Replacement Timing Influence on Mechanical Behavior of Orthodontic Elastic Bands

Objective: To examine the effects of replacement timing of orthodontic elastic bands on their mechanical properties in a laboratory model. Methods: Mechanical properties of medium orthodontic elastic bands of three manufacturers: Ortho Organizers (OO), 3M Uniteck (3M) and Ormco (OR) were studied after simulating different replacing times: night change (first statically stretching for 8 h followed by cycling stretching of 1000 cycles) and day change (first cycling stretching followed by statically stretching). All treatments were conducted under 37°C wet conditions. Mechanical properties were then determined by loading each elastic via a loading machine, stretched to a length of 20 mm (three times its diameter) followed by an additional amplitude of 30 mm for five cycles. The data of force (N) vs. elongation (mm) were acquired automatically, and seven variables were extracted describing the load elongation curves. Results: A significant statistical difference was found between the three manufacturers for the seven mathematical variables (p<0.001). A significant statistical difference was found between the various treatments for six of the mathematical variables (p<0.001). A significant interaction was found between the elastic band manufacturers and the treatments, i.e., the influence of the treatment on the mathematical variable depends on the kind of the elastic band (p<0.001). Discussion: Stretching elastic bands either statically or through periodic cycles affect their mechanical properties. 3M elastics maintained more stable force values compared to OO, which displayed mechanical instability. Cyclic stretching influenced the force that developed in 3M elastics, static stretch had the greatest influence in OR elastics, and in OO elastic bands, the more treatments performed the greater the decline in force values. Conclusions: Different force values were obtained from similar elastics by different manufacturers. However, statistical differences between the force values in day and night replacements are minimal and clinically insignificant.