Scanning Electron Microscopic Observation of the Effect of Calcium Hydroxide on the Adhesion of a Resin System to Dentin

Objectives: The aim of the study was to evaluate the effect of calcium hydroxide on the adhesion of a resin system to dentin by scanning electron microscopy (SEM). Methods: Cavities were prepared on the mesial and distal sides of 10 extracted lower human molars. The mesial cavities were coated with Prime & Bond 2.1 (Caulk, Dentsply) after total etching, and were restored with TPH composite resin (Caulk, Dentsply). The distal cavities were restored with calcium hydroxide (Dycal, Caulk), Prime & Bond 2.1 and TPH Hibrid composite resin, respectively. The teeth were then sectioned and analysed by SEM. Results: Prime & Bond 2.1 adhered closely to dentin, forming a gapfree attachment with a hybrid layer in most of the specimens. However, in the cavities lined with calcium hydroxide, the polymerisation shrinkage of the resin composite caused the separation of the calcium hydroxide from the dentinal surface, forming 15 to 30 μm wide interfacial gaps. Conclusion: The interposition of a layer of calcium hydroxide between dentin and adhesive could reduce the dentinal surface available for adhesion of the restoration and disrupt the continuous adhesion of the bonding agent to dentin.