LeGeros R Z, Kijkowska R, LeGeros J P
Scan Electron Microsc. 1984(Pt 4):1771-7.
Octacalcium phosphate, Ca8H2(PO4)6 X 5H2O (OCP), occurs in pathological calcifications frequently as one of the crystalline components of human dental calculi. OCP has also been presumed a necessary precursor of biological apatites in both normal (enamel, dentine, cementum, bones) and pathological (e.g., phosphatic renal stones) calcifications. This study investigated the optimum conditions for the direct in vitro formation of OCP in solutions and in gel systems and the factors affecting its formation and transformation or hydrolysis to apatite. It was observed in both solution and gel systems that the formation of OCP was dependent on definite conditions of pH and temperature (the higher the temperature the lower the pH at which OCP forms, and vice versa), and on the presence of other ions. The presence of pyrophosphate inhibited OCP formation favoring instead the formation of amorphous calcium phosphate while the presence of citrate or carbonate favored the formation of "apatitic" calcium phosphate at the expense of OCP. The presence of oxalate ions caused the formation of mixed OCP/calcium oxalate phases. Hydrolysis of OCP to apatite was suppressed in the presence of magnesium or pyrophosphate, and promoted in the presence of carbonate or fluoride ions. In the presence of oxalate ions, partial hydrolysis of OCP to calcium oxalate and not to apatite was observed. Results from this study give insights on the factors (e.g., pH, temperature, presence of ions besides calcium and phosphate) which influence the formation of OCP and its transformation to apatite and/or calcium oxalate. Ions which demonstrated significant effect on the formation and/or transformation of OCP were magnesium, pyrophosphate, carbonate, citrate, fluoride and oxalate.
磷酸八钙，Ca8H2(PO4)6·5H2O（OCP），在病理性钙化中经常作为人类牙结石的晶体成分之一出现。OCP也被认为是正常（牙釉质、牙本质、牙骨质、骨骼）和病理性（如磷酸盐肾结石）钙化中生物磷灰石的必要前体。本研究调查了在溶液和凝胶体系中直接体外形成OCP的最佳条件，以及影响其形成、转化或水解为磷灰石的因素。在溶液和凝胶体系中均观察到，OCP的形成取决于特定的pH和温度条件（温度越高，形成OCP的pH越低，反之亦然），以及其他离子的存在。焦磷酸盐的存在抑制OCP的形成，反而有利于无定形磷酸钙的形成，而柠檬酸盐或碳酸盐的存在则有利于“磷灰石型”磷酸钙的形成，以牺牲OCP为代价。草酸根离子的存在导致形成混合的OCP/草酸钙相。在镁或焦磷酸盐存在下，OCP水解为磷灰石受到抑制，而在碳酸盐或氟离子存在下则促进水解。在草酸根离子存在下，观察到OCP部分水解为草酸钙而非磷灰石。本研究结果揭示了影响OCP形成及其向磷灰石和/或草酸钙转化的因素（如pH、温度、除钙和磷之外的离子的存在）。对OCP的形成和/或转化表现出显著影响的离子有镁、焦磷酸盐、碳酸盐、柠檬酸盐、氟化物和草酸盐。
