Inside Dentistry Supplement Dental Adhesives - Summer 2010 : Page 4
LATTA SELF-ETCHING ADHESIVES Self-etch adhesives are available as one-step sys-tems (eg, Xeno IV; Clearfi l S3; Adper Easy Bond; G-Bond; BeautiBond) and two-step systems (eg, AdheSE; Adper SE Bond; Clearfi l SE Bond). These systems do not require an etch-and-rinse proce-dure. There is no need to address residual dentin moisture with the clinical application of these sys-tems. The demineralizing process occurs simulta-neously with the penetration of the adhesive, thus eliminating the potential for over-etching when treating dentin.9 Bond Strength After Thermocycling15 100 20 40 60 80 0 FIGURE 5 Graphic representation of the microtensile bond strength of BeautiBond and Clearfi l SE Bond to dentin upon thermocycling at baseline, 5,000 cycles, and 10,000 cycles. (Courtesy of Kawamoto C, Sano H, et al of Hokkaido University) MECHANISMS OF ACTION — ENAMEL AND DENTIN As with etch-and-rinse adhesive systems, the mechanism of adhesion is thought to be a combi-nation of mechanical and/ or chemical retention for both enamel and dentin. A hybrid layer that mimics the hybrid later formed with etch-and-rinse adhe-sives is produced with these systems, and deep resin tag penetration can also be seen. Self-etching adhesive formulations all contain water to facilitate the acid reaction on the tooth surface, but a great range of pH is observed depending on the specifi c adhesive system. Mild pH self-etch adhesives have shallower resin tags, and the hydroxyapatite with which they interact is not completely demineralized. It is believed that retention may be partly due to a chemical interaction between the monomer and 0 cycle BeautiBond (BB) 5000 cycle 10000 cycle SE Bond FIGURE 6 Scanning electron micrograph of BeautiBond at 5,000 cycles and 10,000 cycles. 10,000 cycles the hydroxyapatite crystal, especially with the less acidic systems.9 Self-etch adhesives are moisture forgiving, and thus they are particularly useful in diffi cult-to-iso-late areas or with diffi cult patients. Self-etch adhe-sives, however, generally contain water in addition to monomers in their formulation. Water is more diffi cult (less volatile) to remove in the drying step after placement. Thus, it is more critical to ensure that the drying of the adhesive after application is effectively completed. In addition, the presence of water in the formulation requires special attention 5,000 cycles to shelf stability on the part of the manufacturers, due to the potential for hydrolysis of the formula components. Since self-etch adhesive systems de-mineralize and penetrate the dentin at the same time, there is no concern over incomplete penetra-tion and residual gaps within demineralized dentin. Depending on the pH of the specifi c adhesive for-mula, the removal of the smear layer is often less complete, so the dentinal tubules may not be as open as in the case of the etch-and-rinse systems. This may reduce the risk of postoperative sensitiv-ity, although the restorative technique is perhaps the key to reduced postoperative sensitivity.9 NEWER ADHESIVE DEVELOPMENTS Most recent developments in adhesive materials have focused on the self-etching approach. One-4 • Dental Adhesives
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