Setsuro Ito

Formation of a high-strength bioactive glass-ceramic in the system MgO-CaO-SiO2-P2O5

Formation of a high-strength bioactive glass-ceramic in the system MgO-CaO-SiO2-P2O5 was investigated by observing the microstructure of the crystallized products. Crystallization of the parent glass in a bulk form led to the occurrence of large cracks in the crystallized product. This was attributed to the precipitation of fibrousβ-wollastonite crystals growing perpendicular to the outer surfaces of the glass after uniform precipitation of fine oxyapatite/fluoroapatite crystals. On the other hand, crystallization of the same glass in a powder compact led to the formation of a crack-free dense crystallized product due to uniform precipitation of both apatite and wollastonite fine crystals throughout the glass article. The uniform precipitation of the wollastonite crystals was attributed to the simultaneous formation of fine crystals in the individual glass particles.

Mechanical properties of a new type of apatite-containing glass−ceramic for prosthetic application

A new type of apatite-containing glass-ceramic in the system MgO-CaO-SiO2-P2O5 can form a tight chemical bond with bones and has a high mechanical strength. The cause for its high mechanical strength was examined by comparing mechanical properties of the glass-ceramics which have an identical chemical composition and different microstructures. It was found that the mechanical strength of the apatite-containing glass-ceramics is considerably increased by the precipitation ofβ-wollastonite crystals due to an increase in fracture surface energy resulting in an increase in fracture toughness.

Fatigue and life-time of bioactive glass-ceramic A-W containing apatite and wollastonite

High-strength bioactive glass-ceramic A-W containing apatite and wollastonite shows the least dynamic fatigue among glass and glass-ceramics of the same composition and of different structure in a simulated body fluid at 38.5° C. An avenge life-time estimated from the fatigue of glass-ceramic A-W is 10 yews under continuous loading of bending stress of 65 MPa in the simulated body fluid, whereas that of a sintered dense hydroxyapatite ceramic is only 1 min. Articles of the glass-ceramic which withstand the stress of 215 M Pa in an inert atmosphere are guaranteed for 10 years life-time in the body environment. The glass-ceramic shows an increase in strength, without having an appreciable change in fatigue, when placed in the simulated body fluid without being loaded. Its practical life-time can therefore be expected to be much longer than that estimated above.

Transparency of LiTaO3-SiO2-Al2O3 glass-ceramics in relation to their microstructure

The glasses with various compositions in the LiTaO3-SiO2-Al2O3 system were heated from room temperature to temperatures ranging from 750° to 1050° C at a rate of 5° C min−1. From the glasses in the LiTaO3-SiO2 system no transparent glass-ceramic was obtained even when their LiTaO3/SiO2 mole ratios were as high as 2.33. The diameter and number of the LiTaO3 crystal grains precipitated in the glasses were 5–15 μm and 108–1010 grains cm−3, respectively. On the contrary, transparent glass-ceramics were obtained from the glasses containing Al2O3; their compositions covered a fairly large area in the LiTaO3-SiO2 -Al2O3 system, which encompasses the compositions with the LiTaO3/SiO2+AlO1.5 mole ratio as low as 0.25. The diameter and number of the LiTaO3 crystal grains precipitated in the transparent glass-ceramics were as small as 10–20 nm and as many as 1016–1018 grains cm−3, respectively. High nucleation rates of the LiTaO3 crystals in the Al2O3-containing glasses were interpreted in terms of structural inflexibility induced in the glass-network by the addition of Al2O3 to the LiTaO3-SiO2 system.