In vitro investigations of the composite/adhesive/dentin interfacial structure have been criticized because the materials were manipulated at the lab bench under dry conditions as opposed to a wet environment characteristic of the oral cavity. Objective: The purpose of this study was to compare the interfacial structure of the adhesive/dentin (a/d) bond in Class II composites restored at the lab bench and under in vitro conditions simulating the wet oral environment. Method: Class II composite preparations were cut in 20 extracted, unerupted human molars; the prepared teeth were randomly separated into 2 groups, i.e. bench and wet. Tooth preparations were randomly selected for restoration at the bench, 25C and ~35% humidity, using Z100 and Single Bond (SB, 3M) or Uno (Pulpdent). Specimens in the wet group were restored in an environmental chamber at 25C and 95% humidity with Z100 and SB or Uno. Thin (3-5 mm) sections of composite/a/d interfaces were cut on a Leica Polycut microtome; collected on glass slides and stained with Goldner's for light microscopic (LM) examination. Results: The differential staining technique provided a morphologic record of several millimeters of the a/d interface in the axial, pulpal and gingival sections. The structure of the a/d interface of Class II composites restored at 95% humidity was highly irregular, 3-4 mm of exposed protein was recorded at intact d/a interfaces, d/a separation frequently occurred in gingival sections. Class II composites restored at the bench had 3-4 mm of exposed protein at d/a interface sections recovered from the gingival and pulpal walls. Conclusions: As compared to preparations restored at the lab bench, the a/d interfacial structure in Class II composites restored at 95% humidity simulating the wet oral environment, was highly irregular with exposed protein and a/d separation at the gingival, axial and pulpal walls. Supported in part by USPHS 12487.

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