bonding in dentistry

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1GOOD MORNING ENDODONTISTS

2BONDING AGENT PRESENTED BY : DR.PRIYANKA MEHTA1ST YEAR POST GRADUATE STUDENTDEPT OF CONS & ENDOPACIFIC DENTAL COLLEGE & HOSPITALGUIDED BY: DR.SANDEEP METGUDDR.AFZAL ALI

CONTENTSIntroduction DefinitionUses of adhesive in restorative dentistry Structure of enamel and dentin-Types of AdhesionAdhesive SystemConditioningEtching3

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4PrimingBondingMechanism of adhesionRequisite of ideal bondingChemistry of Adhesive agent Factors affecting adhesion Adhesion to DentonCriteria For Ideal Dental AdhesiveDry versus Moist Dentin Surface-Modern adhesive Two step total etch adhesiveSelf Etch adhesiveMerits, Demerits of self etch adhesive Smear LayerBonding in other clinical situation ConclusionCONTENTS

INTRODUCTION

Every dental restoration requires retention by some system of connection or attachment.The scientific beginnings of dental adhesion originated in the early 1950s with studies of bonding to enamel and dentin.The most significant development in the history of dentistry over the past 50 years is the ability to bond materials to tooth structure. Now, 50 years later, bonding agents are used routinely in restorative and preventive dentistry.5

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DEFINITION

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

ADHESION is "the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or both.[American Society For Testing And Materials (ASTM; Specification D907)]

The initial substrate is called the ADHEREND, whereas the material producing the interface is generally called the ADHESIVE.

If two substrates are being joined, the adhesive produces two interfaces as part of the ADHESIVE JOINT6

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USES OF Adhesive restorative techniques :

Restore carious or traumatic defects. Restore teeth with amalgam using an adhesive technique.Provide retention for metallic crowns or for porcelain fused- to-metal crowns. Bond all-ceramic restorations . Bond indirect resin-based restorations7

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8STRUCTURE OF ENAMELEnamel is a porous, nonvital substance ,consists of 96 (weight)% inorganic hydroxyapatite and 4% matrix containing proteins and water.

Enamel is the hardest tissue in the human body and has a crystalline structure. The crystals form so-called enamel rods (Schroeder 1987).

In the outer structure, the enamel rods can be 10-15 m long. In this region the crystals are arranged in parallel, perpendicular to the rods. This zone is also called the aprismatic zone.

A pellicle consisting of a protein-fat-carbohydrate complex is found on the enamel surface. When the enamel is cut, the pellicle forms an organic smear layer thus the enamel surface should be conditioned before adhesion (Gwinnett 1994).

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9STRUCTURE OF DENTIN:Dentin consists of approximately 50 (volume)% inorganic material, 30% organic components, and 20% water. The organic matrix of the dentin consists of 91-92% collagen and 8-9% non collagen ground substance (Schroeder 1987).The inorganic components consist mainly of hydroxyapatite crystals that are smaller than those in the enamel. During cutting, a 1-5 m-thick smear layer forms, consisting of burnished components and hydroxyapatite fragments. The smear layer blocks the dentin tubules and stops the tubule fluid escaping, but also prevents the formation of a chemical and/or a micromechanical retention of the dentin bonding agent (Gwinnett 1994).

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(vimal sikri)Chemical adhesion based on primary valence forces such as covalent, ionic or metallic bonds. Physical adhesion relies on secondary valence forces. Such forces occur at molecular dipoles, the interaction of induced dipoles or electron clouds. Mechanical adhesion relies on penetration of one material into a different material at microscopic level

10TYPES OF Adhesion

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ADHESIVE SYSTEM:The adhesive system consist of:Conditioner (etchant), Primer and Bonding agent (adhesive). 11

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CONDITIONINGConditioning Alteration of dentin surface including the smear layer with the objective of producing a substrate capable of micromechanical and possibly chemical bonding to a dentin adhesive.

Conditioning can be performed by chemical ,thermal or mechanical means 12

Both acids and calcium chelators rely on removing the smear layer is used as chemical conditioners.

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ACID CONDITIONERS:

Earlier acid treatment was restricted to enamel and not on dentin with a fear of pulpal damage. But with Fusayamas pioneering research on total etching with 37% H3PO4, simultaneous etching is being accepted.

Acid conditioning remove the smear layer & simultaneously demineralise superficial dentin of 3-7 m to expose collagen into which resin will penetrate.

On intertubular dentin, the exposed collagen fibers are often additionally covered by an amorphous layer of variable thickness and has micro porosities due to denaturation and collapse of residual smear layer collagen. This collagen smear layer may reduce the permeability of underlying dentin to resin monomers and is highly cross linked and insoluble in acids.

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14At the tubule orifices, peritubular dentin is often completely dissolved to form a funnel shape structure and expose circularly oriented collagen fibrils which are often additional retentive sites at the tubule wall. After conditioning, maintenance of a moist dentin surface is recommended, following wet bonding technique to prevent collapse of unsupported collagen and promote wetting and infiltration of subsequently applied resinSeveral acids are used for conditioning include phosphoric acid, maleic acid, citric acid, nitric acid, oxalic acid, pyruvic acid and hydrochloric acid. Among these, H3PO4 was first acid to use as the conditioner at a concentration of 37%. Recently 10% H3PO4 appears to provide better bond strength than the higher concentration. However, results of enamel bond strength become questionable when these lower concentration acids are used.

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Nitric acid is a stronger acid than the phosphoric acid. DBA (Eg. Tenure, Mirage bond) that use nitric acid conditioners are highly adhesive and provide good tubule seals.

10% citric acid continued with 3% Ferric chloride is used as smear layer remover and etchant.

Another combination of etchant is 10% citric acid and 20% CaCl2 (eg. Clearfil linear bond) that decalcifies dentin to a lesser depth, and tubules do not open into a funnel shape.

Maleic acid (eg. Scotchbond) results in removal of smear layer but not smear plugs. 15

Smear layer covers the normal structural component of dentin by 1-2micrometer and penetrate several micro meter(1-5) in to the tubules which are known as smear plugs.15

CHELATORS

A chelator refers to a compound with a central metal ion surrounded by covalently bonded atoms, ions or molecules called legends which possess additional bonds for chemical reaction.

Chelators remove the smear layer without decalcification or significant physical changes on the underlying dentin substrate.

The best known chelator conditioner is EDTA (pH of 7.4). It was developed for use in Gluma system when used for 30 seconds, the smear plugs were not fully removed with this conditioner. 16

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THERMAL CONDITIONING:

The recent trend is to use lasers in conditioning of dentin which may serve as a potential alternative to acids for conditioning of dentin.

It is speculated that the lasers cause recrystallization of dentin resulting in fungiform appearance that increases micro-retention or possible chemical adhesion of a restorative material to the tooth structure. 17

Fungiform appearance : white disquamating appearance17

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Adhesion to enamel Is achieved through acid etching of enamel that enlarges its surface area for bonding. This enamel bonding technique, known as ACID-ETCH TECHNIQUE was introduced by BUONOCORE in 1955. Enamel etching transforms the smooth enamel surface into an irregular surface with a high surface free energy (72 dynes/cm) more than twice that of unetched enamel. Acid etching removes about 10 m of enamel surface and creates a micro-porous layer i.e. 5-50 m deep. Enamel bonding agents are commonly based on BISGMA/UDMA with diluents such as TEGDMA and HEMA. The bond between enamel and the restorative material is established by polymerization of monomers inside the micro-porosities and by copolymerization of remaining carbon carbon double bonds with the matrix phase of the resin composite, producing strong chemical bonds. 19Etching(Operative Dentistry, 2003, 28-3, 215-235)

GLYCOL DYMETHACRYLATE, TRIETRHYLE GLYCOL DYMETHACRYLATE, URATHENE DYMETHACRYLATE, HYDROXY ETHYLE METHACRYLATE19

The most effective approach to achieve efficient and stable bonding to enamel requires only two steps. First, the selective dissolution of hydroxyapatite crystals through etching and is followed by in situ polymerization resin that is readily absorbed by capillary action within the created etch pits.Two type of resin tags interlock within the etch pits.Macro tags filled up the space surrounding the enamel prisms, while the numerous micro tags results from resin infiltration/ polymerization within the tiny etch pit at the core of etched enamel prisms. 20

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Acid Etching process of enamel21

Whether enamel is on primary or permanent teeth. Primary teeth prismless enamel and therefore require longer etching time.

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MECHANISM OF ETCHINGEtching of enamel produces number of effect:Cleanses debris from enamel.Produces a complex three dimensional microtopography at the enamel surface.Increases the enamel surface area available for bonding.Produces micropores into which there is mechanical interlocking of the resins.Exposes more reactive surface layer, thus increasing its wettability.

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enamel etching patternGwinnett and Silverstone et al described three pattern of enamel etching. When seen microscopically, three types of enamel etching pattern are seen.

Preferential demineralization of enamel prism core leaving the prism peripheries intact. Corresponding tags are cone shaped.

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In this pattern tags are of cone shape23

There is preferential removal of inter prismatic enamel leaving the prism core intact. Corresponding enamel tags are cup shaped.

The pattern is less distinct, including areas that resemble type I and II patterns and areas which bear no resemblance to enamel prism.

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In this pattern tags are of cup shapIn this pattern There is Mixture of cone and cup shape prism and there is also presence of some area where total absence of enamel prism seen24

ENAMEL ETCHANTS: Phosphoric acidAs H3PO4 is said to be more aggressive, other alternatives have been suggested like

Ethylene diamine tetraacetic acid is a strong decalcifying agent, promotes only low bond strength to enamel, probably being EDTA does not etch preferentially.

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10%

26Pyruvic acid: 10% buffered with glycine to a pH of about 2.2, promotes high bond strengths to enamel, but has been found to be impractical because of its instability. Sulphuric acid: 2% used for 30 seconds has shown to be as effective as H3PO4 whereas high H2SO4 concentration produce heavy crystal deposits which interfere with bonding and cannot be washed away easily. With the introduction of total-etch systems, in which enamel and dentin are etched simultaneously, weaker acids are applied to enamel. With this total etch concept, the term etching is often referred to as conditioning.Apart from H3PO4 acid used in concentration ranging from 10% to 40% other inorganic acids such as nitric acid 2.5% concentration. Organic Acids: Citric acidMaleic acid Oxalic acid

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PHOSPHORIC ACID AS ETCHANT: Most commonly used etchant.

Etching time also has been reduced from traditional 60 seconds to 15 seconds and it has shown similar surface roughness and etching pattern as that of 60 seconds27

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28ADVANTAGES OF REDUCING ETCHING TIMEAs acid conditioning causes superficial tissue loss, it is desirable that minimal tooth structure be dissolved; therefore, minimal acid-application time should be used.The chemical reaction of the conditioning occurs quickly and, as mineral components are lost, the acid potential decreases by buffering.In cavities involving enamel and dentin,(also called total-etch technique) is controversial because the time should not be longer than 15 seconds in dentin, but this is the minimum time required to achieve a suitable bonding to enamel.So, it has been suggested that the conditioning time be reduced to 15 seconds, which is considered adequate for creating a retentive enamel surface with no difference in the enamel etching pattern or decrease of the bond strengths to instrumented enamel. Reduced chair time.

Enamel Acid Etching:A Review Compendium January 2007;28(1):

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Currently it is recommended that enamel of teeth need not be etched for more than 15-20 second except for the enamel which is acid resistant because of high fluoride content. Primary teeth also require longer etching time since the enamel is more a prismatic than that of permanent teeth.

Advantages of shorter etching time it yields acceptable bond strengths while conserving enamel and saving time. Rinsing time of at least 15 second is important to remove dissolved CaPO4, which otherwise might impair infiltration of monomers into the etched enamel micro-porosities, from the etched surface.

The use of ethanol to remove residual water from the etched pattern has been reported to enhance the ability of resin monomers to penetrate the surface irregularities (Gwinett 1992, Qusit V, Quist J 1985). Modern primers frequently contain drying agents such as ethanol / acetone, with a similar effect

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Recently rinse time of 1 second has been shown not to impair bond strength/ promote micro-leakage at the enamel site. CaPo4= hydrocyappetite+H2Po4

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31(Bellows 2004)1. Cleaning of the surface of the tooth.2. Drying the surface completely.3. Polishing the surface with the flour of pumice.4. Applying gauze for protecting the tooth from saliva and moisture.5. Rinsing the complete surface for 20 to 30 seconds with phosphoric acid.6. The region is dried again.7. The procedure should be repeated if the surface has been contaminated with moisture or if the surface does not appear chalky STEPS OF THE ACID-ETCHING

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35% Acid Etch is being applied for 15 secondsPost etching

PRIMERSPrimers are monomers dissolved in solvents such as water, acetone / alcohol and are applied to the etched / conditioned dentin substrate but are not rinsed off

Promotes wetting of the dentin by penetration of the bonding agent into the dentin.

Primer monomers are amphiphilic (i.e. they contain hydrophilic groups (eg. OH, -COOH) for better compatibility of the resin monomers with the moist dentin or for the exposed collagen fibril arrangement , and hydrophobic methacrylate groups for the co-polymerization with the bonding resin).The objective of this step is to transform the hydrophilic dentin surface into a hydrophobic and spongy state.

Eg.:HEMA ,NTG-GMNA, PMDM, BPDM and PENTA

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. Organic solvents aid in displacing water, expanding or re-expanding the collagen fiber network and thus promoting the infiltration of the monomer into the sub-micron or nanometer sized spaces within the collagen fiber network. In prime and bond and Bisco one step dental adhesive they combine the priming and bonding step.. More recent primers also include a chemical / photo polymerization initiator so that these monomers polymerize inside. Hydroxyl and carboxyl group33

34BONDING

Why bond to tooth tissue?

Prevention of leakage, reducing risk of pulpal damage

Allows more conservative tooth preparations

Bonded restorations strengthen tooth tissue.35

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MECHANISMS OF ADHESION 36

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MECHANICAL ADHESION

Involve the penetration of the adhesive into microscopic or sub-microscopic irregularities in the surface of the substrate. On hardening, the numerous adhesive projection embedded in the adherend surface provide the anchorage for mechanical attachment (retention). 37

The micro-mechanical bonding mechanism has been commonly used in the dentistry because of the absence of truly adhesive cements or restorative materials.

Example: Acid-etching technique where bonding between a dental material and tooth structure is by micro-mechanical bonding.

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382. ADSORPTION ADHESION- Chemical bonding between the adhesive and the adherend. The forces involved may be primary (ionic and covalent) or secondary (hydrogen bonds, dipole interaction, or vander 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.

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Formation of an optimally bonded interface requires that (1) the surface of the substrate be clean

(2) the adhesive wet the substrate well, have a low contact angle, and spread onto the surface

(3) adaptation to the substrate produce intimate approximation of the materials without entrapped air or other intervening materials

INTERFACE FORMATION FOR ADHESION

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(4) the interface include the sufficient physical, chemical and/or mechanical strength to resist intraoral forces of debonding (5) the adhesive be well cured under the conditions recommended for use40

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MECHANISMS OF INTERFACIAL DEBONDINGDebonding of dental joints occurs by a process of crack formation and propagation and subsequent joint failure.

Cracks form at defects along the interface.

Examples of defects include sites of interfacial contamination, excess moisture, trapped air bubbles, voids formed during solvent evaporation, places of poor wetting, bubbles within the adhesive, and curing shrinkage pores41

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This diagram shows four critical things which may lead to debondingEnlarged diagram of third tag that shows inadequate bonding42

Importance of adhesion in dentistry: To reduce tooth preparation needed for retention. To reduce marginal leakage caused by setting contraction of the filling. To reduce post-operative pain and pulp sensitivity caused by leakage. To reduce caries by sealing pits and fissures. Adhesive cements produce better retention of crowns and bridges.

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REQUISITES OF IDEAL BONDING AGENT:It should - Be biocompatible Bond effectively to both enamel and dentin Have sufficient strength to resist failure as a result of masticatory forces Have mechanical properties close to tooth structure Be resistant to degradation in oral environment Be easy to use44

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45CHEMISTRY OF ADHESIVE AGENTS

46Adhesive agents must have the ability to wet and then to adhere to hard dental tissues. Dental bonding systems contain monomers that have hydrophilic and hydrophobic groups.

A freshly acid-etched enamel surface has a surface energy more than twice that of an un-etched enamel surface and easily wetted by the monomer. Good adhesion after polymerization and good adaptation can only be obtained if the polymerization shrinkage is low.

Adhesion to tooth structure depends on several factors:1) There must be intimate contact between the tooth structure and the restorative material.2) Cavity walls must be clean.3) Liquid part of the restorative material must wet both enamel and dentin.4) The surface tension of the liquid must be less than the surface free energy of the enamel and dentin.

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471`A gap may be formed at the filling and dentin interface due to:1. Polymerization shrinkage of the filling material.2. Adhesive strength to dentin being weaker than the polymerization stress.3. Stresses developed from the differences in coefficient of thermal expansion of tooth and filling material.4. Functional occlusal forcesA dentin adhesive with an initial strong bond is needed to resist polymerization shrinkage.

Thecoefficient of thermal expansiondescribes how the size of an object changes with a change in temperature.47

48Types of Chemical Adhesion :1) Primary valence forces.2) 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 Vander waals forces and hydrogen bonds.

49Adhesion based on ionic polymers:Adhesion of the poly (alkenoic-acid) based materials to apatite can be achieved by ionic bonding with calcium ions acting as bridges. Two types of dental materials zinc carboxylate and glass ionomers are classified as poly alkenoates.Polyalkenoates are based on polyacrylic acid, maleic acid or itaconic acid.Ions diffusing from cement particles or from dentin apatite allow cationic bridges to be formed between carboxylic groups of the poly (alkenoic acid) and collagen (acidic groups). The ability of glass ionomer to adhere to enamel and dentin, has led to use G.I. as a base of composite resin (McLean 1985) (Braz Dent J(1997) 8(2): 73-78 ISSN 0103-6440)

50Adhesion by coupling Agents:

1) Silane for Silanization of fillers 3 methacryloyloxypropyl tri methoxysilane2) Another coupling agent was butylacrylate acrylic acid copolymer with free carboxylic acid groups. 3) Coupling agents utilizing the concept of hydrophobic and hydrophilic groups are the monomers based on phosphates or phosphonates. Hydrophillic phosphate group interact with calcium of dentin

Scoth Bond (2nd gen)Clearfil New Bond (2nd)Adaptic Dentin Bond Prisma universal Bond (2nd gen)Examples:

SURFACE CONTAMINATION The surfaces to be attached should be free of debris and contamination. Cleaner surfaces are at an energy state and rapidly absorb contaminants from the air such as moisture or dust. If contaminants are not excluded, the adhesive interface becomes weak. A standard process for cleaning any surface is the application of solvents or acids to dissolve or dislodge contaminants

FACTOR AFFECTING ADHESION51

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Wetting It is difficult to force two solid surfaces to adhere. To overcome this a fluid is used that flows between these irregularities to provide the contact over the greater part of the surface of the solid.To produce adhesion in this manner, the liquid must flow easily over the entire surface and adhere to the solid. This characteristic is called as wetting. 52

Formation of a strong adhesive joint requires good wetting.Liquid wets a solid and readily spreads onto its surface. In case of complete wetting, the contact angle formed is zero. Wetting is an expression of the attractive forces between adhesive and the adherend. It is the process of obtaining molecular bonds

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53Wetting ability of an adhesive depends on-CLEANLINESS OF THE ADHEREND - Cleaner is the surface, greater is the adhesion. Adhesive should be able to fill the irregularities making the surface smooth and wet substrate properly.

SURFACE ENERGY OF THE ADHERED - Generally harder the surface, higher is the surface energy, higher is the adhesive property of a material. The surface tension of the liquid and the surface energy of the adherend determine the degree of wetting. A film of water only one molecule thick on the surface of the solid may lower the surface energy of the adherend and prevent any wetting by the adhesive. An oily film on a metallic surface may also inhibit the contact of an adhesive.

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Lesser is the contact angle, better is the adhesion54

Adherend 1- Enamel &/or dentinAdhesive - bonding agentAdherend 2- composite resin

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CONTACT ANGLE This is the angle formed at the interface of the adhesive and adherend or angle formed between the surface of a liquid drop and its adherent surface.The smaller contact angle indicates better adhesion. The zero contact angles are the best to obtain wetting.If the molecule 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 is formed ( = 0 degree). Thus the force of adhesion is stronger than cohesive forces holding the molecule of the adhesive together.55

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The smaller the contacts angle between an adhesive and an adherend the better the ability of the adhesive to flow into and fill in irregularities within the surface of the adherend.Air pocket may be created during the spreading of adhesive that prevent complete wetting of the entire surface. When the adhesive interfacial region is subjected to thermal changes and mechanical stresses, stress concentration develop around these voids. The stress may become so great that it initiates a separation in the adhesive bond adjacent to the voids.

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SHRINKAGE OF ADHESIVE Some shrinkage occurs when liquid adhesives solidify by the process of evaporation / polymerization. The adhesive may then pull away from the substrate creating stresses that weaken the bond. Shrinkage usually occurs towards the centre of adhesive mass.In case of light cured systems this occurs towards the light source. THERMAL STRESSES If the adhesive and the adherend have different coefficients of expansions, changes in temperature will develop stresses in the bond. For this reason, close matching of coefficients of thermal expansions is required between porcelain, enamels and the alloy.57

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CORROSIVE ENVIRONMENT The presence of water, corrosive liquid or vapour may lead to deterioration of adhesive bond. E.g. Adhesive resins may adhere to clean un-etched tooth enamel but the bond fails when exposed to water. Higher the water content, poorer is the adhesion. Water can react with both the adherend and the adhesive by the high polar group and hydrogen bond, which can hamper the adhesion. 58

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CLINICAL FACTORS AFFECTING ADHESION Salivary and Blood contamination

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.Use of a rubber dam or other dry-field aids is necessary to avoid salivary or blood contamination during placement of tooth adhesive materials. Over use of dry field aids may produce another potential problem related to adhesion / dehydration. 59

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Oil contamination of hand pieces or Air water syringe :-

Oil comes from air compressor. Dentin bonding agent combined with oil contamination provides an unpredictable clinical result and potential clinical failure. Oil filters are placed on the airlines after the air compressor and before the air syringe or hand piece and should be changed frequently. Water and Oil contamination are the most significant negative factors present in tooth adhesion.60

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Surface roughness of tooth structure

Tungsten carbide steel burs make scratches and irregularities in tooth surfaces.Diamonds cut irregularities in tooth structure that are related directly to the size of the diamond particles. Increased surface area created by surface roughness helps in increasing the bond to dentin. 61

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Mechanical under cuts in Tooth preparations

Mechanical undercuts when present helps in holding restorative materials from bodily dislodgment from the preparation, they also resist some microscopic movement of the restorative material caused by thermal or polymerization shrinkage. 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.62

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Fluoride content of teeth

Fluoride presence in dentin appears to influence bonding with dentin adhesive agents negatively. Increased fluoride content of enamel resist acid etching, hence increasing the etching time to allow for acid to degenerate the enamel surface and produce more roughness.

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Presence of plaque, calculus, extrinsic stain or debris

After etching, the plaque-covered surface remains shiny and prevents an etch with 37% phosphoric acid. Penetration of plaque by acids used in dentin bonding agents is not possible and clinical adhesive failure will result. Tooth stains and calculus are easier to see and are removed usually, if not the bonding agents will not work. Enamel or dentin tooth surfaces that are expected to bond to resin to other materials should be cleaned thoroughly before attempting bonding.64

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Presence of bases or liners on prepared teeth

(a) Varnish: Although reduced tooth sensitivity, they should not be used if bonding of subsequent materials to tooth surface is expected.(b) Glass-ionomer liners : Create a moderate bond to dentin but it is lower than the bond created by placing resin on acid-etched enamel. 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 tooth(c) Resin Liners: Resin liners have little or no bond to dentine and subsequent restorations placed over the resin liners have no effect on bond to dentin.65

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Tooth dehydration Bond strength could be related to wetness of dentin (Prati, Pashley and Montanari 1991).(the evalution of bond strength Year: 2014 |Volume: 17 |Issue: 4 |Page: 305-311-JCD.). Overdrying can lead to increased tooth sensitivity. Drying only until the obvious shine of moisture is gone is a good clinical guide.

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Constituents of Temporary Cements Eugenol containing temporary cements or stearate-containing noneugenol temporary cements may have different bonding characteristics to resin. Fresh liquid eugenol placed on dentin or enamel just before attempted bonding could be a negative factor in adhesion.67

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Adhesion to dentin 68

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Adhesion can be affected by the remaining dentin thickness after tooth preparation. Bond strengths are generally less in deep dentin that in superficial dentin. But some dentin adhesives like 4-META monomer do not seem to be affected by dentin depth. Whenever tooth structure is prepared with a bur/other instrument residual organic and inorganic components form a smear layer of debris on the surface. Smear layer fills the orifices of dentinal tubules (forming smear plugs) and decreases dentinal permeability by upto 86%. Composition of smear layer alter natural collagen. Its altered collagen may even acquire a gelatinized consistency as a result of the friction and heat created by preparation procedure.

Smear Plug blocking the entrance of dentinal tubuleSP69

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Removal of smear layer and smear plugs with acidic solutions may result in an increase of the fluid flow onto the exposed dentin surface which may interfere with adhesion, because hydrophobic resins do not adhere to hydrophilic substrate if the resin tags are formed in the dentinal tubules. Additional factors affect dentin permeability Use of vasoconstrictors in local anesthetics decreased pulpal pressure in a fluid flow in tubules. Radius and length of tubulesViscosity of dentin fluidPressure gradientMolecular size of the substances dissolved in tubular fluidRate of removal of substances by the blood vessels in pulp affect permeability. All these variables make dentinal dynamic substrate and consequently a very difficult substrate for bonding. 70

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CRITERIA FOR IDEAL DENTAL ADHESIVE SYSTEM (PHILLIPS AND RAGE) 1961Provide high bond strength to dentin that should be present immediately after placement and that should be permanent. Provide bond strength to dentin similar to that to enamel. Show good biocompatibility to dental tissue including pulp. Minimize micro-leakage at the margins of restorations. Prevent recurrent caries and marginal stainingBe easy to use and minimally technique sensitivePossess good shelf lifeBe compatible with a wide range of resinsSystem should not be toxic or sensitizing to the operators and patients. Should seal the tooth surface from oral fluids. 71

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BONDING TO THE INORGANIC PORTION OF DENTIN: It occurs through ionic interaction between positive Ca2+ ions on the surface of dentin and negative charge on the group X (be phosphate, amino acids and amino alcohol or dicarboxylate) of the adhesive. Agents that use a phosphate group in their bonding to calcium ions are referred to as phosphate bonding systems and are most the common ones employed. When different Ca++ bonding adhesives are combined or used in conjunction with Dentin conditioning, bond strengths of 10-15 Mpa. This is probably due to the phenomenon of interpenetration.Some adhesives that involve bonding to inorganic ions are: Bondlite, Scotch bond, Clearfil , Prisma universal bond ,etc. 72

The reported bond strength of calcium bonding adhesives when used alone are moderate, seldom exceeding 6Mpa.

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BONDING OF THE ORGANIC PORTION OF DENTIN: Bonding to the organic part of dentin involves interaction with the amino (-NH), amido (-CONH2), hydroxyl (-OH) or carboxylate (-COOH) groups present in the collagen of dentin.Removal of hydrogen from any of these groups allows combination with chemicals present in DBA.Compounds that have a capacity to react with one or more groups of collagen are isocyanates, carboxylic acid chlorides, carboxylic acid anhydrides and aldehydes.73

BASIC CHARACTERISTICS OF SOLVENTS COMMONLY USED IN DENTIN ADHESIVESWATEREvaporates slowly consequently more difficult to remove Not sensitive to wetness of dentinLong drying timeCan interfere with adhesive if not removedETHANOLEvaporates less quicklyLess sensitive to wetness of dentinExtra drying timeACETONE Dries quicklyHighly volatile, evaporates quickly after being dispensedSensitive to wetness of dentinMultiple coats may be requiredOffensive odour

74SOLVENT FREEHigher film thicknessNo drying,Single coat

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DRY VERSUS MOIST DENTIN SURFACE-

Vital dentin is inherently wet, so complete drying is difficult to achieve clinically.

Water becomes an obstacle for attaining an effective adhesion of resin to the dentin

In WET state-Wide gaps separate the collagen by the presence which give space to resin infilteration.

In DRY state or air drying-Hydrogen bonds replace water, leaving no interfibrillar space for resin infilteration.75

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By air drying, the alteration(collapse) of collagen fibres occurs that prevents the monomer to penetrate the nanochannels formed by the dissolution of hydroxyapatite crystals between collagen fibers. The use of adhesive on moist dentin is made possible by incorporation of the organic solvents (acetone or ethanol) in theprimers or adhesives as solvent can displace water from both the dentin surface and the moist collagen network, it promotes the infiltration of resin monomers throughout the nanospaces of the dense collagen web.

WET BONDING TECHNIQUE77

78This technique has enhanced the bond strength by preserving the porosity of collagen network available for monomer diffusion.

The clinician must be aware that pooled moisture should not remain on the tooth, because excess water can dilute the primer and render it less effective.

Glistening hydrated surface is preferred

79Clinically, it is very difficult to either assess the ideal amount of moisture that should be left on the dentin surface before the application of the adhesive system.

Ideally, water should form a uniform layer without pooling (overwet) and without dry areas (overdried).

Therefore air-drying with an air-water syringe after rinsing off the etching gel is not recommended because it cannot produce a uniform layer of water on the surface.

A recent study demonstrated that the excess water after rinsing the etching gel can be removed with a damp cotton pellet, a disposable brush, or a tissue paper without adversely affecting bond strengths.

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80CLASSIFICATION OFMODERN ADHESIVES

BASED ON NUMBER OF CLINICAL APPLICATION STEPS & INTERACTION WITH TOOTH SUBSTRATE(sturdevant)

Total etch adhesives[E + P,A] a) Two step etch adhesives[E + P + A] b) Three step etch adhesives

Self etch adhesives [E + P, A] a) Two step self etch adhesives [E + P + A] = [C,P,A] b) One Step self etch adhesives81

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82TOTAL ETCH ADHESIVES:

Total etch adhesives involve a separate etch and rinse phase. Earlier the conditioning step is followed by a priming step and application of the adhesives resulting in three-step total etches adhesives whereas two-step total etch adhesives combine the primer and adhesive resin into one application.

82

83MECHANISM OF BONDING OF MODERN ADHESIVES Bonding to enamel and dentin is essentially an exchange process involving replacement of minerals removed from the hard dental tissue by resin monomers that upon in situ setting become micro mechanically interlocked in the created porosities.

INTERACTION WITH TOOTH SUBSTRATE A) TO ENAMELBonding to acid etched enamel theoretically requires an air dried surface to allow the photo polymerizable hydrophobic bonding agent to be drawn by capillary action into the etch pits. As a result two kinds of tag like extensions are formed.84

Macro tags are circularly formed between enamel prism peripheries.

Micro tags are formed at the cores of enamel prisms.

84

85TO DENTIN

Primarily dentin smear layer is removed by the etch and rinse phase, resulting in a 3 5 m deep demineralization of the dentin surface and collagen fibres are nearly completely uncovered from hydroxyapatite at this state when a successive application of primer and adhesive results in interlocking between collagen network and monomers.

This interlock was first described by Nakabayashi in 1982 and is commonly referred to as Hybrid Layer.

Smear layer is formed by minerals that deposited on the dentinal surface after cavity preparation; this layer is removed by acid etchingHybrid layer is formed by the boning agent which diffuses through the dentinal tubules and micro-pores that was created by aced etching

85

86 DENTIN HYBRID LAYER also known as ADHESION INTERFACE, RESIN-DENTIN INTER-DIFFUSION ZONE, INTER PENETRATION ZONE is a transitional zone of resin reinforced dentin sandwiched between cured resin and the unaltered dentinal substrate (Nakabayashi 1982).

Concurrent, with hybridization, resin tags seal the unplugged dentin tubules and offer additional retention through hybridization of the tubule orifice wall.

87

87

Three specific ultramorphologic features have been observed from this hybridization processa. Shag carpet appearanceThis feature typically appears when the dentin surface after being acid etched has been actively scrubbed with an acidic primer solution. This appearance stands for the loose organization of collagen fibres that are directed towards the adhesive resin and often unravelled in to their micro fibrils.88

TEM photomicrograph of resin-dentin interface produced by Clearfil SE (Kuraray). Note the formation of a 1-m thick hybrid layer with a typical shag-carpet appearance at the transition to the adhesive resin and individual cross-banded collagen fibrils separated by electron lucent interfibrillar spaces.

Transmission electron microscope88

89b. Tubules wall hybridizationRepresents the extension of the hybrid layer into the tubule wall area. It is thought to be favourable in hermetically sealing the pulpodentinal complex against microleakage and the potential subsequent ingress of microorganisms. In particular, the resin tag necks, at the top 5 10 m of the tubule orifices are thought to contribute to retention and sealing effectiveness.

TEM photomicrograph of resin-dentin interface

89

90c. Lateral tubule hybridizationThis has been described as the formation of a tiny hybridization, into the walls of lateral tubule branches. This micro-version of a hybrid layer typically surrounds a central core of resin, and is called a micro resin tag.

TEM photomicrograph of resin-dentin interface

90

The formation of hybrid zone depends on several factors in general.Type of the conditioners.

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 into the tubules. In deep dentin the tubules are so numerous and so large that there is very little intertubular dentinal matrix, therefore there is less amount of hybridized intertubular dentin and large resin tags are seen.

Permeability of the dentin surface.

It conditioning and priming pre treatment procedures.

Diffusability and wettability of monomer resins.

91

92In 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 inside.

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.

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 demineralized dentin, thus stabilizing the dentin matrix. Once the adhesive monomer has penetrated into the demineralized substrate to its fullest extent, it must be made to polymerize in situ at the full penetration depth it has achieved with minimal shrink back.93

94The 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 comprises 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.

Reverse Hybrid layerThe acid etched surface of dentin is further subjected to treatment with NaOCl. This results in dissolution of the collagen fibrils that are exposed. Further the use of self-etching primers results in superficial etching of the surface. Here the hybrid 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 reversed hybrid layer. Reverse hybrid layers form when dentin-bonding agent comes in contact with the pulp.

95

MERITS AND DEMERITS OF TOTAL ETCH ADHESIVES THREE STEP TOTAL ETCH ADHESIVESMERITSSeparate application of conditioner primer and adhesive resin.Lowest technique sensitivityIn-vitro and in-vivo proven effectiveness of adhesion to enamel and dentinBest bond to enamel

DEMERITSRisk of Over etching dentin Time consuming three-step application procedurePost conditioning rinse phase required (time consuming and risk on surface contamination when not using rubber dam)Sensitive to Over wet or Over Dry dentin surface conditionsWeak monomer collagen interaction which may lead to nanoleakage and early debonding96

96

TWO STEP TOTAL ETCH ADHESIVESMERITSSimpler application (reduction of one step)Possibility for single dose packaging, thereby giving the advantage ofConsistent and stable compositionControlled solvent evaporation Hygienic application

DEMERITSNot substantially Faster applicationMore technique sensitiveRisk of over etching dentinPost conditioning rinse phase requiredSensitive to degree of dentin wetnessWeak monomer collagen interaction97

97

98 SELF ETCH ADHESIVES Introduced with scotch bond 2 (3M) in the early 1990s. However, this system was advocated only to be applied on dentin. The current self etch adhesive provide monomer formulation for simultaneous conditioning and priming of both enamel and dentin.Most common self etch adhesives involve two application steps with the self etch primer followed by an adhesive resin; resulting in two-step self etch adhesives.Most recently one-step self etch or all-in-one adhesives, combining the conditioning priming and application of an adhesive resin in to a single application has been marketed.

. 98

CLASSIFICATION OF SELF ETCH ADHESIVES DEPENDING ON THEIR pH

99 STRONG (pH 1)This high acidity results in rather deep demineralization effects. At enamel, the resulting acid etch pattern resembles a phosphoric-acid treatment following an etch&rinse approach.

At dentin, collagen is exposed and nearly all hydroxyapatite is dissolved.

Have low bond strength values, especially at dentin, & residual solvent (water) remains within the adhesive interface, which can hardly can be completely removed.

Eg-Non rinse conditioner and prime and bond NT (Dentsply)

100MILD (pH 2)Demineralize dentin only superficially to a depth of 1 m, keeping residual hydroxyapatite still attached to collagen.

Sufficient surface-porosity is created to obtain micromechanical interlocking through hybridization. The thickness of the hybrid layer is, however, much smaller than that produced by the strong self-etch or etch&rinse approach

Eg Clearfil Liner bond 2V (Kuraray)One up bond F (Tokuyama)Unifilbond (GC)

MERITS, DEMERITS OF SELF ETCH ADHESIVES

MERITSSimultaneous demineralization and resin infiltrationNo post conditioning rinsingNot sensitive to diverse dentin conditions Time saving application procedure Possibly for Single dose packaging Adequate monomer collagen interaction

DEMERITSIn sufficient long term clinical researchAdhesion potential to enamel needs yet to be clinically proven

101

Restoration placed using self-etching bonding systemWear cavity on the buccal surface of a premolar. No cavity preparation required.Application of acidic primer, followed by blowing away of excess material. Application of adhesiveFinal restorationRestoration ten years later102

According to Mode of Action

Those that bond with calcium ion Based on phosphate esters of BISGMA and its modifications bond with calcium ion in the smear layer and dentin surface. The smear layer is therefore left intact. Eg. Scotch bond 1 and Bondlite.

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.

Those that bond with re-precipitated smear layer dentin-bonding agents in this category require partial removal and modification of the smear layer. Bonding is possibly by mechanical entanglement with collagen fibrils on dentin surface. Eg. Scotch-bond 2 and Tenure 103

BASED ON CHRONOLOGICAL ORDERFirst Generation Adhesives :Introduced in the late 1960sIngredients of this generation are 1. Primer- Glycerophopsphoric acid dimethacrylate2. Silane coupling agents--NPG-GMA, the polyurethanes, and the cyanoacrylates.

Buonocore demonstrated that a glycerophosphoric acid dimethacrylate containing resin would bond to acid-etched dentin due to the interaction of bifunctional resin molecule with the calcium ions of hydroxyapatite.

These products ignored the smear layer. 104

(N-phenylglycine glycidyl methacrylate), Nine years later Bowen tried to create the bond using N- phenylglycine and glycidyl methacrylate. NPG-GMA is a bifunctional coupling agent with one end bonding to dentin and other to resin. They were recommended primarily for small retentive class III and class V cavities104

105The mechanism of adhesion was because of deep penetration of the resin tags into exposed dentinal tubules after etching and presence of chelating component (which could bond to the calcium component of dentin). Since they could chelate with calcium ions, the bonding to enamel was stronger than the bonding to dentin.

Problems with 1st generation systems-The bond strength was poor- 1 to 3 MPa. Loss in bond strength over time.Lack of stability of individual components during storage. A six-month study reported a failure rate of 50%.Post-operative sensitivity was common.

106Eg: Cervident( S.S White, Lake wood, NJ) First commercially available bonding agent.Cosmic bond( Amalgamated Dental Company)Palakav( Kulzer, USA)

II. Second Generation DBA

Introduced in the late 1970s and early 1980s. These products attempted to use smear layer as a bonding substrate.

The bonding was by the formation of an ionic bond between calcium and chloro-phosphate groups. These bonds were not strong enough to resist the hydrolysis (saliva exposure or moisture from the dentin) leading to debonding of composite resin from the dentin and hence, micro-leakage.

Since dentin was not etched in these systems much of the adhesion was due to bonding to the smear layer. Some of the second-generation systems were thought to soften the smear layer and thus improve resin penetration.

107

108Problems with 2nd generation systems- Low bond strengths, approximately 4.5 to 6 Mpa, and so mechanical retention in cavity preparation were required. Unstable interface between dentin and resin because of the insufficient knowledge about the smear layer. Long term stability was poor and 1 year retention rates were as low as 70%. Restorations that were extended to the dentin exhibited severe micro-leakage. Significant post-operative sensitivity.

There were three types of second-generation products.

Etched tubule dentin bonding agents- Attempted etching the tubules with 25% citric acid and then employing ethyl methacrylate to mechanically interlock with the etched tubules.

2. Phosphate ester dentin bonding agents- Used analogue of BIS-GMA with attached phosphate esters. The phosphate group apparently bonded with calcium in the tooth structure and the methacrylate end of the molecule bonded to the composite resin. Most systems of this type employed a mild cleanser to modify the smear layer. They showed 10-30 % increase in bond strength.109

110 3. Polyurethane dentin bonding agents- were based on the isocyanate group of the polyurethane polymer that bonded to various groups in dentin (including carboxyl, amino and hydroxyl groups).

Most used di-isocyanates which simultaneously bonded to both the dentin and the composite resin.

The polyurethane's setting reaction was unaffected by the presence of fluid in the dentin tubules or smear layer. Most of these systems left the smear layer intactEg:Clearfil bond system F.Scotch bond dual cure( 3M ESPE).Bondlite ( Kerr).Prisma Universal Bond( Johnson and Johnson).

III. Third Generation Dentin Bonding agent:These systems were developed in late 1980s.Uses 3-component system consisting of an (acidic) conditioner, a (bifunctional resin in a volatile solvent) primer & (an unfilled or partly filled) adhesive resin.Here, etching of the dentin partially removes and/or modifies the smear layer. The acid opens dentinal tubules partially and increases their permeability. The acid must be rinsed completely before the primer is applied.

The primer usually includes 4-META (methydroxyethyl trimellitate anhydride) 6 % phosphate penta-acrylate (PENTA), 30% HEMA and 64% ethanol. The primer contains a hydrophilic group that infiltrates the smear layer and promote adhesion to dentin and another hydrophobic group of the primer creates adhesion to the resin. The phosphate primer, after penetration modifies the smear layer by softening it. 111

Hence in 3rd generation systems, alteration or removal of smear layer is done before bonding in following two ways- 1. Removal of smear layer without disturbing the smear plugs.2. Modifying the smear layer to improve its properties. 111

Advantages of 3rd generation over 1st and 2nd generations- 1. Higher bond strengths (8 to 15 MPa). Some of the products produced bond strengths approaching those formed to the enamel. 2. Reduced microleakage. 3. Form strong bond to sclerotic and moist dentin. 4. Reduced need for retention form in tooth preparation. 5. Can be used for composite and porcelain repairs. 6. Erosion, abrasion and abfraction lesions can be treated with minimal tooth preparation. 7. Clinical retention rates of 100% at the end of 2 years have been reported.

Problems with 3rd generation systems-Decrease in bond strength with time.Increase in microleakage with time.

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113SystemConditionerPrimerAdhesive1.Scotch bond 22.5% maleic acid, 55% HEMA, and a trace of methacrylic acidBis GMA(62.5%)HEMA(32.5%)Photoinitiator2.Tenure(15 Mpa)Oxalate bonding systemAcidic ferric oxalate which cause staining hence replaced by aluminium oxalate5% NTG GMA PMDMBis GMATEG- DMA3.Miragebond(10.9+1.2M)NPG( N phenyl glycine)2.5% Nitric acidPMDM4.Gluma( 15 Mpa)17%EDTA to remove smear layer and free collagen35%HEMA5% glutaraldehyde55% Bis GMATEGDMA.5.

Prisma universal bond 330%HEMA6% PENTA50%UDMA25%TEGDMA4.5% PENTA0.5%GA.

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FOURTH GENERATION ADHESIVES: They were made available in early 1990s. Fusayama and colleagues tried to simplify bonding to enamel and dentin by etching the preparation with 40 percent phosphoric acid. Unfortunately, this procedure over-etched the dentin and resulted in the collapse of exposed collagen fibers. In 1982, Nakabayashi and colleagues reported the formation of a hybrid layer resulting from the interlocking of polymerized methacrylate into demineralized dentin. The complete removal of the smear layer is achieved.

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CompositeDentin Adhesive

Hybrid Layer

115Advantages of 4th generation systems- 1. These systems have ability to bond as strongly to dentin as to enamel. 2. They have ability to bond strongly to moist dentin and are technique insensitive. 3. They may have the ability to bond to many different types of substrates (e.g. enamel, dentin, porcelain, base and noble metals, amalgam). 4. High bond strength to dentin - 17 to 25 Mpa.

These systems consist of - CONDITIONER - commonly 37% phosphoric acid, nitric acid, maleic acid, oxalic acid, citric acid or EDTA. They modify/remove smear layer, demineralize peritubular and intertubular dentin and expose collagen fibers. 116PRIMER Bifunctional monomers like HEMA and 4-META, dissolved in acetone or ethanol. They help in increasing the wettability of the dentin surface; bonding between dentin and resin and encourage monomer infiltration into the demineralized peritubular and intertubular dentin. ADHESIVE - A low viscosity, semi-filled or unfilled resin, which flows and matches the composite resin. They combine with the monomers to form a resin reinforced hybrid layer and resin tags to seal the dentin tubules

117DisadvantagesMultiple steps: Technique sensitive.Unless the primer and adhesive are applied consecutively, the overlying composite resin will not bond to the surface.

118NameBond StrengthConditonerPrimerUnfilled resinAll bond 221.2+7.8Mpa37% phosphoric2%NTG- GMA16%BPDMBisGMA 40%30%UDMA30%HEMAScotch bond multipurpose21.8 MPa to wet dentin 17.8 Mpa to dry dentin10% maliec acid 3Mic M depthAqueous solution of HEMAPolyalkenoate polymersBis GMA containing HEMAAmalgam Bond10% Citric acid19% Ferric ChlorideHEMA with water4- METAMMA-TBB.

FIFTH GENERATION SYSTEMIntroduced in mid 1990sSimplify the clinical procedure by reducing the bonding steps and working time and prevent collagen collapse of demineralized dentin.

119FIFTH GENERATION SYSTEMONE-BOTTLE SYSTEMSELF-ETCHING PRIMER BONDING SYSTEM

119

120One-bottle systems-Combined the primer and adhesives into one solution.This is a misnomer because these products are applied in two steps:

34% to 37.5% phosphoric acid etchant is applied for 15 to 20 seconds to etch enamel and dentin simultaneously Dentin bonding agent is applied (primer + adhesive).

121Self-etching primer bonding systemWatanabe and Nakabayashi developed a self-etching primer that was an aqueous solution of 20% phenyl-P in 30% HEMA for bonding to enamel and dentin simultaneously.

The combination of etching and priming steps :reduce the working timeeliminate the washing out of the acidic geleliminate the risk of collagen collapse.

Disadvantagesthe solution must be refreshed continuously because its liquid formulation cannot be controlled where it is placedoften a residual smear layer remained in between adhesive material and dentin.

These bonding systems create a mechanical interlocking with etched dentin by means of resin tags, adhesive lateral branches and hybrid layer formation. Advantages of 5th generation systems- 1. Easy to use and predictable. 2.They show high bond-strength values both to the etched enamel and dentin 3. Less technique sensitive. 4. Reduced post-operative sensitivity. 5. They adhere well to enamel, dentin, ceramics and metal.122

Problems with 5th generation systems- Many require at least as much time to apply or even more time than three-component products and they lack many of the components necessary to perform multi-substrate bonding. Post operative sensitivity 123

124

125Primer is applied prior to adhesive.Water is used as solvent. A drop from each bottle is taken, mixed and applied to the tooth surface. Available in two bottles: (a) Primer, (b) AdhesiveOne step/ Self etching adhesives/ All in one systemSIXTH GENERATION DBAs(Available since late 1990s and early 2000) Two step/ Non rinsing conditioner/ Self etching primer

Type I Two step/ Non rinsing conditioner/ Self etch primer systems:

NRC Non Rinse Conditioner( Dentsply De Trey, Konstanz, Germany) followed by Prime and Bond NT( Dentsply)Clearfil SE BondTryian( BISCO, Inc, Schaumburg,)Simplicity( Apex Dental Materials, Inc, Sandwich, IL)UniFil Bond(GC America, Alsip, IL)OneCoat Self-Etching Bond(Coltene Whaledent, Cuyahoga Falls )AdheSE( Ivoclar Vivadent).

127Type II 6 Generation Bonding agent :One step/ Self etching adhesives/ All in one systems

Attempt to incorporate all the primary components into a single container.

Incorporating all components and having it remain stable is a significant challenge.

In reality, many of these are not all in- one systems at all but require premixing of chemical components (Prompt-L-Popb) or the use of chemically activating pellets or brushes that come with the kit (Touch & Bond, Brush & Bond).

1286th Generation Type II.

Prompt L Pop( 3M)Touch and Bond ( Parkell)Brush and Bond( Parkell)Xeno III( Dentsply Caulk)One up Bond F( J Morita, Kuraray)

Advantages Advantage of combining the etching and priming steps was the reduction in the working time; the elimination of the washing out of the acidic gel; and also elimination of the risk of collagen collapse. They reduce or eliminate post-treatment sensitivity because (i) They etch the dentin less aggressively than total-etch products.(ii) The demineralized dentin is completely infiltrated by resin during the etching process(iii) Since they do not remove the smear layer, the smear layer plugs are retained in the orifices of the dentin tubules and the tubules remain sealed. Comparable adhesion and bond strengths to enamel and dentin. They form thinner hybrid layer than traditional products which result in complete infiltration of the demineralized dentin by the resin monomers. This gives increased bond strengths. Less technique sensitive as less number of steps are involved.

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Problems with 6th generation systems-Unfortunately the first evaluations of these new systems showed a sufficient bond to conditioned dentin but the bond with enamel was less effective as primer is composed of an acidic solution that has poor shelf life and must be refreshed continuously and they have a pH that is not enough to properly etch enamel.The effectiveness of etching the enamel was less predictable than the result obtained with phosphoric acid gel. So bond strength to enamel is weaker as compared to dentin.Bond strength to dentin is 18 to 23 Mpa. Promote water-sorption.Limited clinical data.

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SEVENTH GENERATION SYSTEMThey achieve the same objective as the 6th generation. But they simplify the multitude of 6th generation into single-component single-bottle system, thus avoiding any mistake of mixing. They also have desensitizing and disinfecting properties. Advantages1. One step procedure, no mixing or rinsing required.2. Fluoride releasing to prevent secondary caries.3. Tolerant to moist and dry environment.4. Radiopaque, easier to differentiate adhesive layer from recurrent caries.5. Little or no marginal discoloration over time.6. Available in light cure and dual cure formulations.7. They provide the bond strength of 20-30 Mpa. to both enamel and dentin.8. Little or no post-operative sensitivity.131

MECHANISMS OF BONDINGTotal-Etch SystemsIn 4th- and 5th-generation bonding agents, application of phosphoric acid, followed by rinsing, completely removes the smear layer and plugs.1,2 The 4th-generation separate primer and adhesive or the 5th-generation primeradhesive combination fills in the dentinal tubules and interacts with collagen fibers to form a hybrid layer.Self-Etch SystemsSixth- and 7th-generation bonding agents use the smear layer as a bonding substrate.3-5 The 6th-generation acidic primer or the 7th-generation primeradhesive combination demineralizes the smear layer and the top layer of the underlying dentin surface.7 They also infiltrate collagen fibers and copolymerize, minimizing voids and potential leakage. Because the etched surface is not rinsed, the demineralized smear layer is incorporated into the hybrid layer, which is typically thicker than the hybrid layer formed with 4th- and 5th-generation systems, ranging from 0.5 m to 5 m.7 This somewhat thicker hybrid layer works as a buffer to minimize postoperative sensitivity.

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Problems with 7th generation systems-Some need refrigeration.Decreased shelf life due to acidic formulation.

132

Eg: I bond( Heraeus Kulzer). G Bond( GC America).

1338TH GENERATION SYSTEMS-

Dual cure self etch adhesive for direct & indirect restorations with self ,light & dual cured resin material

134134BONDING TECHNIQUESAPPLICATION OF BONDING AGENTPRIMER TO COLLAPSED DEMINERALIZED DENTINBONDING AGENT TO NON-COLLAPSED DEMINERALIZED DENTINPRIMER TO DEMINERALIZED DENTINSELF-ETCHING PRIMER TO SMEAR LAYER COVERED DENTIN

SMEAR LAYER:Definition (SUMMIT)

Any debris, calcific in nature, produced by reduction or instrumentation of dentin, enamel or cementum or as a contaminant that precludes interaction with the underlying pure tooth tissue.

The smear layer serves as a natural bandage over the cut dentinal surface because it occludes many of the dentinal tubules with debris called smear plugs

SEM Smear Plug135

SMEAR LAYER & SMEAR PLUG136

Components of Smear Layer

InorganicOrganic: may consist of heated coagulated proteins, necrotic or viable pulp tissue and odontoblastic process, saliva, blood cells and micro-organisms.

Role Of Smear Layer

They are responsible for:Physical barrier for bacteria and bacterial products.Restricting the surface area available for diffusion of both small and large molecules.Resistance to fluid movement.137

DISADVANTAGES OF SMEAR LAYER:Bonding to the smear layer forms a weak union because smear layer can be torn away from the underlying matrix.

Play significant part in increase or decrease in apical leakage which may be the cause of future failure of root canal filling.

In root canal wall it acts like intermediate physical barrier and may interefere with adhesion and penetration of sealers into dentinal tubules.

It causes possibility for leakage of micro-organisms and a source of substrate for bacterial growth.

Helps in the growth of bacteria which may remain in the dentinal tubules.138

Role of smear layer in dentin bonding:Smear layer may serve as a barrier to the penetration of resin to the underlying dentin substrate.

Agents for removalCitric Acid.Polyacrylic Acid.Chelating agent eg : EDTAMaleic Acid.

139

Smear Layer-Modifying AdhesiveSmear 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 monomers infiltrated into the smear layer are expected to reinforce the bonding of smear layer to dentinal surface forming micro mechanical and chemical bond.

The interaction of these adhesives with dentin is very superficial with only a limited penetration of resin into dentinal surface.

This shallow interaction without any collagen fibril exposure confirms the weak acidity of these smear layer modifying primers140

Smear layer-removing adhesiveMechanism is principally based on the combined effect of hybridization and formation of resin tags.

In conventional three steps system, the primer should ensure efficient wetting of the exposed collagen fibrils, displace any residual surface moisture, transform a hydrophilic into hydrophobic tissue state and sufficiently carry monomers into interfibrillar channels.

It forms resin tags that seal the opened dentinal tubules initiate and advance the polymerization reaction, stabilize the formed hybrid layer and resin tags and provide sufficient methacrylate double bond for copolymerization.

In one bottle system the function of primer and adhesive resin should be perfectly combined 141

Smear Layer-Dissolving Adhesives

Also known as self etching adhesives which use slightly acidic primers or so called self etching primers.

Primers partially demineralize the smear layer and underlying dentin without removing or unplugging tubule orifices the smear layer remnants.

142

143

144Bonding In OtherClinicalsituations

BONDING OF GICGIC has an imp property of adhering to enamel and dentin.can also bond to other reactive polar substrate such as base metals.Chemical adhesion.Bonding to enamel is stronger for GI than bonding to dentin because of larger inorganic content of enamel.

145

Carboxyl group og gi can bond strongly with ca ions145

BONDING OF COMPOSITE TO GIGI invariably used as a substitute for dentin under composite resin.This techniqye is also known as bilayered technique in which enamel and cement are etched prior to restorative resin.37% H2PO4 is used to etch GI and the enamelkThe type of GI has shown to influence the bond at the dentin surface and GI/Composite interface.Higher the strength=better the clinical result.Slow setting cement will be weakened if etch prematurlyFast set can be etched after 2-5min.Use of light cured GI can greatly reduce the chances of debondingUse of varnish after GI can reduce the polimerization shrinkage of composite146

BONDING OF COMPOSITE TO PORCELAINBonding is partly because of mechanical interlocking and partly because of chemical unionMechanical retention is obtained by etching the fitting surface of porcelain with dilute hydrofloric acid or grit blasted with alumina to increase surface roughness Shear bond strength have shown to increase by several times when porcelain is etchedChemical reaction b/w porcelain and composite is made by treating the etched surface with a silane coupling agent.Chemical reaction b/w a silicate ceramic surface, silane coupling agent and a composite resin is well documented.147

BONDING OF AMALGAM TO RESINIs relatively new t/t modality & has made bonding b/w amalgam and tooth structure, amalgam amalgam or amalgam and metalBond is micromechanicalAgents that can be used: All bond, liner bond-2, amalgam bond and panavia

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CONCLUSION The reliability of dentine bonding has improved during 1990s and as a result the number of minimally invasive techniques available to the restorative dentist have increased. It is well understood that the effectiveness of adhesive technique to dentin will improve further and the day is not far when all restorations including crowns, will be placed using an adhesive procedure.149

REFERENCESSTURDEVANTVIMAL SIKRISUMMITPHILLIPSMANNAPALLIMARZOUK

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REFERENCESBuonocore Memorial Lecture Operative Dentistry, 2003, 28-3, 215-235

Braz Dent J(1997) 8(2): 73-78 ISSN 0103-6440(The evalution of bond strength Year: 2014 |Volume: 17 |Issue: 4 |Page: 305-311-JCD)McLean J.W. and Wilson A.D. The clinical development of the glass ionomer cements. 1977 Aust Dent J. 22(2) 120-127Schmidlin PR, Huber T, Ghring TN, Attin T, Bindl A.Effectsof total and selective bonding on marginal adaptation andmicroleakage of Class I resin composite restorations in vitro.Oper Dent. 2008 Nov-Dec;33(6):629-35.Bonding to Dentin: Smear Layerand the Process of HybridizationK.Van Landuyt, J.De Munck, E. Coutinho, M. Peumans,P. Lambrechts, B.Van MeerbeekGoogle

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Dont stop when youre tired, stop whenyou are donr.Your only limit is you.If it doesn't challenges you, it wont change you.Work until idols become your rivals.Wake up with determination, Go to bed with satisfaction.152THANK YOU FOR PATIENCE