Objective: To evaluate the effects of Class II maxillomandibular elastics on Invisalign aligners (Align Technology, San Jose, CA, USA) and assess whether the type of fitting or immersion in a medium simulating the oral environment influence possible dimensional changes.
Materials and methods: Twenty new pairs of Invisalign aligners were tested. Ten pairs had inserts for maxillomandibular elastics made by the manufacturer (precision cuts) and ten had cutouts. Epoxy resin casts were created for aligners, and were later mounted on articulators. Class II maxillomandibular elastics were attached to the fittings with a force of approximately 130 gf. The width and anteroposterior distance were measured at predetermined points prior to the use of elastics and 24 hours, 7 days and 14 days after force application began. Ten sets of models, each with a pair of aligners, were immersed in artificial saliva at 37°C over the experimental period, and the other 10 were kept in a dry environment.
Results: Statistically significant changes were observed mainly in the first 24 hours. In the dry environment, the aligners with precision cuts suffered the most considerable deformations. Dimensional changes increased in both groups when they were maintained in a simulated oral environment. The highest values of changes were observed closer to the site where the elastics were fitted.
Conclusion: Class II maxillomandibular elastics cause dimensional deformations of Invisalign aligners. The changes recorded in maxillary intercanine distance and the distance between mandibular first molars in the immersed aligners with both types of fitting were considered statistically and clinically significant.