Antimicrobial efficacy of erythrosine-mediated photodynamic therapy against cariogenic biofilms surrounding orthodontic brackets

Objectives: This study aimed to evaluate the antimicrobial efficacy of erythrosine-mediated photodynamic therapy (PDT) on cariogenic biofilms formed around orthodontic brackets and investigate its synergistic effects in combination with professional prophylaxis.Methods: Sound-extracted premolars were prepared using bonded brackets and were sterilized.Cariogenic biofilms were formed by the incubation of Streptococcus mutans ATCC 25175 for 24 h.Six experimental groups were established: group I (control), group II (prophylaxis), group III (erythrosine application), group IV (erythrosine+prophylaxis), group V (erythrosine+light irradiation), and group VI (erythrosine+light irradiation+prophylaxis).Erythrosine was applied at 40 M concentration for 3 min, followed by light irradiation using a VALO LED curing light at 1,800 mW/cm 2 for 20 s.Prophylaxis was performed for 10 s.After treatment, bacterial counts were measured as colonyforming units (CFU) and analyzed as log 10 CFU/ml.Results: Significant differences were observed between the groups (P<0.05).Erythrosine-mediated PDT (group V) showed significant antimicrobial effects, even when used alone, compared with the control (P<0.001).Erythrosine alone (group III) showed no significant difference from the control (P=0.892)but demonstrated significant effects when combined with light irradiation (P<0.001).Prophylaxis enhanced the antimicrobial effects of all treatment modalities (P<0.001).The highest antimicrobial efficacy was achieved by the combination of erythrosine-mediated PDT and prophylaxis (group VI), with approximately 0.9 log 10 CFU/ml reduction compared to the control.Conclusions: Erythrosine-mediated PDT demonstrated significant effects through a unique antimicrobial mechanism, even when used alone, and showed optimal synergistic effects when combined with prophylaxis.The results indicate that the application of PDT combined with professional prophylaxis in orthodontic patients can serve as a useful and safe preventive strategy for managing biofilms around brackets.