A study of the risk and the prevention of root resorption during orthodontic treatment

本研究旨在探讨正畸治疗过程中牙根吸收的风险，并从基础和临床两方面提出预防牙根吸收的方法。临床研究表明，近40%的患者在正畸治疗过程中发生严重的牙根吸收，在积极治疗之前，牙根形状异常。为探讨正畸牙移动过程中矿物质营养缺乏对牙根形成和牙吸收的影响，在2周龄Wistar大鼠牙根发育期给予低钙饮食，并移动磨牙。实验组动物牙本质矿化度降低，牙本质球间质形成，但对照组和实验组动物牙吸收发生率无明显差异。免疫组化显示成骨细胞分泌骨钙素和糖胺聚糖，具有成骨细胞的特征。破牙本质细胞的形成可能与成牙骨质细胞的形成有关。体外研究表明，人牙周膜（PDL）成纤维细胞在持续压应力作用下可诱导HSP 47、60、70的表达，从而保护细胞免受机械应力的损伤，并调节外周血淋巴细胞破牙细胞样细胞的形成。相反，在大鼠中观察到局部施用双膦酸盐对正畸牙齿移动引起的牙根吸收的抑制作用。提示正畸治疗中牙根吸收的风险可能与牙周组织和牙根的性质有关，某些骨吸收抑制剂可以预防牙根吸收。

The purpose of this study was to examine the risk of root resorption during orthodontic treatment and develop the prevention method of that from the basic and the clinical background. Clinical studies showed almost 40% of patients that developed severe root resorption during orthodontic treatment had abnormally shaped roots before active treatment. To test the effects of deficiencies of mineral nutrients on the formation of roots and the development of tooth resorption during orthodontic tooth movement, 2 weeks-old Wistar rats were fed a low calcium diet during root development period and the molars were moved orthodontically. A hypomineralized dentin with interglobular dentin was observed in the experimental animals, but no significant difference was observed in the development of tooth resorption between control and experimental animals. Immunohistochemical studies showed cementblasts produced osteocalcin and glycosaminoglycans and have simillar characteristics with osteoblasts. The production of them was changed during orthodontic tooth movement and cementblasts suggested to be related with the formation of odontoclasts. In vitro studies showed human periodontal ligament (PDL) fibroblasts induced HSP 47,60,70 with the application of continuous compressive stress to protect cells from mechanical stress and regulated the formation of odontoclast-like cells from peripheral blood lymphocytes. In contrast, inhibitory effects of the topical administration of a bisphosphonate on root resorption incident to orthodontic tooth movement were observed in rats. These results indicate the risk of root resorption during orthodontic treatment may be related with the properties of the periodontium and the roots and some bone resorption inhibitory detergents can prevent it.