Pathways to biomineralization and biodemineralization of calcium phosphates: the thermodynamic and kinetic controls.

Although extensive investigations of calcium phosphate crystallization have been performed, many have focused only on the final structures and morphologies and have not emphasized the need to consider the molecular contacts between mineral and matrix that drive nucleation nor the thermodynamic and kinetic controls imposed by matrix and soluble proteins during the nucleation stage. This review focuses on the earliest events of homo/heterogeneous nucleation from an initial supersaturated solution phase and subsequent growth. We also discuss how the combination of macroscopic constant composition (CC) and microscopic atomic force microscopy (AFM) provides insights into the physical mechanisms of crystal growth and phase stability and the influences of proteins, peptides or other small molecules. In addition, a new model for nanoscale enamel and bone demineralization suggests biodemineralization reactions may be inhibited or even suppressed when particle sizes fall into certain critical nanoscale levels. This size is not arbitrary; rather, it seems to give biominerals such as bones and teeth remarkable physical characteristics including self-preservation in the fluctuating physiological milieu.