In Vitro Evaluation of Force Loss in Orthodontic Latex Elastics

OBJECTIVES: The purpose of this study was to evaluate the time related decrease of force exhibited by orthodontic latex elastic rings of different trademarks. METHODS: The sample comprised elastic rings of four different diameters (1/8”, 3/16”, 1/4" and 5/16”) of four trademarks, that is, Morelli, Uniden, Ormco and Ortho Organizers. For each one of the diameters and trademarks were investigated 7 elastic rings, resulting in a total sample of 112 units. The elastic rings were submerged in 37oC-distilled water and were distended approximately into three times their original diameters. The forces were measured with a dynamometer in the following time-intervals: one hour, 4 hours, 12 hours, 24 hours, 36 hours and 5 days. The statistical analysis employed the student “t” test (p<0.05). RESULTS: After 24 hours and 5 days, the 1/8” elastic rings revealed mean force loss of, respectively, 0.3% and 10.3% (Ortho Organizers), 11.5% and 11.5% (Uniden), 13.9% and 15.2% (Ormco), 22.1% and 24.7% (Morelli). Concerning the 3/16” elastics, the mean values of force reduction were 13.3% (Uniden), 15.6% (Morelli), 17.4% (Ortho Organizers) and 20% (Ormco), without significant changes in these values from the first to the fifth day. Furthermore, 1/4" elastic rings showed mean force loss values of 1.4% and zero (Ormco), 15.5% and 16.7% (Uniden), 21.8% and 27.6% (Morelli), 38.6% and 40.9% (Ortho Organizers). Finally, the 5/16” elastic rings revealed the following mean values: 14.7% and 18.7% (Uniden), 18.3% and 21.1% (Ormco), 17.5% and 21.2% (Ortho Organizers) and 19.8% and 25% (Morelli). CONCLUSIONS: It was concluded that the more intense decrease of force, in all orthodontic elastic rings evaluated, occurred in the first 24 hours, with much more less intense additional reductions in force loss after the first to the fifth day.