Antimicrobial Efficacy of Zinc Oxide Nanoparticle–coated Orthodontic Aligners against Streptococcus Mutans and Candida Albicans: An in vitro Study
Saba Batool *
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
Basanagouda C. Patil
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
Divya Mundada
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
Rachana B Kuppanatte
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
Vishwanath Patil
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
Sudha R Halkai
Department of Orthodontics and Dentofacial Orthopaedics, H.K.E. Society's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India.
*Author to whom correspondence should be addressed.
Abstract
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.
Keywords: Zinc oxide, nanoparticles, clear aligners, streptococcus mutans, candida albicans, antimicrobial coating, orthodontics