Bone-bonding behavior of titanium alloy evaluated mechanically with detaching failure load.

Although titanium (Ti) and Ti alloy are generally classified as bioinert materials in terms of their bonding to bone tissue, it is still unclear whether they bond chemically to bone. In this study, we examined the bone-bonding ability of Ti alloy (Ti-6Al-4V) using smooth-surfaced plates under non-load-bearing conditions. The bone-bonding behavior was evaluated mechanically by means of the detaching test reflecting tensile force. After implantation of the plates into the tibiae of rabbits for 4, 8, 16, and 25 weeks, detaching tests were performed. The failure load of the Ti alloy plates was close to 0 kg at 4 and 8 weeks, but gradually increased with time, reaching 0.334 kg at 16 weeks and 2.852 kg at 25 weeks on average. Histologic examination by Giemsa surface staining and SEM showed no differences between specimens at 8, 16, and 25 weeks, when Ti alloy plate made direct content with bone without any fibrous tissue. By SEM-EPMA, no clear calcium-phosphorus (Ca-P)-rich layer at the interface between the Ti alloy and bone tissue was evident, although a thin bone tissue was observed on the detached Ti alloy plate. The present results indicate that from both mechanical and histologic viewpoints, Ti alloy bonds directly to bone under static conditions after some time, probably more than 8 weeks. The possibility of chemical bone-bonding of Ti alloy was suggested.