PRESENTED BY:

DR.DEEKSHA SHETTY

UNDER THE GUIDANCE OF :

DR.MANOJ SHETTY

INTRODUCTIONINTRODUCTION

Adhesion of restorative material to mineralized tooth

structure has been a goal of dental researchers for many

years.

Accomplishing such a bond has many principle

advantages like:

1.Retention of restoration,

2.Conservation of tooth structure,

3.Elimination of marginal microleakage,

4.Reinforcement of remaining tooth structure

5. Increasing the clinical life time of restorations.

Due to lack of adhesion between dental restorative resins

and tooth structure, microleakage of salivary components

and bacteria occur, which may lead to:

i. Marginal staining.

ii. Breakdown at the margins of the restoration interface.

iii.Secondary caries.

iv.Post operative sensitivity.

v. Pulp pathology.

TERMINOLOGIESTERMINOLOGIES

Acid-Etching-Acid-Etching- Process of roughening a solid surface by exposing it to an acid and thoroughly rinsing the residue to promote micromechanical bonding of an adhesive to the surface. Adhesion-Adhesion- A molecular or atomic attraction between two contacting surfaces promoted by the interfacial force of attraction between the molecules or atoms of two different species; adhesion may occur as physical adhesion, chemical adhesion, mechanical adhesion (structural interlocking) or a combination of all types.Adhesive-Adhesive- Substance that promotes adhesion of one substance or material to another.Adherend-Adherend- A material substrate that is bonded to another material by means of an adhesive.

Adhesive Bonding-Adhesive Bonding- Process of joining two materials by means

of an adhesive agent that solidifies during the bonding

process.

Dentin Bonding-Dentin Bonding- The process of bonding a resin to

conditioned dentin.

Dentin Bonding Agent-Dentin Bonding Agent- A thin layer of resin between

conditioned dentin and the resin matrix of a composite.

Dentin Conditioner-Dentin Conditioner- An acidic agent that dissolves the

inorganic structure in dentin, resulting in a collagen mesh that

allows infiltration of an adhesive resin.

Hybrid Layer-Hybrid Layer- An intermediate layer of resin, collagen, and

dentin produced by acid etching of dentin and resin infiltration

into the conditioned dentin.

Microleakage-Microleakage- Flow of oral fluid and bacteria into the microscopic gap between a prepared tooth surface and a restorative material.Primer-Primer- A hydrophilic, low viscosity resin that promotes bonding to a substrate, such as dentin. Resin Tag-Resin Tag- Extension of resin that has penetrated into etched enamel or dentin.

Smear Layer-Smear Layer- Poorly adherent layer of ground dentin

produced by cutting a dentin surface.

Wettability-Wettability-Relative affinity of a liquid for the surface of a solid.

Wetting- Wetting- Relative interfacial tension between a liquid & the solid substrate that results in a contact angle less than 900.

An adhesive joint is the result of interactions of a layer of

intermediate material (adhesive) with two surfaces (adherends)

producing two adhesive interfaces. .

CLASSIFICATIONCLASSIFICATION The interactions which occur at the interface are classified generally in terms of types of atomic interactions which may be involved. Adhesion is classified as: 1. Physical.

2. Chemical.3. Mechanical. Micro

Macro

Physical bondingPhysical bonding involves Vander waals or other electrostatic

interactions that are relatively weak. It may be the only type of

bonding if surfaces are smooth and chemically dissimilar.

Chemical bondingChemical bonding involves bonds between atoms formed

across the interface from the adhesive to the adherend.

Because the materials are often dissimilar, the extent to which

this bonding is possible is limited and the overall contribution

to bond strength is normally quite low.

Mechanical bondingMechanical bonding is the result of an interface that involves

undercuts and other irregularities that produce interlocking of

the materials.

MECHANISMS MECHANISMS OFOF

ADHESION ADHESION

The oral hard tissues and their environment are complex. In general, the following factors can play major or minor roles in achieving adhe sive bonds:

1. Wetting

2. Interpenetration (formation of a hybrid zone)

3. Micromechanical interlocking

4. Chemical bonding

Wetting is essential for the success of all other adhesion mechanisms. An

adhe sive cannot form micro mechanical interlocks, chemical bonds, or

interpenetrating networks with a surface unless it can intimately contact

the surface, spread onto the surface, and fill microscopic and

submicroscopic irregularities. These conditions are achieved if the

adhesive wets the surface. Although wetting is an essential require ment

for intraoral adhesion, it is not sufficient to ensure durable bonding. For

example, one can readily form strong, durable bonds between sheets of

plate glass by using an epoxy resin. This combination involves no

primary chemical bonding between adhesive and adherend, no micro

mechanical interlocking, and no interpenetration. However, one cannot

expect the same result when tooth structure is the substrate.

Wetting of tooth structure alone does not achieve lasting

intraoral bonds because the principal substrates (adherends),

enamel and dentin, are hydrated, hydrophilic, and permeable

to water. Such adherends require a hydrophilic, hydrolytically

stable adhesive for wetting to occur. However, even if the

surface is initially dried before adhesive application, diffusion

results in one or more monolayers of water that strongly bond

to both the tissue and the adhesive. Unfortunately, water has a

very low shear strength, so the net shear bond strength

between two perfectly flat surfaces is insignificant.

ACIDACIDETCHINGETCHING

Perhaps the most significant discovery in dentistry during the last three

decades is that of Dr. Michael Buonocore in 1955Dr. Michael Buonocore in 1955. Working in New

York, he discovered that the bonding strength between human enamel

and acrylic resin could be tremendously enhanced by exposing the tooth

to a mild acidic solution before applying resin to the enamel surface.

. He etched the enamel surface with acids and then placed an acrylic

restorative material on the micromechanically roughened surface. The

monomers of the acrylic resin wet the etched surface, flowed into the

etch pits, and generated retentive resin tags. One of the surface

conditioning agents he used, phosphoric acid, is still the most widely

used etchant today for bonding to enamel and dentin.

In his first experiments Dr. BuonocoreDr. Buonocore was actually following

the lead of industry. By the mid-1950s it was already

commonplace to pre-treat surfaces, such as metals, with

phosphoric acid before applying resins or paint. In fact, his

original trial used 85% phosphoric acid, which had by then

become the industrial standard.

Almost every case of dental adhesion is based primarily on

mechanical bonding. Chemical bonding may occur as well, but

generally makes only a small contribution to the overall bond

strength. Common method for producing surface roughness

for better mechanical bonding is to grind or etch the surface.

Grinding produces gross mechanical roughness but leaves a

smear layer of hydroxyapatite crystals and denatured collagen

that is approximately 1 to 3 microns thick.

Acid etching or conditioning dissolves this

layer and produces microscopic relief with

undercuts on the surface to create an opportunity

for mechanical bonding. If the interlocked adhesive

and adherend with dimensions less than about 10

microns, then the situation is described as micro-

mechanical bonding.

It is fortunate that there is a difference

between the resistance of the enamel prisms and

the inter-prismatic enamel to acidic attack. Thus, as

Dr. BuonocoreDr. Buonocore discovered, placing a weak acidic

solution on the enamel surface causes a differential

etch rate between these two areas; this results in

an irregular and pitted surface.

Type II

Type I & Type II

Acid etching of enamel is one of the most effective ways to improve

mechanical bonding and to ensure sealed interfacial gaps. This procedure

has markedly expanded the use of resin-based restorative materials

because it provides a strong bond between resin and enamel, forming the

basis for many innovative dental pro cedures, such as resin-bonded metal

retainers, porcelain laminate veneers, and bonded orthodontic brackets.

It has also solved, to a great extent, all of the previous problems that

plagued resin-based restorations, namely, marginal staining caused by

interfacial leakage

Phosphoric acid at a concentration between 30% and 50%, typically

37%, is the preferred etching agent. Concentrations greater than 50%

result in the deposi tion of an adherent layer of monocalcium phosphate

monohydrate on the etched surface, which inhibits further dissolution.

Although aqueous fluids available

as an aqueous gel to allow precise placement over a specific area. These

gels are often made by adding colloidal silica (the same fine par ticles

used in microfilled composites) or polymer beads to the acid. Brushes

are used to place the acidic gel material, or the acid may be supplied in a

disposable syringe from which it can be expressed onto the enamel and

dentin. During placement, it is important to be aware of the risk for air

bubbles that may be introduced at the inter face. If these voids remain,

these regions will not be etched. The optimal application time for the

acid is generally believed to be 60 to 90 seconds.

When properly etched, the tooth should exhibit a dull, frosted, matte dull, frosted, matte

finishfinish. Under-etching results in a tooth that retains its glossgloss. Over-

etching results in a surface chalkychalky in appearance due to the formation of

an insoluble salt during the etching process.

The popular current choice is orthophosphoric acidorthophosphoric acid, which is

commercially available in concentrations ranging from approximately

from 30% to 65%.

This surface must be kept clean and dry until the resin is placed to

form a sound mechanical bond. Although enamel etching raises the

sur face energy of the enamel, contamination can readily reduce the

energy level of the etched surface. Reducing the surface energy, in

turn, makes it more difficult to wet the surface with a bonding resin

that may have a higher surface energy than that of the contaminated

surface. Thus even momentary contact with saliva or blood can

prevent effective resin tag formation and severely reduce the bond

strength. Another potential contaminant is oil that is released from the

air compressor and trans ported along the airlines to the air-water

syringe. If contamination occurs, the con taminant should be removed,

and the enamel should be etched again for 10 see.

FACTORS RELATED TO THE ADHERENDFACTORS RELATED TO THE ADHEREND

Physiochemical properties of Enamel and the effect Physiochemical properties of Enamel and the effect of acid etching:of acid etching:# Inorganic content : 96-97 % by weight # Water : 4%# Organic Content : 1% Collagen

Bonding to enamel is poor because organic pellicle covers the enamel surface.Etching raises the critical surface tension of enamel.The creation of such a high energy surface together with the increase in bonding area and surface roughness make the bonding of hydrophobic resins possible.

Physiochemical properties of dentin that Physiochemical properties of dentin that

complicate dentin adhesioncomplicate dentin adhesion

The ultrastructure and chemical composition of dentin does not permit micromechanical interlocking as occur with the enamel.

Dentin consists 70% hydroxyapatite, 18% 70% hydroxyapatite, 18% organic material (Collagen) and 12% water.organic material (Collagen) and 12% water.

Etching of dentin leaves a sponge-like structure with little compression, tensile or shear strength (Standford 1985 ) .

Dentinal canals at the external surface of roots or

near dentinoenamel junction have small

diameters. Dentinal canals closer to the dental

pulp become larger, older dentin has small

dentinal canals. Dentinal bonding agents use

some form of mechanical attachment into dentinal

canals. In small canals attachment is less and in

larger canals attachment is enhanced.

DentinalDentinal smear layer and dentin permeabilitysmear layer and dentin permeability

When the tooth structure is worked with rotary tools, cutting debris is smeared over the enamel and dentin surfaces. (Pashley 1984 and 1988).EDTA EDTA was found to be the most potent conditioner in removing the smear layer and opening up the orifices of the dentinal tubules. Other Conditioners include:- citric acid, poly acrylic citric acid, poly acrylic

acid, Lactic acid, Phosphoric acid.acid, Lactic acid, Phosphoric acid. (In vitro study).The depth of the smear layer depends on the type of instruments and the condition of irrigation employed normally varying from 1 to 5 mm (Elick and others 1970 Pashley 1984).

DENTIN BONDING AGENTSDENTIN BONDING AGENTSThe intermediate link between dentin and/or enamel and unfilled resin is

known as dentinal bonding or dentin bonding. The relatively thin resin

layer is referred to as a dentin bonding agent. An important breakthrough in dentin bonding occurred when Fusayama et al (1979) used 37% phosphoric acid to etch both enamel and dentin. This study demonstrated that the procedure did not increase pulp damage and that it did improve the restoration retention substantially. A subsequent study by Nakabayashi et al (1982) revealed that hydrophilic resins infiltrated a surface layer of collagen fibers in demineralized dentin to form a hybrid layer consisting of resin-infiltrateddentin. Adhesion by Hybrid Zone/Layer:Adhesion by Hybrid Zone/Layer:When the primer is applied to a properly treated dentin surface, they form ‘micro-tags’‘micro-tags’ into the dentin substrate, there by creating a zone of primer/resin infiltrated dentinzone of primer/resin infiltrated dentin at the interface. Eg: All Bond IIAll Bond II,, Scotch bond multipurposeScotch bond multipurpose, prime and Bondprime and Bond.

Ideally, dentin adhesives should be hydrophilic to wet the surface of

slightly moist, conditioned dentin. Because most matrix resins of

composites are hydropho bic, the bonding agent should contain

hydrophilic groups to interact with the moist dentin surface and

hydrophobic groups to ensure bonding to the restorative resin. The key

to adhesion is to develop hydrophilic monomers that can easily infiltrate

the collagen mesh produced by etching dentin with an acid often called a

conditioner.

CLASSIFICATION OF CLASSIFICATION OF DENTIN BONDING DENTIN BONDING

SYSTEMSSYSTEMS

Dentin bonding agents are often

grouped into generationsgenerations, based on their

bonding procedures and the relative bond

strength they could achieve.

First GenerationFirst Generation “bonding” materials were far

more useful for enamel than dentin. These

bonding agents were designed for ionic bonding

to hydroxyapite or for covalent bonding

(hydrogen bonding) to collagen. These materials

tended to be hydrophobic. With bond strength of

2 Mpa – 6 Mpa2 Mpa – 6 Mpa, they had a tendency to debond

within a short time. The bond strength, was

limited by strength of the bond of the smear layer

to the dentin.

Materials:Materials: A surface active comonomers, N-phenylglycine glycidyl methacrylate (Bowen, 1965) was developed that acted as a primer or adhesion promoter between enamel / dentin and resin materials by chelating with surface calcium. E.g. Cervident.

Disadvantages Disadvantages 1. Poor bond to dentin familiar amalgam type retentive cavities.

2. Used only for small class III and class V restorations where there was adequate enamel in which to bond.

3. Post operative sensitivity in attempted posterior occlusal restorations.

Second Generation Dentin Bonding SystemsSecond Generation Dentin Bonding Systems

Performed better than the 1st generation

products. The 2nd generation of dentin adhesives

primarily used polymerizable phosphates added to

BIS-GMA resins. Adhesives that used phosphate

group to promote bonding to the calcium in

mineralised tooth structure were referred as

phosphate bonding systems. These materials had a

weak bond to dentin (4 to 6 Mpa), hydrophobic. The

bond strength was limited by relative attachment

strength of the smear layer to dentin substrate.

Materials Materials

a) Clearfil

b) Scotch Bond

c) Prisma Universal Bond

d) Dentin AdhesitDisadvantagesDisadvantages1. Weak bond to dentin2. Mechanical retention form was still necessary since bond strength alone was inadequate.3. Margins on dentin were problematic since the low dentinal bond strengths permitted extensive marginal microleakage.4. Restoration failure occurred most commonly due to hydrolytic decomposition.

Third Generation Bonding SystemsThird Generation Bonding Systems

A Newer – generation adhesive system have been developed that use a conditioning step on dentin in conjuction with a bonding agent.Bowen (1982) developed a multistep adhesive system. Importantly third generation adhesives were the frist to bond to metal and ceramics.Components are :Components are :

a) Dentin-conditioner

b) Dentine primers / adhesive

c) Bonding agent

Dentin ConditionersDentin Conditioners :- :- Are agents that either modify or

remove the smear layer and subsequently interact with

superficial dentin and rinsed off after application.

Chelators :- Chelators :- are used to remove the smear layer without

decalcification or significant physical changes to the

underlying substrate.Dentin Primer / Adhesive (Adhesion promoters)Dentin Primer / Adhesive (Adhesion promoters)

A primer is an agent which enhances the wettability of a

bonding agent onto the dentinal surface. The primer

usually contains an adhesion promoter in a solvent such

as water, ethanol water, ethanol or acetone acetone

Fourth Generation Dentin Bonding SystemFourth Generation Dentin Bonding System

The fourth generation dentin bonding system are characterized by hybrid zone formationhybrid zone formation in the dentin. The concepts of total etchtotal etch and moist dentinal moist dentinal bondingbonding (for acetone containing primers) are also hallmarks of the fourth generation materials.

Fifth Generation Bonding SystemFifth Generation Bonding System

The current state of the art in bonding materials is the single component bonding systems. This system provide entire priming and bonding sequence in a single liquid and single bottle. Dentin adhesives are based on combinations of conventional hydrophobic resins such as BIS-GMA, together with hydrophilic resins and solvents. HEMA (Hydroxyethyl methacrylate) is often used as a hydrophilic monomer. Acetone, alcoholAcetone, alcohol or a combination of both can be used as hydrophilic solvents. Several systems include water in various quantities to make the compound as an aqueous solution.

MaterialsMaterials

1) Prime & Bond

2) One Step Bond

3) Tenure Quick

4) Syntac single

5) Opti Bond

AdvantagesAdvantages1) Dentin bond strength are well above 15mpa.

2) Post-operative sensitivity is extremely rare.

3) Some of the 5th generation systems have

incorporated fluoride release and elastomeric

components to improve marginal integrity.

4) Time saving, and simplicity of use.