Photodynamic inactivation of planktonic cultures and Streptococcus mutans biofilms for prevention of white spot lesions during orthodontic treatment: An in vitro investigation.

INTRODUCTION: This study evaluated the efficacy of photodynamic inactivation (PDI) with hematoporphyrin IX (H) and modified hematoporphyrin IX (MH) at 10 μmol/L, using a blue light-emitting diode (LED), fluence of 75 J/cm,2 over planktonic cultures and biofilm of Streptococcus mutans (UA 159).

METHODS: Suspensions containing 107 cells/mL were tested under different experimental conditions: a) H and LED (H+L+), b) MH and LED (MH+L+), c) only LED (P-L+), d) only H (H+L-), e) only MH (MH+L-), and f) control group, no LED or photosensitizer treatment (P-L-). The study also evaluated the effect of PDI on S mutans biofilm on metallic or ceramic brackets bonded on specimens of human teeth. The strains were seeded onto Mitis salivarius-bacitracin-sacarose agar to determine the number of colony-forming units.

RESULTS: H and MH under LED irradiation were effective on planktonic cultures (P <0.0001). H and MH (H+L+ and MH+L+) caused a reduction of 3.80 and 6.78 log10  CFU/mL. PDI with the use of H or MH and LED exerted a strong antimicrobial effect over S mutans showing 54% and 100% reduction, respectively. PDI on S mutans biofilm on metallic and ceramic brackets with the use of H was not effective (P = 0.0162, P = 0.1669), however, MH caused a significant reduction of 44% and 53% of the cell count on metallic and ceramic brackets, respectively (P = 0.0020, P = 0.004).

CONCLUSIONS: In vitro planktonic cultures with the use of H or MH and LED exerted significant antimicrobial activity. No effect was observed on S mutans biofilm on either bracket type with the use of H, MH showed better results, suggesting a promising use against dental caries and white spot lesions.