Mophological Study Of Mandible Evolution During 3000 Years

During the human evolution, the masticating apparatus have been weakened by the changes of producing and living style. Jaw bones of the ancient people can be used not only to reflect the physical and physiological status, lifestyle, and culture in the certain period, but also to understand the jaw bones development and variation. The main changes of masticating apparatus are in teeth and jaws,but as the jaws are difficult to preserve, so the studies on jaw bones are still rare, furthermore the studies related to mandibles are even less. In this study, human mandibles of different periods were collected. Observing and measuring were carried out to investigate the trend of mandible evolution.1. MaterialMandible of different periods were selected respectively in this study, including 150 mandibles of modern people (105 male and 45 female), provided by the department of anatomy of the Fourth Military Medical University; 49 male mandibles samples of 2000 years ago provided by the archiological institute of Shaanxi province and 56 mandibles of 3000 years ago ( 24 male, 32 female) provided by archiological institute of Shaanxi province.2. Method Every data was noted in detail by the standards and methods described in"Human Skeleton Measurement"(Wu Rukang,Wu Xinzhi,1965) ,"Anthropometric Handbook"(Shao Xiangqing, 1985) and"Phsical anthropology"(Zhu Hong, 2004).3. Results1. Results of Linearity measurements and nonlinearity measurements in different periods are reported respectively.2. The comparisons among the mandible data of different periods show that①Compared with modern people group , the mandible data in group of 3000 years ago and the group of 2000 years ago were much larger, especially in mandibular body, mandibular ramus and mandibular arch. And the mandibular measurements of the group in 3000 years ago were bigger than measurements of the group in 2000 years ago, except bigonial breadth, height of the mandibular ramus and so on. In all measuring items, there were 7 items which have statistical significance between the group of 3000 years ago and the group of 2000 years ago. In three samples, the whole size of mandible decreased gradually to date. Among measuring items, the decreasing of mandibular body and mandibular angle were more obvious, and the decreasing in breadth of mandibular ramus were more obvious than the decreasing in height of mandibular ramus. Moreover, there were no obvious changes in interior～exterior diameter of the condyle process.②Results of nonlinearity measurementsThere was no statistic significance in different measuring items between three groups(P>0.05).4. Conclusions By measuring and observing, obtained mandibular data were reported. The results of our study have provided data for human mandibular evolution and anthropology.Compared with mandibular data in three different periods, the whole size of mandible decreased gradually to date. These changes may relate to lifestyle and environmental changes. But to investigate the trend of mandible evolution, we still need further studies on this issue.