Abstract
The frequency and morphology of mandibular tori and the correlations between their development and environmental factors (number of teeth, degree of deviation of dental position, and degree of dental attrition) were examined in 105 Jomon people, 90 medieval Japanese and 105 modern Japanese. The palpable tori were found in 83.5% of Jomon people, 62.3% of medieval Japanese and 64.8% of modern Japanese. The perceptible tori were found in 70.1% of Jomon people, 18.2% of medieval Japanese and 22.0% of modern Japanese. The distributions of torus classes were statistically significantly different between Jomon people and medieval and modern Japanese. Mandibular tori were most frequently found under the first premolar in medieval and modern Japanese peoples. However, in Jomon people, tori were most frequently found under the second premolar. The distributions of torus positions were statistically significantly different between Jomon people and medieval and modern Japanese. In Jomon people, the torus size positively correlated with the degree of dental attrition. In medieval Japanese, the torus class and size positively correlated with the degree of dental attrition. A high degree of dental attrition might indicate that teeth and the mandible suffered considerable masticatory stress or they suffered masticatory stress for long time. Therefore, these results suggested that masticatory stress might be one of the causes of torus development. We also considered that a genetic factor might affect torus development.
