The comprehensive study of the causes of non carious cervical lesions and mandibular tori

对日本离体牙齿（276颗上切牙，179颗上犬齿）的非龋齿性宫颈病变（NCCL）的发生频率和形态进行了研究。在考试之前，我们定义了一个新的分类系统。在38%的门齿和63%的犬科中发现了NCCL。根据矢状面轮廓和表面轮廓对NCCL的形状进行分类。在门齿和犬齿中，发现了不同类型的NCCL，并且提示NCCL的原因因牙齿种类而异。通过绳纹人、镰仓人和现代日本人的骨骼材料、现代日本牙科病人的石膏模型、现代日本学生和现代巴布亚新几内亚高地人的石膏模型，研究了下颌环体的频率和形态，以及环体的发育（环体的种类和大小）与环境因素（牙齿数量、拥挤程度和牙齿磨损程度）之间的相关性。在考试前，我们定义了一个新的环面评分系统。男性和女性、左侧和右侧在环体类别和位置的分布上无统计学差异。83.5%的绳纹人、62.3%的镰仓人、64.8%的现代日本人、76.6%的现代日本病人、72.0%的现代日本学生和80%的现代巴布亚新几内亚高地人有可触及的tori。在绳纹人的第二和第一磨牙下最常见的是托里。在其他人群中，托瑞最常见于第一和第二前臼齿。托瑞的发育与牙齿磨损程度、牙齿数量和年龄呈正相关，与拥挤程度负相关。生物力学研究表明，环面在下颌骨发育，骨密度较高。

The frequency and morphology of non carious cervical lesions (NCCL) were examined in Japanese isolated teeth (276 upper incisors, 179 upper canines). Before examinations, we defined a new classification system. NCCL were found in 38% of incisors and in 63% of canines. The shapes of NCCL were classified by the contour of sagittal section and by the contour on surface. In incisors and canines, different types of NCCL were found, and the causes of NCCL have been suggested to be different by the kind of tooth.The frequency and morphology of mandibular torus, and the correlations between the development of tori (the class of tori and the size of the tori) and environmental factors (the number of teeth, the degree of crowding and the degree of dental attrition) were examined by skeletal materials of Jomon people, Kamakura people and modern Japanese people, plaster casts of present-day Japanese dental patients, present-day Japanese students and present-day Papua New Guinea Highlanders. Before examinations, we defined a new torus grading system. There were no statistically significant differences between males and females and between left sides and right sides in the distribution of torus classes and positions. 83.5% of Jomon people, 62.3% of Kamakura people, 64.8% of modern Japanese, 76.6% of present-day Japanese patients, 72.0% of present-day Japanese students, and 80% of present-day Papua New Guinea Highlanders had palpable tori. In Jomon people, tori were most frequently found under the second and first molars. In other groups, tori were most frequently found under the first and second premolars The development of tori has been suggested to positively correlated to the degree of dental attrition, the number of teeth, and age, and negatively correlated to the degree of crowding. Biomechanical study has suggested that tori develop in the mandible with more high density of compact bone.