Regional differences in D/L aspartic acid ratios in the human mandible as a possible indicator of the bone remodeling rate.

Abstract

In slowly metabolizing tissue such as tooth, bone and ocular lens, D-amino acids converted from L-amino acids accumulate with age and thus reflect the tissue turnover rate. To investigate whether D-amino acids play a role in determining the bone remodeling rate, we measured the accumulation of D-aspartic acid, which has the fastest rate of racemization, in various areas of the mandible. The level of D-aspartic acid was higher in the ramus than in the body (P < 0.01), and within the body, the level was higher in the basal area than in the alveolar area (P < 0.01). Within the alveolar area, the level of D-aspartic acid was higher in the molar region than in the incisal region (P: 0.05-0.01). No correlation was found between the accumulated level of D-aspartic acid with age, because all the specimens were obtained from elderly people with only a few years difference in age. There was also no correlation between D-aspartic acid and sex. In conclusion, we suggest that accumulation of D-aspartic acid in the mandibular bone reflects the differences in remodeling associated with occlusion. The incisal portion of the alveolar area of the mandible (above the mandibular canal), shows the greatest evidence of active remodeling.