Time Effect on the Durability of Orthodontic Elastics

Objectives: To investigate the force generated by various latex and non-latex orthodontic elastics and the duration that these elastics can effectively stay in the mouth before replacement. Methods: For the study, 15 latex and non-latex elastics (3M, Ortho Organisers, Masel), diameter (1/4, 3/16, 1/8) and thickness (heavy, medium, light), were tested “as received” (D0) and after simulation of clinical usage. A special thermal bath was constructed where the elastics were statically stretched to a pre-determined length simulating mean Class I or Class II elastics in closed mouth. Elastics were immersed in the bath for 1, 5, 10, 15 and 21 days (D1, D5, D10, D15 and D21, respectively). Periodic 2500 maximal/minimal stretching cycles, simulating mouth opening and closing were performed once a day (minimal 10/25 mm and 25/40 mm stretching, for vertical and Class II, respectively). After each period, the forces generated by the elastics for maximal (Fmax) and minimal (Fmin) stretching were determined with the use of a loading machine. Survival test (Logistic regression) was also conducted. Results: For both types of elastics, Fmax degradation occurred between D0 and D1 (mean 23%, p<0.001). Lower degradation occurred between D1 and D5 (20%) with no further significant degradation until D21. D0 elastics were tested “as received”, i.e., in a dry condition. In D5 to D21, elastics were maintained in a wet environment and cycle-loaded. Latex elastics had less degradation (p<0.001), and non-latex elastics had less durability. Conclusion: Latex elastics do not have to be replaced every day as opposed to non-latex elastics.