A standardized protocol for clear aligner thickness measurement using a 3D-printed auxiliary device

Objectives To develop and validate a standardized protocol for clear aligner (CA) thickness measurement using a three-dimensional (3D)-printed auxiliary device to improve measurement reliability. Materials and Methods 24 pairs of digital dental models (D0s) were included and 3D-printed into physical models (P0s), from which CAs were thermoformed using 0.75-mm polymer sheets. Measurement auxiliary devices (MADs) were designed on D0s through measurement point selection, direction determination, electronic gauge mapping, and base shaping, and then 3D-printed. Two operators measured CA thickness (40 points per CA, 48 CAs) using an electronic gauge both directly (direct measurement, D-M) and with MADs (auxiliary measurement, A-M) across three sessions. Measurement precision (repeatability and reproducibility) of D-M and A-M were analyzed using intraclass correlation coefficients (ICCs) and repeated-measures analysis of variance (ANOVA) or Friedman tests. Bland-Altman plots were used to evaluate intersession agreement. Results A-M demonstrated superior intersession repeatability with ICC > 0.90 at all points and high intersession agreement with a narrow 95% limit of agreement (LoA) and minimal outliers. Interoperator reproducibility for A-M was also higher, with ICCs above 0.75 at all points, compared to D-M, which showed ICCs below 0.75 at almost all points. Conclusions The 3D-printed auxiliary device-based protocol provides a precise and operator-independent method for CA thickness measurement, offering a tool for quality control and providing a foundation for future research on material advancement and design optimization to improve aligner functionality.