Abstract
Purpose The aim of the present study was to investigate the effects of the type and thickness of the zirconia material on the microhardness of the underlying dual-cure resin cement. Materials and Methods Eight disk-shaped zirconia specimens with a 4-mm diameter and four varying thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated from two different monolithic zirconia materials: posterior monolithic zirconia (Prettau) and anterior monolithic zirconia (Prettau Anterior). Dual-cure resin cement specimens with a 4-mm diameter and 5-mm height were prepared using Teflon cylinder molds and activated by light beneath the eight zirconia disks and without any zirconia disk for 20 s (n=12). A total of 108 specimens were embedded in acrylic. Vickers hardness of each specimen was measured at three different depths using a microhardness device with a 50-g load. All data were statistically evaluated using three-way ANOVA, one-way ANOVA, independent samples t-tests, and Bonferroni corrected post hoc tests (α=.05). Results Dual-cure resin cement's microhardness was significantly higher for the samples polymerized beneath anterior monolithic zirconia compared to posterior monolithic zirconia. The hardness decreased as the thickness increased for both types of zirconia; the latter was attributed to an attenuated curing efficiency. Conclusion Microhardness of the dual-cure resin cement is influenced by both the type and the thickness of the monolithic zirconia restoration. Polymerization efficiency for resin cement cured under anterior monolithic zirconia may be superior to cured beneath posterior monolithic zirconia.
Highlights
Sintered yttria-stabilized zirconia ceramics (Y-TZP) have been widely used as alternatives to metal-ceramic restorations because of their superb mechanical properties and favorable esthetic characteristics [1, 2]
The analysis model showed that the main effect of the zirconia type, measurement depth, and zirconia thickness and all two-way interactions of these parameters were statistically significant, whereas three-way interaction of the parameters was insignificant (Table 3)
One-way ANOVA test showed that Vickers Hardness Number (VHN) of the dualcure resin was significantly different between PRZ, PRA, and control groups at measurement depths of 100, 300, and 500 μm (p
Summary
Sintered yttria-stabilized zirconia ceramics (Y-TZP) have been widely used as alternatives to metal-ceramic restorations because of their superb mechanical properties and favorable esthetic characteristics [1, 2]. Light transmission through zirconia-based restorations is critical, and the translucency of these restorations has been found to be less than that of glass ceramics because of the high crystalline content of zirconia [5, 6] For this reason, after milling, zirconia cores have to be veneered with porcelain using a layering technique in order to overcome the esthetic problems associated with inadequate translucency of the material. These porcelain veneers exhibit a lower strength than zirconia, resulting in chipping and cracking problems during chewing [7] To overcome this problem, single-layer zirconia restorations fabricated from translucent zirconia blocks with full anatomical contours have recently become available as an alternative to bilayered restorations for dental applications [8]. It is fabricated with an increased yttria content (>8 mol%) in order to achieve full stabilization and improved translucency due to the increased cubic phase [10, 11]
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