Micromorphological relationship between resin and dentin in vivo and in vitro

This study examined the relationship between resin and dentin both in vitro and in vivo using phosphoric acid conditioning. Four groups of 10 teeth each had standardized Class V preparations made with the gingival cavosurface margin in the root. In Group 1, involving freshly extracted teeth, the enamel and dentin was conditioned with 37% phosphoric acid gel for 15 seconds. NTG-GMA/PMDM was applied to the enamel and dentin followed by an application of BIS-GMA/HEMA and restoration with P50. Group 2 served as a control omitting the conditioning step. Groups 3 and 4 were treated similarly to Groups 1 and 2 except in vivo and extracted 2 weeks after restoration placement. All teeth were sectioned longitudinally through the restoration. Impressions were taken of the tissue/restoration interface and examined by SEM for disclosure of gaps. The teeth were then demineralized and the fitting surface of the restoration was examined by SEM for evidence of resin penetration into the tissue. The results showed a total absence of gaps both in vitro and in vivo after acid conditioning compared to the controls commonly showing gaps. Penetration of resin into the dentin to form a zone of diffusion or hybrid layer was observed only in the conditioned specimens. The phenomenon was observed both in vivo and in vitro. It was concluded that a significant potential exists for phosphoric acid conditioning of dentin to promote bonding.