Crystal Structure Properties of Human Teeth as a Function of Age

We report on crystal structure studies of human teeth as a function of age in the range of 5-87 years. The crystallinity of the hydroxyapatite, which is the main dental mineral phase in teeth, decreases with age in a systematic way starting at $\sim $ 40 years old teeth. The average crystallite size decreases from $\sim $40 nm to $\sim $12 nm in the age range 30 to 60 years old and then it remains practically constant. The a-lattice constant decreases in a similar systematic way and it is associated with the carbonate content of the tooth. Development of the secondary phases with the tooth-age questions the crystallographic structure of the dental apatite. FTIR spectroscopy reveals both types of carbonate substitution, but B-type substitution is greater by a factor of 4 than the A-type. An increase of the carbonate content with the tooth age is also deduced from the ratio of the v$_{2}$ CO$_{3}$ to the v$_{1}$ PO$_{4}$ IR modes from 17 to 70 years of age. TGA measurements confirm the results of both experimental methods.