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Study of stress relaxation of orthodontic elastomers: Pilot method report with continuous data collection in real time

AIM: Development of an experimental set-up capable of reliably recording changes of forces applied by an elastomeric chain, under constant strain, in real time and with continuous data recording and the study of differences in stress relaxation between open (with intermodular link) and closed (without link) chains of the same manufacturer. MATERIAL AND METHOD: An original mechanical set-up was designed comprising electronic parts and a mounting system for the suspension of elastomeric materials. System behavior was recorded under loading, the appliance was calibrated using a dynamometer, a curve correlating appliance units with grams was created and the conversion coefficient of appliance measuring units into grams was investigated. Both open and closed types of elastomeric chain (ORMCO) were used in this study; the chain was stretched by 50% of its original length and was studied for 2 weeks. Stress relaxation results were analyzed using the two- variable (time, chain type) ANOVA method at a level of significance of ·=0.05. RESULTS: The pilot study did not show any differences in the force delivered at the initial stretching between the open and closed chain types. No differences between the two types were observed concerning force degradation rate during the course of the study. Based on the data, a mathematical formula was suggested in order to describe the phenomenon of stress relaxation during the first 24 hours, when force decay is maximal. CONCLUSIONS: The suggested set-up enables us to record force decay of elastomeric materials under constant strain