Experimental Study Of The Force Decay Of NiTi Closed Coil Spring And Elastomeric Chain

Objective: To investigate the force decay character of different brands of NiTi closed coil spring and elastomeric chain by measuring the remaining force at different time when they were stretched to produce the intended force to provide clinical reference for application of NiTi closed coil spring and elastomeric chain.Methods: 0.010 inch NiTi closed coil spring of 3 brands (A1,B1,C1) and large filament elastomeric chains of four loops of 2 brands(D1,E1) were stretched to produce the initial force of 150g, and 0.012 inch NiTi closed coil spring(A2,B2,C2) of 3 brands and mini filament elastomeric chains of five loops of 2 brands (D2,E2)were stretched to produce the initial force of 250g on Instron Universal Testing Machine, and then recorded the stretched length(L0+L).Maitained the stretched length of different NiTi closed coil springs and elastomeric chains on the self-designed experimental fixture and put the experimental apparatus in artificial saliva enviroment of 35.5℃, simulated the teeth movement by regulating the experimental fixtures to decrease the strenched length of NiTi closed coil springs and elastomeric chains at 0.35 mm/per week in operation of cooling-heating cycle, and recorded the remaining force of them at 8 time pionts (4 hour,24 hour, 1th week,2nd week,3rd week ,4th week,6th week,8th week) by operating Instron Universal Testing Machine .Then calculated the percentage of remaining force and analysed the results.Results:The study simulated tooth movement in artificial saliva environment of 35.5℃,operated an experiment of cooling-heating cycle, and measured the remaining force of NiTi closed coil springs and elastomeric chains of different brands at different time when stretched.1 The force of elastomeric chains decreased significantly in the first 4 hours,the remaining force was75% to 85% of the initial force,and it still comparatively obviously decreased , the remaining force was 65% to 78% of the initial force.Then the remaining force continuously decreased with tooth movement between 1 week and 8 week,but more gently compared to that in 24 hours.The remaining force was 42% to 48% of the initial force after 4 weeks,and 33% to 37% after 6 weeks,and 22% to 26% after 8 weeks.The force decay of NiTi closed coil spring was gentle: the remaining force was 85% to 96% of the initial force after the first 4 hours, 76% to 91% of the initial force after 24 hours.Then the remaining force continuously decreased with tooth movement between 1 week and 8 week. The remaining force was 46% to 69% of the initial force after 4 weeks;35% to 56% of the initial force after 6 weeks;26% to 44% of the initial force after 8 weeks.2 The remaining force between NiTi closed coil springs of three brands and elastomeric chains of two brands had statistically significant difference(P<0.05),the remaining force of NiTi closed coil spring is larger than that of elastomeric chains.The remaining force of brand C was larger than that of brand B ,and brand B's was larger than that of brand A's,the remaining force of three brands NiTi closed coil springs had statistically significant difference(P<0.05),and the difference of remaining force of two brands elastomeric chains had no statistical significance by comparing of remaining force in initial force of 150g group at different time(P>0.05).Comparision of remaining force in initial force of 250g group at different time:the difference between brand A and brand B NiTi closed coil spring had no statistical significance(P>0.05),the difference between brand C and brand A or brand B NiTi closed coil spring had statistical significance(P<0.05), the remaining force of brand C was larger than that of brand B or brand A. Difference of remaining force of brand D and brand E elastomeric chains had statistical significance(P<0.05), the remaining force of brand E was larger than that of brand D.Conclusions:1 The force of elastomeric chains decreased observably in initial 4 hours ,and it still decreased comparatively quickly in 24 hours,however it decreased gently at the following time.The force of NiTi closed coil spring decreased more gently at different time compared to that of elastomeric chains.2 The force decay of NiTi closed coil springs of all brands was smaller than that of elastomeric chains of all brands at different time.It indicates that NiTi closed coil springs could produce better mechanical effects in teeth movement in clinic .