The purpose of this study was to evaluate the force degradation rate of synthetic elastomeric chains during space closing phase of orthodontic treatment. Two kinds of synthetic elastomeric chains(RMO, 3M) were selected which were commonly used in~clinics. All of the samples were extended and tested for 4 weeks under the simulated intraoral condition. The results can be summarized as follows
1. Time related residual force showed typical logarithm function. Residual force after 4 weeks was 41.2-64.6 % of original force, and difference between two kinds of elastomeric chain existed
2. Elastic force decreased greatly during first 10 minutes, so 20-25 % of original force disappeared. After that, this decreasing tendency was diminished significantly, average rate of elastic force after 1 week to 4 weeks were 1.5 % demonstrating rather constant force.
3. Even though the same brand of elastomeric chiain was used, as extension rate of elastomeric chain increased, force degradation rate increased by decreasing of residual force.
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