Glass-reinforced hydroxyapatite composites: Secondary phase proportions and densification effects on biaxial bending strength

CaO-P2O5 glasses with additions of MgO and CaF2 were used as a sintering ai d of hydroxyapatite, and glass-reinforced hydroxyapatite composites obtaine d, Glasses promoted significant changes in the microstructure of the compos ites, namely with the formation of tricalcium phosphate secondary phases, b eta and alpha-TCP, Quantitative phase analysis was performed by the Rietvel d method using General Structure Analysis Software, Grain size measurements were carried out on SERI photomicrographs, using a planimetric procedure a ccording to ASTM E 112-88, Flexural bending strength was determined from co ncentric ring-on-ring testing. Flexural bending strength (FBS) of glass-rei nforced hydroxyapatite composites was found to be about twice or three time s higher than that of unreinforced hydroxyapatite and tended to depend more on porosity and beta and alpha-TCP secondary phases, rather than on grain size. Traces of alpha-tricalcium phosphate significantly enhanced the stren gth of the composites, Using the rule of mixtures to estimate the zero poro sity bending strength, the Duckworth-Knudsen model applied to the composite s gave a porosity correction factor, b, with a value of 4.02. Weibull stati stics were also used to analyze biaxial strength data and the level of rein forcement obtained by comparing failure probability for the composites and for the unreinforced hydroxyapatite. Lower activation energies for grain gr owth were observed for the composites compared to unreinforced hydroxyapati te, which should be attributed to the presence of a liquid glassy phase tha t promotes atomic diffusion during the sintering process. (C) 1999 John Wil ey & Sons, Inc.