Impact of common cleaning protocols on the surface integrity and nanoscale topography of PET-G clear aligners: an AFM and profilometric study.

OBJECTIVE

To evaluate the scale-dependent surface response of PET-G clear aligners to routine home-care cleaning protocols using contact profilometry (macroscopic) and atomic force microscopy (nanoscale).

METHODS

Eighty PET-G samples were divided into four groups: Control, Listerine® mouthwash, Corega® cleansing tablets, and Toothbrush with Colgate® toothpaste. Cleaning protocols were applied once daily for 14 days. Surface roughness (Ra) was measured by profilometry, whereas the nanoscale parameters (Sa, Sq, St, Sp, Sv) were ascertained via AFM. For between-group comparisons, one-way ANOVA with Tukey's HSD post-hoc test (α = 0.05) was used for normally distributed variables, and the Kruskal-Wallis test with Mann-Whitney U pairwise testing (Bonferroni correction, adjusted α = 0.0083) was used for nonnormally distributed variables. Test-retest repeatability was assessed by repeating measurements after 24 h and computing intraclass correlation coefficients (ICC).

RESULTS

Overall, a statistically significant difference across groups was observed for the profilometric Ra (p = 0.027(. Tukey's HSD post-hoc tests revealed a statistically significant pairwise difference between the Listerine® and control groups (mean difference = 0.30 μm; Tukey's p = 0.028), whereas other pairwise comparisons were not significant at α = 0.05. In contrast, all the AFM-derived nanoscale parameters (Sa, Sq, Sp, Sv, St) showed clear and statistically significant differences across groups (p < 0.001). AFM images and metrics indicated that chemically cleaned specimens (Listerine® and Corega® groups) showed smoother and more uniform nanostructures, whereas mechanically cleaned specimens (Toothbrush group) exhibited localized micro-scratches and irregular topographic features consistent with mechanical abrasion.

CONCLUSION

Common cleaning protocols were associated with scale-dependent surface effects. Listerine® was associated with higher macroscopic Ra compared to the control, whereas AFM revealed that chemically cleaned specimens (Listerine® and Corega®) showed substantially smoother nanoscale surfaces. Brushing was associated with nanoscale micro-scratches without significant macroscopic Ra change.