Wear and fatigue resistance: An in-vitro comparison of three polyethylene terephthalate glycol and thermoplastic polyurethane materials for vacuum-formed retainers

Objective: To test the wear and fatigue resistance of three materials (Essix ACE®, Taglus®, and Zendura A®) for the fabrication of vacuum-formed retainers in an artificial oral environment. Material and methods: Wear resistance was tested by subjecting 21 retainers of each Essix ACE®, Taglus®, and Zendura A® to 12,000 wear cycles at 75 N to simulate one year of retainer wear with moderate nighttime bruxing. Post-wear retainer thickness was compared to baseline measurements to calculate wear depth. Fatigue resistance was tested by flexing 15 retainers of each material at an angle of 25 degrees for 1,825 cycles to simulate one year of removing and reinserting a retainer five times per day. Retainers were visually inspected for fractures. Pairwise t-tests with correction using Tukey's method were used to determine significant differences between materials. Results: The mean wear depths were 0.155 ± 0.021 mm, 0.168 ± 0.031 mm, and 0.096 ± 0.033 mm for Essix ACE®, Taglus®, and Zendura A®, respectively. The wear depth of Zendura A® was significantly lower than that of both Essix ACE® (P < 0.001) and Taglus® (P < 0.001). There was no significant difference in wear depth between Essix ACE® and Taglus® (P = 0.312). Under the parameters set for the fatigue resistance test, fractures did not occur on any of the tested materials. Conclusions: Under the assumption of moderate nighttime bruxing for one year, Zendura A® is the most wear-resistant among the materials tested. With the assumption of retainer removal and reinsertion five times per day for one year, all three materials tested have the same ability to resist fatigue.