Microhardness of different resin cement shades inside the root canal

Abstract

Objectives: To compare microhardness along the root canal post space of two resin cements in different shades and a dual-cure resin core material. Study Design: Root canals of 21 bovine incisors were prepared for post space. Translucent posts (X•Post, Dentsply DeTrey) were luted using one the following resin luting agent: Calibra (Dentsply DeTrey) in Translucent, Medium and Opaque shades, RelyX Unicem (3M ESPE) in Translucent, A2 and A3 shades and the dual-cure resin core material Core•X flow. All materials were applied according to manufacturers’ instructions and were all photopolymerized (Bluephase LED unit, Ivoclar Vivadent, 40s). After 24 hours, roots were transversally cut into 9 slices 1 mm thick from the coronal to apical extremes, three corresponding to each root third. Then, VHNs were recorded (100 gf, 30 s) on the resin luting materials along the adhesive interface in all sections. Data were analyzed by two-way ANOVA and SNK tests (α=0.05). Results: A significant influence on microhardness of resin luting material in their respective shades (p<0.001), root third (p<0.001) and interactions between them was detected (p<0.001). RelyX Unicem cement showed the highest microhardness values and Calibra the lowest, regardless of the shade selected. All resin luting materials tested exhibited a significantly higher microhardness in the cervical third. Conclusions: Microhardness of resin luting agents tested inside the canal is dependent on material brand and resin cement shade seems to be a less relevant factor. Microhardness decreased along the root canal, regardless of the shade selected. Key words:Cement shade, degree of conversion, dual-cured resin cements, fiber posts, microhardness, root thirds.

Shelf life effects on the bond strength and microhardness of self-adhesive resin cements

“…The highest mean bond strength value recorded for root region ( Table 4 ) was observed in the cervical third, which presented significantly higher mean values (20.3) than the ones observed for the middle (17.3) and apical thirds (17.1), which did not differ from each other. It happened due to the prevalent polymerization type observed in this region, which was similar to the one mentioned in microhardness ( 14 , 16 , 17 , 19 ). It also happened due to the larger number and permeability of dentinal tubules in the cervical portion of the root, than those observed for the medium and apical thirds.…”

“…Studies carried out by Vignolo et al . (2012) ( 16 ) and Geng et al . (2020) ( 17 ) have found similar results, according to which, microhardness has gradually decreased along the root canal.…”

Effect of energy density and delay time on the degree of conversion and Knoop microhardness of a dual resin cement

“…High Knoop hardness test values might be related not only to high degree of conversion values, but also to the high cross-linked density in the polymeric matrix, the chemical composition (amount of filler), the matrix composition, the shade, and the translucency of the material. 22 Rapid light curing promotes multiple growth centers, providing a larger number of covalent bonds among different chains. A slow rate of polymerization, such as the chemical curing in dual-cure resin cements, results in fewer growth centers, forming a more linear polymeric structure and decreasing the Knoop hardness test values.…”

“…22 Rapid light curing promotes multiple growth centers, providing a larger number of covalent bonds among different chains. A slow rate of polymerization, such as the chemical curing in dual-cure resin cements, results in fewer growth centers, forming a more linear polymeric structure and decreasing the Knoop hardness test values.…”