Effect of Exposure Time on the Polymerization of Resin Cement Through Ceramic

Purpose: This study measured the effects of using three different exposure times to cure one resin cement through two types of ceramic. Materials and Methods: One light-curing resin cement (Variolink II, Ivoclar Vivadent) was exposed for 20 s, 40 s, or 60 s with a BluePhase G2 light (Ivoclar Vivadent) on the high power setting through 1.0 mm of either ZirPress (ZR) or Empress Esthetic (EST) ceramic (Ivoclar Vivadent). The degree of conversion (DC) of the resin was measured 100 s after light exposure. The Knoop microhardness (KHN) was measured 5 min after light exposure and again after 24 h. The DC and KHN results were analyzed with ANOVA followed by Scheffe's post-hoc multiple comparison tests at α = 0.05. Results: Increasing exposure time had a significant effect on the KHN and DC values for the resins exposed through both ceramics. As exposure times increased, the influence of the ceramic was reduced; however, the microhardness values were greater for the cement exposed through EST ceramic. When the exposure time was increased from 20 s to 40 s, microhardness values for the resin increased by 39.6% through the EST ceramic. When exposed for 60 s, there were no differences between the 100-s DC values or 5-min KHN values using either ceramic (p > 0.05). There was an excellent correlation between the DC at 100 s and the microhardness values measured at 5 min. Conclusion: Resin polymerization was greater through EST than ZR ceramic. At least 40 s to 60 s from the Blue- Phase G2 on high power mode is required to cure this resin cement through 1.0 mm of ceramic. Keywords: leucite-reinforced glass ceramic, fluorapatite glass ceramic, resin-based cement, light curing, resin polymerization, Knoop microhardness, degree of cure