Purpose: This study aimed to evaluate the microhardness and hardness ratios of hybrid resin composites using different irradiance lights. Materials and Methods: Light-curing units were light emitting diode (LED) light-curing unit (Demi Ultra). The light-cured resin composites were Clearfil AP-X (shade A3) and Clearfil Photo Bright (shade US). Composite specimens of 2-mm thickness were polymerized in Teflon molds using an energy density of 24,000 mJ/cm2. Light irradiances were 1,200 mW/cm2 20 s and 600 mW/cm2 40 s. Just after light curing, the Knoop hardness (KHN) was measured at the top and bottom surfaces of each specimen using a hardness tester. The hardness ratio was calculated as follows: KHN of bottom surface/KHN. All experiments were performed at room temperature of 23 ± 2˚C with humidity of 50 ± 10%. Results: Immediately after light curing, the KHN at the bottom surfaces of resin composites was significantly lower than that at the top surfaces for every group (< 0.05). The 1,200 mW/cm2 20 s showed significantly smaller hardness ratio compared with that of the 600 mW/cm2 40 s for both Clearfil AP-X and Clearfil Photo Bright resin composites ( < 0.05). Conclusion: When the energy density was the same, the polymerization of resin composites at the bottom surface was more inhibited than that of at the top surface using high-irradiance light.

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Purpose: The purpose of this study was to evaluate the long-term durability of the bonds between self-adhesive luting agents and yttria-stabilized partially stabilized zirconia (Y-PSZ) and the effect of phosphoric acid etching as a surface pre-treatment to Y-PSZ. Materials and Methods: A total of 180 Y-PSZ disks were divided into two groups; the control group and the phosphoric acid etching group prior to the bonding with one of three self-adhesive luting agents; Panavia SA Cement Plus Automix (SAP), RelyX Unicem2 Automix (UC2), or Maxcem Elite Chroma (MXE). Bonded specimens were stored in distilled water, for 1 day, 30 days, or 150 days. After storage, the tensile bond strength was measured using a universal testing machine. The data were statistically analyzed using Welch's -test and Welch's -test with Bonferroni correction ( = 0.05). Results: The tensile bond strength of each luting agent measured more than 15 MPa after 1 day of immersion in distilled water with or without phosphoric acid etching. There were no significant differences between SAP and UC2 after 30 days and 150 days ( > 0.05) of immersion. SAP and UC2 showed significantly higher bond strength than MXE after 30 days and 150 days < 0.05) of immersion. There were no significant differences between with/without phosphoric acid etching in all groups ( > 0.05). Conclusion: Durability of self-adhesive luting agent to Y-PSZ was material-dependent. A surface pre-treatment with phosphoric acid etching to Y-PSZ did not affect the bond strength of self-adhesive luting agent to Y-PSZ.

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Purpose: The purpose of this study was to evaluate the effect of ultraviolet ray (UV) on tooth bleaching using titanium dioxide photo catalyst in vitro. Materials and Methods: Hematoporphyrin-stained paper (HSP) and artificially discolored bovine teeth (BT) were bleached by an in-office bleaching material containing low concertation of hydrogen peroxide and titanium dioxide photocatalyst. For the bleaching, light irradiation was performed at wavelengths of 265, 310, 365, 405, and 450 nm for HSP, and 265, 300, and 405+470 nm for BT. Before and after bleaching, color was measured to obtain CIE L*a*b* values. The color differences (ΔE) were calculated and were statistically analyzed. Results: In the HSP experiment, the 265 and 310 nm groups showed a remarkable bleaching effect and ΔE of the 310 nm group was statistically the highest (p < 0.05). In the BT experiment, ΔE of the 265 nm group was statistically the highest followed by 300 nm, then 405+470 nm groups (p < 0.05). Conclusion: UV-C (265 nm) and UV-B (300 and 310 nm) showed high bleaching effect with an in-office bleaching material containing low concentration of hydrogen peroxide and titanium dioxide photocatalyst.

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