Effect of Different Prestretchings on Force Decay of Synthetic Orthodontic Elastomeric Modules at Different Time Intervals (An In vitro Study)

Background: This study aims to investigate the effect of prestretching on the force degradation of elastomeric chains. Materials and methods: 500 samples from Ormco company both generation I and generation II elastics were divided into control and experimental groups for prestretching including 1 time 50% prestretching, 3 times 50% prestretching, 1 time 75% prestretching and 3 times 75% prestretching groups. Experimental groups are prestretched in one or three stretchings in quick sequential manner using dental clamp holder inside boxes made to give an increase of 50% or 75% of the elastics initial length. Samples were applied to pins fixed in acrylic plates made with a fixed distance so that all control samples deliver 200 grams of force initially. Samples were stored in artificial saliva at 37C in an incubator. Forces were measured at five-time intervals. Statistical analysis included one-way analysis of variance ANOVA test, Tukey HSD test, and independent t-test. Results: Patternof force degradation was similar in all durations beinghigher in control group followedby1 time50% prestretching, 3 times 50% prestretching, 1 time 75% prestretching and 3 times 75% prestretching group. There was non-significant difference between 1 time 50% prestretching and 3 times 50% prestretching and between 1 time 75% prestretching and 3 times 75% prestretching in most of the testing periods. Conclusion: Generation I elastics showed more force degradation than generation II in all groups and time intervals with more force decayed in the sixth week. 75% prestretching groups showed least force loss compared to 50% and control groups. Number of times of prestretching is of questionable clinical benefit.