The impact of methylene blue photosensitizer, aPDT and a calcium hydroxide-based paste on the physicochemical and mechanical characteristics of root canal dentin and the bonding interface of fiberglass posts.

PURPOSE: To investigate the influence of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) and calcium hydroxide (CH) medication on the mechanical characteristics, degree of conversion (DC), quantification, and volume of gaps at the adhesive interface of glass fiber posts (GFPs) luted to distinct thirds of root canal dentin. Additionally, the microhardness (MH), elastic modulus (Eit), morphology, and chemical structure of the intraradicular dentin were assessed. MATERIALS AND METHODS: 6 experimental groups were formed by sorting 102 bovine incisors. Canals receiving deionized water irrigation as a negative control; canals receiving deionized water irrigation and filled with CH as a positive control; groups treated with CH + MB at 50 and 100 mg/L without irradiation; and groups treated with CH + MB at 50 and 100 mg/L irradiated by red laser for 60 s (660 nm; 100 mW; 6.5 J; 72 J/cm2). MH, Eit, and DC properties were evaluated for both the resin cement layer and root dentin substrate (n = 8). Volume and quantification of gaps at the bonding interface (n = 6), and dentin morphology and chemical content were investigated (n = 3). Data were analyzed using a repeated-measures 2-way ANOVA followed by Tukey post hoc analysis (α = 0.05). RESULTS: The distinct intraradicular thirds and treatment with MB-mediated aPDT, whether activated or not, in combination with CH, had a significant impact on the mechanical characteristics of the root dentin. This effect was also observed in the MH, Eit, DC, quantification, and volume of gaps at the luting interface (P < .05). In general, a higher concentration of MB, whether activated by a red laser or not, led to lower values in the mechanical properties of the root dentin, as well as in MH, Eit, and DC at the adhesive interface (P < .05). Additionally, these groups exhibited higher values for quantification and volume of gaps at the luting substrate (P < .05). Scanning electron micrographs and energy dispersive X-ray spectra showed qualitative similarity among all groups, except for the negative experimental control group. CONCLUSIONS: MB-mediated aPDT at 50 mg/L, in combination with CH, demonstrated favorable physico-chemical and mechanical characteristics in intraradicular dentin, along with satisfactory mechanical features and the adhesive interface integrity for GFPs at all intraradicular depths. CLINICAL SIGNIFICANCE: MB-mediated aPDT at a concentration of 50 mg/L combined to CH medication represents a suitable choice for photosensitization in the context of intracanal disinfection following the biomechanical procedure and prior to luting of intraradicular restorations.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.