Elastics

Elastic chains are the most commonly used auxiliary for space closure. It is important to remember that the environment in the oral cavity (i.e., with humidity, warmth, functional stress, and an abrasive chemical milieu) will lead to a decline in the elastic properties very rapidly after the initial application ( Fig. 2.36a, b ). These parameters were tested as shown in Table 2.2 .

In our own study, we tested elastic chains that had been immersed in artificial saliva (37°C). The elastic chains were stretched to twice their original length, which is a realistic simulation of a clinical scenario. The tension was held constant for 24 hours, and after a further 24 hours we measured the increase in the length of the elastic chain. After only 1 day, an increase in the length of the chain of approximately 5%, was seen. This in turn means that the molecular structure of the elastomeric chain was permanently changed. Elastomer chains should conform with the EN ISO 21606:2007 standard for “Elastomeric Auxiliaries for Use in Orthodontics” ( Fig. 2.36c ).