Oper.ii 08
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The document discusses the steps of bonding to enamel and dentin in adhesive dentistry, highlighting the importance of proper etching and rinsing techniques. It details the roles of etch-and-rinse adhesives, including selective acid demineralization, primer application, and adhesive resin use, while also addressing the pros and cons of these systems. Effective bonding is emphasized, with recommendations for using specific materials and techniques to ensure optimal outcomes and longevity of dental restorations.
Oper.ii 08
- 2. College of Dentistry Operative Dentistry II Introduction to Adhesive Dentistry -2- Dr. Hazem El Ajrami
- 3. • Steps of bonding to enamel and dentin: The steps of bonding to tooth substrate differ to some extent depending on the category of adhesive used. Adhesive systems generally aim to remove, dissolve or modify smear layer and create microporosities in enamel and dentin for micromechanical interlocking. Manufacturer's instructions for application of each adhesive system should be strictly followed, and the use of the adhesive system with its recommended composite is mandatory.
- 4. 1. Etch-and-rinse adhesives: (smear layer removing adhesives): A. Selective acid demineralization (conditioning, etching): Conditioning is defined as any chemical alteration on the substrate surface by acids with the objective of removing the smear layer and simultaneously demineralizing the surface. Etching is a form of conditioning usually termed if a strong acid is used, particularly on enamel surface.
- 5. • Etch-and-rinse adhesives incorporate a separate etching step which is used for total etching of enamel and dentin, followed by thorough rinsing. Generally, use of phosphoric acid concentration between 30% and 40% and an etching time of no less than 15 seconds are recommended to achieve the most receptive surface for bonding.
- 6. • Acid etchant is supplied in the form of a liquid or colored gel. The gel form is preferred because its application is easier to control. The etchant must be thoroughly rinsed with water for 5-10 seconds to remove the acid remnants and the dissolved calcium phosphates.
- 7. • Enamel etching: The goals of enamel etching are to remove the organic pellicle and prismless enamel in uncut enamel and to remove the smear layer in cut enamel. Enamel etching partially dissolves the mineral crystals transforming smooth enamel surface into an irregular surface with numerous microporosities, thus enlarging its surface area for bonding, increasing its surface energy more than twice that of unetched enamel and lowering contact angle of wetting.
- 8. • Selective demineralization of enamel surface produces dissolution and microporosities in the interprismatic substance (interprism etching) (black arrow) in addition to microporosities in the enamel prism core (intraprism etching) (white arrow).
- 10. • Dentin etching: The goal of dentin etching in Etch-and-rinse adhesives is the total removal of the smear layer, including the smear plugs and to demineralize the superficial dentin surface. This removes the minerals from this superficial layer and exposes a microporous layer of organic collagen fibers, thus increasing the microporosity of the intertubular dentin.
- 11. • When the acid etching unplugs the dentinal tubules, it demineralizes the peritubular dentin to a lesser extent producing more funneling of the dentinal tubules. The exposed collagen fibrils function as a microretentive network for micromechanichal interlocking of the resin polymers.
- 12. B. Primer: Acid-etched enamel has high surface energy and does not need a separate primer application to achieve effective bonding. On the contrary to enamel, etching of dentin decreases its surface energy. This is due to the high protein extent exposed after etching (exposed collagen).
- 13. • In addition, the increased permeability and wetness of dentin hinder adhesion. Thus, a primer should be used to ensure sufficient wetting to dentin, displace residual water and sufficiently carry monomer into created microporosities. Primers are thus called adhesion-promoting monomers.
- 14. • Effective primers should contain hydrophilic monomers, e.g. Hydroxyethyl Methacraylate (HEMA), that have an affinity for wet dentin and a hydrophobic part that co-polymerizes with the subsequently applied adhesive resin. The primer could contain organic solvents, such as acetone or ethanol.
- 15. • Because of their volatile characteristics, these solvents act as water-chaser; it displaces water from the dentinal surface, promoting the infiltration of monomers through the exposed collagen. A primer application time of at least 15 seconds should be performed to allow proper interdiffusion of monomers to full depth of demineralized dentin.
- 16. C. Adhesive resin: The adhesive resin, also called "Bonding agent", is a solvent-free, filled (i.e. containing filler particles) or unfilled solution containing mainly hydrophobic monomers. It co- polymerizes with the previously applied primer and the subsequently applied resin composite.
- 17. • When adhesive resin infiltrates the etched enamel, two types of resin tags are subsequently formed; Macro-tags at the prism peripheries with the etched interprismatic substance and Micro-tags at the cores of enamel prisms (with intraprism etching). Macro-tags probably contribute more to bond strength because of their greater quantity and larger surface area.
- 19. • When the adhesive resin infiltrates primed dentin, it fills up the interfibrillar spaces left between the collagen fibrils leading to hybridization with dentin. This hybrid layer or hybrid zone occurs mainly with demineralized intertubular dentin. It also forms with demineralized peritubular dentin (tubule wall hybridization).
- 21. • The adhesive also enters dentinal tubules forming resin tags. It was found that intertubular hybridization is more important than resin tags in the bonding process. It contributes more to the bond strength of an adhesive system.
- 23. • In addition, peritubular or tubule wall hybridization provides a firm attachment of the resin tag necks to the tubule walls and more importantly guarantees proper hermetic sealing of the tubules. The resin also infiltrates lateral tubule branches forming submicron lateral resin tag formation.
- 25. • A commercial example for three-step etch- and-rinse adhesive system is Scotchbond Multipurpose (3M ESPE). In two-step etch- and-rinse adhesives, primer and adhesive bonding components are combined into one solution that should fulfill both functions. An example is Excite Bond (Ivoclar Viva-dent).
- 27. • Wet versus dry bonding: Following etching and rinsing, enamel and dentin present different conditions for priming and bonding. Whereas enamel should be dry to achieve good bonding, a certain amount of water is needed in dentin to prevent the collagen fibrils in dentin from shrinking.
- 28. • Conventionally, acid etched enamel was dried with short intermittent blasts of air until the enamel shows a chalky white appearance. However, this was found to cause collapse of dentinal unsupported collagen network preventing proper infiltration of collagen with monomers.
- 30. Dentin was kept moist Dentin was air-dried
- 31. • To overcome this problem in dentin bonding, two different approaches can be followed depending on the primer of the adhesive system. The first approach, known as the dry bonding technique, involves air drying of enamel and dentin and applying a water-based primer capable of re-expanding the collapsed collagen network.
- 32. • An alternative approach, wet bonding technique, is to leave dentin moist, thereby preventing any collapse of collagen, and use a solvent- containing primer, known for its water-chasing capacity. The solvent displaces dentinal water, thereby carrying the monomers into the opened dentinal tubules and through the nanospaces of the collagen web. The solvents of the primer are then evaporated by gentle air-drying, leaving the active primer monomers behind.
- 33. • N.B.: Although enamel does not need a separate priming step, it needs dry bonding for effective wetting of the adhesive. Thus, when using wet bonding technique, primers are indicated to be applied on acid etched enamel to displace residual water through solvent evaporation.
- 34. • Advantages of Etch-and-rinse adhesives: 1. Proven effective bonding with enamel and dentin with sufficient long-term clinical results. Three-step adhesives are considered the gold standard for adhesives.
- 35. 2. Three-step adhesives have low technique sensitivity due to separate application of primer and adhesive resin; each applied to serve a specific function. Two-step etch-and- rinse adhesives have more simplified application but are more technique sensitive than three-step adhesives. 3. Possibility for particle-filled adhesive. Filled adhesives act as shock absorbers and increase the bond strength of adhesives.
- 36. • Disadvantages of Etch-and-rinse adhesives: 1. Time consuming due to multi-steps required. 2. Separate post-etching rinsing step is required.
- 37. 3. Risk of over-etching dentin due to aggressive etching of phosphoric acid. This will cause demineralization to a depth that might be inaccessible for complete resin impregnation, leading to a porous zone in the hybrid layer. This discrepancy between depth of demineralization and the depth of resin infiltration results in nanoleakage which is basically the presence of submicrometer-sized gaps within the hybrid layer. By time, this may compromise the durability of the bond due to hydrolysis of exposed collagen.
- 38. 4. Total removal of smear layer can cause post- operative sensitivity due to dentinal fluid movement. It also increases dentin permeability leading increased wetness of dentin. 5. Sensitive to over-wet or over-dry dentin condition. When using wet bonding technique, over-wetting of dentin should be avoided to prevent dilution of the adhesive. Over-drying dentin causes collapse of collagen fibers as discussed before.
- 39. Thank You