In vivo comparison of force decay between injection molded and die-cut stamped elastomers.

Introduction: Elastomeric chains are used extensively in orthodontic treatment, and their clinical behavior should be evaluated in vivo. The aim of this randomized clinical trial was to determine whether elastomeric chains made by different fabrication procedures have different force-decay levels.
Methods: Twenty-four consecutive orthodontic patients at a university orthodontic clinic who fulfilled the selection criteria were grouped to evaluate force decay at 1 hour, 24 hours, 48 hours, 7 days, 14 days, and 21 days. Oral hygiene and diet pH (between 5.8 and 7) were controlled. For each patient, 2 types of elastomeric chains (injection molded and die-cut stamped) made by the same company were randomly assigned to a different arch and arch side (split-mouth design). Each traction unit (3-piece elastomeric chain with ligature wire) was adjusted to deliver an initial calibrated force of 200 g during canine retraction. This force level was reactivated for each study period with a new calibrated traction unit. Mean and standard deviations for the force decay in grams and percentages were calculated. Student t tests for independent and paired samples were used.
Results: No statistically significant difference was found in the force decay between elastomeric chain types during the 3-week study period. The mean remaining force (about 150 g) after 3 weeks was considered clinically adequate for canine retraction. The behavior of the elastomeric chains in both arches was statistically and clinically similar.
Conclusions: Both types of elastomeric chain produced the same clinical effects.