems against Streptococcus mutans, Lactobacillus acidophilus, and Actinomyces viscosus through disk diffusion method.

Materials and Methods: The antibacterial effects of Single Bond (SB) and Adper Prompt (AP) and aqueous solution of chlorhexidine 0.2% (positive control) were tested against standard strain of S. mutans, L. acidophilus, and A. viscosus using the disk diffusion method. The diameters of inhibition zones were measured in millimeters. Data was analyzed using Kruskal-Wallis test. Mann-Whitney U test was used for pairwise comparison.

Result: Of all the materials tested, AP(Adper Prompt) showed the maximum inhibitory action against S. mutans and L. acidophilus. Aqueous solution of chlorhexidine 0.2% showed the maximum inhibitory action against A. viscosus. Very minimal antibacterial effect was noted for SB(Single Bond).

Conclusion: The antibacterial effects observed for the tested different dentin bonding systems may be related to the acidic nature of the materials.

BIOCOMPATIBILITY

Biological testing of DBA is a delicate and complex process.

Unlike most dental materials, many dentin bonding systems are made up of more than one material e.g. cleanser , primer , bonding resin etc.

1st generation.• A very limited number of reports have been published on the

biocompatibility of the first generation. Which may be due to their inferior physical properties.

• Van Leeuwen et al showed no severe reactions even in extremely deep caries in their study.

2nd generation.

• Most studies are carried out using Scotch Bond.• It might have a adverse effect on pulp tissue when placed in

contact with vital tooth and proper pulpal protection was recommended.

3rd generation.

• Tests showed that the bonding material as well as the individual components were toxic.

International endodontic journal.Volume 44 number 9 september 2011.

*Aim *

To evaluate the genotoxicity of four different adhesives, Clearfil SE Bond,SL Bond, i Bond and Clearfil Protect Bond and the primers of Clearfil SE Bond and Clearfil Protect Bond.

*Results *

A significant increase (*P* < 0.001) compared to untreated controls in DNA damage was observed with 'Clearfil Protect Bond' and 'Clearfil SE Bond' primer in human lymphocytes at concentrations of 2.5 and 5.0 mg mL-1.

Clearfil Protect Bond and Clearfil SE Bond adhesives induced significant (*P* < 0.001) DNA damage only at the higher concentration of 5.0 mg mL-1. No significant increase in DNA damage was observed with SL Bond and i Bond.

Nosignificant DNA damage was observed with any dentine bonding agents at the

lower concentration of 1.25 mg mL-1.

*Conclusions * 'Clearfil Protect Bond' and 'Clearfil SE Bond' primers/adhesives increased DNA

damage in human peripheral lymphocytes in high doses.

CLINICAL FACTORS AFFECTING ADHESION

Flow of saliva and/or blood contamination Moisture contamination from handpiece or air water syringe Oil contamination of handpieces or air-water syringes Fluoride content of teeth Location and size of dentinal tubules Presence of plaque,calculus,extrinsic stains or debris Presence of bases or liners on prepared teeth Tooth dehydration Presence of residual intermediary cements

BONDING TO AMALGAM

Bonding of amalgam restoration to tooth is still a debatable topic.

The use of adhesive systems beneath amalgam restoration reduces or prevents microleakage, makes cavosurface angle less susceptible to demineralization when compared to varnish.

There is reduction in sensitivity and more conservative cavity preparation can be achieved when amalgam is bonded to tooth.

Staninec M (1989) showed that retention with amalgam bonding is equal to or superior to traditional means of mechanical retention.

Tig IA, Fodor O, Moldovan M et al (2005) noticed that at higher

magnification, teeth restored with unbonded amalgam had more spaces and artifacts at the amalgam-tooth structure interface when compared with those

Failures can occur at various levels:

between mineralised and demineralised dentin between demineralised dentin and bonding agent within layer of bonding agent between bonding agent and composite resin.

Affected by –

dentin wetness tooth flexure arch size of lesion substrate material factors

CONCLUSION

In today’s era, numerous improvements in materials and procedures have been made to meet the growing aesthetic demands of the patients.

In all the aesthetic restorations a bonding step is involved to ensure durability and reliability.

Thus the ideal bonding system should be biocompatible, bond perfectly to enamel and dentin, have sufficient strength to resist to failure as a result of masticatory forces, have mechanical properties close to those of tooth, and be resistant to degradation in oral environment and easy to use.

BIBLIOGRAPHY

STURDEVANT'S ART & SCIENCE OF DENTISTRY-4TH, 5TH & 6TH EDITION

PHILLIPS-SCIENCE OF DENTAL MATERIALS...11TH EDITION

TOOTH COLORED RESTORATIVES-PRINCIPLES AND TECHNIQUES..9TH EDITION

PICKARD'S MANUAL OF OPERATIVE DENTISTRY...8TH EDITION

TEXTBOOK OF OPERATIVE DENTISTRY-SUMEETHA SANDHU..1ST EDITION

MATERIALS USED IN DENTISTRY….S.MAHALAXMI

M.Bourbia, D.Ma, D.G Cvitkovitch et al.Cariogenic bacteria degrade dental resin composite and adhesives.J Dent Res 92(11):989-994,2013.

Bernd Haller et al.Quintessence International,1,nov-dec2013. .Arora R, Rao MH. Comparative evaluation of antibacterial effects of four

dentin bonding systems: An in vitro study.J Conserv Dent 2013;16:466-70 2.Taha MY, Al-Shakir NM, Al-Sabawi NA. Antibacterial effect of Dentin Bonding Agents:An in vitro study. Al-Rafidain Dent J. 2012;12(2):228-

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4.Hegde MN,Hegde P,Shetty V,Sampath P B.Assessment of antibacterial activity of self-etching dental adhesive systems:An in vitro study .J Conserv Dent 2008;11:150-3