The addition of potassium iodide (KI) enhanced the antibacterial efficacy of photodynamic therapy (PDT) with riboflavin at sub-minimum inhibitory concentrations (MIC).

PDT with riboflavin at 50 μg/mL (¼ MIC) combined with KI achieved antibacterial effects comparable to 0.2% chlorhexidine.

KI-enhanced riboflavin-mediated PDT can provide a non-invasive antimicrobial method to improve hygiene around miniscrews.

This study investigated the effect of potassium iodide (KI) on the antibacterial efficacy of riboflavin-mediated photodynamic therapy (PDT) against Aggregatibacter actinomycetemcomitans biofilms formed on orthodontic miniscrews.

The minimum inhibitory concentration (MIC) of riboflavin was 200 μg/mL. Biofilms were grown on orthodontic miniscrews and divided into ten groups (n = 6): PBS (negative control), 0.2 % chlorhexidine (CHX; positive control), LED, KI, PDT with riboflavin at ½ MIC (100 μg/mL), ¼ MIC (50 μg/mL), and ⅛ MIC (25 μg/mL), and the same PDT conditions combined with 100 mM KI. Biofilm viability was assessed by colony-forming unit (CFU) counts.

All treatments significantly reduced CFU/mL compared with PBS (P < 0.001). The addition of KI enhanced the antibacterial effect of riboflavin-mediated PDT at sub-MIC concentrations, with the strongest effect at 25 μg/mL riboflavin + KI (P = 0.001 vs. riboflavin alone). CHX and PDT with 100 μg/mL riboflavin + KI showed the highest inhibition, with 97.56 % and 95.12 % reductions, respectively. Notably, PDT with 50 μg/mL riboflavin (¼ MIC; LED 450 ± 5 nm, 1000–1400 mW/cm², 60–80 J/cm², 1 min) plus 100 mM KI achieved an antibacterial effect comparable to 0.2 % CHX.

PDT mediated with riboflavin at 50 μg/mL combined with KI effectively reduced A. actinomycetemcomitans biofilms formed on orthodontic miniscrews.

Photodynamic therapy

Riboflavin

Inorganic salt

Potassium iodide

Orthodontic miniscrew

© 2025 The Author(s). Published by Elsevier B.V.