【摘要】 <正> 下颌第三磨牙阻生是口腔科常见的疾病之一,国内外一些学者对阻生的病因曾作过不少研究,指出可能与内分泌紊乱、局部炎症、牙胚不正及牙萌出位置缺乏等一系列全身或局部因素有关,但至今尚无定论。本文仅就下颌骨与下颌第三磨牙阻生的关系加以探讨。更多还原

【Abstract】 302 specimens of adult mandible were examined. According to the eruption of the mandibular third molar we divided these mandibles into three groups: the normal group, the group with impaction of the third molar and the group with absence of the third molar. We measured the size of the space posterior to the second molar, the angle of the mandible, the length of the mandibular body, the oblique length of the mandible, the thickness of the mandibular body (M1, M2), the least breadth of the mandibular ramus, the distance between the two condyloid processes and the ridge-alveolar margin angle. The results obtained herein revealed that the rate of the impacted third molar in male and female combined was 10.60%. and that the rate of impaction in the female was greater than that in the male. On macroscopic examination none of the third molars was found to have erupted in 106 mandibles. However, upon X-ray photographic examination third molars were noted to be embedded in 5 mandibles. Thus, the rate of absent mandibular third molars amounted to 33.44%. The data obtained indicated that the sizes of the space posterior to the second molar, of the oblique length of the mandible, of the length of the mandibular body and the distance between the two condyloid processes in the impacted group and the absent third molar group were less than those of the normal group. Lack of space for eruption might be one of the direct causes of the impacted teeth. Our studies suggest that the absence of the third molar might be the result of the balanced degeneration of the mandible and the tooth in human evolution, and the impacted third molar might be the transitional stage from the presence to the absence of the third molar in human evolution.更多还原