Lee Wei-Cheng, Ni Chih-Wei, Lin Fu-Gong, Chiang Cheng-Yang, Li Chung-Hsing, Chiu Hsien-Chung, Fu Earl
Department of Periodontology, School of Dentistry, National Defense Medical Center, Taipei City, Taiwan, ROC.
Division of Orthodontics and Dentofacial Orthopedics, School of Dentistry, National Defense Medical Center, Taipei City, Taiwan, ROC.
J Dent Sci. 2016 Jun;11(2):189-195. doi: 10.1016/j.jds.2015.07.007. Epub 2016 Mar 15.
BACKGROUND/PURPOSE: Most mandibular first molars have two roots. A major common variation of this tooth is the presence of a distolingual root, which is a common Mongoloid trait in certain populations. The aim of this article was to examine crown morphology in relation to the presence of the distolingual root.
Using dental casts, the crown morphology of 141 mandibular first molars from 71 Taiwanese individuals was analyzed. Periapical radiographs were used to detect distolingual roots. The length and width of the crowns and the crown units (i.e., trigonid and talonid) were measured. Ten intercuspal distances and five cusp angles were examined.
The buccolingual dimension of the crown and its ratio to the mesiodistal dimension were significantly increased in molars with a distolingual root, compared to molars without a distolingual root. Mesiodistal crown dimensions were similar; however, the crown unit dimensions were different: molars with a distolingual root had a shorter mesiodistal trigonid dimension but a longer talonid dimension, compared to molars without a distolingual root. The intercuspal distances from the three buccal cusps to the distolingual cusp were significantly longer, however, the distance between the mesiobuccal cusp and mesiolingual cusp was significantly shorter in teeth with a distolingual root than in teeth without a distolingual root. A significantly wider mesiolingual angle and narrower distolingual angle were observed in molars with a distolingual root, compared to molars without a distolingual root.
The presence of a distolingual root significantly increased the buccolingual dimension of the crown and the location of distolingual cusp is significantly closer to the lingual side.
背景/目的：大多数下颌第一磨牙有两个牙根。该牙齿的一个主要常见变异是存在远中舌侧根，这在某些人群中是常见的蒙古人种特征。本文的目的是研究与远中舌侧根的存在相关的牙冠形态。
使用牙模，分析了71名台湾个体的141颗下颌第一磨牙的牙冠形态。使用根尖片检测远中舌侧根。测量了牙冠及其各部分（即三角嵴和跟管）的长度和宽度。检查了十个牙尖间距离和五个牙尖角度。
与没有远中舌侧根的磨牙相比，有远中舌侧根的磨牙牙冠的颊舌径及其与近远中径的比值显著增加。近远中牙冠尺寸相似；然而，牙冠各部分尺寸不同：与没有远中舌侧根的磨牙相比，有远中舌侧根的磨牙近远中三角嵴尺寸较短，但跟管尺寸较长。从三个颊尖到远中舌尖的牙尖间距离显著更长，然而，有远中舌侧根的牙齿中近中颊尖和近中舌尖之间的距离比没有远中舌侧根的牙齿显著更短。与没有远中舌侧根的磨牙相比，有远中舌侧根的磨牙近中舌侧角显著更宽，远中舌侧角更窄。
远中舌侧根的存在显著增加了牙冠的颊舌径，且远中舌尖的位置显著更靠近舌侧。
