Does photodynamic therapy with methylene blue affect the mechanical properties and bond strength of glass-fiber posts in different thirds of intraradicular dentin?

Abstract

There are few studies on the influence of methylene blue as a photosensitiser on the mechanical properties and adhesion of glass-fiber posts to intraradicular dentin. Thus, this in vitro study aimed to evaluate the influence of photodynamic therapy with a methylene blue photosensitizer on the Martens hardness, elastic modulus, and bond strength of glass-fiber posts in different thirds of intraradicular dentin. Eighty bovine teeth were divided into the following five groups: a control using deionized water, and four other groups according to the methylene blue concentration (50 mg/L or 100 mg/L) and substrate treatment (with or without red laser action). Ultramicrohardness test was used to evaluate the mechanical properties in different regions of the root dentin (n = 8). Push-out analysis was evaluated using a universal testing machine (n = 8). Data were subjected to the Kruskal-Wallis test, followed by Dunn's test for comparing groups, and the Friedman test for comparing thirds (α = 0.05). Representative scanning electron microscopy images were obtained. In general, methylene blue in distinct concentrations, with or without laser action, did not cause differences in the mechanical properties or bond strength in different regions of root dentin (P > 0.05). Methylene blue at a higher concentration, activated with laser, produced lower bond strength values in the middle third of the root canal (P < 0.05). Methylene blue at 50 mg/L had no influence on the mechanical properties of the bovine tooth and the bond strength of the glass-fiber posts to intraradicular dentin.