Morphological Study On Evolution Of Mandible Back Part Of Human During 2,000 Years

【Foreword】Development from ape to human has witnessed a great change in human head structure. Learning more about the usage of fire and tools, about further processing foods, human have a more delicate stomach with little stimulating on their masticate organ. Therefore, the growth potential for the organ makes possible its degradation pass on from one generation to the next. Researching on human mandible, which is the most complex and delicate part of the masticate organ, helps us learn more not only about the mandible development, but also about human corporeity, physical state, living environment and culture concurrent in different era.【Objective】Discovered regularities and characteristics about the mandible degradation have contributed much valuable experience for anthropology research in China. Measures and studies on relative data of mandibles from modern adults, adults of 1,000 and 2,000 years before will add more new information for further research on human mandible back part of 2,000 years.【Method】One hundred and two male adults'mandibles with 36 of 2,000 years before, 28 of 1,000 years before and 38 of modern time are measured in this experiment. All of the above mandibles must be in good condition with mandible molar and teeth. Two continuous edentulous mandible are excluded. All mandibles which are classed into Eruption Group, Congenital absence Group, Impacted Group are measured to be noted in accordance with the mandible third molar growth in the same era. The measure is independently made by the author referring to the anthropometric handbook. The measurement and the statistics are composed of the length of mandible (OB), the length of retromolar space(BX), the gonial angle, the crystal-marginal angle, ratio between OB and BX(OB/BX) and ratio between the gonial angle and the crystal-marginal angle(a/b).【Result】①Longitudinal comparison with mandibles in the same era shows that the length of mandible and the length of retromolar space in Eruption group are significantly different from that of Impacted group and Congenital absence group (p<0.05) with p<0.05 of ANOVA analysis. There is, however, no significant differences in these groups between the gonial angle and the crystal-marginal angle (p>0.05).②Comparing mandibles of Different era reveals that the length of mandible(OB) and the length of retromolar space (BX) is shortened with time(people of 2,000 years before>of 1,000 years before> modern people) and that the gonial angle and the crystal-marginal angle is prolonged with time(modern people> people of 1,000 years before > of 2,000 years before) which result from the masticate organ degradation of the mandible deficiency growth.③This displays that OB and BX change are not in the same pace with that of BX which has shortened a little more than that of OB. On the contrary, little length changes in mandibles among people of 2,000 years before and modern people indicate the same change speed pace of the gonial angle and the crystal-marginal angle.【Conclusion】①The above results indicate that the whole mandible especially the retromolar is the primary factor to the mandible third molar growth. However, the gonial angle and the crystal-marginal angle have little influence on its growth.②With the continuous degeneration of the masticated organs, the growth of human mardibular kept pace with the negative trend.③And the degeneration degree of the length of retromolar space of modern people is much larger than that of ancient people.The above data linkage is established by 102 male adults mandible relative data employing in the regression equation whose results demonstrate a correspondence connection between OB and BX, OB and OB/BX, BX and OB/BX, a/b with no such relation being showed in the rest data.In one word, the paper learns the mandible back part of human living in different time, analyzes factors influencing the mandible third molar growth and researches on mandible back part changes by observing and measuring mandibles from different period(2,000 and 1,000 years before, modern), which offer data and references for further research on human mandible forms.