Dimensional stability of pet-g clear aligners with different thickness through cyclic compressive load tests: An in vitro study

Background: The purpose of this in vitro study was to evaluate the dimensional stability of PET-G clear aligners. Material and Methods: Two starting passive aligners of different thicknesses (0.75 mm and 0.88 mm) were subjected to cyclic compressive loading tests using the Instron 3343 testing machine in the laboratory, both with and without saliva. The intermolar and intercanine distances, measured in the occlusal direction, and the intermolar and intercanine Facial Axis (FA) distances, calculated between the most vestibular points of the crowns defined as Facial Axis points, were recorded using the dedicated software 3Shape Orthoviewer. Finally, the aligners were scanned using a laboratory scanner (3Shape TRIOS®) and then compared with the untested aligners of the control group. Results: The 0.75-mm-thick aligners exhibited greater dimensional stability than the 0.88-mm-thick aligners when measuring intercanine distance, both with and without saliva. In contrast, the 0.88-mm-thick aligners demonstrated greater stability than the 0.75-mm-thick aligners when measuring intermolar distance under the same conditions. In the measurement of FA distances, higher values were observed at the molar level when the tests were conducted both with and without saliva, whereas no significant changes were observed in the intercanine distance. Conclusions: The 0.88-mm-thick aligners demonstrated better dimensional stability during tests with and without saliva in the intermolar distance, while the 0.75-mm-thick aligners showed better dimensional stability in the intercanine distance.