Wear volumes of flowable and sculptable resin composite attachments and their correlation with retentive force of clear aligners: a laboratory study.

Abstract

Background: Aligner attachment integrity is important for clear aligner retention and overall treatment efficacy. This study aimed to evaluate the wear volume of clear aligner attachments and the retentive force change of clear aligners over a simulated 24-week insertion/removal period, along with their correlation.

Methods: Attachments made from Tetric N-Flow (flowable), Beautifil Injectable X (flowable), or Filtek™ Z350 XT (sculptable) resin composites (n = 6 each) were bonded to the first premolars of maxillary dental resin models. Each model underwent a simulated 3-cycle daily insertion and removal of 12 clear aligners, with each aligner tested for 14 days, using a universal testing machine. Attachment wear volume was quantified through 3D scanning and superimposition. Average daily retentive force of aligners was measured. Data were analyzed using mixed-design ANOVA to evaluate differences in retentive force and wear volume among composites, and Pearson's correlation to assess the relationship between wear and retentive force change. Statistical significance was set at p < 0.05.

Results: Significant attachment wear was observed primarily in gingival regions, without significant differences in wear volume among the three composites. Retentive force decreased significantly from days 1 to 2 and continued to decline until day 14 (p < 0.01), without significant differences in retentive force among aligners nor composite types. No significant correlation was found between attachment wear volume and the retentive force difference between the 1st and 12th aligners.

Conclusions: Despite reductions in attachment volume across all three composites over the 24-week period, no significant change in mean retentive force among aligners was observed. The tested composites demonstrated comparable wear resistance during repeated aligner insertion and removal over 24-week, with stable aligner retentive force, supporting their feasibility for use in clear aligner therapy.