Force Degradation Of Elastomeric Chains By Prestretching In Vitro

Objective：The aim of the study was to analysis the influence patterns of suchfactors as the number of loops、level and duration of prestretching on forcedegradation of elastomeric chains to help clinical practice.Methods： All chains were classified to the experimental (including9groups) andthe control group (including3groups) through the orthogonal design. Theexperimental group samples were stretched according to different levels ofprestretching (1/3、1/2and one time of original length) and different durations ofprestretching (1、10and30minutes). Record the stretched length measured by anInstron Universal Testing Machine when the initial force is150g. Then various chainswere maintained respectively in artificial saliva environment of37℃. The remainingforce of various chains were recorded at the different moment in4weeks. Thencalculated the percentage of remaining force, and analysed the results.Results：1.When the stretched force after prestretching was150g, the stretched length ofelastomeric chains was between1.16mm and3.37mm, and the strerched length of2,3,4loops was increased in sequence.2. The remaining force of the experimental group was more than that of theexperimental group at the different moment in4weeks. The remaining force of theexperimental group was between92.12±4.35g and131.22±6.42g, that of the controlgroup was between70.06±7.12g and94.13±2.78g.3. The force of all elastomeric chains degraded most rapidly at the initial24hours, the percentage of remaining force the experimental group was between70%and90%, that of the control group was between60%and70%. Then it degradedslowly, the percentage after4weeks was between61%and87%, that of the controlgroup was between46%and62%.4. The percentage of remaining force of2,3,4loops was increased in sequence,and the percentage of remaining force of prestretched1/3、1/2and one time of original length was increased in sequence. The influence of f loops and levels ofprestretching on force degradation of elastomeric chains was statistically significant,whereas the different durations of prestretching showed no statistical significant.Conclusions：1. The force of all elastomeric chains degraded most rapidly during the initial24hours, and more stable after one week. The remaining force of the prestretchedelastomeric chains was more than that of the unprestretched elastomeric chains at thedifferent moment in4weeks.2. Under the same conditions, the number of loops and the level of prestretchingincrease, the more slowly the force both degraded. However, the different durationsof prestretching have no influence on force degradation rate.