Evaluation of various methods of methylene blue removal from the post space after photodynamic therapy on the bonding interface using different resin cementation systems

•One of the most widely used dyes in photodynamic therapy is methylene blue.•The use of methylene blue can cause staining of the dental structure.•The chemical substances and ultrasonic irrigation can remove of the methylene blue.•The removal of methylene blue with NaOCl reduced the formation of dentinal tags.•The removal of methylene blue with NaOCl reduced the formation of bond strength. To evaluate the effects of three protocols for removing 0.01 % methylene blue from the post space after photodynamic therapy on bond strength and tag formation in the dentin of the fiber post space, using a conventional cementation system with an etch-and-rinse or universal adhesive system. Sixty human canines were endodontically treated for fiber post cementation. The specimens were randomized into 6 groups (n = 10): G1, G2, G3, G4, G5, and G6. The G1, G2, and G3 groups were irrigated with saline solution, 2.5 % sodium hypochlorite (NaOCl), and 2.5 % NaOCl, agitated by passive ultrasonic irrigation (PUI), respectively. In these groups, a conventional cementation system with etch-and-rinse adhesive was used. The G4, G5, and G6 groups were irrigated with the respective solutions mentioned above and cemented using a conventional cementation system with universal adhesive. Tag formation in the dentin was evaluated by confocal laser scanning microscopy. The push-out bond strength test was performed on three thirds of the specimens. In the cervical and middle thirds, the greatest extent of dentin tag formation occurred in the G1 (p = 0.023 and p = 0.033, respectively). In the apical third, G1, G2, and G3 demonstrated similar tag formation between themselves (p = 0.089). In the cervical and middle thirds, G4 demonstrated the highest bond strength when compared to the other groups (p