成人下颌第三磨牙先天性缺失的调查与分析

A RESEARCH OF THE ABSENCE OF THE THIRD MANDIBULAR MOLAR

本文对701例成人下颌M进行了直观检查,对无M者进行了X线拍片。发现M先天性缺失者36例,缺失率为5.14%,其中男4.44%,女6.23%,男女间无明显差异(P>0.05),与年龄也无关P>0.05。M缺失率山区低于平原P<0.001。M的退化是人类进化过程中的必然。其先天性缺失是下颌骨与牙齿均衡退化的结果,是适应性退化,而阻生是人类进化从有第三磨牙向无第三磨牙演化的过渡阶段。

The third molar of the mandible were examined among 701 humad adults.Upon those with no third molar under macroscopic examination,X-ray photographic examination were proceeded.The result obtained proved that the rate of the absence of the third molar in male and female combined was 5.14%.There was no obviously difference between male and female(P>0.05).The absence of the third molar did not relate to the age(P>0.5).The rate of the absence of the third molar in the mountain area was less than that on the plain(P<0.001).Our studies sugested that the absence of the third molar might be the result of the balanced degeneration of the mandible and the tooth in the human evolution.The absence of the third molar was the adaptable degeneration.The impact of the third molar might be the transitional stage from the presence of the absence of the third molar in the human evolution.