Removal Torque Value and Histometric Evaluations of HA Coated Implants

Objectives: This study presents biomechanical and histometric comparison of bone response to implants with various area of HA coating. Methods: The implants were placed in the tibia of 10 rabbits weighing 2.5-3.5kg. Control group had machined surface, exp. 1 group had 50µ thick HA coated in a band form, and exp. 2 group had 50µ thick HA coated on the entire surface. 8 weeks after implantation, the animals were sacrificed. Removal torque was measured and histologic preparation was also performed. Bone to implant contact and percentage of bone area inside threads were measured. ANOVA post hoc, and t-test were used for statistical analysis. Results: 1. Removal torques were 9.4±5.6Ncm, 48.4±16.7Ncm, and 82.4±22.6Ncm for the control, exp. 1, and exp. 2 group respectively. Statistically significant difference were found among all the groups(p<0.05). 2. Bone to implant contact in cortical bone were 38.9±10.9%, 66.9±14.1%, 73.0±19.4%, in marrow bone, 8.3±5.4%, 14.6±5.9%, 18.5±11.8%, and in total, 22.4±10.1%, 31.2±7.5%, 41.4±12.2% respectively for control, exp.1, and exp. 2 group. In cortical bone, exp. 1, and exp. 2 group showed statistically significantly higher contact compared to control group. Total contact and in marrow bone, only exp. 2 group showed statistically significantly higher contact compared to control group(p<0.05). In all the groups significantly higher contact were observed in cortical bone compared to the marrow bone(p<0.05). 3. Percentage of bone area inside threads in cortical bone were 55.7±7.3%, 55.2±13.2%, 57.0±13.3%, in marrow bone, 12.3±14.6%, 17.6±20.0%, 20.3±12.8%, and in total, 30.3±12.5%, 31.6±15.2%, 34.3±12.6% respectively for control, exp.1, and exp. 2 group. There was no statistical difference among the groups. In all the groups significantly higher bone area were observed in cortical bone compared to marrow bone(p<0.05). Conclusions: Increase of HA coating area improves removal torque value and enhances bone to implant contact both in the cortical and marrow bone.