Calcium Orthophosphates: Crystallization and Dissolution

In order to understand the fundamental processes leading to CaP-based biomineralization, this review focuses on the earliest events of homo/ heterogeneous nucleation from an initial supersaturated solution phase and subsequent crystal growth involving various possible precursor phases (amorphous or crystalline) to the final mineral phase by specific templating and the influences of other modulators. Analysis of the effects on crystallization kinetics has abundantly shown the regulation of crystal growth by organic molecules. However, the range of biomineralized structures in nature indicates that their role in nucleation is also crucial. Biominerals often grow in exact locations (cell compartments) within complex crystal composites and exhibit specific crystallographic orientations. Such features can only be determined during the nucleation stage. Indeed, a substantial body of circumstantial evidence suggests that proteins and other organic molecules in a wide range of biomineral structures serve as nucleation "templates", providing preferential sites for nucleation and controlling the orientation of the resulting crystals. We also discuss how the combination of macroscopic constant composition and microscopic atomic force microscopy provides insights into the physical mechanisms of crystal growth and phase stability and the influences of proteins, peptides, or other small molecules. Biodemineralization reactions of tooth enamel and bone may be inhibited or even suppressed when particle sizes fall into certain critical nanoscale levels. This phenomenon actually involves particle size-dependent critical conditions of energetic control at the molecular level. This size is not arbitrary; rather, it appears to give biominerals such as bone and tooth remarkable physical characteristics. © 2008 American Chemical Society.