The most appropriate (Ca+Zn)/P molar ratio to minimize the zinc content of ZnTCP/HAP ceramic used in the promotion of bone formation.

The (Ca+Zn)/P molar ratio of zinc-containing tricalcium phosphate and hydroxyapatite composite ceramics (ZnTCP/HAP) was investigated in the range from 1.50 to 1.66 to reveal the minimum zinc content possible in ceramics used in the promotion of osteoblastic cell proliferation and bone formation. The release rate of zinc increased with an increase in the (Ca+Zn)/P molar ratio up to 1.64 (ZnTCP/HAP1.64) and then decreased over 1.64 even when the zinc content of ZnTCP/HAP was the same. The zinc release rate of ZnTCP/HAP1.64 with a 0.21 Zn wt % nearly coincided with that of ZnTCP/HAP1.60 with a 0.316 Zn wt %, which was found be the most effective for promoting bone formation in rabbit femora. This means that the zinc content needed to promote bone formation can be reduced by 34% when the (Ca+Zn)/P molar ratio is increased to 1.64. The relative growth rate of MC3T3-E1 cells cultured on ZnTCP/HAP1.64 had a maximum value of 1.3 at a zinc content of 0.51 wt %; however, a 1.20 Zn wt % is required to attain the same value in relative growth rate in the case of ZnTCP/HAP1.60. A reduction in zinc content at a certain zinc release rate results from an increase in zinc content of the ZnTCP phase in ZnTCP/HAP. The ZnTCP/HAP1.64 would be better than any other ZnTCP/HAP relative to material safety because the risk of an accidental burst of zinc from the material is minimized due to the low zinc content. Copyright 2002 Wiley Periodicals, Inc.