[Elastomeric chains in orthodontics. An in vitro evaluation of ten different types].

This study is an evaluation and a comparison assessment of ten different types of orthodontics elastomeric chains in an in vitro situation simulating the clinical therapy for the canine tooth distalisation.We designed and produced two custom made systems in order to simulate the clinical movement and to measure the elastic recovery. The first device was suitable to activate the elastomeric chains up to 100\% of its extension and successively to reduce this extension through the time, as it happens during the clinical practice. Simultaneously with the activation of the chains, it was possible to submit the device to two different termocycling procedures. The measuring system was a linear guide skid-mounted on a balance which provided two grasps in the order to achieve the activation rate and to measure it. The force showed by the elastic recovery was relieved at the starting of the experience and after 1, 7, 14, 21 days.We relieved that the elastomeric chains decreased their elastic recovery to the 50-70\% of the starting rate during the first day of activation, after which the force holded fairly uniform and after three weeks it was the 20-40\% of the value corresponding to the starting activation.The tested elastomeric chains provide forces reliable to produce the tooth movement for a maximum of a three/four weeks period; than they have to be changed since the induced movement is nullifying its efficacy. At the comparative analysis the diaphanous type shows a lower decrease of the elastic force than the gray type, and the Short& e X-Short shapes show the same behaviour and generate forces much more performing than Long shapes.