Effect of glass-ceramic microstructure on its in vitro bioactivity.

Two routes were used to obtain a glass-ceramic composed of 43.5 wt % SiO(2) - 43.5 wt % CaO - 13 wt % ZrO(2). Heat treatment of a glass monolith produced a glass-ceramic (WZ1) containing wollastonite-2M and tetragonal zirconia as crystalline phases. The WZ1 did not display bioactivity in vitro. Ceramizing the glass via powder technology routes formed a bioactive glass-ceramic (WZ2). The two glass-ceramics, WZ1 and WZ2, were composed of the same crystalline phases, but differed in microstructure. The in vitro studies carried out on WZ2 showed the formation of an apatite-like layer on its surface during exposure to a simulated body fluid. This paper examined the influence of both chemical and morphological factors on the in vitro bioactivitity. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Measurements of the pH made directly at the interface of the two glass-ceramics were important in understanding their different behavior during exposure to the same physiological environment.