中文摘要：

目的探讨中国现代人群下颌第三磨牙（M3）的萌出特点。方法将第三磨牙分为3种类型，正常、半退化、缺失，然后比较不同时代间（新石器时代55例，青铜铁器时代191例，近代112例）各个类型出现率的差异。结果M3正常的出现率随时代而降低，缺失的出现率随时代而升高，半退化的出现率随时代而升高。结论M3正常的出现率随时代而降低，可能与下颌骨尺寸随时代的持续减小有关。

英文摘要：

Objective To understand the degeneration of the lower third molars （M3 ） of Chinese recent population. Methods This study was conducted on 358 human mandibles from China. M3 was divided into 3 types： normal, degeneration and absent. Comparisons were made among different time periods. Results The frequency of the degeneration of the lower third molars was the highest in modern people, and the lowest in Neolithic age. Conclusion The frequency of the degeneration of the lower third molars goes up as time period goes by, which may be caused partly by the obvious size decrease of mandibles.