Dynamic Force Decay Evaluation of Latex and Non-Latex Orthodontic Elastics

Objectives: To evaluate the force decay over time of latex and non-latex orthodontic elastics subject to repeated stretching under simulated intraoral conditions.
Methods: Four different types of intermaxillary orthodontic elastics from a single supplier (American Orthodontics
1/4" 4.5 oz and 1/4” 6.5 oz, each with and without latex) were submerged in artificial saliva at 37 degrees Celsius and subjected to repeated stretching using a custom-fabricated apparatus. Elastics were initially stretched to three times marketed internal diameter and then dynamically stretched to 4.5 times marketed internal diameter with a cycle duration of 10 seconds and a frequency of 360 cycles/hour for 24 hours. Forces generated by the elastics were measured at three times marketed internal diameter at 0, 1, 2, 4, 8, 12, and 24 hours using a computerized data-acquisition system connected to a 10N load cell. A sample size of 25 elastics per group was tested.
Results: All types of elastics generated similar initial forces that were statistically insignificantly below the marketed force. Latex elastics tended to generate more variable forces than non-latex elastics, which were more consistent at all time points tested. Dynamic stretching caused consistent force decay in all types of elastics, which was significantly higher in the non-latex elastics than in the latex elastics. This difference occurred primarily within the first 4 hours and was then sustained over the remaining trial period. The percentage of initial force remaining at 4, 8, and 24 hours was 69%, 67%, 46%, and 47%, 40%, 27% for latex and non-latex elastics, respectively.
Conclusions: Latex elastics retained significantly more force over time than their non-latex equivalents. Because of higher rates of force loss that continued throughout testing, it is more important that non-latex elastics be changed at regular intervals ideally not exceeding 4 hours.