73 - Wear of Orthodontic Aligners Through Simulated Bruxing

Abstract

Studies to simulate bruxing on polymeric materials can provide clinicians with important information when selecting materials for fabricating orthodontic aligners/retainers. The aim of this study was to evaluate and compare the wear produced by one-year equivalent of simulated nighttime bruxing on clear aligners. A set of upper and lower first and second premolars and molars were milled out of a zirconia puck and then micro-CT scanned for manufacturing the aligners. The aligners (n=2 for each material) were made of six materials: Bioacryl (B) ComfortTrack (CT) Duran (D) Endure (E) Hard Cast (HC) and Invisacryl (I). 12k cycles, i.e. approximately one-year equivalent, of moderate nighttime bruxing at 75 N was applied to the samples using the chewing simulator at the Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB). The MDRCBBs contact profiling system and the corresponding software Ansur were used to measure the volume, surface area, and maximum and mean depths of wear. Furthermore, micro-CT images of the samples were taken for fracture analysis. The combined volume loss ranged from 0.056 mm (CT) to 0.502 mm (B), with CT < D < E < HC < I < B. The wear surface area for the maxillary ranged from 1.8 mm (D) to 10.9 mm (B), with D < CT < I < HC < E < B. That for the mandibular ranged from 2.7 mm (CT) to 20.15 mm (HC), with CT < D < B < E < I < HC. The maxillary maximum wear depth ranged from 32.83 m (D) to 137.61 m (B), with D < I < HC < E < CT < B. The mandibular maximum depth ranged from 60.11 m (CT) to 112.75 m (B), with CT < I < HD < D < E < B. Fractures were observed at the mandibular internal fitting surface of the buccal-lingual & mesial distal cross-sections of both samples of E and CT and on one of the HC samples. Only one maxillary of D had a fracture observed at the same area. The wear rate of orthodontic aligners under bruxing was highly material-dependent. Samples with higher wear rates did not fracture but those with the lower wear rates fractured.