LAUSR

Elastomeric chains are widely used by orthodontists for incisor retraction and space closure. However, force degradation and permanent deformation are expected to occur. OBJECTIVES The present study was designed to compare the force degradation of closed, open, grey and transparent power chains from four orthodontic companies (American orthodontics® (AO®), Dentsply®, Ormco® and Rocky Mountain Orthodontics® (RMO®)) over time. MATERIALS AND METHODS Universal testing machine was used to measure the force of the power chains elongated to 25mm at 0hours, and after storage in artificial saliva at 24hours, 1 week, 2 weeks, 3 weeks, and 4 weeks. A Tukey's honestly significant difference test was performed. RESULTS Most of the power chains showed less than 30% of force decay at 24hours of elongation. The AO® transparent open elastomeric chains presented the lowest percentage of force remaining at almost all times: 24hours (58.9%), 1 week (67.7%), 2 weeks (43.2%), 3 weeks (72.4%), and 4 weeks (63%). Most of the power chains had an increase of force measured after 2 weeks of storage in artificial saliva. Three of the sixteen groups (Ormco® grey open, RMO® grey and transparent closed) displayed an increase in the force at 4 weeks of elongation compared to the force registered at 0hours. CONCLUSION The results indicated that the force generated by elastomeric chains at 4 weeks remains optimal for a physiologic tooth movement.