Evaluation of Antibacterial Effect and Mechanical Properties of Thermoformed Clear Aligners Coated with Chitosan and Cellulose Nanocrystals.

BACKGROUND: Though aligners are considered more hygienic, they are linked to a higher occurrence of white spot lesions. These lesions pose clinical challenges and compromise aesthetics. PURPOSE: The aim of present study was the evaluation of antibacterial effect and mechanical properties of thermoformed clear aligners coated with chitosan and cellulose nanocrystals. MATERIALS AND METHOD: This in vitro study evaluated five experimental groups of aligners including (1) Passive control, (2) Active control, (3) Aligners coated with chitosan (CH), (4) Aligners coated with cellulose nanocrystals (CNCs), and (5) Aligners coated with a combination of CH/CNCs. Each group consisted of 30 samples that consisted of 10 discs for antimicrobial testing, 5 cubes for surface microhardness, and 15 cubes for the three-point bending test. Surface morphology was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Antibacterial properties were assessed through disc diffusion and serial dilution methods against Escherichia coli (E. coli) and Streptococcus mutans (S. mutans). Mechanical properties, including surface microhardness and maximum force under bending, were evaluated using Vickers hardness and three-point bending tests. Statistical analysis was performed using ANOVA and Kruskal-Wallis tests, with p Value< 0.05 considered significant. RESULTS: The CH/CNC group showing the highest microhardness (13.37±1.00 VHN) and the CNC group demonstrated the highest force resistance (62.31±7.36 MPa), though the difference was not statistically significant (p> 0.05). In the disc diffusion test, CH coatings showed significant antibacterial activity, especially against E. coli (10.8±1.09mm zone of inhibition, p= 0.006), and while CH/CNC showed significant antibacterial activity, especially against S. mutans (6.00±5.47, p= 0.020). CNC coatings showed no bacterial inhibitory effect (p> 0.05). CONCLUSION: The results of our study suggested that applying CNC combined with chitosan as coatings on orthodontic aligners offers a viable strategy to improve both antimicrobial and mechanical properties.