Time-dependent Microhardness Gradients of Self-adhesive Resin Cements Under Dual- and Self-curing Modes

Abstract

Clinical Relevance Acid-functional monomers in self-adhesive resin cements may decrease their self-curing polymerization ability. Light irradiation optimizes polymerization performance. SUMMARY Purpose: The aim of this study was to investigate Knoop microhardness of self-adhesive resin cements under dual- and self-curing modes in simulated canals for describing the polymerization behavior. Methods and Materials: Slots in lightproof silicone cylinders with one open end were filled with the following eight materials: a traditional resin cement (Duolink), a core build-up resin material (MultiCore Flow), and six self-adhesive resin cements (RelyX Unicem 2, G-Cem Automix, Maxcem, Biscem, Multilink Speed, and PermaCem 2.0). The resins were exposed to light through the open end and then stored in a lightproof box. The Knoop hardness gradient for each resin was measured after 1 hour and 120 hours. Surface readings were obtained at 1-mm intervals from 1 mm to 10 mm away from the open ends. The data were analyzed by two-way analysis of variance and the Student-Newman-Keuls test (α=0.05). Results: All the resin materials had stable Knoop hardness numbers (KHNs) at a certain depth; their KHNs in the self-curing mode did not change (p>0.05). The region above this certain depth was regarded as having undergone the dual-curing mode, and the KHN decreased gradually with depth (p<0.05). Between 1 and 120 hours postexposure, the ratio of the KHN at a 5-mm depth (self-cured) to that at a 1-mm depth (dual-cured) increased in Duolink and MultiCore Flow. However, the ratios of the six adhesive resin cements varied. Conclusion: Without light, most self-adhesive resin cements differed from traditional dual-cured resin materials in terms of Knoop micro-hardness, and they had a lesser capacity for chemical-induced curing.

Impact of adhesive primer and light‐curing on polymerization kinetics of self‐adhesive resin cement in association with free radical reaction

“…The Hv values were ranked in the order P(+)L(+) > P(+)L(−) > P(−)L(+) > P(−)L(−). The finding that the resin cement polymerized by light-curing [L(+)] resulted in higher hardness than by chemical curing alone [L(−)] was in line with previous studies [34,35]. Based on the results obtained in the present study, the initial hardness of the resin cement would determine the final hardness.…”

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.…”

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

“…3 ), cervical third microhardness recorded higher values (30.3) than the ones observed for the middle (28.7) and apical thirds (27.4). This finding can be explained by the fact that the cervical region was closer to the light incidence focus, which is the curing light used to trigger the setting in a light-activated way, whereas the middle and apical thirds were further away from it ( 14 , 15 - 17 ). Because they received lower light incidence, their setting was mainly chemical, and it may have resulted in lower hardness after the final setting, in comparison to the cervical region.…”

Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials

“…The high surface microhardness of composites may improve the wear resistance of the materials. The surface microhardness of resin composites usually correlated well with the polymerization and cross-linking of the materials [ 74 ]. This was in agreement with the result of the current study.…”