This study was performed to analyze the effects of forces to the alveolar bone by various molar uprighting spring such as helical uprighting spring, T-loop spring, Modified T-loop spring and open coil spring. The simplified two-dimensional photoelastic model was constructed with a lower left posterior quadrant containing the second molar, the first and second premolars and the canine, with the first molar missing. Several molar uprighting springs were fabricated from 0.017 by 0.022 inch blue Elgiloy and applied to the photoelastic model. Two-dimensional photoelastic stress analysis was performed, and the stress distribution was recorded by photography.
The results obtained were as follows ;
1. In all the kinds of the springs, the center of rotation of the mandibular second molar was observed at the apical 1/5-1/6 between the alveolar crest and the root apex.
2. In all the kinds of the spring, the stress induced in the mesial root surface of the manibular second molar was relatively homogeneous but there was some difference in the magnitude of the stress.
3. In the kinds of the springs, the distal crown tipping moment of the second molar was increased in turn as open coil spring, helical uprighting spring, T-loop spring, and modified T-loop spring.
4. The largest extrusive force was occured in the T-loop spring, intrusive force was occured in Modified T-loop spring only, and the largest distal tipping force was occured in open coil spring.
5. In the T-loop spring with activation, the stress induced in the mesial root surface of the second molar was increased gradually from the root apex to the alveolar crest and highly concentrated in the alveolar crest.
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