Srinivasan Bhadrinath, Kailasam Vignesh, Chitharanjan Arun, Ramalingam Arthi
Department of Orthodontics, Faculty of Dental Sciences, Sri Ramachandra Univeristy, Porur Chennai, India.
Orthodontics (Chic.). 2013;14(1):e66-74. doi: 10.11607/ortho.841.
The present study aimed to measure the magnitude of the collum angle (crown-root angulation) of maxillary central incisors present in Class II, division 2 malocclusion and to relate the changes in its magnitude with variations in the lower lip line.
A set of 120 conventional lateral cephalograms were selected and divided into three groups of 40 each based on the type of malocclusion presented: Class II, division 2 (group 1); Class II, division 1 (group 2); and Class I (group 3). The collum angle of the maxillary central incisor was measured, and the lower lip line was recorded.
Analysis of variance (ANOVA) revealed that the mean collum angle was statistically significantly different in the three groups. The mean collum angle was greatest in Class II, division 2 malocclusion (group 1). The mean collum angles were 3.24 ± 4.69 degrees, 0.95 ± 1.06 degrees, and 1.05 ± 1.50 degrees in groups 1, 2, and 3 respectively. In χ ² test comparison of the location of the lower lip line (incisal, middle, or apical third of the central incisor) among the three groups, the lower lip line was found to contact the middle third of the central incisor most frequently in Class II, division 2 malocclusion. ANOVA followed by Tukey honestly significant difference (HSD) test showed that the mean collum angle is significantly increased when the lower lip is in the middle third (P < .05) of the central incisor.
Variations in magnitude of the collum angle with the change in the lower lip line suggest a probable etiologic role of the lower lip line in the development of the collum angle.
本研究旨在测量安氏II类2分类错牙合中上颌中切牙的冠根角度（牙冠与牙根的夹角）大小，并探讨其大小变化与下唇线变化之间的关系。
选取120张传统头颅侧位片，根据错牙合类型分为三组，每组40张：安氏II类2分类（第1组）；安氏II类1分类（第2组）；安氏I类（第3组）。测量上颌中切牙的冠根角度，并记录下唇线位置。
方差分析显示，三组的平均冠根角度在统计学上有显著差异。安氏II类2分类错牙合（第1组）的平均冠根角度最大。第1、2、3组的平均冠根角度分别为3.24±4.69度、0.95±1.06度和1.05±1.50度。在对三组中下唇线位置（中切牙切缘、中部或根尖三分之一处）进行χ²检验比较时，发现安氏II类2分类错牙合中，下唇线最常接触中切牙的中部三分之一处。方差分析后进行Tukey真实显著差异（HSD）检验表明，当下唇位于中切牙的中部三分之一处时，平均冠根角度显著增加（P<.05）。
冠根角度大小随下唇线变化，提示下唇线在冠根角度形成过程中可能起病因学作用。
