External Root Resorption DuringStandardised Orthodontic Tooth Movement In Young And Adult Rats

目的：比较研究幼鼠和成年鼠正畸牙齿移动过程中的牙根吸收。材料与方法：本研究包括两组大鼠，其中幼鼠30只(年龄约6周)，成年鼠30只(年龄约9～12个月)。大鼠上颌牙一侧用于实验侧，另一侧用于对照。实验侧的三颗磨牙用结扎丝颌粘接剂固为一个整体，在超弹性拉簧作用下(力值为0．1牛顿)向切牙侧移动。1，2，4，8和12周时给予大鼠过量麻醉剂，材料用于组织学研究。上颌第一磨牙的近中颊侧根为根吸收研究对象。压力侧和张力侧的牙根吸收程度在显微镜下进行长度测量。实验侧与对照侧，压力侧与张力侧，幼鼠与成年鼠之间的牙根吸收程度分别以实验时间为参照，在统计学手段下进行了组间和组内分析和比较，以探讨牙齿移动时间和年龄因素对于牙根吸收的影响。结果：实验侧的牙根吸收在幼鼠与成年鼠之间在1，2，4，8周时均没有统计学差异。而在第12周时，成年鼠实验侧牙根吸收大于幼鼠(P＜0．05)。成年鼠实验组压力侧的牙根吸收明显大于对照组压力侧，而在幼鼠组没有发现这一差异。两组年龄幼鼠的实验组其压力侧和张力侧的牙根吸收均高度相关。结论：相对于对照侧，正畸牙齿移动并没有在幼鼠的实验侧诱发更多的牙根吸收。在成年鼠，长期的正畸作用力倾向于诱发更多的牙根吸收。这些研究结果表明对于正畸成年病人的后期治疗要更加注意防止牙根吸收。

External Root Resorption During Standardised Orthodontic Tooth Movement In Young And Adult Rats

Objective: To evaluate root resorption during orthodontic tooth movement in young and adult rats. Material and Methods: Standardised orthodontic tooth movement was performed in two groups of 30 male rats; a juvenile group aged 6 wks and an adult group aged 9-12 months. A split mouth design was chosen. The three maxillary molars at the experimental sides were moved as one unit mesially by a Sentalloy coil spring delivering a force of 10 cN over a long range of activation. The contra-lateral molars served as controls. At 1, 2, 4, 8, and 12 weeks groups of animals were killed for histological evaluation. The first (also the largest) root of the first molar was chosen as the study root. Root resorption was measured as the resorbed root length at both pressure and tension sides. Differences between the experimental and control sides, between pressure and tension sides were calculated across time and were compared within and between the two age groups as measures for the effects of orthodontic intervention and the effect of age. Correlation of root resorption at experimental and control sides were also calculated. Results: Root resorption at the experimental pressure sides showed no difference between young and adult rats at 1, 2, 4 and 8 wk. But at 12wk it was significantly higher in adult than in young rats ( P <0.05). In adult but not in young rats root resorption at experimental pressure sides was significantly higher than at control pressure sides ( P <0.01). Root resorption at experimental pressure and tension sides were significantly correlated in both groups ( P <0.01). Conclusion: Orthodontic forces did not induce more root resorption in juveniles. Root resorption is quite an accompanying phenomenon in tooth movement. Persistent orthodontic force tended to induce increased root resorption in adults, which implicit that more attention are needed to prevent root resorption in the late phase of tooth movement in adults.