| Co-Investigator(Kenkyū-buntansha) |
GOTO Tetsuya Kyushu Dental College, Orthodontics, Associate preofessor, 歯学部, 助教授 (70253458)
NODAI Tetsuo Kyushu Dental College, Orthodontics, Lecturer, 歯学部, 講師 (00128802)
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| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Duration of force application is an important factor, together with the magnitude of force, in stimulating osteoclast recruitment in the periodontal ligament. The purpose of this study was to examine the effect of duration of force application on the amount of molar tooth movement and root resorption in rats using two intermittent and continuous forces. One hundred forty four molars of 57 rats were randomly assigned to continuous, 8-hour intermittent, 18-hour intermittent and sham-operation groups.. A calibrated Ni-Ti coil spring exerting 40 g of initial force was suspended between the maxillary first molars and incisors for 13 days. Tooth movement was measured on roentgen radiographs. Root resorption was measured under microscope. Results: Initial tooth displacements were 24.7μ(100%) in continuous, 22.7μ(91.9%) in 8-hour intermittent, and 25.8μ(104.5%) in 16-hour intermittent group. There was no significant difference in the displacement among three groups. Actual tooth movements at day 13 were 57.8μ(100%) in continuous, 38.1μ(65.9%) in 8-hour intermittent, and 50.8μ(87.9%) in 16-hour intermittent group. Total tooth movements (initial displacement-actual tooth movement) at day 13 were 82.5μ(100%) in continuous, 60.8μ(73.7%) in 8-hour intermittent, and 76.6μ(92.8%) in 16-hour intermittent, The amount of movement achieved by intermittent force exceeds the expected value predicted by the duration (33.3%, 66.7%). Root resorption rates caused by the mesial movement at day 13 were 47.5%, 24.4%, and 17.1%. Compared with the continuous group, root resorption rates were 45.4% and 25.1%.
Our results suggest that the amount of tooth movement in response to intermittent force is lower than that in response to continuous force, but that the amount of tooth movement achieved by intermittent force exceeds the expected value predicted by the duration of force application, with less root resportion.
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