Methods: 1907 persons from 4 different nationalities were selected to measure the length of mandibule and the retromolar space and the incidence of impaction.

• 方法:分别测量汉、维吾尔、哈萨克、锡伯族共1907人一侧下颌体长度及第二磨牙后间隙的距离,并调查其下颌智齿阻生率。