Bonding Agents Introduction Many of the restorative material

Bonding Agents

Introduction �Many of the restorative material used in dentistry will not adhere chemically to enamel / dentin thus increasing the chances of micro leakage. �An BONDING AGENT permits the placement of a more conservative restoration (composite), reduces microleakage and dentin sensitivity.

What are bonding agents ?

Dental adhesives / bonding agents �Are solutions of resin monomer that join a restorative material with a dental substrate (enamel dentin, rarely cementum) after the monomer sets by polymerization reaction OR �Material of low viscosity, when applied on the tooth surface, can form thin layer (after setting ), strongly bond to tooth surface, on which composite resin is applied

Advantages of adhesive in dentistry �Retention of restoration �No need to use undercut or mechanical lock , so less tooth structure is removed �More conservation of natural tooth structure �Reduction in microleakage- ↓post operative sensitivity, ↓ staining �Reduction in recurrent caries �Reinforcement of tooth structure

Classification of bonding agent � 1. According to the bonding mechanism �Mechanical bonding through acid etching – Composite resins , Bis GMA, TEGDMA, Cyanoacrylates �Chemical bonding – Zinc polycarboxylate cements , GIC

� 2. According to the application �Enamel bonding agents – Thin composite resins, TEGDMA, Cyanoacrylates, GIC �Dentin bonding agents – Several dimethacrylate systems, NPG-GMA, Cyanoacrylates, Bis GMA, Polyurethanes , -META, Ferric oxalate systems 4

�REQUIREMENTS OF BONDING AGENTS �Should have strong bond to withstand the stresses caused by polymerization contraction of composites. Optimum bond strength 17 Mpa – 20 Mpa. �Should form long-term durable bond �Should be biocompatible � Low viscosity to flow easily on the surface of tooth �Wet the tooth structure easily – Low S. T & C. A �Similar COTE as tooth (11. 4 ppm/*c), Prevents microleakage by reduced gap formation between tooth structure and restorative material.

�Should prevents recurrent caries and marginal staining. �Should be easy to use and minimally technique sensitive. �Have a reasonable shelf-life. �Low film thickness �Good dimensional stability �Should have both hydrophilic & hydrophobic reactive groups �Low thermal conductivity

Basic Concepts �Adhesion �Cohesion

Cohesion : �Cohesions is the molecular force of attraction between the like molecules (e. g. : -molecules of water) , responsible for holding the material together. �Examples : - 1. GOLD FOILS Bonding between two pieces of pure gold together under pressure, results from metallic bond.

Adhesion �Word adhesion comes from Latin word “adhere” means “to stick”. �Adhesion is defined as state in which two surfaces are held together by interfacial forces, which may consist of valance forces or interlocking forces or both. � OR § Attraction or bonding between dissimilar molecules of two materials.

Components of adhesive system: �Adhesive: is the material (usually liquid) that used to produce adhesion. �Adherend: is the Substrate (enamel, & dentin , rarely cementum surface) to which the adhesive is applied.

Components of adhesive system: Adhesive Adherend

Adhesive Junction The transition layer between the two surfaces of adhesive and adherend. Adherend (substrate) Adhesive junction Adherend (substrate)

Types of adhesion in dentistry Mechanical adhesion Microscopic Penetration Stresses Diffusion Ionic Bonds Primary valence forces Chemical adhesion Covalent bonds Metallic bonds Secondary valence forces Van der Waals forces Hydrogen bonding

Factors improving wetting & adhesion 1. Clean surface – adherend with clean surface , without any impurities such as - oil of cutting instrument, moisture, debris , smear layer etc. 2. High surface energy - of the adherend (acid etching increases surface area & energy 3. Low surface tension of adhesive 4. Low angle of contact of adhesive

Mechanism of adhesion �Adhesion to tooth structure is by exchange of inorganic tooth material (Hydroxyapatite) by synthetic monomer resins by the process of 1. Removing the Hydroxyapatite to create more micropores 2. Infiltration of resin monomer (bonding agent) into the micropores & subsequent polymerization � As a result, resin tags are formed that forms micromechanical interlocking with the tooth structure

Resin -tags Micro-pores

� Obstacles to bonding are 1. Un-homogenous composition of enamel and dentin. 2. Variation in the composition of enamel & dentin it self. 3. Inherent wetness of the surface of dentin. 4. Tenacious (adherent) microscopic debris in the prepared cavity (called Smear Layer)

�Smear Layer:

� Smear Layer: Thin tenacious adherent layer (1 -5 microns thickness) develops during cutting or grinding of tooth structure (both enamel & dentin ) after cavity preparation. Ø Contains of: a. Dentin chips. b. Saliva. c. Bacteria. d. Collagen. e. Blood. Ø Left smear layer on the tooth surface prevents strong bonding. So acid is used to remove smear layer from both enamel & dentin Ø

ADHESION TO ENAMEL AND DENTINE

Bonding to enamel

Bonding to enamel �Enamel has a complex surface structure with enamel rods inside & more organic components on the surface �Low Surface energy 84 erg/cm 2 (less than many restorative materials) , which do not help for wetting �Surface has moisture & other contamination is also decreases the wetting & proper bonding �So �Mechanical bonding is achieved by acid etching �Chemical bonding is achieved by the use of adhesive cements like polycarboxylate & GIC

Acid etch technique �Was first used in 1955 by Michael Buonocore �Mechanism : �Phosphoric acid is used to etch tooth enamel. It reacts with hydroxyapatite of enamel or of the enamel rods & cause selective dissolution. So that micro porosities forms on the surface. To which resin monomer (bonding agent) flows & subsequently polymerize to form resin tags & bonds mechanically to tooth structure

ENAMEL ETCHING : -

�ENAMEL ETCHING : Phosphoric acid as an etchant: In 1955 Michael Buonocore etched with 85% phosphoric acid for 30 sec 50 % phosphoric acid for 60 seconds - reacts with enamel , results in formation of mono calcium phosphate – monohydrate , which will prevent further etching. Concentrations below 25% - dicalcium phosphate monohydrate precipitate Concentrations above 40% - Dissolve less calcium and etch the patterns with poor definitions Finally 37% for 15 sec is considered appropriate.

Enamel Etching Dentin Etching

Enamel surface 37% phosphoric acid. 15 seconds wash dry Bonding agent

�Etching of enamel with 37% orth - phosphoric for 15 -30 secs, removes smear layer & about 10 mm of the enamel surface to expose prisms of enamel rods to create a honeycomb like appearance (micropores). �Then rinsed away with stream of water for 20 sec. �Enamel is dried completely with warm air , until it takes a white frosted appearance �This surface must be kept clean and dry until the resin bonding agent is placed.

Surface of etched enamel

Mechanism of etching �Etchant phosphoric acid reacts with HAP of enamel or of enamel rods & cause selective dissolution �Patterns of etching may be 1. Type 1 etching ; dissolution of the enamel rods centers. 2. Type 2 etching ; dissolution of the enamel rod peripheries. 3. Type 3 etching ; combination of both type 1 and type 2. �Etching Produces a microporosities on the surface, has - 6 µm in diameter & 10 -20 µm in length

Type III

�When a low viscosity resin monomer is placed , it wets , flows & infiltrates into micropores & polymerizes to form a RESIN TAGS (6 µm in diameter & 10 -20 µm in length), leading to micromechanical interlocking �Bond strength→ 20 -25 Mpa (after etching ) �Bond strength→ 5 -10 Mpa (without etching )

Etchant �Common etchant – phosphoric acid. conc. 37% �About 30% - 50% aq solution , also can be used �Alternative acids was tried e. g. - pyruvic acid, sulphuric acid, maleic acid, nitric acid , citric acid and oxalic acid.

�Available as liquids (acid) in syringes or gel form �Gel etchants are made by adding colloidal silica or polymer beads to the H 3 PO 4 & applied with brush.

Steps : �Cleaning – enamel surface by pumice slurry & then washed with water �Etching - phosphoric acid. conc 37% for 15 sec �Washing – acid should be rinsed away thoroughly with a stream of water for 20 sec �Drying – with a mild stream of air �Bonding agents are applied immediately before the etched surface gets contaminated with moisture , saliva & blood

Precautions 1). Acid etchant should not come in contact with the exposed dentin , acid ions penetrate through the dentinal tubules , cause irritation. (So Ca(OH)2 is placed over exposed dentin as a precautionary measure ) 2. Etched surface should not get contaminated with blood , saliva, moisture or oil of cutting instrument , before the bonding resin is applied 3. Delicate etched surface has thin fragile sections, this should not be damaged by touching with instruments

Bonding to dentin

Bonding to dentin why difficult? �Dentin etching is more technique sensitive than enamel etching because 1. Dentin is more humid & organic than enamel, hence bonding to this hard tissue extremely difficult 2. Dentin surface has complex structure – dentin consist of 50 vol% of inorganic HAP Crystal , 30 vol% of organic material (mainly type I collagen) hence less calcium ions are available for chemical bonding 3. Remaining is 20 vol% is fluid , coming out of exposed dentin tubule, prevents the bonding 4. Presence of smear layer on exposed dentin tubules.

Dentin etching : � In 1979 Fusayama et al used 37% phosphoric acid to etch both enamel and dentin (“Total etch technique” ) �Showed that it did not damage pulp & improved the bond strength. �In 1984 Nakabayashi et al. discovered formation of hybrid layer of resin infiltrated resin. � 1990`s dentin etching gained world wide acceptance.

HYBRID LAYER �Also known as interdiffusion zone, or resin supported dentine layer. � This is the zone where the adhesive resin of the dentin bonding agent micromechanically interlocks within the intertubular dentin and surrounding collagen fibers �The hybrid layer seals off the dentinal tubules from the ingress of microorganisms

�Hybrid layer is formed in following manner: � 1. Etching removes smear layer and exposes collagen fibers �It also removes hydroxyapatite with in the intertubular dentin � 2. Primers penetrate the collagen network. � 3. Adhesive resins along with the primers form resin micro tags within the intertubular dentin

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Unfilled resin bonding agent Hybrid layer Unaltered dentine with dentinal tubules

Steps of bonding to dentin Etching/ Conditioning primer bond The aim of bonding to dentin is to obtain what’s called “ LAYER ” which is “Resin-reinforced dentin layer”. HYBRID

Clinical steps of bonding to dentin � 1. Apply the conditioner ( is a type of acid used to alter or remove smear layer) passively to the prepared dentine not longer than 15 seconds � 2. Wash the conditioner with water and then dry � 3. Using a brush apply the primer immediately to the dentine surface to minimize the seepage of dentinal fluid to the dentine surface. � 4. Apply the adhesive resin, which penetrates dentine to form hybrid layer � 5. Apply the restorative resin.

Dentin bonding agents �Designed to provide strong interface between restorative composite & tooth structure to withstand mechanical forces & shrinkage stress

composition �Etchants �Primer �Resin monomers �Solvents �Initiators �Inhibitors �Fillers �Antimicrobial agents (some times used)

ETCHANTS �Used to remove smear layer �Phosphoric acid 37% used �Conc. above 50% - Monocalcium phosphate monohydrate forms on etched surface �Available in liquid or acid (in a disposable syringe ) or gel form �Gel form - consist of adding colloidal silica or polymer beads to the H 3 PO 4 �Brushes are used to place acidic gels.

Primers �Dentin etching is highly technique sensitive because demineralized collagen network readily collapses when dried �So a priming steps required to maintain a hydrated collagen network. �Hence priming is necessary to maintain collagen network for the infiltration of hydrophobic adhesive monomer �Primers are solution containing hydrophilic monomer HEMA (2 - hydroxylethyl methacrylate) dissolved in a solvent – acetone , ethanol, or water � primers defined as - a hydrophilic, low viscosity resin that promotes bonding to an adherend substrate (dentin)

Self-etching primers �The primers that contain etchants are sometimes referred to as self-etching primers. OR �If a primer has the ability to do both etch & prime called as self etching primer �Self –etching primers contains Acidic monomer like – HEMA – phosphate , phenyl –P, 10 -MDP (10 -metacryloxyethyle trimellitic acid, 4 - META (4 metacryloxyethyle trimellitic anhydride) , MAC (11 methacryloyloxy -1, 1 -undecanedicarboxylic acid)

Solvents � Water, ethanol, acetone �Solvent improves bond adhesion �Water ionizes acidic monomer & as well as re-expand the collapsed collagen network �Acetone or ethanol – volatile, can displace water from dentinal surface & keeps the collagen frame work moist

Adhesive Resins �They penetrate the etched dentine and copolymerize with the primer to form the Hybrid layer & resin tags to provide micromechanical retention �Function 1. Adhesive fills the interfibrillar space of collagen network , & creates a hybrid layer & resin tags to provide micromechanical retention 2. Prevent fluid leakage along the restorative materials margin �Adhesive resins are usually hydrophobic monomers - BIS- GMA , TEGDMA , UDMA & small amount of hydrophilic monomer HEMA

Initiators : �Photosensitizer – Camphoroquinone �Initiator – tertiary amine �Chemical initiator- BP

Filler �Nanometer –sized silica particles �Filler size- 40 nm �Fillers modifies the adhesive viscosity to a thicker, pastier consistency

Different generation dentin bonding agents Different generations of dentin bonding agents are : Generation - I -2 -3 -4 -5 -6 -7

First Generation (1950 -1970’s) �These products ignored the smear layer. �Bonding to the enamel and dentin by chelation with calcium on the tooth surface only, not to the collagen of dentin. �They included NPG-GMA (N- Phenylglycine Glycidyl methacrylate), the polyurethanes and the cyanoacrylates. �Bond strengths was 2 -3 Mpa.

�Hydrophobic monomers �First commercial dentinal adhesive �Cervident �Trade - SS White (1965) name – Cosmic bond

Limitations: �Low bond strength of 2 -3 MPa �Loss in bond strength over time �Lack of stability of individual components during storage �Based on carbon-13 NMR analysis – No ionic bonding develops between NPG-GMA and hydroxyapatite

2. Second generation (60’s - 80’s) �Here smear layer may play certain role in bonding to dentin. �Comprised of phosphate - esters material (Phenyl – P & HEMA in ethanol). �Bonding mechanism was based on polar interaction between -vely charged phosphate group in resin & + vely charged calcium in smear layer. �Bond strength only – 5 to 6 Mpa & did not improve much due to weak smear layer �E. g. Scotch. Bond (3 M dental), Prisma, universal bond, Bonolite and Clearfil bond system.

Drawbacks �Loosely attached smear layer �Hydrophobic resin, did not wet dentin well nor penetrate the entire depth of the smear layer & could not reach superficial dentin to establish ionic bonding. � Bond strength were less than 10 Mpa

Third Generation (mid-80’s) �Designed not to remove the entire smear layer, but rather to modify it & allow penetration of acidic monomer such as Phenyl – P or PENTA (Dipentaerythritol penta-acrylate monophosphate) �Here, the conditioner, primer and adhesive resin are applied in different steps �Conditioner – HEMA dissolved in maleic acid as in Scotch Bond II & 2% Nitric acid in Tenure �Primer - bi-functional monomer in a volatile organic solvent �Adhesive is a unfilled or partially filled resin �Bond strength - 3 -8 Mpa �E. g- Scotch. Bond 2, Tenure, universal bond 2, Coltene ART

�Steps 1) Application of dentin conditioner ( is a type of acid used to alter or remove smear layer) 2) Application of Primer bonding agent (a monomer dissolved in an organic solvent ) 3) Application of adhesive - Unfilled resin 4) Composite restoration on it

Etch - & - Rinse Adhesives are 1) 4 th generation ( 3 - step) � Conditioner (Total etching), primer, adhesive 2) 5 th generation (2 – step) Conditioner, (primer & adhesive)

Fourth Generation (early 1990’s) �Consist of 3 -step �Acid etching (TOTAL ETCHING IS DONE ) gel, rinsed off �Application of primer – consist of hydrophilic monomer dissolved in an organic solvent such as acetone , ethanol, or water �Application of unfilled or filled fluid bonding agent (consist of hydrophobic Bis. GMA + hydrophilic HEMA) �High bond strength – 13 - 30 Mpa

4 th generation- 3 STEP PROCEDURE Conditioner Primer Adhesive resin

Steps 1) Total etching- etch enamel & dentin simultaneously with Conditioner (phosphoric acid) for 15 sec, removes smear layer & exposes collagen network 2. Rinse to remove etchant 3. Dry with air , without desiccating the collagen mesh 4. Slightly moisten the surface 5. Absorb excess water with a cotton pellet 6. Apply primer ( 1 -6 coats ) which infiltrates collagen & allow it to polymerize 7. Dry thoroughly to remove primer solvent 8. Apply adhesive bonding agent (thickness 50 µm ) to enamel & dentin. 9. Light cure – the primers & bonding agents 10. Apply composite resin over adhesive 11. Cure the matrix resin of composite resin

Examples �All – Bond II , Scotch. Bond Multi-Purpose �Optibond FL

Fifth Generation(late 1990’s) �One step or one bottle products. �Misnomer as these products are applied in 2 steps- Etchant Single component Primer + Adhesive resin First step Second step (One bottle)

5 th generation conditioner Combined (single component) Primer adhesive resin

�Consist of 2 -step �Available as “one bottle” or “one –step” adhesive system (but product applied in 2 –step) �Step 1. - Separate etching/ conditioning �Step 2. - Primer & adhesive resin (Used together) into one application �Etchant – 30 -40% phosphoric gel , rinsed away , promotes the dissolution of enamel rods , creating more porosities , filled by bonding agent followed by polymerization �In case of dentin phosphoric acid exposes a collagen network , resin infiltrates the collagen mesh , forming a hybrid layer. On polymerization hybrid layer provides micromechanical bonding �High bond strengths 3 -25 Mpa �E. g - prime & bond , Single bond, Opti. Bond Solo Plus

Self – etch Adhesives 1. Two – step (6 th generation ) � Self etching primer (conditioner + primer), adhesive 2. One – step (7 th generation )

Sixth Generation(late 1990’s) � 2 step (self – etch PRIMER) �Does not involve a separate etching step �In this case acidic monomer is used to condition & prime the tooth at the same time � 2 types of self etch adhesive – mild & strong �Mild(PH=2), partially dissolves dentin surface, so substantial amount of HAC remain available with in the hybrid layer �Strong (low PH ˂1)

�These systems use self etching primers to partially demineralize the smear layer and the underlying dentin surface without removing the dissolved smear layer. � 2 - step Self etch primer Adhesive Resin First step Second step

6 th generation Adhesive resin Self –etching Primer

Seventh Generation (most recent) �Comprise of the one – step self etch system (single solution) �Also named “All-in-one” adhesives �In this all primary component - conditioner, primer & bonding resin are into a single solution �No mixing �Low bond strengths �E. g – - Promp L Pop (ESPE) - Prime and Bond NT (Dentsply)

Self –etching Adhesive Single solution (all in one )

Currently Available Generations �Fourth Generation �Three-step: � 1. Etch & rinse 2. Primer � 3. adhesive �Fifth Generation �Two-step: 1. Etch & rinse, 2. primer & adhesive � Mix �Sixth Generation �Two-step Self-etch � No mix �One-step Self-etch � mix �Seventh Generation �One-step Self-etch � no mix

Clinical application �For bonding composite core – 3 -step, etch-&-rinse (4 th generation) �Anterior & posterior composite , resin cementation of veneers – 2 –step etch & rinse ( 5 th generation) �Posterior composite – self etch , 2 -step (6 th) �Dual –cure esthetic posts& ceramic restoration – one step , self –etch (7 th) �Light cure posterior composite - one step , self –etch (7 th)

Uses � 1. Adhesion of restorative resin to GIC -base � 2. Bonding amalgam restorations to cavity walls using amalgam bond. � 3. Repair amalgam restorations by condensing new amalgam on a freshened old amalgam after applying the adhesive of amalgam bond. � 4. Luting of cast restorations e. g. panavia � 5. Management of dentine hypersensitivity.