正畸治疗中磨牙的拔除和保留(二十一)——应用全颌曲面断层片对下颌磨牙冠根形态的比较研究

目的：统计分析下颌第一、第二、第三磨牙牙冠近远中宽度、牙体长度、分根情况以及相关因素。方法：选择下颌无缺失牙,下颌第三磨牙牙根发育已完成的全颌曲面断层X线片249张进行测量分析。结果：牙体长度下颌第一磨牙至第三磨牙依次递减;牙冠近远中宽度下颌第一磨牙最大,第二、第三磨牙无差别;分根率下颌第一磨牙至第三磨牙依次递减,根分叉程度下颌第一磨牙最大,第二、第三磨牙无差别;下颌第三磨牙萌出组牙体长度大于第三磨牙阻生组,并且与其牙冠近远中宽度成正相关,分根率也偏大;下颌第三磨牙相对宽度在单根、双根组间有差别;下颌第三磨牙牙冠宽度/磨牙后间隙长度比值与下颌第三磨牙相对长度比成负相关关系。结论：下颌第一磨牙冠根形态最好;第二、第三磨牙冠根形态有较大的相似性,只要有足够的空间,下颌第三磨牙牙根就能得到良好的发育。

Orthopantomographic comparative research of mandibular molar morphologic of crown and root of tooth

Objective:Statistical analysis of mandibular molar mesiodistal crown width and tooth length and development of root. Method:To measure orthopantomographic of mandibular none loose and the root of mandibular third molar finish developed 249 subjects. Result:First molar tooth length was longer than second ,and second molar was longer than third; first molar mesiodistal crown width was biggest, second and third molar did not differ; first malor ratio of root division was biggest, second and third molar did not differ; first malor degree of root division was biggest, second and third molar did not differ; third molar erupted groups tooth length and ratio of root division was bigger than impacted groups, and there was positive relationship between third molar erupted groups tooth length and mesiodistal crown width, third molar width single root groups were differences with double root groups; third molar tooth crown width/eruption space ratio was inversely associated with third molar tooth length ratio. Conclusion:Mandibular first molar crown and root form were best. Third molar crown and root form was the same with second molar, as long as enough room third molar root can well development.