University of sulaimany

prepared by Azheen Mohamad

References:Sturdevant's Art and science of operative

dentistry.2013 Mosby Elsevier . Sixth Editionchapter 4

Contemporary esthetic dentistry .2012 Mosby Elsevier. first Edition chapter8

Introduction of dental material. 2007 Richard van Noort . Third Edition chapter 1.10

INTRODUCTION

The introduction of adhesive technique ,the increasing demand for restorative and non-restorative esthetic treatment ,and the ubiquity of fluoride have combined to transform the practice of operative dentistry .the classic concepts of tooth preparation were advocated in early 1900s,but these have changed drastically .this transformation in philosophy has resulted in a more conservative approach to tooth preparation ,with a regard to not only the basic concepts of retention form but also the resistance form of the remaining tooth

structure.

Bonding techniques allow more conservative tooth preparations ,less reliance on micromechanical retention , and less removal of unsupported enamel.Two example of new , adhesive restorative procedures that spring to mind readily are resin-bonded bridge and porcelain veneers . these procedures have been possible because of our improved knowledge and understanding of the surface characteristics of enamel and dentin , and of the requirements that need to be satisfied in order to obtain good bonds to them.

DEFINITION

Adhesion can be defined as the force that binds two dissimilar materials together when they are brought in to intimate contact . Bonding agents can be defined as material of low viscosity, when applied on the tooth surface and forms thin film after setting. This thin film strongly bonded to tooth surface , on which the viscous composite restorative resin is applied. this sets forming an integrated resin restoration.

BRIFE HISTORY OF CLINICAL DEVELOPMENT AND EVOLATION OF THE PROCEDURE

The "generation" definitions help to identify the chemistries involved , the strengths of the dental bond

,and the ease of use for the practitioner. Ultimately this type of classification benefit the dentist and patient by

simplifying the clinicians chair side choice.

•GENERATION OF DENTAL ADHESIVES

*First Generation(1970s)

- 1 to 3 MPa adhesion to dentin.- Bonded well to enamel through resin tags in to enamel.- 50% failure at 6 months.- Examples: N-phenyl glycine and glycidyl methacrylate, NPG-GMA.

*Second generation(early 1980s)

2 to 8 MPa adhesion to dentin.Phosphate –ester bonding agents.Bonded to smear layer(organic debris).Weak ionic bond to calcium undergoes hydrolysis.Examples : scotch bond , dentin adhesit , bondlite

*Third generation(late 1980s)

- 8 to 15 MPa adhesion to dentin. - Etching of dentin removed or modified smear layer.- Spaghetti-like projections of resin into dentinal tubules.- Examples : sotch bond 2,Gluma,Tenure,XR Bond.

*Fourth generation (early 1990s)

-17 to 25 MPa adhesion to dentin.-Total etch : complete removal of smear layer and collapse of exposed collagen fibers.-Bonds to enamel ,"moist“ dentin ,metal , porcelain.-Multibottle , multistep.-Examples: scotchbond MP , Imperva , gluma 2000,syntac,Allbond 2,permagen.

*Fifth generation(mid-1990s)

-20 to 25MPa adhesion to dentin.-Single component in a single bottle.-Bonds to enamel ,moist dentin ,metal , porcelain.-Etching required.-Moist surface required (wet or moist bonding).

-Examples' : pulpdent UNO-DUO , prime and Bond NT , Gluma comfort bond , singleBond , one step, Bond 1,Excite.

*Sixth generation (2000)

-17 to 22 MPa adhesion to dentin.-No separate etching step.-Multibottle , multistep.-Bonds to dentin , metal , porcelain.-High incidence of enamel interface fructures.-Example : Adh e SE, SE Bond , Tyrian ,Prompt L-Pop , Xeno III.

*Seventh generation(2003)

-20 to 30+ MPa adhesion to dentin.-Single bottle- no mixing.-Bonds to enamel, dentin , porcelain , metal.-Moisture independent.-No technique sensitivity.-Examples: BeatiBond , Bond force.-the most innovation of seventh-generation adhesives is the added advantage of moisture independence . the acidbase reaction of the seventh-

STEPS OF GENERATION

Fourth generation

Fourth generation

GENERATION OF DENTAL ADHESIVES

Seventh generatinseventh generation bonding agents are ideal forbonding indirect restorations, and for direct compositeresin (where bonding is mandatory regardless of thematerial and technique being used).

The most innovation of seventh-generation adhesiveon the dentin surface is that of an acid acting on anorganic base. this chemical reaction generates organicsalt and water . Thus , seventh-generation adhesiveprocedures effectively create their own moisture.

They can be applied to a "moist surface"(however that may be defined)or a dried surface(much more easily described).Because seventh generation systems are supplied in a single premixed container and require a single application step , and no moist or wet surface , few mistakes are possible and there is no technique sensitivity. The process is simple ; apply the adhesive

to the tooth surface , agitate or scrub if required , and then, after a brief wait ,simply air dry the surface . once the bonded surface is dry(no longer moist with bonding),it is light cured . there are no separate etching or conditioning steps , and the smear layer is not removed . there has been virtually no post –operative sensitivity reported with seventh-generation bonding agents . the hybrid layer is created by the chemistry of the adhesive . the number of bottles is one ; the number of steps is one . there is no post-operative sensitivity, and dentin bonds of 23 to 30 MPa and higher have been reported.

Seventh generatin

Total-Etch Procedure

In total-etch systems the finalized cavity preparation is treatedwith phosphoric acid gel, which is applied and left in place for15 seconds. The acid gel is then vigorously washed away, followedby air-dispersal drying for 2 seconds. An alternate methodfor removing the water consists of wiping the preparation witha dry cotton pledget. When the wiping is finished, the surfaceshould exhibit a slight sheen.

Once the etching process has been completed, the dentinprimer is applied. An applicator is saturated with the primer andthen rubbed or swabbed onto the surface of the preparationcontinuously for 15 seconds. After air dispersing, the processmay be repeated if called for in the manufacturer instructions,then the surface of the preparation is light cured for 15 seconds.The preparation surface is now hybridized and ready for application of the composite resin restorative material.

Total-Etch Procedure and Self-Etch Dentinal Adhesive

The greatest advantage of the self-etching dentin bonding system is a substantial reduction in the observed post-operative sensitivity.

However, there are a number of disadvantages, with the

primary one being the incompatibility between the dentin

bonding agent and dual- and self-cured resins, including luting agents and core materials.

Advantages and Disadvantages of Self-Etch Dentinal Adhesive

MECHANISM OF ADHESION

Four different mechanisms of adhesion have been described , as follows:-1-Mechanical adhesion:-interlocking of the adhesive with irregularities in the surface of the substrate , or adhered.

2-Adsorption adhesion:-chemical bonding between the adhesive and the adhered ; the involved may be primary( ionic and forces covalent)or secondary(hydrogen bonds , dipole interaction , or van der Waals ) valence forces.

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 adhesion:-an electrical double layer at the interface of a metal with a polymer that is part of the total bonding mechanism.

In dentistry , bonding of resin-based materials to tooth structure is a result of four possible mechanisms , as follows:_

1-Mechanical:-penetration of resin and formation of resin tags within the tooth surface.

2-Adsorption:-chemical bonding to the inorganic component(hydroxyapatite)or organic components (mainly type I collagen) of tooth structure.

3-Diffusion:-precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically.

4-A combination of the previous three mechanisms.

For good adhesion ,close contact must exist between the adhesive and the substrate(enamel or dentine).The surface tension of the adhesive must be lower than the surface energy of the substrate.

Failure of adhesive joints occur in three locations , which are generally combined when an actual failure occurs:-

1-Cohesive failure in substrate.

2-Cohesive failure within the adhesive.

3-Adhesive failure, or failure at the interface of substrate and adhesive.

A major problem in bonding resins to tooth structure is that all methacrylate-based dental resin shrink during free-radical addition polymerization . Dental adhesives must provide a strong initial bond to resist the stress of resin shrinkage.

INDICATIONS FOR CLINICAL APPLICATION:-

-All direct composite resin restoration , both anterior and posterior.-For bonding indirect composite resin inlays , onlays and veneers.-For bonding indirect ceramic veneers , inlays and onlays.-Bonded amalgam restorations.-Management of dentin hypersensitivity.-Luting post and core restorations.-For the repair of fractured porcelain , amalgam and resin restorations.

Indirect restoration

-For pit and fissure sealants.-Bond orthodontic brackets. -Bond periodontal splintand conservative tooth replacement prosthesis( composite , amalgam , ceramic , or ceramometal ).-Bond fractured fragments of anterior teeth.

BOND FRUCTURE FRAGMENT (a) Pre-operative view, labial (b) pre-operative view, occlusal (c) fractured fragment (d) teeth isolated with a rubber dam (e) pulp protection with Dycal and GIC (f) recess created in fractured fragment using round bur (g) Mylar

strip placed interproximally before rebonding (h) post-operative view, labial

CONTRA INDICATIONS:-

-There are no contraindications to adhesions in clinical

dentistry .There have been no reports of allergy to materials. Restorations that failed have done so only when the adhesion was improperly implemented , or early in the adhesive era when bond strengths were simply too weak. It is very important that adhesion be accomplished rigorously, following the instructions and requirements of the materials involved.

ADVANTAGE OF BONDING TECHNIQUE:-

-Adhesion of composite resin restorations to enamel and dentin.-Minimizes removal of sound tooth structure.-Management of dentin hypersensivity .-Adhesion reduce microleakage at tooth restoration interface. -Adhesion expands the range of esthetic possibilities.

-Bonding of porcelain restorations , e.g.: porcelain inlays , onlays and veneers.-Reinforces weakened tooth structure.-Reduction in marginal staining.

IDEAL REQUIRMENTS

-Biocompatible .-Non toxic , non irritant , non poisonous.-Low film thickness , low viscosity.-Form strong permanent bond.-Good dimensional stability.-Low thermal conductivity.-Good shelf life.-Prevent micro leakage.

CONDITIONING OF DENTIN

*Conditioning of dentin is defined as an alteration of dentin surface including the smear layer with the objective of producing a substrate capable of micromechanical and possibly chemical bonding to dentin adhesive.

1*Acid conditioners :-several acids like phosphoric acid , maleic acid citric acid , nitric acid , oxalic acid and hydrochloric acid are used.-commonly used 37 percent phosphoric acid.-not only remove smear layer but also exposes microporous collagen network in to which monomer penetrates.

Exposes microporous collagen network

in to which monomer penetrates

-usually it forms exposed collagen fibrils which are covered with an micro porous layer , a combination of denatured collagen fibers and the collapsed residual collagen layer.

2* Chelators :- remove the smear layer without decalcification or significant physical changes on underlying dentin substrate.Best known chelator conditioner is EDTA

3*Thermal conditioning :-recent trend is to use lasers in conditioning teeth ,these may serves as

potential alternative to acid for conditioning of dentin.it is speculated that the laser cause recrystalization of dentin resulting in fugi form appearance that contributes to increased microrelation or possible chemical adhesion of a restorative material to the tooth structure.

PRIMIMING OF DENTIN

-Primers are agents which contain monomers having ahydrophylic end with affinitly for exposed collagen fibrils and hydrophilic end with affinitly for adhesive resin.-Commonly used primers have HEMA and 4- META monomers , dissolved in organic solvents.-Primers are used to increase diffusion of resin in to moist and demineralized dentin and thus optimal micromechanical bonding for optimal penetration of primer in to demineralized dentin , it should be applied in multiple coats .-It is preferred to keep the dentin surface moist , otherwise collagen fibers get collapsed in dry condition resisting the entry for primer and adhesive resin.

HYBRID LAYER

-This is zone where the adhesive resin of the dentin bonding agent micromechanically interlocks within the inter tubular dentin and surrounding collagen fibers.

-Hybrid layer is formed in following manner:-

Hybrid layer is formed in following manner:_

1-etching removes smear layer and exposes collagen fibers.It also removes hydroxyl apetite with in the intertubular dentin.

2-primers penetrate the collagen network.

3-adhesive resins along with the primers form resin microtags within the intertubular dentin.

-Hybrid layer also called resin-dentin Interpenetration/ interdiffusion zone.

ROLES OF SMEAR LAYER

-Whenever tooth surface is cut with hand or rotary instruments , it causes small particles of the cut tooth surface to the tooth producing the smear layer.

-Smear layer is defined as any debris , calcific in nature, produced by reduction or instrumentation of enamel , of dentin or cementum.

-It has two phases:-

A*Solid phase:-made up of cutting debris primarily denaturated collagen and mineral.

B*Liquid phases:-made up of tortuous fluid filled channels around the cutting debris.-Bacteria entrapped in smear layer can survive and multiply beneath the restoration.-Retention of smear layer:-1-Lowers dentin permeability.2-Prevent decrease in bond strength.3-Lowers effect of pulpal pressure on bond strength.-Recent generations adhesives involves modification of smear layer to facilitate bonding.

ENAMEL BONDING

-To bond to enamel ,it is very important to focus on the mineral component (hydroxyapatite)of enamel.-Buonocore,1955Was the first to reveal the adhesion of acrylic resin to acid etched enamel.Used 85 percent phosphoric acid for etching.

-Silverstone revealed that the optimum concentration of phosphoric acid should range between 30 to 40 percent to get a satisfactory adhesion the enamel.

-If concentration is greater than 50 percent -monocalcium phosphate monohydrate may get precipitated.-Concentrations lower than 30 percent -dicalcium phosphate monohydrate is precipitated which interferes with adhesion.-Percentage of etchants used %35-Use of lower concentration of phosphoric acid and reduced etching time has shown to give an adequate etch of the enamel while avoiding excessive demineralization of the dentine.

DENTIN BONDING

The classic concept of operative dentistry were challenged in the 1980s and 1990s by the introduction of new adhesive techniques, first for enamel and then for dentine . nevertheless , adhesion to dentine remains difficult . adhesive materials can interact with dentine in different ways-mechanically , chemically , or both. The importance of micromechanical bonding , similar to what occurs in enamel bonding , has become accepted.

Dentine adhesion relies primarily on the penetration of adhesive monomers in to network of collagen fibers left exposed by acid etching. However ,for adhesive materials that do not require etching ,such as glass ionomer cements and some phosphate-based self etch adhesives , chemical bonding between polycarboxylic or phosphate monomers and hydroxyapatite has been shown to be an important part of the bonding mechanism.

CRITICAL STEPS IN BONDING

-Proper isolation:-by using rubber dam , saliva contamination can block mechanical bonding.-Pulp protection:-by using calcium hydroxide liner.-Acid etching of enamel and dentin:-by using 37% phosphoric acid for 15 second then wash.-Dentin surface must be kept moist . if dentin is over dried it would result in collapse of exposed collagen fibers.-Careful application and curing of bonding agents.-Placing the composite resin.

FACTOR AFFECTING ADHESION

1.Wetting -Wetting is an expression of the attractive force between molecules of adhesive and adherent. In other words, it is the process of obtaining molecular attraction.-Wetting ability of an adhesive depends up on two factors :_A-Cleanliness of the adherend :- cleaner surface , greater adhesion.

B-Surface energy of the adherend:-more surface energy, greater adhesion.

2.Water

-The higher the water content ,the poorer is the adhesion.-Water can react with both materials by the high polar group and hydrogen bond which can hamper the adhesion.3.Contact angle

-Refers to the angle formed between the surface of a liquid drop and its adherent surface.-The stronger the attraction of the adhesive for the adherent ,the smaller will be the contact angle. The zero contact angle is the best to obtain wetting.

FACTOR AFFECTING ADHESION

4.Surface contamination

-The substrate surface should be clean as contamination prevents the adhesion. Adhesive should be able to fill their regularities making the surface smooth allowing proper or intimate contact.

5.Acid application time : Ideally 10 seconds

-Studies show that enamel should not be etches for more than 15 to 20 seconds.

PROBLEMS IN BONDING TO DENTIN

-Dentin is a dynamic tissue that changes due to ageing , caries or restorative procedures.

-Dentinal tubules are filled with dentinal fluid which constantly flow outward from the pulp.

-Dentine has considerable amount of organic material and water.-Dentine is close to pulp , so different chemical used for bonding and etching may irritate the pulp.