现代人类下牙弓的发育，在青少年后期到二十多岁之间，有很强的拥挤趋势，不论其牙齿最初排列的多么整齐［’］。不同作者报导，此现象早至17～18岁，晚至25～26岁出现，且常发生于下切牙区［’j，临床上称为下牙弓后期拥挤、青春期后期拥挤等［‘j。关于这种拥挤发生的原因一 The development of the lower dental arch in modern humans tends to be crowded during late teens to their twenties, no matter how neat their teeth are initially arranged. Different authors have reported that this phenomenon as early as 17 to 18 years old, as late as 25 to 26 years old, and often occurs in the inferior incisor area ['j, clinically known as the lower arch of the late crowded, late adolescent crowded [] j. One of the reasons for this congestion