van Loenen M, Degrieck J, De Pauw G, Dermaut L
Orthodontic Department, School of Dentistry, University of Ghent, De Pintelaan 185 P8, B-9000 Ghent, Belgium.
Eur J Orthod. 2005 Jun;27(3):258-62. doi: 10.1093/ejo/cji007.
This study was undertaken to determine the variation in crown-root angle (CRA) of the upper incisors and canines as well as the variation in their labial contour. In addition, the influence of the variability of the labial contour and of different bracket heights on torque was evaluated. Proximal radiographs were taken of 160 extracted maxillary teeth (81 incisors and 79 canines). They were digitized and analysed with Jasc Paint Shop Pro 7TM and Mathcad 2001 Professional. The incisal edge, the centre of the cemento-enamel junction (CEJ), and the root apex were digitized to define the crown and root long axis. For all teeth the CRA was measured. At several heights of the labial surface a tangent was determined, enabling measurement of the inclination of the labial surface. The CRA had great variability, ranging from 167 to 195 degrees for the canines (mean value 183 degrees) and from 171 to 195 degrees for the incisors (average 184 degrees). The mean inclinations of the labial surfaces for the incisors varied greatly. Between 4 and 4.5 mm from the incisal edge the standard deviations (SD) were the smallest and between 2 and 4.5 mm from the incisal edge the labial surface angle differed by approximately 10 degrees. For the canines the mean inclinations of the buccal surface also varied. This angle differed by around 10 degrees between 2 and 4.5 mm from the incisal edge, but the SD were much larger than for the incisors. It can be concluded that placement of a bracket on a tooth at varying heights, still within a clinically acceptable range, results in important differences in the amount of root torque.
本研究旨在确定上颌切牙和尖牙的冠根角（CRA）变化以及其唇面轮廓的变化。此外，还评估了唇面轮廓变异性和不同托槽高度对转矩的影响。对160颗拔除的上颌牙齿（81颗切牙和79颗尖牙）拍摄了近中根尖片。将其数字化，并使用Jasc Paint Shop Pro 7TM和Mathcad 2001 Professional进行分析。将切缘、牙骨质-釉质界（CEJ）中心和根尖数字化，以确定冠和根的长轴。测量了所有牙齿的CRA。在唇面的几个高度处确定一条切线，从而能够测量唇面的倾斜度。CRA具有很大的变异性，尖牙的CRA范围为167至195度（平均值为183度），切牙的CRA范围为171至195度（平均值为184度）。切牙唇面的平均倾斜度变化很大。在距切缘4至4.5毫米处，标准差（SD）最小，在距切缘2至4.5毫米处，唇面角度相差约10度。对于尖牙，颊面的平均倾斜度也有所变化。在距切缘2至4.5毫米处，该角度相差约10度，但标准差比切牙大得多。可以得出结论，在临床上可接受的范围内，将托槽放置在牙齿的不同高度会导致根转矩量产生重要差异。
