Root Resorption in Maxillary Central Incisors during Active Orthodontic Treatment-A Radiographic Study-

本研究的目的是探讨是否有可能在主动正畸治疗中早期发现上切牙牙根吸收的放射学变化。提出了一种结合头颅侧位片测量牙长的新技术。10个干燥颅骨的实验研究表明，测量牙齿长度的效果良好，但临床应用的牙齿长度的测量并不令人满意。测量失败的原因是几何因素、患者的开牙合、切牙边缘不清晰等综合因素。牙周间隙和硬脑膜厚度的测量结果与X线牙合片的观察结果有良好的相关性。G. .患者或医师挂号后不配合，或腭裂患者、发生肿瘤）。44例患者仍在积极的正畸治疗。本次分析了后续40例患者。主动正畸治疗时间3 ~ 31个月，平均20个月。在主动正畸治疗期间每3个月拍摄一次X线片。在开始留置前或留置后1个月拍摄最终X线片。26例（65%）明显发生牙根吸收，6例（15%）可疑牙根吸收。首次发现牙根吸收的时间为3个月至1年或更长。在重度吸收病例中，首次发现牙根吸收的时间是在第一次X线片中非常早。早期发现牙根吸收是牙根吸收的高危因素，这一点对牙周病医生来说很重要。牙根吸收组与非吸收组的硬脑膜和牙周间隙的变化也不同。我们将在该项目完成后报告这一点。

The purpose of this study was to investigate whether it is possible to detect an early radiographic changes of root resorption in upper incisors during active orthodontic treatment. A newly occlusal technique for measurement of tooth length combined with lateral cephalogram was developed. Although experimental study with 10 dry skulls showed a good results to measure tooth lengths, clinical use for measurement of tooth length in patients was not satisfactory. The cause of failure in measurement was that a geometric factor, patients' open bite, ill-defined incisor edge, and so on were combined. The measurement of the thickness of periodontal space and lamina dura showed a good correlation with the observation of the occlusal radiograms.Out of registered 120 volunteer patients in this study, 36 patients were quit because of some reasons(e. g. . non-cooperation of the patients or orthodontists after registration, or the patients with cleft palate, occurrence of tumor). Forty-four patients were still in active orthodontic treatment. Subsequent 40 patients were analyzed this time. The duration for active orthodontic treatment was 3 to 31 months, mean 20 months. The radiograms were taken every 3 months during active orthodontic treatment. The final radiograms were taken at one month before or after starting the retention. The root resorption was clearly occurred in 26 patients(65%)and suspected in 6 patients(15%). The first detection of root resorption was from 3 months to one year or more. In the severe resorption cases, the timing of the first detection of root resorption was very early in the first radiogram. It is important for orthodontists to know that the early detection of root resorption sucgests the high risk of root resorption. Also the changes of lamina dura and periodontal space were different between root resorption patients and non-resorption patients. We will report about this point after this project is finalized.