COMPARATIVE EVALUATION OF ANTIMICROBIAL EFFICACY OF NANOCHITOSAN-COATED ORTHODONTIC BRACKETS AGAINST FOUR ORAL MICROORGANISMS: AN IN VITRO STUDY

Abstract

Background and Aim. Fixed orthodontic appliances create plaque-retentive microenvironments that promote colonization by cariogenic and opportunistic microorganisms, increasing the risk of enamel demineralization and white spot lesion (WSL) formation. Conventional compliance-dependent preventive strategies demonstrate limited long-term efficacy. Surface modification of orthodontic brackets with antimicrobial nanocoatings offers a promising compliance-independent approach. This study aimed to comparatively evaluate the antimicrobial efficacy of nanochitosan-coated stainless-steel orthodontic brackets against four clinically relevant oral microorganisms in an in vitro setting.

Methods. A total of 160 pre-adjusted edgewise stainless-steel maxillary premolar brackets (MBT prescription, 0.022″ slot) were divided into two groups of 80 each: Group A (nanochitosan-coated) and Group B (uncoated control). Nanochitosan nanoparticles (molecular weight 3,800–20,000 Da; mean particle size ~50 nm) were deposited on bracket surfaces via a standardized hydrothermal method and confirmed by scanning electron microscopy (SEM) and field emission SEM (FESEM). Four microorganisms Streptococcus mutans, Lactobacillus acidophilus, Enterococcus faecalis, and Staphylococcus aureus were standardized to 10⁵ CFU/mL using a spectrophotometer (OD 600 nm) and inoculated into Mueller–Hinton broth containing bracket samples. Colony-forming unit (CFU) counts were recorded at T0 (1 h), T1 (6 h), T2 (12 h), T3 (24 h), and T4 (72 h). Intragroup and intergroup comparisons were performed using paired t-test and one-way ANOVA, respectively, at a 95% confidence level (p ≤ 0.05).

Results. No microbial growth was detected in either group at 1 and 6 hours. From 12 hours onward, uncoated brackets demonstrated a progressive and statistically significant increase in CFU counts for all four organisms, reaching mean values of 123.75 ± 2.446, 124.45 ± 2.459, 123.80 ± 2.876, and 124.65 ± 1.954 × 10⁵ CFU/mL at 72 h for S. mutans, L. acidophilus, E. faecalis, and S. aureus, respectively. In contrast, nanochitosan-coated brackets maintained consistently low and stable CFU counts (22–24 × 10⁵ CFU/mL) across all time points. Intergroup differences were highly significant for all organisms at all post-baseline intervals (F values 1,025–27,604; p < 0.001).

Conclusions. Nanochitosan surface modification significantly enhances the antimicrobial properties of stainless-steel orthodontic brackets, providing broad-spectrum, sustained inhibition of bacterial adhesion and proliferation. This compliance-independent coating strategy holds considerable potential for reducing biofilm accumulation, enamel demineralization, and white spot lesion formation during fixed orthodontic treatment. Further in vivo studies are warranted to confirm clinical durability and biocompatibility.