School of Dentistry, College of Medicine, China Medical University, and Department of Dentistry, China Medical University Hospital, Taichung, Taiwan.
J Formos Med Assoc. 2010 Jan;109(1):69-74. doi: 10.1016/s0929-6646(10)60023-x.
BACKGROUND/PURPOSE: Knowledge of root canal anatomy is important for dental practice and for identifying features of anthropological significance. Three-rooted permanent mandibular molars are considered an anatomical variant of the Mongoloid race. This study aimed to determine the prevalence of three-rooted primary mandibular first molars in Taiwanese subjects.
Vertical bite-wing radiographs of 227 subjects, which had been obtained previously in the Department of Pediatric Dentistry, Taichung Veterans General Hospital, Taichung, Taiwan, from January 2004 to December 2007, were screened retrospectively. Images of 121 subjects [54 boys and 67 girls; mean age (range), 5.8 (2.4-10.4) years] who had bilateral primary mandibular first molars were studied. The sex, symmetry and frequency of occurrence of three-rooted primary mandibular first molars were recorded and statistically analyzed.
The overall prevalence of subjects with three-rooted primary mandibular first molars was 5.0% (6/121), and 83.0% of the molars were unilateral. The prevalence of teeth that showed an extra root among all teeth examined was 2.9% (7/242). Such prevalence did not differ significantly between the right and left sides of the mandible, bilateral and unilateral, or with sex.
The data presented here indicate that approximately 5% of Taiwanese subjects had a threerooted mandibular primary first molar and 80% of such teeth occurred unilaterally. Dentists should take into account the prevalence of these three-rooted variants in primary mandibular first molars among Taiwanese patients during their daily endodontic and exodontic procedures.
背景/目的：了解根管解剖结构对于口腔临床实践和鉴定人类学特征具有重要意义。三根恒磨牙被认为是蒙古人种的一种解剖变异。本研究旨在确定台湾人群中三根恒下颌第一磨牙的发生率。
回顾性分析 2004 年 1 月至 2007 年 12 月于台湾台中荣民总医院儿童牙科拍摄的 227 名患者的垂直咬翼片。共分析 121 名患者（54 名男性，67 名女性；平均年龄 5.8 岁[2.4-10.4 岁]）的双侧下颌第一恒磨牙图像。记录了三根恒下颌第一磨牙的性别、对称性和发生频率，并进行了统计学分析。
具有三根恒下颌第一磨牙的患者总体发生率为 5.0%（6/121），其中 83.0%为单侧。在所有检查的牙齿中，出现额外根的牙齿发生率为 2.9%（7/242）。这种发生率在左右下颌骨、双侧和单侧以及性别之间无显著差异。
本研究表明，约 5%的台湾人群具有三根恒下颌第一磨牙，其中 80%的牙齿为单侧发生。牙医在日常牙髓病学和拔牙治疗中应考虑台湾患者下颌第一恒磨牙中这些三根变异的发生率。
