Correlation between collum angle and lower lip position in different Class II malocclusions - A retrospective cephalometric study

<b>Purpose</b>: Significance of analysing collum angle in class II malocclusions with respect to lip position may lend greater credibility to variable torque brackets (mainly in the anteriors) that are fast gaining traction. Determine the magnitude of collum angle of maxillary central incisors in Class II division 1, division 2 malocclusions and changes in measurement brought about by variations in lower lip position and incisal contact. <b>Materials and methods</b>: 154 lateral cephalograms were divided into three groups- 55(Angle’s class I), 52 (Angle’s class II division 1) and 47 (Angle’s class II division 2). The collum angle was measured along with lower lip line (in Class II division 2) and lower lip contact (in Class II division 1) malocclusions. <b>Results</b>: The mean collum angles were 2.12 ± 1.43°, −0.84 ± 0.87° and 4.67 ± 2.23° in Groups 1, 2, and 3, respectively. Mean collum angle is significantly increased when the lower lip was found to contact the middle-third of the central incisor(in Group 3)and significantly decreased when the anterior one-third of the lower lip was in contact with the incisal edge of the central incisor (in Group 2). ANOVA followed by Tukey HSD test was carried out to determine statistically significant differences (p <b>Conclusion</b>: Collum angle is significantly decreased in Class II division 1 malocclusions necessitating variable torque prescriptions and segmental mechanics of maxillary anteriors. Appropriate alveolar bone support must be assessed prior to en-masse retraction and intrusion respecting the cortical boundaries. <b>KEY MESSAGES</b>: Variable torque brackets are rapidly gaining credence for their ability to provide sufficient alveolar bone support in different clinical scenarios. In this study, we have emphasized upon utilizing similar mechanics to treat class II malocclusions by utilizing the lower lip position as a reference guide.

<b>研究目的</b>：分析安氏II类错𬌗（Angle’s class II malocclusion）中牙颈角（collum angle）与唇位置的关联意义，可为当前逐步获得广泛应用的可调转矩托槽（variable torque brackets，主要应用于前牙区）提供更充分的临床佐证；本研究同时拟测定安氏II类1分类、2分类错𬌗患者上颌中切牙（maxillary central incisors）的牙颈角大小，并明确下唇位置变化与切牙接触状态对该测量值的影响。
<b>材料与方法</b>：本研究纳入154张头颅侧位片（lateral cephalograms），将其分为3组：安氏I类错𬌗组（55例）、安氏II类1分类错𬌗组（52例）及安氏II类2分类错𬌗组（47例）。针对安氏II类2分类错𬌗患者，同步测量下唇线与牙颈角；针对安氏II类1分类错𬌗患者，则测量下唇接触状态与牙颈角。
<b>结果</b>：3组的平均牙颈角分别为2.12±1.43°、-0.84±0.87°及4.67±2.23°。当下唇接触中切牙中1/3区域时（第3组），平均牙颈角显著升高；当下唇前1/3区域接触中切牙切缘时（第2组），平均牙颈角显著降低。本研究采用方差分析（ANOVA）结合Tukey HSD检验，以验证组间差异的统计学显著性（p<）。
<b>结论</b>：安氏II类1分类错𬌗患者的牙颈角显著降低，提示需采用可调转矩矫治方案及上颌前牙分段矫治技术。在对前牙进行整体内收与压低操作前，需评估牙槽骨（alveolar bone）支持状态，并严格遵循皮质骨边界（cortical boundaries）进行临床操作。
<b>核心要点</b>：可调转矩托槽因其可在不同临床场景下提供充足牙槽骨支持的特性，正快速获得临床认可。本研究强调，可将下唇位置作为参考依据，采用同类矫治技术治疗安氏II类错𬌗。