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This research aims to probe the porosity profile and polymerization shrinkage of two different dual cure resin cements with different dentin bonding systems. The self-adhesive resin cement RelyX U200 (named RU) and the conventional Allcem Core (named AC) were analyzed by x-ray microtomography (lCT) and Scanning Electron Microscopy (SEM). Each cement was divided into two groups (n 5 5): dual-cured (RUD and ACD) and self-cured (RUC and ACC). lCT demonstrated that the method of polymerization does not influence the porosity profile but the polymerization shrinkage. Fewer concentration of pores was observed for the conventional resin cement (AC), independently the method used for curing the sample. In addition, SEM showed that AC has more uniform surface and smaller particle size. The method of polymerization influenced the polymerization shrinkage, since no contraction for both RUC and ACC was observed, in contrast with results from dual-cured samples. For RUD and ACD the polymerization shrinkage was greater in the lower third of the sample and minor in the upper third. This mechanical behavior is attributed to the polymerization toward the light. mCT showed to be a reliable technique to probe porosity and contraction due to polymerization of dental cements. K E Y W O R D Sdental composite, photo-cure, polymerization contraction, self-cure, X-ray microtomography

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Electron Paramagnetic Resonance (EPR) was used as an alternative method to study the conversion degree of dual cure resin cement and verify the influence of prefabricated translucent fiberglass post on the dual cure resin cement polymerization at different restoration points. The post cementation of White Post DC (FGM, Joinville, SC, Brasil) was simulated using the dual cured resin cement Allcem (FGM, Joinville, SC, Brasil) in three different protocols: cement irradiated for 40 s; no light irradiation and cement irradiated with sealed cementation line. 2mm samples were obtained from three post sections and EPR spectra were obtained 10 minutes and 24 hours after mixing the base paste and catalyst of the cement. Results shows that the light curing protocol influenced the concentration of free radicals up to 8mm of the restoration, and the capacity of light transmission of the post was significant for the first 8mm of restoration and is non-existent in the deepest points of a simulated root canal. The cure in the apical part of restoration is exclusively chemical.

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This research aimed to study the influence of the geometrical configuration of a translucent fiberglass post on the dual cure resin cement polymerization by electron paramagnetic resonance (EPR) spectroscopy. A 20-mm long, White Post DC no. 1 fiberglass post (FGM, Joinvile, SC, Brazil) was sectioned in half to obtain two different groups of posts: cylindrical and conical. Each post was cemented with AllCem A1 dual cure resin cement (FGM, Joinvile, SC, Brazil) using a root canal model and light cured for 40 s. Following cementation, the post was removed and sectioned to obtain 2 mm samples at different depth of cementation. EPR spectra were obtained 10 min and 24 h after cementation to determine the concentration of free radicals (FR) in the surrounding hardened (cured) dental cement, once the concentration of FR is proportional to the light intensity at the restoration point. No significant decrease was observed in light transmission through the cylindrical post that affected the FR concentration, at depths up to 5.5 mm. In contrast, a decrease was verified for all samples conical geometry. The light conduction was effective up to 5.5 mm of curing depth when a cylindrical post was used. The cylindrical configuration was more efficient at conducting light to the deepest points of the restoration compared with the conical configuration.