Bioactive titanium: Effect of sodium removal on the bone-bonding ability of bioactive titanium prepared by alkali and heat treatment

As reported previously, bioactive titanium is prepared by simple alkali and heat treatment, and can bond to living bone directly. The purpose of this study was to accelerate the bioactivity of bioactive titanium in vivo. In i n vitro study, sodium removal by hot water immersion enhanced the apatite-f orming ability of bioactive titanium in simulated body fluid dramatically. The specific anatase structure of titania gel was effective for apatite for mation in vitro. In the current study, we investigated the in vivo effect o f sodium removal on the bone-bonding strength of bioactive titanium. Sodium -free bioactive titanium plates were prepared by immersion in an aqueous so lution of 5 M NaOH at 60 degreesC for 24 h, followed by immersion in distil led water at 40 degreesC for 48 h before heating them at 600 degreesC for 1 h. Three kinds of titanium plates were inserted into rabbit tibiae, includ ing untreated cp-Ti, conventional alkali- and heat-treated Ti, and sodium-f ree alkali- and heat-treated Ti. In vivo bioactive performance was examined mechanically and histologically after 4, 8, 16, and 24 weeks. Sodium remov al enhanced the bone-bonding strength of bioactive titanium at 4 and 8 week s postoperatively; however, its bone-bonding strength was inferior to that of conventional alkali-and heat-treated titanium at 16 and 24 weeks. Histol ogical examinations after the detaching test revealed breakage of the treat ed layer in the sodium-free alkali- and heat-treated titanium group. In con clusion, sodium removal accelerated the in vivo bioactivity of bioactive ti tanium and achieved faster bone-bonding because of its anatase surface stru cture, but the loss of the surface's graded structure due to the complete r emoval of sodium decreased the adhesive strength of the treated layer to th e titanium substrate. Further investigations are required to determine the optimum conditions for preparation of bioactive titanium. (C) 2001 John Wil ey & Sons, Inc.