A study on the location of center of rotation of the tooth subjected to the load using a magnetic sensing system for three dimensional displacement.

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  • Yoshida Noriaki
    <I>Department of Orthodontics, School of Dentistry, Nagasaki University</I>
  • Koga Yoshiyuki
    <I>Department of Orthodontics, School of Dentistry, Nagasaki University</I>
  • Jost-Brinkmann Paul-Georg
    <I>Department of Orthodontics and Dentofacial Orthopedics, Humboldt University of Berlin</I>
  • Abe Risako
    <I>Department of Orthodontics, School of Dentistry, Nagasaki University</I>
  • Kobayashi Kazuhide
    <I>Department of Orthodontics, School of Dentistry, Nagasaki University</I>
  • Yamada Yoshiaki
    <I>Department of Oral Physiology, School of Dentistry, Niigata University</I>

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  • 荷重時の歯の回転中心に関する研究　　磁気センサを応用した３次元変位測定システムの生体への応用

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Abstract

The type of tooth movement is described simply by the center of rotation. Therefore, orthodontic tooth movements can be predicted, when each location of the center of rotation under various force systems is clarified. The purpose of this study was to develop a magnetic sensing system for three dimensional displacement and to determine the location of center of rotation of the maxillary central incisor. Lingually directed forces were applied at different horizontal levels in human subjects. The main part of the system is composed of eight hall elements and a samarium cobalt magnet. The relationship between the location of center of rotation and theposition of the force application was discussed. It was concluded as follows;<BR>1. Rresolution was determined to be less than 1μm and distortion of the system was calculated at less than 0.7% within the range of ±300μm. This system was estimated to be stable and sensitive enough to be applied in the oral cavity and to measure the tooth movements in vivo.<BR>2. When a lingually directed force was applied at the bracket position of the tooth, the center of rotation was observed at a point 0.44 times the root length from the alveolar crest. This indicated that the tooth crown tended to move lingually and the root tended to move labially, or oppositely when only a single force was applied to maxillary incisors during the anterior teeth retraction.<BR>3. When the point of force application was moved cervically, the center of rotation also moved toward the same direction. It was shown that the center of rotation is located at the root apex when the force was applied at a point 5mm cervical from the bracket position.<BR>4. As the location of force application moved further apically, the direction of rotation changed from crown-lingual to root-lingual at a point between 6 and 8 mm cervical from the bracket position.<BR>This study was supported by DFG Grant Mi198/4-1.

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