Effect of treated zirconium dioxide nanoparticles on the flexural properties of autopolymerized resin for interim fixed restorations: An in vitro study.

STATEMENT OF PROBLEM: Fractures of interim fixed restorations are a common complication. The autopolymerized polymethyl methacrylate resin materials used for interim fixed restorations have limited mechanical properties, but whether adding treated zirconium dioxide nanoparticles improves mechanical properties is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of treated zirconium dioxide nanoparticles on the flexural strength and elastic modulus of autopolymerized polymethyl methacrylate resin. MATERIAL AND METHODS: A split-metal mold (60×10×3.3 mm) was used to fabricate 40 autopolymerized acrylic resin specimens. The specimens were divided into 4 groups (n=10) according to zirconium dioxide nanoparticle concentration: control (unmodified resin) and zirconium dioxide nanoparticle contents of 1, 2.5, and 5 wt%. The specimens were mixed and polymerized according to the manufacturer's instructions and stored in distilled water for 48 ±2 hours at 37 °C. The flexural strength and elastic modulus were evaluated based on the 3-point bend test where data were analyzed by using 1-way analysis of variance and Tukey post hoc tests (α=.05). RESULTS: The flexural strength of the 1-wt% zirconium dioxide nanoparticle specimens was significantly higher than that of the control group (P<.001) but did not significantly increase further with the higher nanoparticle content (P>.05). Elastic modulus significantly decreased with 2.5-wt% zirconium dioxide nanoparticles (P=.019), while no significant changes were found with other test groups (P>.05). CONCLUSIONS: The addition of treated zirconium dioxide nanoparticles at low concentrations increased the flexural strength of autopolymerized polymethyl methacrylate resins used in fixed interim restorations.

Effect of thickness, cement shade, and coffee thermocycling on the optical properties of zirconia reinforced lithium silicate ceramic.

OBJECTIVE: To investigate the effect of thickness, cement shade, and coffee thermocycling (CTC) on the optical properties of zirconia reinforced lithium silicate (ZLS) paired with different shades of a resin cement. MATERIALS AND METHODS: Thirty ZLS specimens were prepared in two different thicknesses (0.8 and 1.5 mm) and three different resin cement shades (Tr, A2, and A3) were applied (n = 5). Color determinations were done before and after 5000 CTC by using a noncontact spectroradiometer. Color change due to CTC and relative translucency parameter (RTP) before and after CTC were calculated by using CIEDE2000. Data were analyzed using ANOVA and Bonferroni-corrected t-tests(α = 0.05). RESULTS: Material thickness and resin cement shade (P < 0.001) affected baseline color. Material thickness affected color difference (P = 0.025). Thickness, resin cement shade, and CTC (P ≤ 0.0001) affected RTP. The difference between the color changes of the 0.8- and 1.5-mm specimens combined with A2 shade cement after CTC was significant (P = 0.01). RTPs of all pairs decreased after CTC (P < 0.001). CONCLUSIONS: Cement shade and material thickness affected the baseline color. The thickness of ZLS affected the color change after CTC only with A2 resin cement and the color change was less when the ZLS was thicker. CTC reduced the translucency of all pairs. CLINICAL SIGNIFICANCE: Clinicians and patients should be aware of a potential color change after long-term coffee consumption when zirconia reinforced lithium silicate is used particularly for laminate veneers with A2 shade of the tested resin cement.

Fracture analysis of monolithic CAD-CAM crowns.

PURPOSE: The aim of this study was to compare the integrity of zirconia, lithium disilicate, and zirconia-reinforced lithium silicate CAD-CAM crowns after being subjected to cyclic loading and then subjected to static loading until fracture. MATERIAL AND METHODS: Zirconia (Zirkonzahn), lithium disilicate (LDS, Ivoclar Vivadent AG), and zirconia-reinforced lithium silicate glass ceramic (ZLS) (Vita Suprinity, Vita Zahnfabrik) monolithic crowns were milled (n = 6). The crowns were bonded using composite resin cements and subjected to cyclic loading under wet conditions. Three specimens from each group were loaded for 10 000 cycles, and the other three specimens were loaded for 50 000 cycles with 250 N. Specimens were subjected to loading until fracture. Load-to-fracture values were analyzed with 2-way (ANOVA) and Tukey-Kramer post hoc test (α = 0.05). Specimens from each group were examined using an SEM. RESULTS: Mean load-to-fracture values among materials were significantly different from each other (P < 0.05). No significant effect of the number of cycles was found on the load-to-fracture values of crowns (P > 0.05). CONCLUSION: Load-to-fracture values of zirconia were higher than those of LDS, which were higher than those of ZLS. The number of fatigue loading cycles did not affect the load-to-fracture of the tested crowns for a given material. CLINICAL SIGNIFICANCE: More research needs to be conducted before considering the routine use of ZLS for molars in patients with high risk of parafunctional habits.