Comparison of the stress strain capacity between different clear aligners

Background: The rife use of aesthetic appliance in orthodontic treatment requires the study of the properties of the materials they are made of. Objective: The aim of the present study was to evaluate the dimensional stability of clear aligners made of three different materials after the application of in-vivo dynamic stress and in-vitro static stress. Methods: Three different aligners made of different materials (PET-G; PET; SmartTrack® ), prepared on the dental arch of the same patient, were tested. For each material, three aligner samples were manufactured: one to be used in-vivo, one to be tested in-vitro, and one to be used as a control. To evaluate the effects of the dynamic stress produced in-vivo, each aligner was worn by a single patient 22 hours per day, followed by a wash-out period of two weeks. To evaluate the effects of static stress, each aligner was exposed to the in-vitro continuous force of 50N. The tested and control aligners were scanned, then linear measurements were taken to evaluate their dimensional stability after different types of stresses. Results: PET seems to have the lowest percentage of deformation; PET-G and SmartTrack® showed a reduced deformation going from the posterior to the anterior area. The contact with human saliva induces a greater deformation. Conclusion: Different materials show different behavior following application of static stresses and dynamic stresses in the oral cavity. PET showed the highest dimensional stability.