The purpose of this study was to evaluate the effect of occlusion on the mechanical strength of periodontal fibers during retention periods after experimental tooth movement. In the Sprague Dawley male rats weighing 200 g or more, the intraoral elastics were inserted into the both right and left interproximal space between upper first and second molars for tooth movement. After 4 days later, the left lower first, second, and third molars were extracted for differentiating the non-occlusal side from the occlusal side in the same mouth. At the same time the elastics were removed and then light cured resin was placed in the space between upper first and second molars following undercut was made for retention bilaterally. From the beginning of retention, 7 rats were sacrificed at 0, 4, 8, 12, 16, 20 days respectively. For evaluating of magnitude on the mechanical strength of periodontal tissue, the maximal shear load of the upper first molars were measured bilaterally during extraction using Instrein Universal Testing Machine. {
The results of thus study were obtained as follows
1. In the occlusal side, the maximal shear load was increased from no retention to retention 20 days group as time was going and statistically difference was shown from retention 12 days group (p<0.05).
2. In the non-occlusal side, the maximal shear load was increased slightly from no retention to 20 days group as time was going but there was no statistically difference (p>0.05).
3. The result compared with the maximal shear load between occlusal and nonocclusal side showed no statistically difference until retention 8 day group (p>0.05), but showed statistically difference from retention 12 day to 2C day group (p<0.05).
These results show that occlusion had an effect on mechanical strength of the periodontal fibers during retention periods after experimental tooth movement; therefore, it is suggested that occlusion should be considered while the retainer types and retention period are planned.
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