Abstract
The juvenile mandible of the modern Japanese has a lower symphysis than that of the prehistoric Jomon, while the adult symphysis is conversely higher in the modern Japanese. This cannot be explained from population differences in masticatory environments. As an alternative factor that may influence symphyseal height, we examined tooth crypt size and placement patterns in the skeletal growth series of the two populations. Results showed that although the Jomon mandible had larger bicanine breadth than in the modern Japanese during growth, the modern Japanese has faster growing anterior teeth that became larger than those of the Jomon by the time of eruption, necessitating greater space. This is expressed as the faster growth rate of anterior alveolar height in the modern Japanese, measured as corpus height above the mandibular canal. Canine eruption distance and root length were greater in the modern Japanese than in the Jomon, corresponding to the increased difference of anterior corpus height between the two populations after canine eruption. However, the influence of tooth root length on anterior corpus height during later growth cannot be evaluated by this study. The present study suggests that the size and spatial dispositions of the developing anterior teeth have significant effects on symphyseal dimensions of the mandible until the time of tooth eruption.
