MECHANICAL AND HISTOLOGICAL INVESTIGATION OF HYDROTHERMALLY TREATED AND UNTREATED ANODIC TITANIUM-OXIDE FILMS CONTAINING CA AND P

In a previous study a new method for forming thin hydroxyapatite (HA) layers on titanium was described. Titanium was anodized at 350 V in an electrolytic solution containing sodium beta-glycerophosphate and cal cium acetate, and an anodic titanium oxide film containing Ca and P (A OFCP) was formed on the surface. Then numerous HA crystals were precip itated on the AOFCP during hydrothermal treatment in high-pressure ste am at 300 degrees C. In this study three types of hydrothermally treat ed films differing in amounts of precipitated HA crystals and tensile adhesive strength, and untreated films were histologically and mechani cally investigated in a transcortical rabbit femoral model for 8 weeks of implantation using light microscopy, scanning electron microscopy (SEM), and push-out tests. Machined titanium and HA ceramics served as control materials. The push-out shear strength and bone apposition of the AOFCP significantly increased after hydrothermal treatment, and w ere equivalent to those of HA ceramics, although the HA layer on the A OFCP was thin at 1-2 mu m. From SEM observation of the pushed-out spec imen, it was found that the thin HA layer had directly bonded to bone but the AOFCP had not. The push-out strength of the hydrothermally tre ated film resulted from the chemical bonding of the bone-HA layer inte rface, while that of the untreated film resulted from mechanical inter locking force between bone and the microprojections. There was a small difference in bone apposition but no significant difference in push-o ut strength with the amount of precipitated HA crystals on the treated films. Among the treated films, the film formed at the lowest electro lyte concentration showed the lowest bone apposition because of incomp lete covering by the HA crystals, and showed the highest stability aga inst mechanical failure because the adhesive strength was very high at about 38 MPa. Also, the hydrothermally untreated anodic oxide films, whose surfaces were rough as a result of the large microprojections, s howed much higher push-out strength and bone apposition than titanium. The good hard-tissue compatibility may be attributed to the surface r oughness and the possible inhibition of titanium ion release from the specimen. (C) 1995 John Wiley & Sons, Inc.