Journal of biomedical materials research vol:35 issue:2 pages:191-7
When transmission electron microscopy (TEM) is used to evaluate resin-dentin interface specimens for completeness of hybridization, the epoxy resin embedding medium that normally facilitates ultrathin sectioning may produce a secondary or artifactual hybrid layer. This secondary hybrid layer, composed of epoxy resin rather than adhesive resin, may fill the pores that remain as evidence of incomplete resin infiltration, obscuring the fact that they ever existed. In this study, resin-dentin interfaces produced by two dentin adhesive systems, Optibond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M), were comparatively investigated by TEM in epoxy-embedded and nonembedded nondemineralized sections. The hypothesis advanced was that no difference in ultramorphology of the hybrid layer would result from either specimen preparation method. The two adhesive systems were applied to four mid-coronal dentin disks per manufacturer's instructions. One half of each sample was processed following common procedures for TEM sample preparation with epoxy embedding, whereas the other half was not embedded but instead immersed in hexamethyldisilazane (HMDS), dried and mounted so that it protruded from a base of cold-cure acrylic resin. Each sample was then sectioned using a diamond knife in an ultramicrotome. With either means of preparation, a hybrid layer with a relatively uniform electron density and a loose collagen fibril arrangement with electron lucent interfibrillar channels was formed by OPTI. At the base of the hybrid layer, collagen fibrils were anchored in the underlying unaffected dentin, and no microporosities or gaps were observed. Similarly, whether SBMP was embedded or nonembedded, it was found to have a hybrid layer of variable electron density and an electron dense phase localized at the surface of the hybrid layer. No porosities were evident at the base of the hybrid layer. Thus, with either of the two adhesive systems, no ultrastructural difference in hybrid layer formation was observed between epoxy-embedded and nonembedded sections, and no direct evidence of ineffective resin-infiltration of the demineralized collagen scaffold was found.