Structural Studies of Biological Minerals in Dental Research
M Mathew, S. Takagi
The crystallography program at the American Dental Association Health Foundation, Paffenbarger Research Center, National Institute of Standards and Technology was initiated in the early 1970's to provide a broad structural basis for understanding the various chemical phenomena associated with tooth and bone minerals.Although x-ray powder diffraction was used extensively for the identification of materials and for the study of gross phase/structural changes, the major emphasis was on single crystal structural studies of biological minerals and related compounds directly or indirectly associated with mineralization processes. The primary importance was on calcium phosphates, but extended to calcium pyrophosphates, calcium carbonates and calcium bisphosphonates. A large number of highly hydrated magnesium and alkaline earth phosphates and arsenates were also investigated for comparative insights into nucleation phenomena.Hydroxyapatite, Ca10(PO4)6(OH)2 (OHAp), has been considered as the prototype for tooth mineral. However, apatites as they occur in biological tissues, mineral formations and laboratory products can incorporate a wide variety of impurities and are seldom found in pure stoichiometric form. We have determined the structures of a number of substituted apatites to evaluate the structural changes associated with the substitution. For example, in a lead apatite, an apparent covalent Pb-O bond may account for the incorporation of Pb into bone mineral.