Evaluation Of Force Attenuation In Vivo And In Vitro After Orthodontic Elastic Auxiliaries Are Applied

Background:Closing the gap by means of elastic traction with elastic accessories is a common procedure in orthodontic treatment.In clinical application,it is found that there is a loss of force after the auxiliaries are applied.To better control tooth movement,professionals are interested in changes in the properties of elastomers.There have been many laboratory studies on elastic materials,but the clinical and laboratory conditions are not completely similar at different stages of treatment.Purpose:Test the force loss of the clinical commonly used 6 kinds of orthodontic elastic accessories(nickel titanium tension spring and 5 kinds of polyurethane elastic accessories)under the condition of in vivo,in the laboratory and in air at different time points within 28 days with the same initial force(200 g).Verify the power loss model in vivo and whether the type elastomers and environment conditions lead to different force loss.Materials and methods:1.Material group:the 6 types of elastic samples were divided into 6 groups according to their types:group 1 transparent ligatures,group 2 silver ligatures,group 3 separators,group 4 elastic threads,group 5 power chain,and group 6 Ni-Ti spring.2.Experimental device:the stretched auxiliaries are fixed on the retainer,and the tensile degree is when the tension value is displayed as 200g on the moving tension test machine.3.Test environment:each group of accessories was placed under three conditions:in vivo(20 in each group),in artificial saliva(10 in each group)in 37℃ in the laboratory and air(10 in each group).4.Test time:measure residual elasticity of auxiliary parts in 4h,24h and 2d,4d,7d,14d,21 d and 28d.5.Statistical analysis:the mean force loss rate and standard deviation of the six groups of auxiliary parts under three conditions were calculated respectively.One-way ANOVA was used to compare the difference of force loss rate between different accessory types and different media types at the same time point,and student’s t test was used to compare the difference of adjacent time force loss rate between the same accessory types and the same media types.Results:1.The law of force loss rate changing with time:the force loss of six auxiliary components increases gradually with time under three conditions.The force loss increases significantly in the first 4h and becomes stable after 24h.2.Comparison of force loss rate of 6 auxiliary parts:the influence of auxiliaries on force loss was statistically significant at each time point(P<0.05).After activation for 28 days,the loss rate in vivo was as follows:separators(62.05%)>silver ligatures(61.96%)>transparent ligatures(54.55%)>power chains(51.69%)>elastic threads(50.65%)>Ni-Ti tension springs(15.36%);Laboratory:separators(58.12%)>silver ligatures(54.73%)>transparent ligatures(49.21%)>power chains(47.71%)>elastic threads(43.02%)>Ni-Ti tension springs(15.75%).Air:separators(49.27%)>silver ligatures(49.19%)>transparent ligatures(40.53%)>elastic threads(40.52%)>power chains(38.90%)>Ni-Ti springs(7.45%).3.Comparison of force attenuation rates under three environmental conditions:elasticity of five kinds of polyurethane auxiliary parts has a large loss in vivo,and Ni-Ti springs has a larger loss rate in vivo than air and in the laboratory(P<0.05).Conclusion:1.Under the three conditions,the elastic auxiliaries loses the force rapidly in 4h,and the force loss tends to be stable after 24h.2.When the initial force is the same,the loss of polyurethane accessories is greater than that of Ni-Ti spring.3.The loss rate of elastic accessories is greater in vivo than in laboratory and air.