Micro-computed tomography assessment of regional and overall accuracy of thermoformed retainers and intraoral scanners.

Introduction: This retrospective in vitro study aimed to assess the accuracy of retainers fabricated using Essix (Dentsply Sirona, Charlotte, NC) and Zendura (Zendura Dental, Fremont, Calif), and to compare the accuracy of intraoral scanners iTero (Align Technology, San Jose, Calif) and TRIOS (3Shape, Copenhagen, Denmark). In addition, regional accuracy across different areas of the mandibular arch was analyzed.

Methods: A total of 20 standard tessellation language files from postorthodontic treatment mandibular arches (from January 2019 to August 2024) were selected based on specific inclusion criteria. The standard tessellation language files were 3-dimensional printed and scanned using iTero Element 2 and TRIOS 4, then used to fabricate 20 sets of each thermoformed retainer (Zendura and Essix). All models were scanned using micro-computed tomography (Scanco Medical AG, Brüttisellen, Switzerland), serving as the gold standard for accuracy comparisons. Root mean square (RMS) error analysis was used to assess overall and regional accuracy.

Results: The RMS error between gold standard and retainers differed significantly overall (P = 0.044), particularly in the anterior (P = 0.030) and premolar (P = 0.017) regions, with greater discrepancies in Zendura retainers. RMS error differences were not significant between intraoral scanners across most regions, except for borderline significance in the anterior region (P = 0.058), in which TRIOS showed larger deviations.

Conclusions: Both intraoral scanners demonstrated comparable accuracy. However, Zendura retainers exhibited greater inaccuracies than Essix. Regional analysis showed higher deviations in the molar and lingual regions for scanners and the molar regions for retainers. Importantly, these discrepancies were low and clinically insignificant.