A confocal optical microscope study of the morphology of the tooth/restoration interface using Scotchbond 2 dentin adhesive.

It is difficult to avoid specimen damage when one is preparing an adhesive/adherend interface for examination using conventional optical or scanning electron microscopy. Fluorescence imaging with a confocal optical microscope has facilitated evaluation of the distribution of Scotchbond 2 dentin adhesive, in an in vitro study with P50 composite resin used as the restorative material. The adaptation of the adhesive and restoration to the tooth was excellent. Gap formation between the restoration and the tooth was observed only when the adhesive system was used incorrectly. Contributions of the primer film former (Scotchprep) and hardening film former (Scotchbond 2) to the adhesive interface with the tooth and overlying composite restoration could be identified. The dentin smear layer was incorporated by the Scotchprep and subsequently impregnated by the Scotchbond 2. Control of the film thickness was difficult. Cracking and cohesive failure within the adhesive were observed when the film thickness exceeded 70 microns, with such thicknesses easily achieved in internal line angles. The extent of the slippery air-inhibited layer was considerable, but could be reduced if the adhesive was wiped with a cotton wool pledget. The distribution of the Scotchbond 2 within the tooth was localized to the smear layer and dentin up to 50 microns deep to it. This study has shown the penetration of Scotchbond 2 dentin adhesive within the tooth and its distribution within the restoration.