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.
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.
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