Clear aligner attachment accuracy and composite excess using flowable composite resins of varying viscosities

To evaluate the accuracy of clear aligner attachments and quantify excess composite volume when using flowable composite resins with different viscosities in an in vitro setting. The null hypothesis was that viscosity would not significantly impact accuracy or excess.

A total of 120 samples was evaluated. Four attachment types: ellipsoid (EA), rectangular (RA), beveled (BA), and half-moon (HMA), were applied using three flowable composites: Estelite Universal Flow High (HF), Medium (MF), and Super-Low (SLF) viscosity (Tokuyama Dental, Japan). Attachments were bonded on three-dimensionally printed typodont models and digitally scanned. Digital scans were aligned with reference models using local best-fit analysis. Surface deviation was measured at five points, and overall deviation was represented by arithmetic mean and standard deviation (sigma) values. Excess composite area and volume were calculated. The data were nonnormally distributed, so nonparametric tests were used: Kruskal-Wallis for group comparisons and Mann-Whitney U for pairwise analyses (P < .05).

Significant differences in attachment accuracy and excess composite were observed among viscosity groups. In EA and RA groups, HF composite showed significantly greater accuracy than MF and SLF (P = .016, P = .018). In BA, SLF exhibited lower accuracy than HF and MF (P = .005). Excess composite volume was significantly higher in EA and HMA with HF composite (P = .011 and P = .002, respectively).

Composite viscosity and attachment shape influence accuracy and excess. High-viscosity resins improve precision but increase excess; low-viscosity resins reduce excess but may compromise accuracy. Both material and attachment design should guide clinical choices in clear aligner treatment.