A TEM STUDY OF 2 WATER-BASED ADHESIVE SYSTEMS BONDED TO DRY AND WET DENTIN

To keep the exposed collagen scaffold penetrable to resin, it has been recommended that the conditioned dentin surface be maintained in a vi sibly moist condition, a clinical technique commonly referred to as we t bonding. In this study, resin-dentin interfaces produced with two wa terbased adhesive systems-OptiBond (OPTI, Kerr) and Scotchbond Multi-P urpose (SBMP, 3M)-were compared by transmission electron microscopy, f ollowing the application of either a dry-or a wet-bonding technique. T he hypothesis advanced was that the ultramorphology of the hybrid laye r would differ depending on which bonding method was applied. A morpho logically well-organized hybrid layer of collagen fibrils intermingled with resin in tiny interfibrillar channels was consistently formed by the OPTI system. The SBMP system was found to produce a hybrid layer with a more variable ultrastructure, less distinctly outlined collagen fibrils, and a characteristic electron-dense phase located at its sur face. No major differences in hybrid layer ultrastructure were observe d when the two adhesive systems investigated were bonded to either dry or wet dentin. When the adhesives were dry-bonded, no ultrastructural evidence of collapsed demineralized collagen, incompletely or not at all infiltrated by resin, could be detected. In addition, when the two adhesives were bonded to wet dentin, no signs of overwetting phenomen a, that would have indicated that water was ineffectively removed, wer e apparent. It has been hypothesized that the amount of water provided with the hydrophilic primer solution of either of the two adhesive sy stems investigated suffices to re-hydrate and re-expand the gently air -dried and collapsed collagen network. Further research should be dire cted to determine whether this hypothesized self-rewetting effect can be extrapolated to other adhesive systems that provide water-based pri mers.