Ultraviolet light versus chlorhexidine plus cetylpyridinium chloride: in vitro efficacy on Streptococcus Mutans–contaminated toothbrushes

Abstract

Background: Toothbrushing is the most widely used method of oral hygiene; however, toothbrushes may become contaminated during routine use and act as reservoirs for microorganisms.

Objective: To compare, in vitro, the disinfectant efficacy of ultraviolet light (UVL) with a solution containing 0.12% chlorhexidine (CHX) and 0.05% cetylpyridinium chloride (CPC) on toothbrushes contaminated with Streptococcus mutans.

Methods: Forty manual toothbrushes were inoculated with Streptococcus mutans ATCC 25175 and allocated in a 1:1 ratio to UVL exposure or immersion in CHX+CPC (n = 20 per group). Bacterial load was quantified as colony-forming units (CFU) and transformed as log₁₀(CFU/mL + 1). Intragroup changes were assessed with the Wilcoxon signed-rank test, and logarithmic reductions were compared with the Mann–Whitney U test; p < 0.05 was considered statistically significant.

Results: Both interventions significantly reduced bacterial counts (p < 0.001). Median bacterial load decreased from 8.26 to 7.83 log₁₀(CFU/mL + 1) in the UVL group and from 8.28 to 0.00 log₁₀(CFU/mL + 1) in the CHX+CPC group. Median logarithmic reductions were 0.43 and 8.23, respectively, with a significant intergroup difference (p < 0.001).

Conclusion: Under the reported in vitro conditions, CHX+CPC produced a substantially greater apparent reduction in recoverable Streptococcus mutans than UVL. Because an antimicrobial neutralization procedure and the assay detection limit were not reported, the 0.00 post-treatment value should be interpreted as no recoverable colonies under the assay conditions rather than proof of sterilization. UVL produced a modest reduction and requires further protocol optimization and clinical evaluation.