The removal torque of titanium implant inserted in rabbit femur coated with biomimetic deposited Ca-P coating

A number of experimental data on biomimetic deposition CaP (BDCaP) coating implants have reported promising outcomes by histological evaluation. But little is investigated on the role of the BDCaP coating and osseointegration mechanism by interface shear strength. To make a direct biomechanical comparison between the BDCaP coating implants and the uncoated rough titanium implants (control), a well-established animal model for implants removal torque testing was employed in rabbits, using a self-matching experimental design. All implants had an identical cylindrical screw shape without any macroscopic retentive structure. After 2, 4, 6, 8 and 12 weeks of bone healing, removal torque testing was performed to evaluate the interfacial shear strength of each implant type. The torqued implants were sputter-coated with gold for morphology observation and observed with a field-emission electron microscopy. Results showed that the interfacial shear strength of the BDCaP coating implants was similar to that of the uncoated rough implants at 2 and 4 weeks of healing. The mean removal torque values of the BDCaP coating implants were lower than those of control implants (P < 0.05) after 6 weeks of healing. The removal torque values for both types of implants revealed similar mean values after 8 and 12 weeks of healing; there were no significant difference between the two types of implants (P > 0.05). It can be concluded that the BDCaP coating implants had no beneficial effect on the interfacial shear strength at early bone healing stage.