Three-dimensional Investigation of the relation between stress distribution and periodontal tissue changes incidental to orthodontic tooth movement

1.正畸力引起的早期组织变化成年猫左上尖牙用闭合螺旋弹簧向远侧移动。所使用的力为100 g持续4天、100 g持续7天、200 g持续4天和200 g持续7天。完成牙齿移动后，猫灌注布因和标本包埋在火棉胶。连续组织切片用H. E.和AZAN，并在光学显微镜下检查。然后，对连续切片进行拍照，并在描图纸上描绘组织学元素。这些描记被输入到三维重建系统中。(1)光镜观察结果：所有实验牙颈部压力侧均存在嗜酸性、均匀的“无细胞区”和存在于无细胞区之间的“内变性区”，内变性区内有成纤维细胞核固缩。(2)三维重建图像所见：（1）无细胞带呈环形，包绕着变性带。(2)4d时，在无细胞区周围有大量破骨细胞。100 g-7 d时，破骨细胞广泛分布于颈远中、颊侧和近中根尖区。而200 g-7 d时，破骨细胞仅分布于颈远中端和近中端。100 g的力比200 g的力更接近正畸牙齿移动的最佳力.牙齿移动的三维测量为了计算牙齿的三维移动，用牙模型光学测量系统测量了猫的牙模型。在测量之前，该系统已被改进，在水平和垂直方向上都具有0.05*SS的更高精度。

1. Early tissue changes due to orthodontic forcesThe upper left canines of adult cats were moved distally with a closed coil spring. The forces used were lOOg for 4days, lOOg for 7days, 200s for 4days and 200g for 7 days. After the completion of the tooth movement, cats were perfused with Bouin and the specimens were embeded in celloidin. Serial tissue sections were stained with H. E. and AZAN and were examined under a light microscope. Then, the serial sections were photographed and the histological elements were traced on tracing papers. These tracings were input into a three-dimensional reconstructive system.(1) Light microscopic findingsAt pressure side in the cervical region of all experimental teeth, there were "cell free zone" which was eosin-stainable and homogeneous, and "intra-degenerated zone" which existed between cell free zones and had pyknofic nuclei of fibroblasts.(2) Findings from three-dimensional reconstructed images(1) Cell free zone was ringshaped and enclosed intra-degenerated zone.(2) In 4days cases, there were a fbw osteoclasts around cell free zone. In lOOg-7days case, osteoclasts were widely distributed in the distal-cervical, the buccul and the mesial-apical areas. To the contrary, osteoclasts were found only in the distal-cervical and mesial-apical areas in 200g-7days case. The force of 100g was more approximate to the optimal force for orthodontic tooth movement than the force of 200g in this experiment.2. Three-dimensional measurement of tooth movementTo calculate the tooth movement three-dimensionally, dental casts of cats were measured by the optical measurement system of dental cast. Prior to the measurement, the system had been improved to have a higher accuracy of 0.05*SS in both horizontal and vertical directions.