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Glasses having a chemical composition based on combeite [Na(2)Ca(2)Si(3)O(9)]-fluoroapatite [Ca(5)(PO(4))(3)F] and forsterite [Mg(2)SiO(4)] system were crystallized through controlled heat-treatment. Two forms of sodium calcium silicate e.g. combeite Na(2)Ca(2)Si(3)O(9) and pectolite Na(2)CaSi(3)O(8), were formed together with diopside (CaMgSi(2)O(6)) and monticellite (CaMgSiO(4)) in addition to fluoroapatite (Ca(5)(PO(4))(3)F) phases by thermal treatment of the glasses. Selected glass-ceramics were exposed to a simulated body fluid solution (SBF) which is close to human plasma for 3 weeks. Energy dispersive X-ray analysis (EDX) and inductive coupled plasma (ICP) analysis confirmed the formation of an apatite layer which indicate bioactivity in the all crystallized sample. A decreasing of surface bioactivity with increasing Mg(2)SiO(4)/Na(2)Ca(2)Si(3)O(9) replacement was observed as indicated by the decrease in the amount of apatite layer on the surface of the crystallized specimens. The Vicker's microhardness of the studied glass-ceramic materials are between 5,047 and 6,781 MPa.

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a b s t r a c tThe study concerns about the crystallization behaviour and in vitro bioactivity of a glass-ceramic prepared from a series of glasses in the Na 2 O-K 2 O-CaO-SiO 2 -F system. A minor amount of cerium oxide was also added instead of calcium oxide in some selective glass batches. The main crystalline phases, formed after the appropriate heat treatments, were wollastonite solid solution and pseudo-wollastonite-like phases. There is a preferential tendency for wollastonite (CaSiO 3 ) to accommodate K, Na, F, and Ce ions in its structure forming wollastonite solid solution with variable formulas. The bioactivity of the resulting crystalline materials was examined in vitro by immersion in simulated body fluid at 37 • C. An increase of the surface bioactivity of glass-ceramic with the Na 2 O/K 2 O replacement was observed which is attributed to the augmentation solubility of the crystalline sample. On the other hand, the bioactivity of the crystalline sample with CeO 2 /CaO replacement was improved by the crystallization of pseudo-wollastonite phase together with wollastonite solid solution phase.

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