January 2023

Introduction: Antimicrobial photodynamic therapy (aPDT) is an adjuvant treatment for periodontal disease. Methylene blue (MB) and toluidine blue O (TBO) are commonly used as photosensitizers in aPDT. However, the pH of blue dyes is a rarely discussed topic. Objectives: The aim of this study was to evaluate dentin demineralization and optical properties of acidified (pH1) MB and TBO. A secondary objective of this paper was to discuss the regular pH of blue photosensitizers and their clinical applications. Materials and Methods: Acid TBO and MB (pH1) were compared to conventional dyes and/or treatments. Dentin demineralization was measured by profilometry and microhardness test. Optical properties were evaluated by absorbance measurements and photodegradation rate. Statistical analyses were performed with Kruskal-Wallis test (p<0.05). Results: Acid TBO promoted dentin demineralization like positive control (citric acid/ tetracycline) (p>0.05). Acidification of MB and TBO promoted no photodegradation and change of absorption band, respectively. Acid MB and TBO promoted similar demineralization of dentin surfaces as citric acid/tetracycline. Conclusion: Acidification impaired a photodynamic reaction, impeding the use of acidified photosensitizers in aPDT procedures.