Johnsson M S, Nancollas G H
Chemistry Department, State University of New York, Buffalo 14124.
Crit Rev Oral Biol Med. 1992;3(1-2):61-82. doi: 10.1177/10454411920030010601.
Studies of apatite mineral formation are complicated by the possibility of forming several calcium phosphate phases. The least soluble, hydroxyapatite (HAP), is preferentially formed under neutral or basic conditions. In more acidic solutions phases such as dicalcium phosphate dihydrate (Brushite, DCPD) and octacalcium phosphate (OCP) are often found. Even under ideal HAP precipitation conditions the precipitates are generally nonstoichiometric, suggesting the formation of calcium-deficient apatites. Both DCPD and OCP have been implicated as possible precursors to the formation of apatite. This may occur by the initial precipitation of DCPD and/or OCP followed by transformation to a more apatitic phase. Although DCPD and OCP are often detected during in vitro crystallization, in vivo studies of bone formation rarely show the presence of these acidic calcium phosphate phases. In the latter case the situation is more complicated, since a large number of ions and molecules are present that can be incorporated into the crystal lattice or adsorbed at the crystallite surfaces. In biological apatite, DCPD and OCP are usually detected only during pathological calcification where the pH is often relatively low. In normal in vivo calcifications these phases have not been found, suggesting the involvement of other precursors or the formation of an initial amorphous calcium phosphate phase (ACP) followed by transformation to apatite.
磷灰石矿物形成的研究因可能形成多种磷酸钙相而变得复杂。在中性或碱性条件下优先形成溶解度最低的羟基磷灰石（HAP）。在酸性更强的溶液中，通常会发现诸如磷酸二钙二水合物（透钙磷石，DCPD）和八钙磷酸酯（OCP）等相。即使在理想的HAP沉淀条件下，沉淀物通常也是非化学计量的，这表明形成了缺钙磷灰石。DCPD和OCP都被认为可能是磷灰石形成的前体。这可能通过DCPD和/或OCP的初始沉淀，然后转变为更具磷灰石性质的相来发生。尽管在体外结晶过程中经常检测到DCPD和OCP，但在骨形成的体内研究中很少显示出这些酸性磷酸钙相的存在。在后一种情况下，情况更为复杂，因为存在大量可掺入晶格或吸附在微晶表面的离子和分子。在生物磷灰石中，通常仅在pH值相对较低的病理性钙化过程中检测到DCPD和OCP。在正常的体内钙化中未发现这些相，这表明涉及其他前体或形成初始无定形磷酸钙相（ACP），随后转变为磷灰石。
