Influence of two photodynamic therapy sessions and different photosensitizers on the bond strength of glass-fiber posts in different regions of intraradicular dentin.

BACKGROUND: Although photodynamic therapy associated with photosensitizers can promote microbial reduction, studies evaluating the consequences of two photodynamic therapy sessions associated with different photosensitizers on the bond strength of glass-fiber posts to endodontically treated intraradicular dentin are scarce. This in vitro study aimed to investigate the influence of two photodynamic therapy sessions using methylene blue or curcumin photosensitizers on the bond strength of glass-fiber posts to intraradicular dentin in different root thirds. METHODS: Seventy-two teeth were divided into 9 experimental groups according to photosensitizer type, concentration and light-activation: Control - deionized water; Methylene blue 50 mg/L; Methylene blue 50 mg/L + laser; Methylene blue 100 mg/L; Methylene blue 100 mg/L + laser; Curcumin 500 mg/L; Curcumin 500 mg/L + LED; Curcumin 1000 mg/L; and Curcumin 1000 mg/L + LED. Push-out bond strength of the fiber posts to endodontically treated dentin was evaluated using a universal test machine (n = 8). Bond strength data underwent Kruskal-Wallis test, followed by Dunn test for comparison between treatments, and Friedman test for comparison between thirds (α = 0.05). Illustrative scanning electron microscopy images were obtained to qualify the failure mode. RESULTS: Curcumin at higher concentration, activated or not by blue LED, decreased the bond strength values in the apical region when compared with the control group (P < 0.05). There was no difference between two photodynamic therapy sessions using methylene blue photosensitizer (activated or not) and the control group regardless of concentrations and root canal depth evaluated (P > 0.05). Regarding intraradicular depth, the different thirds showed no statistical difference on bond strength values (P > 0.05). All experimental groups presented predominance of mixed-type failure, excepting the methylene blue group at higher concentration activated by red laser, and the curcumin photosensitizer at both concentrations activated by blue LED. CONCLUSIONS: Methylene blue at a 50 mg/L concentration can be applied in two PDT sessions, after biomechanical preparation and before glass-fiber post luting, as it presents no influence on root dentin bond strength in in vitro conditions.

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.