No abstract

Although hydroxyapatite (HAP) and tricalcium phosphate (TCP) are currently used as bone graft substitutes or coatings on metallic prostheses because of their excellent biocompatibility and osteoconductivity, they do not stimulate bone formation or inhibit bone resorption. Zinc, an essential trace element in many animals, has a direct specific proliferative effect on osteoblastic cells and has a potent and selective inhibitory effect on osteoclastic bone resorption in vitro. Therefore, zinc-containing beta-tricalcium phosphate (ZnTCP) ceramics and composite ceramics of ZnTCP and HAP (ZnTCP/HAP) were implanted in the femora of New Zealand White rabbits for 4 weeks to promote bone formation. The implants were sintered ceramics with zinc contents of 0 (control), 0.063, 0.316 and 0.633 wt %. Histological and histomorphometrical investigation of the undecalcified sections revealed an increase by 51% (p =.0509) in the area of newly formed bone around the ZnTCP/HAP implants of 0. 316 Zn wt % compared with the control. Plasma zinc concentration was unchanged. An increased bone resorption on the endosteal surface was observed when ZnTCP and ZnTCP/HAP of 0.633 Zn wt % were implanted. To promote bone formation, the optimum zinc content of the calcium phosphate ceramics was therefore 0.316 wt %.

No abstract

No abstract

Using zinc-containing tricalcium phosphate (ZnTCP) as the zinc carrier for zinc-releasing calcium phosphate ceramic implants promoted bone formation around the implants. Because no quantitative information was available on the equilibrium solubility and resorbability of ZnTCP, in vitro equilibrium solubility and in vivo resorbability of ZnTCP were determined and compared quantitatively in this study. The solubility of ZnTCP decreased with increasing zinc content. The negative logarithm of the solubility product (K(sp)) of ZnTCP was expressed as pK(sp) = 28.686 + 1.7414C - 0.42239C(2) + 0.063911C(3) - 0.0051037C(4) + 0.0001595C(5) in air, where C is the zinc content in ZnTCP (mol %). The solubility of ZnTCP containing a nontoxic level of zinc (<0.63 wt %) decreased to 52-92% of the solubility of pure tricalcium phosphate (TCP) in the pH range 5.0-7.4. However, the in vivo resorbed volume of ZnTCP containing the same amount of zinc was much lower than that expected from the in vitro solubility, becoming as low as 26-20% of that of TCP. Cellular resorption of TCP is substantially a process of dissolution in a fluid with an acidic pH that is maintained by the activities of cells. Therefore, the reduction of the resorbability of ZnTCP could be attributable principally to its lowered cellular activation property relative to that associated with pure TCP.