Influence of photodynamic therapy and calcium hydroxide on the properties of intraradicular dentin and the resin cement, bond strength of fiberglass posts, morphology and characterization of the adhesive interface

Abstract

The objective of the present study was to evaluate the effect of photodynamic therapy (PDT) and the intracanal medication of calcium hydroxide, on the mechanical properties and the degree of conversion. Furthermore, it is intended to evaluate the bond strength of glass-fiber posts (GFP), to analyze the morphology and characterization of the adhesive interface. It will be used bovine incisor teeth, which the biomechanical preparation (BP) in all root canals (RC) will be performed. To realize the PDT the methylene blue PS will be used, activated with Red Laser. Experimental groups: G1-BP + Deionized Water (Negative Control); G2-BP + Deionized Water + Ca(OH)2 (Positive Control); G3-BP + AM 0,005% + Ca(OH)2; G4-BP + AM 0,01% + Ca(OH)2; G5-BP + AM 0,005% + Red Laser (PDT) + Ca(OH)2; G6-BP + AM 0,01% + Red Laser (PDT) + Ca(OH)2. After the period of 14 days of intracanal medication, it will be removed and the RC will be filled and prepared for the cementation of the GFPs. Study 1: The specimens will be cut perpendicular to the long axis, obtaining slices of the cervical, middle and apical thirds. The mechanical properties of Martens hardness and the elastic indentation modulus will be evaluated on the substrate of the intraradicular dentin and the resin cement using an ultramicrodurometer. The degree of conversion of the resin material will be analyzed by Raman Spectroscopy, in different thirds of the intraradicular dentin. Study 2: The bond strenght of the GFP on the intraradicular dentin will be measured by the push-out test in a universal test machine with the slices obtained in the cervical, middle and apical thirds. The fracture pattern of the representative samples will be qualified by Scanning Electron Microscopy (SEM). The identification of the chemical composition of the intraradicular dentin substrate will be analyzed by Dispersive Energy Spectroscopy (EDS). The morphology of the interface between resin cement and intraradicular dentin tissue will be characterized by fluorescence confocal microscopy (CFM) and the volume and presence of bubbles will be analyzed by computed microtomography (micro-CT). The data obtained in the studies will be submitted to the normality test and the averages compared by specific statistical tests (p=0,05). (AU)