Diet and discrepancy between tooth and jaw size in the Yin-Shang period of China.

Tooth to denture base discrepancy (the discrepancy) is the difference between the dental arch length and the sum of crown diameters of teeth in the jaw, a concept which was originally developed in orthodontics. Since the cause-effect relationship between a soft diet and the discrepancy has been demonstrated, the size of the discrepancy should indicate the amount of load on the masticatory system from chewing foods in jaws from archaeological periods. The dietary condition of 71 citizens compared to that of 186 slaves from the Yin-Shang period of China was reconstructed through a study of the discrepancy. The prevalence of the discrepancy in the Yin-Shang period was around 15%, almost the same as it was during the later Jomon to Yayoi (3000-2000 BP) periods, when rice agriculture was introduced into Japan, and also the same as for present-day pastoralists around Lake Turkana, Kenya. Although the frequency of the discrepancy was slightly higher in male citizens, there were no significant differences in the frequencies between male citizens and female citizens or slaves. The differences in diet may not have been fundamental since the Yin-Shang period would be at the very beginning of the age in which differences of diet according social class began to appear, with implications for the load on the masticatory system. At that time agriculture may not been sufficiently intensified in variety or quantity to have produced a differentiation of the diet between social classes.