PURPOSE: To compare the torsional strengths and the effects of functional loading on five different implant surface structures. MATERIALS AND METHODS: This in vivo longitudinal study of 9 months' duration examined osseointegration in 180 stepped cylindric implants placed into the mandibles of 18 healthy sheepdogs. Implants with five different surface structures were placed (n = 36 in each group): (1) smooth surface; (2) deep profile structure (DPS); (3) titanium plasma sprayed (TPS); (4) hydroxyapatite coated; and (5) sol-gel hydroxyapatite coated (SGHA). All implants were investigated under standardized conditions. At uncovering (3 months), half the implants were loaded with prefabricated crowns for 6 months, and the other half remained unloaded. Removal torque values were evaluated at 3, 6, and 9 months after implant placement. The data were analyzed using analysis of variance and Scheffé correction (alpha <.05). RESULTS: All smooth-surface and SGHA implants failed in succession during the fourth and ninth months of the study. After 3 months the removal torque resistance of DPS, TPS, and hydroxyapatite-coated implants was significantly higher (P <.001) than that seen in the other two groups. Initially, the removal torque resistance of unloaded hydroxyapatite-coated implants was superior, and the decrease during the observation period was not significant. The increase in removal torque resistance under functional loading was not significant for the DPS implants. A significant increase was found in removal torque resistance for the loaded TPS implants (P <.05). The unloaded DPS and TPS implants showed no change in removal torque levels after the closed healing period of 3 months. CONCLUSIONS: Successful osseointegration was achieved with DPS, TPS, and hydroxyapatite-coated implants, and smooth-surface and SGHA implants failed. Removal torque resistance was enhanced with controlled functional loading.
