Studying the coating of Alumina and Hydroxy Apatite on Tapered Dental Implant (In Vivo and In Vitro Study)

Background : In clinical trial studies, the success of dental implant depends on excellent biocompatibility, mechanical strength and characteristic of material such as surface properties of material. The Objective of this study was to evaluate the effects of coating implants with two materials (Al2O3 &HA) .And this was in mixture form or in two layers form. Then their effect on the bond strength at the bone/implant interface with cell compatibility was evaluated.  Materials and methods: Electrophoretic deposition technique (EPD) was used to obtain a uniform coating for each one of two types of coated layers on the screws (mixture of 50%HA and 50% Alumina and two layers). For examination of the changes occurred on the surface, structural ,elemental analysis and morphological investigations were carried out on the modified surfaces of the Ti-6Al-7Nb alloy using different techniques, namely X-ray diffraction (XRD), and Energy Dispersive X-ray Fluorescence (EDXRF). The in vivo study was done by the implantation of tapered screw–shaped uncoated and coated implants of 3mm diameter, 8 mm length (the threaded part is 5 mm and the smooth part is 3 mm) and 0.5mm pitch height.The tibia of white New Zealand rabbits were chosen as implantation sites. The right tibia of rabbit received two screws, (one uncoated and coated) while the left tibia of a rabbit received coated screws of two layers. To understand the bone-implant interface, biomechanical test was performed after 2, 6 and 18 weeks healing periods. 15 rabbits were sacrificed for each period. A removal torque was done for ten animals in each group, whereas the other five ones were used for histological testing with optical microscope.  Results: The results indicates that there was a rapid reaction of bone towards coated Ti-6Al-7Nb alloy implants as compared with the uncoated one and more mature bone was observed after 6 weeks of implantation in screws coated with a mixture of Alumina and HA. The biomechanical test revealed that there was an increase in the torque mean value at bone-implant interface with time, with the highest mean values of bond strength in implants coated with a mixture of 50% HA and 50%Alumina. Also the bond strength of two layers coating was more than that of uncoated. The results of histological examination revealed a well tissue response with the formation of a lamellate and haversian type of osteon tissue after 18 weeks.  Conclusion : this study concludes that coating by electrophoresis proved to be a valuable process to coat metallic implants with an osteoconductive material, and to form a uniform biocomposite and multiple layer coating. The biomechanical and biological properties of the bone-implant interface associated with the coated implants were improved comparing to the uncoated ones they have better mechanical properties and excellent biocompatibility through the improved performance of bone at the site of a bone implant contact area than the uncoated implants.