Wear and Fatigue Resistance: An In-Vitro Comparison of Three Materials for Vacuum-Formed Retainers

Abstract

AbstractAim: To test the wear and fatigue resistance of three materials for the fabrication of vacuum-formed retainers in a simulated oral environment. Methods: Three materials were tested: Essix ACE, Taglus, and Zendura. To test wear resistance, 21 maxillary retainers of each material (63 overall) were mounted on zirconia models into an Artificial Resynthesis Technology machine to simulate wear in an oral environment. Each sample underwent 12,000 cycles of wear at 75 Newtons to simulate one year of retainer wear with moderate nighttime bruxing. Lateral movement was set to 2 mm with a frequency of 2 Hertz. Post-wear retainer thickness was measured using a digital micrometer and compared to baseline measurements to calculate the depth of wear. To test fatigue resistance, 15 maxillary retainers of each material (45 overall) were mounted and flexed at an angle of 25 degrees for 1825 cycles at a frequency of 1 Hertz to simulate one year of removing and reinserting a retainer at a rate of 5 times per day. Retainers were visually inspected for fractures. Pairwise t-tests with correction using Tukey’s method were conducted to determine which pairs of material groups were significantly different at α=0.05. Results: For the wear resistance test, the mean baseline thickness was 0.51 ± 0.033 mm, 0.492 ± 0.029 mm, and 0.515 ± 0.047 mm for Essix ACE, Taglus, and Zendura, respectively. The mean post-wear thickness was 0.354 ± 0.033 mm, 0.323 ± 0.038 mm, and 0.42 ± 0.027 mm for Essix ACE, Taglus, and Zendura, respectively. The overall wear was 0.155 ± 0.021 mm, 0.168 ± 0.031 mm, and 0.096 ± 0.033 mm for Essix ACE, Taglus, and Zendura, respectively. The wear depth of Zendura was significantly lower than 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, visual fractures did not occur on any of the retainer materials for Essix ACE, Taglus, or Zendura. Conclusions: Under the assumption of moderate nighttime bruxing for one year, Zendura is the most resistant to wear among the materials tested. With the assumption of retainer removal and reinsertion five time daily for one year, all three materials tested exhibit the same ability to resist fatigue.