Abstract

Background: Composite attachments play a key role in clear aligner biomechanics; however, their structural stability and wear behavior under repetitive insertion–removal cycles remain poorly understood. Limited evidence exists regarding how composite resins degrade volumetrically and whether such changes influence aligner retention during simulated clinical use. This study evaluated the performance of three commonly used composites for orthodontic attachments. Methods: Digital hemi-arch models were 3D printed and attachments were fabricated using two low-viscosity composites (Transbond™ Supreme LV and Filtek™ Bulk Fill Flow) and one high-viscosity composite (Filtek™ Z250XT). Baseline attachment volumes were assessed using micro-computed tomography (microCT). Nine aligners per model were fabricated to simulate three months of treatment, with each aligner subjected to 30 insertion–removal cycles (270 cycles/model). The maximum tensile force required for aligner detachment was recorded for every cycle. Following mechanical testing, attachments underwent post-test microCT scanning. Intragroup volumetric changes were analyzed using paired t-tests; intergroup differences were assessed with ANOVA, followed by ANCOVA. Tensile-force patterns were evaluated using repeated-measures ANOVA. Results: Significant volumetric loss occurred for Transbond™ Supreme LV and Filtek™ Z250XT, whereas Filtek™ Bulk Fill Flow exhibited minimal wear. Nonetheless, intergroup volumetric differences were not statistically significant. Tensile forces were statistically different between groups for most measurements, yet within each set of 30 cycles, they exhibited a similar pattern of progressively decreasing force. Conclusions: During the simulated three-month period, all three composite resins exhibited some degree of volumetric wear and a progressive decrease in aligner detachment force within each set of cycles. The Filtek™ Bulk Fill Flow exhibited numerically higher and more consistent forces and minimal surface wear; however, no statistically significant differences were observed in total volumetric loss among groups, and the observed variations in tensile forces did not appear to compromise the overall performance of attachments, suggesting that all tested resins maintained clinically relevant retention under the conditions of this study.

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