Comparison of tissue reaction and osteointegration of metal implants between hydroxyapatite/Ti alloy coat: an animal experimental study.

BACKGROUND: One important clinical application of hydroxyapatite (HA) is coating on metal implants to stimulate osteo-integration thus enhancing fixation of the implant to bone, especially plasma-sprayed HA coating applied on Ti alloy substrate. The poor bonding strength between HA and Ti alloy has been of great concern to orthopedists. The biocomptable coat such as Ti alloy (TiO2) coat is one method to improve adhesive strength. OBJECTIVE: The objective of this study was to detect and analyze possible differences in bone formation, bone integration and tissue reaction between group I (uncoated Titanium), group II (Hydroxyapatite coated Titanium), and group III (Hydroxyapatite/TiO2 coated Titanium) implant specimens when embedded into bony hosts. METHOD: Rectangular specimens were implanted into the femoral bone of adult dogs in randomly different sites including: proximal left, proximal right, distal left, distal right. The tailor-made implant specimens were inserted in 5 x 5 mm preprepared sockets. Radiographic evaluation was taken at 0, 1, 3 and 6 months. All animals were sacrificed at 3 and 6 months post implantation. The femoral bone containing implants were dissected and then prepared to be further investigated. The bone-implant interface was analyzed by H&E surface staining, radiography and scanning electron microscopy. Data concerning percentage of osteointegration and adhesiveness of hydroxyapatite layer from different kinds of implants along the entire length of each implants were collected and analyzed for evaluation of any significant differences. RESULTS: No osteo-integration was noted in Group I, but there was 25.57 per cent osteointegration in Group II and 28.63 per cent in Group III. No statistically significant differences were observed between Group II and Group III. However, the coating layer in Group II was found to have detached, in some area, from the metal substrate. Histologically, no adverse tissue reaction was found around any kind of implant. CONCLUSION: Biocompatable bond coat is one of the methods to improve adhesive strength of hydroxyapatite coated implants. In the present study it could be concluded that, besides the improvement in adhesiveness, the intervening TiO2 coating layer had no negative effect concerning bone formation and integration and also showed no adverse surrounding soft tissue reaction.