Fundamental concepts of enamel and dentin adhesion
- 1. FUNDAMENTAL CONCEPTS OF ENAMEL AND DENTIN ADHESION Dr. Richa Singh Reader Conservative dentistry and Endodontics
- 2. • The word adhesion comes from the latin ‘adhaere’ (‘to stick to’). • Adhesion is defined as the state in which two surfaces are held together by interfacial forces, which may consist of valence forces, or interlocking forces or both.
- 3. • Adhesive is a material, frequently a viscous fluid that joins two substrates together by solidifying, resisting separation and transferring a load from one surface to the other. • Adhesive strength is the measure of the load- bearing capacity of an adhesive joint.
- 4. Mechanisms of Dental Adhesion 1. Mechanical Adhesion: Interlocking of the adhesive with irregularities in the surface of the substrate, or adherend. This would involve the penetration of adhesive resin and formation of resin tags within the tooth surface.
- 5. 2. Adsorption adhesion: Chemical bonding between the adhesive and adherend; the forces involved may be primary valence forces (ionic and covalent) or secondary valence forces (hydrogen bonds, dipole interaction, or van der Waals). This would involve the chemical bonding to the inorganic component (hydroxyapatite) or organic components (mainly type I collagen) of tooth structure.
- 6. 3. Diffusion adhesion: Interlocking between mobile molecules, such as the adhesion of two polymers through diffusion of polymer chain ends across an interface. This would involve the precipitation of substances on the tooth surfaces to which resin monomers can bound mechanically or chemically.
- 7. 4. A combination of the previous three mechanisms.
- 9. Criteria for optimal adhesion • For good adhesion to take place, five fundamental attributes are:
- 10. Indications for Adhesive Dentistry 1. Restore class I, II, III, IV, V, and VI carious or traumatic defects 2. Change the shape and color of anterior teeth. 3. Improve retention for porcelain fused to metal or metallic crowns 4. Bond all ceramic restorations 5. Seal pits and fissures 6. Bond orthodontic brackets
- 11. 7. Bond periodontal splints and conservative tooth- replacement prostheses 8. Repair existing restorations 9. Provide foundations for crown 10. Desensitize exposed root surfaces 11. Seal beneath or bond amalgam restorations to tooth structure. 12. Impregnate dentin that has been exposed to the oral fluids, making it less susceptible to caries.
- 12. 13. Bond fractured fragments of anterior teeth 14. Bond prefabricated fiber or metal posts and cast posts 15. Reinforce fragile endodontically treated roots internally 16. Seal root canals during endodontic therapy 17. Seal apical restorations placed during endodontic surgery.
- 13. Enamel Adhesion: Buonocore’s Acid Etch Technique • Buonocore in 1955, envisioned the use of acids to etch enamel for sealing pits and fissures • The formation of resin microtags within the enamel surface is the fundamental mechanism of resin-enamel adhesion.
- 15. Resin microtag mechanism of enamel adhesion: Acid etching transforms the smooth enamel into an irregular surface and increases its surface free energy Application of a fluid resin-based material to the irregular etched surface, facilitates penetration of the resin into the surface aided by capillary action Monomers in the material are then polymerized, and the material becomes interlocked with the enamel surface.
- 16. Etch Pattern 3 different micromorphologic patterns: 1. Type I etch pattern involves the dissolution of prism cores without dissolution of prism peripheries. 2. Type II etch pattern is the opposite of type I. The peripheral enamel is dissolved, but the cores are left intact. 3. Type III etch pattern is less distinct than the other two patterns. It includes areas that resemble other patterns and areas whose topography is not related to enamel prism morphology.
- 18. Etchant Concentration: Most current phosphoric acid gels have concentrations of 30-40%, with 37% phosphoric acid being the most common. Etch Time: Currently, an etching time of 15 sec is recommended. Bond Strength: Shear bond strengths of composite to phosphoric acid-etched enamel usually exceed 20 Mpa depending on the test method used.
- 19. Dentin Adhesion: Mechanism and Challenges • Adhesive materials can interact with dentin in different ways- mechanically, chemically or both. • Dentin adhesion relies primarily on the penetration of adhesive monomers into the network of collagen fibers left exposed by acid etching. • Dentinal adhesion is a clinical challenge due to the following reasons: i. Structure of dentin ii. Smear layer iii. Stresses at the resin-dentin interface
- 22. I. Structure of Dentin • Bonding to enamel is a relatively simple process where as bonding to dentin presents a much greater challenge. • Enamel is a highly mineralized tissue composed of more than 90% (by vol) hydroxyapatite, where as dentin is an intrinsically hydrated tissue, penetrated by a maze of fluid-filled tubules.
- 23. • Dentin also contains a dense network of dentinal tubules that connect the pulp with the dentino enamel junction. The relative area occupied by dentin tubules decreases with increasing distance from the pulp. • A cuff of hyper mineralized dentin called peritubular dentin lines the tubules. The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding. • Adhesion can be affected by the RDT after tooth preparation. Bond strengths are generally less in deep dentin than in superficial dentin.
- 25. II. Smear Layer • Whenever tooth structure is prepared with a bur or other instrument, residual organic and inorganic components form a layer of debris on the surface of the substrate which is termed as smear layer. • The smear layer fills the orifices of dentin tubules, forming smear plugs and decreases dentin permeability by nearly 90% • Thickness of smear layer- 0.5- 2um • Thickness of smear plug- 1-10um
- 27. Composition: Smear layer is predominantly made up of hydroxyapatite and altered denatured collagen. This altered collagen can acquire a gelatinized consistency because of the friction and heat created by the preparation procedure. The factors determining the composition of the smear layer include the following: i. Type of cutting/abrading instrument used ii. Type and method of chemicals/disinfectants employed iii. Composition of tooth structure, which would vary according to the site iv. Presence or absence of bacteria
- 28. Clinical Considerations i. The presence of intact smear layer is detrimental for optimal bonding to take place. ii. Optimal dentin bonding can take place by: a. Complete removal of the smear layer prior to the bonding procedure by using etch and rinse adhesives. b. Incorporation of the smear layer into the bonding layer by using self-etch adhesives c. Complete removal of the smear layer increases the permeability of dentinal tubules by more than 90%
- 29. III. Stresses at the Resin-Dentin Interface • Composites shrink as they polymerize, creating considerable stresses within the composite mass, depending on the configuration of the preparation.
- 30. i. Configuration Factor (C- Factor) When the composite is bonded to one surface only, stresses within the composite are relieved by flow from the unbonded surface. Stress relief within a three-dimensional bonded restoration is limited, however, by its configuration factor.
- 31. ii. Coefficient of Thermal Expansion Each time a restoration is exposed to wide temperature variations in the oral environment, the restoration undergoes volumetric changes of different magnitude compared with those of the tooth structure. This occurs because the linear coefficient of thermal expansion of the composite is about four times greater than the tooth structure.
- 32. iii. Occlusal Loading Loading and unloading of restored teeth can result in transitional or permanent interfacial gaps. Additionally, the tooth substrate itself might be weakened by cyclic loading.
- 33. Classification of Dentinal adhesives 1. Historical strategies: i. First generation (1965) ii. Second generation (1978) iii. Third generation (1984) 2. Current strategies: i. Etch and rinse adhesives a. Three step- etch and rinse adhesive (fourth generation) b. Two step- etch and rinse adhesive (fifth generation)
- 34. ii. Self-etch adhesives a. Two component- self-etch adhesive (sixth generation) - Two step- two component – self-etch adhesive - One step- two component – self-etch adhesive b. Single component- one step – self-etch adhesive (seventh generation)
- 35. I. Historical Strategies i. First Generation (1965) Chemical- Surface-active co-monomer NPG- GMA (N-phenylglycine glycidyl methacrylate) This co-monomer could chelate with calcium on the tooth surface to generate water- resistant chemical bonds of resin to dentinal calcium.
- 36. Brand name- Cervident (SS White) Bond Strength- Only 2-3MPa Clinical result- Poor
- 37. ii. Second Generation (1978) Chemical- It was phosphate-ester material (phenyl-P and hydroxyethyl methacrylate in ethanol) It was based on the polar interaction between negatively charged phosphate groups in the resin and positively charged calcium ions in the smear layer.
- 38. Brand names 1. Clearfil Bond System F 2. Scotchbond 3. Bondlite 4. Prisma Universal Bond Bond strength Only 1-5 Mpa Clinical result- unacceptable
- 39. iii. Third generation (1984) Chemical- It was a phosphate-based material containing HEMA and a 10-carbon molecule known as 10-MDP (10- Methacryloyloxy decyl dihydrogen phosphate) The concept of phosphoric acid-etching of dentin before application of a phosphate ster- type bonding agent was introduced by Fusayama et al in 1979. Clearfil New Bond was the only third generation bonding agent to follow the etched dentin philosophy.
- 40. Most of the other third-geneation materials were designed not to remove the entire smear layer but, rather, to modify it and allow the penetration of acidic monomers, such as phenyl-P or PENTA (Dipentaerythritol penta-acrylate monophosphate). Brand names- 1. Clearfil New Bond 2. Scotchbond 2 Clinical result- Results were mixed
- 41. II. Current Strategies for Resin- Dentin Bonding i. Etch and Rinse Adhesives The smear layer is considered to be an obstacle that must be removed to permit resin bonding to the underlying dentin substrate. The next generation of dentin adhesives was introduced for use on acid etched dentin. The clinical technique involves simultaneous application of an acid to enamel and dentin, this method was originally known as the total- etch technique. Now more commonly called etch- and-rinse technique, it was the most popular strategy for dentin bonding during the 1990s and remains somewhat popular today.
- 42. Mechanism of action of etch and rinse adhesives: Application of acid to dentin results in partial or total removal of the smear layer and demineralization of the underlying dentin Acids demineralize intertubular and peritubular dentin, open the dentin tubules, and expose the collagen fibers, increasing the microporosity of the intertubular dentin Dentin is demineralized by up to appx 7.5um, depending on the type of acid, application time, and concentration.
- 43. The primer in the system is designed to increase the critical surface tension of dentin, which gets decreased after the acid etching step Bonding mechanism i. When primer and bonding resin are applied to etched dentin, they penetrate the intertubular dentin, forming a resin-dentin interdiffusion zone, or hybrid layer ii. They also penetrate and polymerize in the open dentinal tubules, forming resin tags
- 45. Moist bonding technique • Complete drying of dentin after completion of the acid etching procedure is not clinically recommended as vital dentin is inherently wet. • Drying the dentin surface with air would cause the dentinal collagen to collapse which would prevent the monomers from penetrating the nano channels formed by dissolution of hydroxyapatite crystals between collagen fibers. • The moist bonding technique used with etch-and- rinse adhesives prevents the collagen collapse that occurs on drying demineralized dentin.
- 46. • The use of etch-and-rinse adhesive systems on moist dentin is made possible by incorporation of the organic solvents acetone or ethanol in the primers or adhesives. • Because the solvent can displace water from the dentin surface and the moist collagen network, it promotes the infiltration of resin monomers throughout the nanospaces of the dense collagen web.
- 47. a. Three step: Etch and rinse adhesives (fourth generation) Components: Etchant gel + primer (bottle I) + adhesive bottle (bottle II) These include 3 essential components that are applied separately and sequentially: 1. Phosphoric acid – etching gel that is rinsed off 2. Primer containing reactive hydrophilic monomers in ethanol, acetone, or water 3. Unfilled or filled resin bonding agent – adhesive. It contains hydrophobic monomers such as Bis-GMA, frequently combined with hydrophilic molecules such as HEMA.
- 48. • Step I- Application of etchant gel for 15 sec • Step II- Rinse the etchant off thoroughly and blot dry the substrate (moist bonding technique) • Step III- Application of primer (bottle I) on the substrate • Step IV- Application of adhesive (bottle II) on the substrate • Step V- Light cure
- 49. Brand names 1. All-Bond 2 and All-Bond 3 2. OptiBond FL 3. Adper Scotchbond multi-purpose Bond Strength- 17-30MPa Clinical result- successful
- 50. b. Two step: Etch and rinse adhesives (fifth generation) Concept- In order to simplify the clinical procedure a number of dental materials manufactures are marketing a simplified, two- step etch-and-rinse adhesive system. They are sometimes called one-bottle systems because they combine the primer and bonding agent into a single solution. Components: Etchant gel + Primer and adhesive present in a single bottle
- 51. • Step I: Application of etchant gel for 15 sec • Step II: Rinse the etchant off thoroughly and blot dry the substrate • Step III: Application of primer and adhesive (single bottle) on the substrate • Step IV: Light cure Brand names: 1. Prime and Bond NT 2. Adper Single Bond 3. ExciTE 4. One Coat Bond 5. XP Bond
- 53. ii. Self-Etch Adhesives Concept An alternative bonding strategy is the self-etch approach that involves the omission of a separate etching step. The elimination of the etching procedure has the following advantages: 1. Clinician friendly procedure 2. Less technique sensitive
- 55. Two types of self-etch adhesives are available: 1. Two component- self etch adhesives (sixth generation) i. Two step: two component- self-etch adhesives These are also described as nonrinsing conditioners or self-priming etchants. Mechanism of action- These acidic primers include a phosphonated resin molecule that performs two functions simutaneously (a) Etching and Priming of enamel and dentin (b) Incorporating smear plugs into the resin tags
- 56. • Step I: Bottle I (conditioner+primer) application on the tooth surface • Wait for 10 sec and no need to rinse the substrate • Step II: Bottle II (adhesive) application on the tooth surface • Step III: Light cure Brand names 1. Clearfil SE Bond 2. AdheSE 3. Optibond Solo Plus Self-etch
- 58. ii. One step: Two component- self-etch adhesives Concept They comprise of a two bottle system containing the conditioner, primer and adhesive resin which has to be mixed before applying to the bonding substrate. Step I: Dispense and mix one drop each from bottle I (conditioner + primer) and bottle II (adhesive) Step II: Apply on the tooth surface (no need to rinse the substrate) Step III: Light cure
- 59. Brand names 1. Xeno III 2. One up Bond 3. Prompt L Pop
- 60. 2. One step: Single component-self-etch adhesives (Seventh generation) Concept Continuing the trend toward simplification, no-rinse, self-etching materials that incorporate the fundamental steps of etching, priming and bonding into one solution have been introduced Conditioner + Primer + Adhesive = Single Bottle
- 61. • Step I: Dispense and apply on the tooth surface (no need to rinse the substrate) • Step II: Light cure Mechanism of action In contrast to conventional adhesive systems that contain an intermediate light-cured, low-viscosity bonding resin to join the composite restorative material to the primed dentin-enamel substrate, these one-step self-etch or ‘all-in-one’ adhesives contain uncured ionic monomers that contact the composite restorative material directly.
- 62. Brand names: 1. AdheSE One F 2. Adper Easy One 3. Clearfil S3 Bond 4. iBOND Self-Etch 5. Xeno V+
- 65. Clinical Factors in Dentin Adhesion 1. Sclerotic Dentin: The dentin that undergoes compositional changes in which the tubules become obliterated with tricalcium phosphate crystals is called sclerotic dentin and is much more resistant to acid-etching than normal dentin. Consequently, the penetration of a dentin adhesive is limited.
- 66. 2. Occlusal Forces Masticatory forces might not only cause noncarious cervical lesions but also might contribute to the failure of class V restorations. Although this stress may be of very low magnitude, the fatigue caused by cyclic stresses may cause failure of bonds between resin and dentin.
- 67. 3. Solvent The solvent used in the adhesive monomer solution has been shown to influence the clinical behavior of dentin adhesives. An acetone-based adhesive resulted in lower retention rate than an ethanol-based adhesive as it is more technique sensitive.
- 68. 4. Type of Composite Composites shrink as they polymerize, but the amount of shrinkage depends on the inorganic load of each specific composite. Microfilled composites have a low elastic modulus, which means that they are better able to relieve stresses caused by polymerization or by tooth flexure. Materials that have a higher young’s modulus do not relieve stresses by flow; they are unable to compensate for the stresses and subsequently get transferred to the adhesive interface and cause debonding.
- 69. 5. Polymerization Shrinkage Stresses Polymerization is initiated on the surface of the restoration, close to the light source, eliminating this surface as a potential stress relief pathway. The use of a flowable composite between the composite and the tooth wall serve as a shock absorber and simultaneously protect the interface against fatigue stresses.
- 70. 6. Biocompatibility Dentin adhesive system are well tolerated by the pulp-dentin complex in the absence of bacterial infection. Adverse pulpal reactions after a restorative procedure are not caused by the material used in that procedure but by bacteria remaining in, or penetrating, the preparation.
- 71. 7. Microleakage Microleakage is defined as the passage of bacteria and their toxins between restoration margins and tooth preparation walls. An adhesive restoration might not bond sufficiently to etched dentin to prevent gap formation at margins. The occurrence of gaps at the resin-dentin interface may not cause immediate debonding of the restoration. However, if a dentin adhesive system does not adhere intimately to the dentin substrate, an interfacial gap eventually develops, and bacteria are able to penetrate through this gap.
- 72. 8. Nanoleakage The term nanoleakage has been used to describe small porosities in the hybrid layer or at the transition between the hybrid layer and the mineralized dentin that allow the penetration of minuscule particles of a silver nitrate dye. When ammoniacal silver nitrate is used, silver deposits penetrate the hybrid layer formed by either etch-and-rinse or self-etch adhesive materials.
- 73. Penetration of ammoniacal silver nitrate results in two distinct patterns of nanoleakage: 1. A spotted pattern in the hybrid layer of self- etch adhesives, which might be caused by incomplete resin infiltration. 2. A reticular pattern that occurs in the adhesive layer, most likely caused by areas where water was not totally removed from the bonding area.
- 75. Types of failure Failures of adhesive joints occur in three locations, which are generally combined when an actual failure occur: 1. Cohesive failure in the substrate 2. Cohesive failure within the adhesive 3. Adhesive failure or failure at the interface of substrate and adhesive.
- 76. Amalgam Bonding System Amalgam bonding systems were introduced to seal underlying tooth structure and bond amalgam to enamel and dentin. 4-methyloxy ethyl trimellitic anhydride (4- META) based systems were used frequently as amalgam bonding agents. This monomer molecule contains hydrophobic and hydrophilic ends.
- 77. Bonding mechanism 1. Although good bonding to the tooth structure occurs, micromechanical bonding at the interface of amalgam and the bonding system is poor. 2. Most debonding occurs by fracture along this interface. As no chemical bonding occurs at this interface, it is important to develop micromechanical bonding. 3. To accomplish this, the bonding system is applied in much thicker layers(10-50um) so that amalgam being condensed against the
- 78. resin adhesive layer forces the fluid components of amalgam to squeeze into the unset bonding adhesive layer and produce micromechanical laminations of the two materials. Bond Strength Macroshear bond strengths for joining amalgam to dentin are relatively low (2-6 Mpa).