Effect of orthodontic forces on root length of immature mandibular second premolars: a split-mouth randomized clinical trial

ABSTRACT Objective: To assess the effect of orthodontic forces on changes in root length of immature mandibular second premolars. Methods: Sixty-four mandibular second premolars (MSP) with immature apices (left and right sides) of 32 patients aged between 10 and 13 years were evaluated. Orthodontic treatment was started after obtaining periapical radiographs (T1) from the MSPs of each patient. Brackets were bonded, except the ones of MSPs (left or right by random as control MSP, and the other side as test MSP). After 9-12 months, a second periapical radiograph (T2) was obtained from the MSPs of each patient. Then, brackets were bonded to the control MSPs, which were not bonded before. After 18 ± 3 months, a third periapical radiograph (T3) was obtained. Changes in root length were evaluated by using a new formula. The test and control MSPs at T1, T2 and T3 were compared using repeated measures ANOVA and parametric tests. P-value smaller than 0.05 was statistically significant. Results: There was no significant difference between the test and control groups in the mean root length of MSP at T1 (p= 0.48) and T3 (p= 0.078). The root length at T2 (p= 0.001) was significantly different between test and control MSPs, and the test group showed longer root length than the control group. Conclusions: Orthodontic force applied for leveling and alignment of immature MSPs may not have destructive effects on the roots, and may accelerates root formation in short-term. Normal root length was achieved at the end of root development.

摘要 研究目的：评估正畸力对未成熟根尖下颌第二前磨牙（mandibular second premolars, MSP）牙根长度变化的影响。研究方法：选取32名年龄10~13岁患者的64颗根尖未成熟的下颌第二前磨牙（左右侧各1颗）作为研究对象。首先获取每位患者下颌第二前磨牙的根尖片（periapical radiographs，T1基线），随后启动正畸治疗。除下颌第二前磨牙外，其余牙齿均粘接托槽；将患者的左右侧下颌第二前磨牙随机分为对照侧与实验侧。术后9~12个月，再次为每位患者的下颌第二前磨牙拍摄根尖片（T2随访）。随后为此前未粘接托槽的对照侧下颌第二前磨牙粘接托槽。在18±3个月时，拍摄第三次根尖片（T3终末随访）。采用全新公式评估牙根长度变化，通过重复测量方差分析（repeated measures ANOVA）与参数检验对比T1、T2、T3三个时间点下实验组与对照组下颌第二前磨牙的牙根长度差异，以P<0.05为差异具有统计学意义的判定标准。研究结果：T1时间点（p=0.48）与T3时间点（p=0.078），实验组与对照组的下颌第二前磨牙平均牙根长度均无显著统计学差异；T2时间点两组牙根长度差异具有统计学意义（p=0.001），且实验组牙根长度长于对照组。研究结论：针对未成熟根尖下颌第二前磨牙的排齐整平操作所施加的正畸力，不会对牙根造成破坏性影响，且可在短期内促进牙根形成，最终在牙根发育完成时可达到正常牙根长度。