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

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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.