This study presents a biomechanical and histometric comparison of bone response to implants with various area of hydroxyapatite(HA) coating.

The implants were placed in the tibia of 10 rabbits weighing 2.5-3.5kg. The control group had a machined surface, the experimental group 1 had 50µm thick HA coated in a band form, and the experimental group 2 had 50µm 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 for histologic and histometric analysis. Bone to implant contact as well as percentage of bone area inside threads were measured. ANOVA post hoc, and t-test were used for statistical analysis with p-value p<0.05.

1. The removal torques were 9.36 ± 5.64 Ncm, 48.40 ± 16.66 Ncm, and 82.37 ± 22.56 Ncm 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 the cortical bone were 38.94 ± 10.9 %, 66.90 ± 14.1 %, 73.00 ± 19.4 %, in the marrow bone, 8.30 ± 5.4 %, 14.59 ± 5.9 %, 18.54 ± 11.8 %, and in total, 22.40 ± 10.1 %, 31.19 ± 7.5 %, 41.41 ± 12.2 % for the control, exp.1, and exp. 2 group respectively . In the cortical bone, exp. 1, and exp. 2 group showed statistically significantly higher contact compared to control group. Total contact and in the 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 the cortical bone compared to the marrow bone(p<0.05).

3. Percentage of bone area inside threads in the cortical bone were 55.68 ± 7.25 %, 55.19 ± 13.19 %, 57.04 ± 13.33 %, in the marrow bone, 12.34 ± 14.61 %, 17.56 ± 20.04 %, 20.26 ± 12.83 %, and in total, 30.30 ± 12.46 %, 31.57 ± 15.15 %, 34.25 ± 12.56 % for the control, exp.1, and exp. 2 group respectively. There was no statistical difference among the groups. In all the groups significantly higher bone area were observed in the cortical bone compared to the marrow bone(p<0.05)