Age-related changes in D-aspartic acid of rat teeth

In addition to L-aspartic acid, D-aspartic acid was detected in the protein (collagen) of rat teeth. The content of D-aspartic acid in rat molars increased significantly with age, showing a close correlation with age (r = 0.965-0.993), whereas in rat incisors D-aspartic acid did not increase. This suggests that there is little metabolic activity in rat molars after their formation. The amount of D-aspartic acid present in molars of a single rat was in the order first molars > second molars > third molars. This indicates that the amount of D-aspartic acid is higher in teeth formed earlier, corresponding to the time of their formation. The rate of racemization in rat molars was about ten-fold higher than that in human dentin, suggesting the importance of body temperature in the rate of racemization. These findings also suggest that D-aspartic acid is present in the teeth of other animals.