Antimicrobial Efficacy of Zinc Oxide Nanoparticle–coated Orthodontic Aligners against Streptococcus Mutans and Candida Albicans: An in vitro Study
Saba Batool, Basanagouda C. Patil, Divya Mundada, Rachana B Kuppanatte, Vishwanath Patil, Sudha R Halkai
International Journal of Research and Reports in Dentistry · pp. 675–685 · Published 27 Aug 2026
10.9734/ijrrd/2026/v9i2334Abstract
Background: Clear orthodontic aligners create plaque-retentive occlusal surfaces that favour colonisation by Streptococcus mutans and Candida albicans, increasing the risk of enamel demineralisation and gingival inflammation during treatment. Objective: To evaluate the antimicrobial effect of zinc oxide (ZnO) nanoparticle-coated orthodontic aligners against S. mutans and C. albicans in vitro. Methods: Eighteen aligner specimens were divided into an experimental group (n = 9, ZnO-coated by magnetron sputtering at 200 °C) and a control group (n = 9, uncoated). Coating morphology and elemental composition were verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Antimicrobial activity was assessed by colony-forming unit (CFU) counting at 12 hours and days 1, 2, 4, 7 and 15, and by agar well diffusion assay. One-way repeated-measures ANOVA with Tukey's post hoc test was used for statistical comparison. Results: ZnO-coated specimens showed no immediate antibacterial effect but demonstrated a significant, progressive reduction in S. mutans CFU counts from 375.0 ± 35.4 at day 2 to 58.0 ± 10.5 at day 7 (84.5% reduction; F = 323.6, p < 0.0001), sustained through day 15. Uncoated controls showed uncontrolled proliferation (too numerous to count) from day 1 onward. No antifungal activity against C. albicans was observed in either group at any time point. The agar well diffusion assay produced a 13 mm zone of inhibition against S. mutans (versus 18 mm for chlorhexidine) and no zone against C. albicans. Energy-dispersive X-ray spectroscopy confirmed 37.8% zinc by weight on the coated surface. Conclusion: ZnO nanoparticle coating of orthodontic aligners produces significant, time-dependent antibacterial activity against S. mutans but lacks antifungal activity against C. albicans, suggesting selective utility in reducing bacterial biofilm load during clear aligner therapy.
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