Effect of glass ceramic crystallinity on the formation of simulated apatite layers

In silicate glasses the kinetics of apatite layer formation is usually rapid but the adhesion to the base glass is poor. Glass ceramics promote a stronger bonding between layer and substrate but decrease the rate of the apatite layer formation. In this work a glass of composition (wt%) 54,89%C3P-24,81%SiO2-20,30%MgO has been studied. This glass was heat treated at four temperatures (840 degrees C, 870 degrees C, 890 degrees C and 910 degrees C) to obtain glass ceramics with different contents of the same crystalline phase. A calcium magnesium phosphate phase was formed in all glass ceramics in a volume percent increasing with temperature. The apatite layer precipitated after immersion in simulated body fluid (SBF) formed faster on the glass than on the glass ceramics and a decrease in the amount of apatite formed was observed with the increase in crystallinity. It was generally concluded that heat treatment can turn a reactive glass into glass ceramics of different surface behaviors, from bioactive to quasi bio inert materials.