INVIVO BEHAVIOR OF GLASSES IN THE SIO2-NA2O-CAO-P2O5-AL2O3-B2O3 SYSTEM

Sixteen glasses in the SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 system were studied. The glasses were implanted in rabbit tibia. According to their in vivo behaviour, they were divided into five groups. A phenomenological equation for the in vivo behaviour was developed. The solubility of the glasses was determined in vitro as weight loss in Tris buffer solution. The tissue response is discussed in relation to the glass composition and the solubility. For bone-bonding glasses calcium phosphate formation takes place within a silica-gel at the glass surface. The gel must be sufficiently hydrated and flexible to allow calcium phosphate to build up. The results suggest that alumina can inhibit bone bonding by retarding the formation rate of a silica-rich layer, by stabilizing the silica structure enough to prevent calcium phosphate build-up within the layer, or by either disturbance of the bone mineralization or bone incompatibility of an alumina-containing calcium- and phosphorus-rich surface layer. The mechanism responsible for the lack of bone adherence is determined by the glass composition. Up to about 1.5 wt % Al2O3 can be included in the glass without destroying the bioactivity.