A study on a computerized support system for orthodontic treatment

根据正畸医生的经验和技能，正畸治疗必须在患者身上进行几年的时间。我们研究了用于正畸治疗的计算机辅助系统的可行性，并展示了优化治疗程序的巨大潜力。(1)开发了一种计算机治疗计划系统，使正畸医生可以在计算机图形显示器上建立设置模型。该系统是基于我们先前开发的装置所获得的牙科模型轮廓数据的3D移动。使用该系统，正畸医生可以在治疗前定量预测每颗牙齿的3D运动。(2)我们还开发了一套系统，可以根据矫治过程中的3D牙齿移动和正畸力来调整正畸矫治器。力的大小和方向，包括防转和山形弯曲引起的动量，都是通过有限元方法得到的。(3)估算患者牙槽骨的吸收率。通过牙齿、牙周膜和牙槽骨的有限元模型计算牙齿的三维运动和应力分布，得到牙周膜和牙槽骨的应力分布。吸收率与应激有很好的相关性，约为4um/g/mm~2/d。(4)将该系统应用于上、下牙间距离分布的测量，以评价牙合接触情况。治疗过程中牙合接触面积增大。这一结果验证了该系统作为治疗评估手段的有效性。

Orthodontic treatment must be conducted over a period of a few years on a patient, depending on experience and skill of an orthodontist. We have studied feasibility of a computerized support system for orthodontic treatment and demonstrated enormous potentialities to optimize a treatment procedure.(1) A computerized planning system for the treatment has been developed, which allows an orthodontist to construct a setup model on a computer graphic display. This system is based on the 3D movements of dental cast profile data obtained by our apparatus previously developed. Using this system an orthodontist can predict quantitatively the 3D movement of each tooth prior to the treatment. (2) We have also developed a system to readjust an orthodontic appliance on the basis of 3D tooth movements during the treatment and orthodontic forces. The magnitude and direction of the forces, including the momentum caused by anti-rotation and gable bends, are obtained by a finite element method (FEM). (3) We estimated a resorption rate of alveolar bone on patients. The rate was obtained from both the 3D tooth movement and the stress distribution calculated with a FEM model of a tooth, periodontal membrane and alveolar bone. The resorption was correlated well with the stress and was found to be about 4 mum/g/mm^2/day. (4) To evaluate the occlusal contact the system was also applied to the measurement of distance distribution between upper and lower teeth. The occlusal contact area increased during the treatment. This result verifies the usefulness of the system as a mean of treatment evaluation.