下颌第三磨牙是全口牙齿中萌出最晚的、常因萌出位置不足（主要是第二磨牙后区位置不足）使其阻生，易形成盲袋，诱发冠周炎。位置不正的第三磨牙近中与第二磨牙紧密相接触，常压迫第二磨牙或嵌塞食物，使第二磨牙牙根吸收或形成龋齿，导致第二磨牙过早丧失，故对阻生第三... Mandibular third molars is full of teeth in the eruption of the latest, often due to lack of eruption (mainly the second molars posterior area lack of position) to stop it, easy to form blind bags, induced pericoronitis. The third molars whose position is not in close contact with the second molars are close contact with each other and often force the second molars or impaction food so that the second molars absorb or form dental caries which leads to the premature loss of the second molars. ...