Estimation of age from dentin by utilizing the racemization of aspartic acid: influence of pH.

The rate of racemization of aspartic acid is considered to be influenced by environmental factors. The influence of pH (4 and 9) on teeth was investigated by a heating experiment for precise estimation of age at death. The rate of racemization of aspartic acid in dentin (D/L ratio) was determined by gas chromatography. The reaction rate was highest in dentin in a pH 9 environment, followed by that in water, that in a pH 4 environment, and that in a dry state. The age estimated from teeth left in these environmental states (16 degrees C) for 1 year showed only a slight increase of < 0.2 years for teeth in a dry state; a pH 4 environment and in water. However, the age estimated from teeth in the pH 9 environment showed an increase of 0.6 years and that from teeth left for 5 years showed an increase of 3.2 years. These results suggest that careful attention should be paid to age estimation from specimens left in an alkaline state for an extended period (several years). Previous studies on estimation of age from bones have-shown no influence of pH 4 or 9 on teeth. It is interesting to consider whether these conflicting findings are attributable to differences between experimental methods or differences in components between bone and tooth.