Load-extension-time behavior of orthodontic Alastiks.

Typical elastomeric behavior displayed by Alastik orthodontic bands resulted in load-extension curves that depended on the rate of extension as well as the amount of extension. Initially, the modules tested at the faster speeds had higher moduli and were stronger; but as extension continued, the trend reversed, and at breakage the more slowly stretched modules were the strongest. Therefore, although the Alastiks appear to be uniformly produced, the clinician still needs to know his rate of deformation and degree of stretching to accurately assess the module force. In addition, the module, once in position, will not maintain a constant force but will experience a decrease in applied load with time kept at a constant extension. Because the initial load decay is more rapid for both faster extension and higher load, it seems reasonable to suggest that care be taken by the clinican to stretch the module more slowly into place. This should result in a higher load level for a longer period of time. Although the measured changes in loads are not necessarily of sufficient magnitude to seriously influence the clinical result, a clearer understanding of the module behavior, such as currently presented, will hopefully assist in more comprehensive clinical evaluations.