Bonding to root canal: Structural characteristics of the substrate

Purpose: To evaluate in vitro the dentin morphology in root canals in terms of tubule orientation, density and increase in surface area after etching. Materials and Methods: Thirty anterior teeth were divided in 3 groups at r andom: the samples of Group 1 were used to study tubular morphology in SEM. Groups 2 and 3 samples were etched with 32% phosphoric acid. The teeth in Group 2 were examined by SEM without further treatment. The samples in Grou p 3 were treated with a bonding system and fiber posts were luted into the canal. These teeth were then processed for evaluation of hybrid layer forma tion and resin tags in dentin tubules. The observations were made according to location in the root dentin, tubule density was estimated, and the incr ease in area available for bonding after etching was calculated. Results: T he observations revealed variability in tubule density and orientation with in different areas of any one sample. Statistically significant differences in the density of tubules were found depending on location. The dentin sur face area available for bonding increased by 202% after etching in the cerv ical third, 156% in the middle third, and 113% in the apical third of the r oot dentin. Group 3 samples showed that the thickness of the hybrid layer d epended on the density of tubules. In the sectors with a low density of tub ules, the hybrid layer was significantly thinner than in areas with a highe r density of tubules. The increase in dentin surface area might be responsi ble for the enhanced bond strength after acid etching, but not all areas ex hibited equal responses to etching.