INTRODUCTION

•Bonding agents can be defined as material of low viscosity, when applied on the tooth surface, 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.

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• Biocompatible• Non toxic, Non irritant, Non poisonous• Low film thickness, Low viscosity• Form strong permanent bond• Good dimensional stability• Similar C.O.T.E as tooth• Low thermal conductivity• Good shelf life• Prevent micro leakage

ENAMEL BONDING• Enamel is the hardest tissue of human body consists of

95% mineralized inorganic substance i.e. hydroxyapatite crystals.• Due to high mineral content the bonding in enamel is

good as compared to dentin.• Enamel is etched using 37% phosphoric acid applied

for 15-30 seconds.• Etching creates 5-50 microns deep microporous layer

into which adhesive resin flow.• This results in long lasting enamel bond achieved via

micromechanical interlocking between resin and enamel.• Bond strength: 15-25 Mpa.

Effects of Conditioning / Etching:1.Removes 10 µM of surface enamel & creates a microporous layer.2.Increases wettability.3.Increases surface area.4.Increases surface energy.

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• Buonocore, 1955 • was the first to reveal the adhesion of acrylic resin to acid

etched enamel. • used 85 % phosphoric acid.

• Percentage of etchants used: 37%

Teeth requiring longer application - Acid resistant teeth ( with high F content/

Fluorosis).Primary teeth (More aprismatic).

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MECHANISM OF ETCHINGAcid etching

smooth enamel converted into irregular surface [surface free energy ]

Resin monomer penetrate (b/c of low viscosity) into the irregular etched surface [aided by capillary action].

Monomer polymerize, material become interlocked within the enamel surface. [Microtag formation]

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• Macrotags – resin tags formed at periphery of enamel rods ( between prisms )

• Microtags - smaller tags formed at end of each rod where individual hydroxyapatite crystal has been dissolved. More important because of greater number and surface area.

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DENTİN BONDİNG

• Bonding to dentin has been proven more difficult and less reliable than to enamel.

• This is basically because of difference in morphologic, histologic and compositional differences between enamel and dentin.

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PROBLEMS IN BONDING TO DENTIN

1)It has considerable amount of organic material & water (30% organic material ; 20% fluid).

2)Random arrangement of hydroxyapatite crystals in the organic matrix. (They have a regular pattern in enamel).

3)Presence of dentinal fluid which flows outward, adversely affects bonding.

4)Sclerosed dentin is difficult to penetrate as peritubular dentin becomes wider.

5)Dentin contains dentinal tubules which contain vital processes of the odontoblasts. This makes the dentin a sensitive structure.

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6) Cut dentin surface is covered by smear layer, that fills the orifice of dental tubules, & blocks dentin permeability upto 86%.

6) Because of close proximity to pulp, various chemicals used for etching & dentin bonding may irritate the pulp.

7) It’s a dynamic tissue, that shows changes due to ageing, caries or restorative procedures.

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• ETCHENTS / CONDITIONERS

• PRIMERS

• ADHESIVES

ETCHENTS / CONDITIONERS

• ORGANIC ACID:- Maleic acid ,EDTA ,citric acid, tartaric acid.

• POLYMERIC ACID:- poly acrylic acid

• INORGANIC ACID:- phosphoric acid, nitric acid.

CONDITIONING/ ETCHING

CHANGES AFTER CONDITIONING:

Removal or modification of smear layer.Opening of dentinal tubule orifices. Exposes the microporous collagen network.Decalcification of inorganic portion.

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PRIMERS

• HEMA : 2- Hydroxyethyl Methacrylate

• PENTA: Dipenta Erythritol Penta Acrylate Monoohosphate

• NPG-GMA: N- Phenyl Glycine Glucidyl Methacrylate

PRIMERS • These are adhesion-promoters.

• Amphiphilic bifunctional molecules• Hydrophillic binds to : Dentin (exposed collagen fibrils)

• Hydrophobic binds to : Adhesive resin

• The priming step converts the hydrophillic dentin into a hydrophobic and spongy state for penetration by the adhesive resin.

• The primers are usually dissolved in acetone, ethanol or water.

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• These solvents are volatile and displace water (water chasing ability) from the dentin surface and the moist collagen network.

• This will allow the monomer of the primer to penetrate through the spaces in the collagen network.

• For proper penetration, 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.

• Priming is done after etching. It should be applied in multiple coats.

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ADHESIVE RESINS Hydrophobic monomers BIS-GMA UDMA

Diluent TEGDMA

Wetting agent HEMA

SMEAR LAYER

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

• 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

• It has two phases• Solid phase-made up of cutting debris , primarily

denaturated collagen and mineral• Liquid phase- 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 permeability2)decrease in bond strength3)lowers effect of pulpal pressure on bond strength• Recent generations adhesives involves

modification of smear layer to facilitate bonding

Role of water in bonding process• Water act as a plasticizer for collagen and keep it in soft

state • If dentin is excessively dried it will leads to collapse of

dentin • If critical water concentration exists, that prevents

collapse of collagen network and allows expansion of dried dentin.• Critical amount of water is essential for bonding but an

over wet condition decreases bond strength and formation of blister like structures at the interface

HYBRID LAYER• This is the 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:-• 1.etching removes smear layer and exposes collagen

fibers• It also removes hydroxy 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

• When a bonding agent is applied, part of it penetrates into the collagen network, known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration.

• Intratubular penetration or the formation of resin tags upto a limited depth of 10-20 microns.

• Given by Nakabayashi in 1982.

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DEVELOPMENT OF DENTIN BONDING SYSTEMSFIRST GENERATION DENTIN ADHESIVE:•Given by S.S White .•There is development of surface active copolymer NPG-GMA (N-phenylglycine glycidyl methacrylate)•This copolymer could bond on the tooth surface to generate water resistant chemical bonds of resin to dentinal tubules.•It bonds to the calcium component of dentin.•Since they could bond with calcium ions in tooth structure, they form stronger bonds with enamel then dentin.

• Smear layer is ignored.• Example: Cervident.

LIMITATIONS OF FIRST GENERATION

BONDING AGENT:

• Low bond strength: 2-3Mpa.• Loss of bond strength over time.• Lack of stability of individual

component during storage.

SECOND GENERATION DENTIN ADHESIVE:•Clearfil Bond system F was the first product of second generation bonding agent which was introduced in Japan in year 1978.•It was a phosphate ester material.•Its mechanism of action was based on the popular interaction between the negatively charged phosphate group of resin & positively charged calcium in smear layer.

LIMITATIONS:•Smear layer was the weakest link in the system because of relatively loose attachment to dentin surface.•Bond Strength was low : 1-5MPa.

THIRD GENERATION DENTIN ADHESIVE:•Introduced in 1979.•These were designed not to remove the entire smear layer, but rather to modify it and to allow penetration of acidic monomers.•Involves the concept of phosphoric acid etching before application of phosphate ester type of bonding agent.

LIMITATIONS:•But because bonding agent have hydrophobic nature, acid etching did not produce the significant improvement in dentin bond strength inspite of flow of resin into open dentinal tubules.•Pulpal inflammatory responses were thought to be triggered due to application of acid.

FOURTH GENERATION DENTIN ADHESIVE:•These are introduced for the use on acid –etched dentin.•Multiple bottle adhesive system.•Smear layer is considered as an obstacle that must be removed so that resin can be bonded to the underlying dentin substrate.•Fourth generation adhesives are basically composed of:

I. An acid etching gel that is rinsed off.II. A solution of primers that are relatively hydrophilic monomers in

ethanol, acetone and/or water.III. Fluid bonding agent.

•Acid open up the dentinal tubules, thus creating microporosity of intertubular dentin.•When primer and bonding resins are applied to etched dentin, they penetrate the intertubular dentin, forming resin dentin interdiffusion zone or “hybrid layer”.

• Examples:1. All Bond-22. Scotch Bond Multipurpose3. Optioned FL4. Clearfil Liner Bond 2

FIFTH GENERATION DENTIN ADHESIVES:•Commercially available adhesive proves to be satisfactory but it contain several time consuming steps to be applied.•So “one bottle” adhesive system was introduced.•In this there is combination of primer and bonding agent steps, but a separate etching step. Total etch adhesive system:•Simultaneous application of an acid to enamel and dentin, known as the total etch technique.•It was initiated in Japan .•In this phosphoric acid etching of dentin is done before applying phosphate ester type of bonding agent.•Bond strength: 17-30MPa.

• Examples:1. Prime and bond2. Optibond solo3. Single Bond

SIXTH GENERATION DENTIN ADHESIVES:•Introduced in 2000.•These are single bottle adhesives combine etching, priming & bonding in a single solution & as single step.•It consists of self etching primers which are used in place of separate etchant•Less effective bond with enamel as compared to dentin due to high acidic content.•These are further of 2 types:• Self-etching primer & adhesive.• Self-etching adhesive.

• Self-etching primer & adhesive:• Two bottles: Liquid 1(acidic primer) Liquid 2(adhesive)• Acidic primer applied to the tooth followed by adhesive.• Light cure formulations.• Solvent is water.

• Self-etching adhesive:• Two bottles consisting of acid primer and adhesive.• A drop of each liquid is mixed and applied to the tooth.• Light cure formulations.

• Examples:• Xeno III

SEVENTH GENERATION DENTIN ADHESIVE:•The self etching primers was introduced in Japan.•These acidic primers include a phosphonated resin molecules that performs two functions simultaneously- Etching & Priming of dentin and enamel. •Unlike conventional etchants, self etching primers are not rinsed off.•In addition to simplifying the bonding technique, the elimination of rinsing and drying steps reduces the possibility of overwetting or overdrying.•They also have properties of disinfection & desensitization.•Bond strength: 20-28MPa.•Example: I bond G bond

CLINICAL INDICATIONS OF DENTIN BONDING AGENTS:

1.Bonding of directly placed resin based restorative materials.

2.Treatment of cervical abrasion.3.Bonding of prefabricated and cast posts.4.Sealing of pits and fissures of posterior teeth.5.Reattachment of fractured tooth fragments.6.Bonding orthodontic brackets.7.Bonding periodontal splints.

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SIDE EFFECTS 1)Sensitizing reaction (burning sensation) : Seen in

patient with a hypersensitivity to any of its ingredients. Its treatment is that the material should be removed.

2) Gingival Tissue reaction : It is white in appearance ,but not painful, has been reported after extended contact with these materials. The reaction ceases within few days.

INTERACTIONS Materials containing Eugenol or Clove oil inhibits

the polymerization of DBA. These types of materials should not be used in conjunction with DBA.

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