Methods:Macrography was used to observe the morphology of the mesiobuccal root,the degree of abrasion,the morphology of the floor of pulp cavity, the number and type of apical foramen.

• 方法:肉眼观察近颊根外形,牙合面磨耗程度,髓室底形态,根尖孔数目及类型;游标卡尺测量各项长度指标及根尖孔到牙根顶点的距离;