Inside Dentistry Supplement Dental Adhesives - Summer 2010 : Page 3
penetration into demineralized crypts within the crystals. On dentin, the etchant creates a demineralized surface 3 µm to 5 µm in depth and, upon rinsing the acid, the smear layer and other debris are removed from the surface. Fail-ure to remove the smear layer reduces dentin permeability, as that layer acts as a barrier and prevents adhesion to the underlying intact tooth structure. Following acid conditioning, col-lagen contained in the dentin is exposed. The adhesive system monomers then envelope the exposed collagen and remaining mineral, pen-etrating to the residual intact mineralized dentin within this microscopic etched surface. This in-terface is referred to as the “hybrid layer”’ and is observed in three distinct areas: within the nents, thus simplifying the application process into only one step. Some have suggested that the two-step systems may introduce greater variability into bonding results. There is, how-ever, evidence of excellent clinical performance over the years. One key performance factor that infl uences the success of etch-and-rinse systems includes the thorough removal of the etchant prior to bonding.12 It is also critical to ensure that the dentin remains moist when the primer and adhesive (or primer-adhesive com-bination) are applied so that adequate space is retained between the exposed collagen to allow for penetration of the etched surface by the res-in monomers. Restorations comprising greater dentin surface area relative to the enamel sur-Bond Strength After Thermocycling15 To Enamel 100 H2C H3C To Dentin C RO H2COH P OH 20 40 60 80 0 Low Concentration FIGURE 3 Phosphonic Acid Monomer High Concentration FIGURE 4 Graph of shear bond strength of BeautiBond’s phosphonic acid monomer to dentin and enamel. Graphic representation of the microtensile bond strength of BeautiBond and Clearfi l S3 Bond to enamel upon thermocycling at baseline, 5,000 cycles, and 10,000 cycles. (Courtesy of Kawamoto C, Sano H, et al of Hokkaido University) dentinal tubules, in the microscopic branches lateral to the tubules, and in the intertubular dentin.11 Three-step etch-and-rinse systems contain an etchant, a primer, and a bonding resin (ie, an adhesive). The primer is used to displace resid-ual moisture, thus creating a surface to which the hydrophobic bonding resin can adhere. The hydrophilic solvent in the primer facilitates pen-etration of the resin monomers into the tooth surface. The subsequently applied bonding resin (ie, the adhesive) fi lls the residual space and seals the dentinal tubules. Two-step sys-tems combine the primer and adhesive compo-face area are more demanding in regard to this consideration. Larger posterior cavities and full-coverage crown preparations with extensive dentin surface areas are particularly subject to postoperative sensitivity if the dentin is dried, the collagen collapses, and inadequate resin penetration is developed.9 There is proven long-term bond stability us-ing etch-and-rinse systems with both enamel and dentin. Most studies have shown bonding to enamel is more consistent, with higher ini-tial bond-strength values and less breakdown at the enamel margin over time than with self-etching adhesive systems.13 0 cycle BeautiBond (BB) 5000 cycle 10000 cycle S3BOND (S3) Summer 2010 • 3 Low Shear Bond Strength High
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