Dental acid etchant as a sensitizing agent in photodynamic therapy to reduce S. mutans in dentinal carious lesions.

Abstract

The study aims to assess the utility of dental acid etchant containing 37% phosphoric acid and methylene blue dye (DAE) as a sensitizing agent for photodynamic therapy (PDT) to reduce Streptococci mutans in dentinal caries. Forty-five permanent third molars were sectioned and the coronal dentin exposed. A cariogenic challenge was performed using brain-heart infusion (BHI) supplemented with 0.5% yeast extract, 1% glucose, 1% sucrose, and S. mutans ATCC 25175 standardized to 0.5 McFarland turbidity. Specimens were incubated in anaerobic jars at 37°C for 15days. During this period, BHI broth was renewed every 24h. After 15days, specimens were randomly divided into three groups (n = 15): DAE, application of dental acid etchant containing 37% phosphoric acid and methylene blue dye for 15s; LLL, application of low-level laser (wavelength 660nm, energy 4J/cm2, power 5W) for 15s; and PDT, application of DAE for 15s followed by LLL irradiation (660nm, 4J/cm2, 5W). Carious tissue from each specimen was collected before and after the applications. Five decimal dilutions were performed and the resulting solution was seeded in mitis-salivarius-bacitracin agar. Plates were incubated in anaerobic jars at 37°C for 48h. Analysis of variance (ANOVA) with post hoc Tukey's test was used to compare total S. mutans counts. Significant reductions in S. mutans were observed after DAE application (40.70%, p < 0.0001), LLL (12.35%, p = 0.0036), and PDT (55.22%, p < 0.0001). Dental acid etchant containing 37% phosphoric acid and methylene blue dye can be used as a photosensitizing agent for PDT to reduce S. mutans burden in dentinal caries.