Microhardness of dual-polymerizing resin cements and foundation composite resins for luting fiber-reinforced posts

Statement of problem. The optimal luting material for fiber-reinforced posts, to ensure the longevity of foundation restorations, remains undetermined. Purpose. The purpose of this study was to evaluate the suitability of 3 dual-polymerizing resin cements (DRCs) and 2 dual-polymerizing foundation composite resins (DFCRs) for luting fiber-reinforced posts by assessing their Knoop hardness number (KHN). Material and methods. Five specimens of DRCs (SA Cement Automix [SAC], G-Cem LincAce [GLA], and Panavia F2.0 [PF2]) and 5 specimens of DFCRs (Clearfil DC Core Plus [DCP] and Unifil Core EM [UCE]) were polymerized from the top by irradiation for 40 seconds. KHNs were measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5 hour and 7 days after irradiation. Data were statistically analyzed by repeated measures analysis of variance (ANOVA), 1-way ANOVA, and the Tukey compromise post hoc test (α=.05). Results. At both times after irradiation, the 5 resins materials showed the highest KHNs at the 0.5-mm depth. At 7 days after irradiation, the KHNs of the resin materials did not differ significantly between the 8.0-mm and 10.0-mm depths (P>.05). For all materials, the KHNs at 7 days after irradiation were significantly higher than those at 0.5 hour after irradiation at all depths (P<.05). At 7 days after irradiation, the KHNs of the 5 resin materials were found to decrease in the following order: DCP, UCE, PF2, SAC, and GLA (P<.05). Conclusions. The KHN depends on the depth of the cavity, the length of time after irradiation, and the material brand. Although the KHNs of the 2 DFCRs were higher than those of the 3 DRCs, notable differences were seen among the 5 materials at all depths and at both times after irradiation. Clinical Implications Within the limitations of this in vitro study, dual-polymerizing foundation composite resins may be preferable to dual-polymerizing resin cements for luting fiber-reinforced posts into cavities because of their superior KHNs at all cavity depths.