[Estimation of age from teeth using the racemization of aspartic acid (racemization method)]

We report a method for estimation of age from teeth using the racemization of amino acids (racemization method). This method is based on the characteristics of the constant age-related increase in the amount of D-aspartic acid in dentin. We estimated age by measuring the ratio of D-aspartic acid to L-aspartic acid, i.e. the ratio of racemization ¿ratio of D/L, ln[(1 + D/L)/(1 - D/L)]¿. Because different D/L ratios have been obtained from different teeth in the same individuals and from different sites of dentin in the same tooth, we usually prepare bucco-lingual longitudinal sections at the central part of each tooth, and prepare samples of powdered whole dentin. This powder is then mixed and used to measure the D/L ratio in the dentin. To accurately estimate age from forensic specimens, we simultaneously measured the D/L ratios in more than four control teeth of the same type obtained from subjects of known age. Use of control teeth is necessary because it is sometimes difficult to maintain constant running conditions for gas chromatography to obtain reproducible values in different runs. Therefore, for every measurement, we determined an equation for calculating age from the D/L ratios of control teeth, and estimated the age of the specimen tooth by substituting in its D/L ratio. The most reliable results were obtained using samples of lower incisors or premolars, which are single-rooted teeth with a relatively small volume of dentin. Thus sampling of the dentin is easier than for other teeth. It is better to keep control teeth desiccated because racemization does not proceed readily under such conditions. The deviation from the actual age in the cases we examined was less than 3 years. Thus, racemization of amino acids can be used for accurate estimation of age from teeth.