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Principals of Bonding
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- 2. Basic Principles ofBonding In dentistry, the term bond, or bonding, is used to describe the process of attaching restorative materials to the tooth by adhesion. When describing cosmetic restorations, such as porcelain or composite veneers, patients often use the term bonding. The basic principles of the bonding process involve preparing the surface of the tooth or restoration.
- 3. Basic Principles ofBonding Preparing the tooth surface includes removing decay, plaque, and debris. The tooth then is etched or conditioned with a 10% to 42% solution of phosphoric acid. This conditioning removes microns of tooth to provide a rough surface to which bonding can occur. https://www.youtube.com/watch?feature=player_detailpage &v=IHoBkQtVdeo
- 4. Bonding to anetched surface: When a resin bonding agent or primer is flowed over the etched surface, it penetrates into the microscopic pores. When a resin bonding agent cures, it forms resin tags that adhere to the etched surface of the tooth. The resin bonding agent then will chemically bond to other resins placed over it, such as composite resin.
- 5. Primary and secondarybonds: The primary or chemical bond occurs through adhesion when the bonding agent and the composite resin material adhere to each other. The chemical bond is stronger than a secondary or physical bond. An example is adhesion of paint to a metal surface.
- 6. Surface wetting: Etching increasesthe ability of the bonding material to wet the tooth surface by creating a high surface energy. Good wetting increases the contact of the material and the tooth; poor wetting prevents complete contact. For this reason, bonding agents are typically made of a low-viscosity material.
- 7. Bond strength: The strengthof the bond is determined by the amount of force needed to break the two materials apart. This is accomplished by pulling the two materials apart or by applying force until the bond fails. An enamel bond is typically stronger than a dentinal bond.
- 8. Enamel Etching Removes asmall portion of the surface Removes the smear layer Etching times Suggested times for Permanent teeth 20-30 seconds Highly mineralized teeth Up to 60 seconds Primary 60 seconds or more 8
- 9. Enamel Etching Thesmall surface of the enamel that is removed with etching reduces the enamel rods and opens porosities among the rods. The removal of the smear layer also occurs during etching, and the smear layer is made up of debris on the enamel or dentinal surface that results from the cutting of tooth structure during the cavity preparation. The smear layer comprises bacteria, salivary components, and tooth dust.
- 10. Enamel Etching Clinicaltrials show good results in some teeth in as short as 10 seconds of etching. For permanent teeth, the etch time is usually 20 to 30 seconds. Highly mineralized teeth may be more resistant to etching and may require up to 60 seconds of etching. Primary teeth should be etched for longer periods (60 seconds or more), because the enamel has a prism pattern that is not well structured. Etching should take approximately 20 to 60 seconds, depending on the manufacturer’s instructions and the type of procedure to be completed.
- 11. Enamel Etching Theetched surface should have a frosty appearance when dried. When a cavity preparation involves the etching of both enamel and dentin and the preparation is left slightly moist for wet denting bonding, the frosty appearance of the enamel cannot be determined.
- 12. Enamel Etching Theacid etchant comes as a liquid and a gel. The application of the etchant depends on the form that is being used. The recommended rinsing times for acid gels is approximately 10 seconds or longer. (we say 20-30 seconds) Rinsing times shorter than 5 seconds may not remove residual silica. Rinsing times for liquid etchants can be shorter – 5 to 10 seconds.
- 13. Dentin Etching Smear layer Acidicprimers Phosphoric acid etching Moist dentin for bonding 13
- 14. Dentin Etching The dentinhas a higher water content because of its organic makeup. It also contains collagen and other fluids from the pulp chamber. The smear layer, which is made up of debris on the enamel or dentinal surface resulting from the cutting of tooth structure during cavity preparation, must be removed before the bonding procedure is performed.
- 15. Smear layer The smearlayer contains plaque, bacteria, pellicle, salivary components, blood, and tooth dust. The smear layer sticks tenaciously to the surface, plugs the openings of the dentinal tubules, and cannot be washed off with use of air-water spray.
- 16. Dentin Etching Bonding agentsthat use acidic primers to etch the enamel and dentin penetrate the smear layer and incorporate it into the bonding agent, since there is no rinsing used with these systems. https://www.youtube.com/watch?feature=player_ detailpage&v=TMiN029CWLU
- 17. Dentin Etching Etching dentinwith phosphoric acid dissolves the smear layer first, and then portions of the hydroxyapatite crystals from the surface of the dentin, creating a porous surface and exposing the meshwork of collagen fibrils that are part of the dentin matrix. This opens the dentinal tubules, which leaves a rough, porous surface.
- 18. Dentin Etching Dentin hasa lower mineral content and needs to be etched for only about 10 seconds. Over-etching leaves a weaker bond.
- 19. Dentin Etching Wet dentinfor bonding is where the acid is removed by rinsing for at least 10 seconds. The excess water is removed by a gentle stream of air, but the dentin surface must be moist to keep the collagen fibrils fluffed up. https://www.youtube.com/watch?feature=player_detai lpage&v=EZr8Tpy3GtM
- 20. Enamel Bonding Enamel bonding resins Singlecomponent Resin tags 20
- 21. Enamel Bonding Bonding agentsare low-viscosity resins dissolved in solvents, typically acetone or ethyl alcohol, that penetrate porosities in the tooth surface created by etching.
- 22. Enamel Bonding Bonding agentsfor enamel requires only a single component – low-viscosity liquid.
- 23. Enamel Bonding Whenthe resin is cured by a chemical process or by light- activation, it locks into the microscopic spaces and irregularities, producing resin tags. The resin tags secure the resin to the enamel and create a very strong bond. Contaminates on the surface, such as saliva or blood, can dramatically lower the strength of the bond to the enamel. This is the major reason why good isolation is so important.
- 24. Dentin Bonding Dentin bondingresins Resin primer Solvents Adhesive resin 24
- 25. Dentin Bonding Bonding agentsfor dentin are viewed as two types: (1) the resin primer that penetrates etched dentin and enamel and lays down a resin layer and (2) adhesive resin (bond) that is applied over the primer. The two resins chemically bond to each other.
- 26. Dentin Bonding The initialresin prepares or "primes" the tooth surface (hence why we call it “prime/primer”), and the second resin chemically bonds to the primer. The primer is placed first and is dried, to remove the solvent and the remaining water.
- 27. Dentin Bonding The firststep of bonding to dentin requires the primer to penetrate water on the surface of the tooth. In order for the resin to penetrate through the water, it must be dissolved in a solvent that can penetrate water and carry the resin with it.
- 28. Dentin Bonding Resins The primer is composed of hydrophilic (water-tolerating) monomers and molecules that allow it to penetrate water. Usually HEMA (2-Hydroxyethyl methylacrylate) The bonding agent is applied over the primer. This is usually bis-GMA, TEGDMA, and urethane dimethacrylate The initial resin prepares (or primes) the tooth, and the second chemically bonds to the primer. Some manufacturers have combined the primer and bonding resin into one bottle to eliminate one step in the process.
- 29. Wet Dentin Bonding Bonding to moist dentin was the first technique to achieve good bond strengths in dentin. The dentin is kept moist to keep the collagen fibrils from collapsing into a thick mat that blocks penetration of the bonding agents. A primer is more important to dentin bonding than enamel because the primer contains hydrophilic groups that penetrate wet, etched dentin and keep the meshwork of collagen fibrils expanded, so that the adhesive resin can penetrate
- 30. Solvents For the resinto penetrate through the water, it must be dissolved in a solvent that can penetrate water and carry resin with it The solvents allow the resin to penetrate water on the dentin an din dentin tubules, and to penetrate around collagen fibrils and into porosities in the tooth surfaces created by etching
- 31. Solvents Solvents areusually acetone, ethanol (ethyl alcohol), or a combination of ethanol and water In general, the solvent is the largest portion of the bonding agent, making up 60% or more of the material Acetone is a highly volatile solvent Its rapid evaporation may require that two or more coats of the bonding resin be applied to ensure adequate sealing of the dentin. Ethanol evaporates more slowly, so it may need a longer drying time. All bottles must be recapped immediately after dispensing, to prevent evaporation of the solvent, which leads to gradual thickening of the resin with less ability to penetrate etched dentin.