LONG-TERM EVALUATION OF TITANIA-BASED CERAMICS COMPARED WITH COMMERCIALLY PURE TITANIUM IN-VIVO

Fifty-four cylinders (2.8 mm in diameter) machined from hot isostatica lly pressed titania (TI) and titania-hydroxyapatite (TI/HA-15vol%) sin tered at 925 degrees C, as well as commercially pure titanium (c.p.Ti) , were implanted in the femoral cortical bone of New Zealand white rab bits for 1, 3 and 12 months. The shear strength between bone and impla nt was measured by a push-out test. The Tl/HA composite showed a signi ficantly higher bonding strength to bone compared to c.p. Ti at all ti mes, while no differences were observed between TI and c. p. Ti at 1 a nd 3 months after implantation. Titania-based materials had a signific antly higher bonding strength than that of c.p.Ti one year after impla ntation. The results indicate that bioactivity of HA in Tl/HA composit e contributes to the early bone apposition reflected by high bonding s trength, while the stability of the oxide, determines the development of long-term bonding strength. Both effects may be explained by the le vel and type of ions released from the ceramic implant. HA has a posit ive conduction to bone ingrowth while TI has a limited interaction to the bone apposition due to the extraordinary low ion release in vivo. Under light microscopy, similar patterns of bone-implant interfaces we re seen from titania-based materials and c.p.Ti in 3-month samples, in dicating high biocompatibility of these materials. However, histologic al evaluation by light microscope cannot identify the differences betw een physical contact and chemical bonding of implant-bone interface, a nd thus does not give information on bonding mechanism and the level o f shear stresses developed.