Crystallographic Properties of Physiological Hydroxyapatite as a Function of Age

Hydroxyapatite with 4-6 wt {\%} B-type carbonate substitution is the major mineral component in our teeth and bones. Crystal structure properties of human teeth as a function of age between 17 and 91 years are investigated. X-ray powder diffraction reveals a partial phase transition from the hexagonal Ca$_{5}$(PO$_{4})_{3}$OH (Hydroxyapatite) to the triclinic Ca$_{4}$H(PO$_{4})_{3}$.2H$_{2}$O (Calcium Hydrogen Phosphate Hydrate) at the 70 year old tooth. This phase becomes predominant in the diffraction pattern of a 91 year old tooth. Correlation of such transition with physical properties of synthetic hydroxyapatite could provide useful insights in dentistry and medicine.