Byline: Rashin. Giti, Shekoofeh. Haghdoost, Elham. Ansarifard
Background: This study aimed to evaluate the effect of different coloring techniques and surface treatment methods on the surface roughness of monolithic zirconia ceramic. Materials and Methods: In this in vitro study seventy-two disk-shaped monolithic zirconia (2 mm × 10 mm) were divided into three coloring techniques groups (white, internal staining, external staining) (n = 24). Each group was subdivided into four surface treatment subgroups (n = 6), as unpolished, polished with Shofu polishing kit, polished with dental direct polishing kit, and glazed. Profilometer was used to measure the Ra (roughness average) and Rz (roughness height) surface roughness values (µm) and scanning electron microscopy (SEM) for visual inspection of the surface morphology. The surface roughness parameters were calculated and analyzed with two-way ANOVA and Tukey's post hoc test (a = 0.05). Results: The coloring technique, surface treatment method, and interaction of these two parameters significantly affected the Ra and Rz parameters (P < 0.05). Concerning the surface treatment, the Rz value was significantly higher in the unpolished subgroup, followed by the glazed and polished subgroups. However, the two polishing systems were not significantly different. The internal staining group had significantly higher Rz value than the other staining method, when the specimens were glazed or polished with Shofu kit. SEM showed multiple scratches in unpolished samples which were smoothened by glazing and specially by polishing. Conclusion: Among all the studied surface treatment methods, the lowest surface roughness was observed in highly polished monolithic zirconia, which was even less than the glazed one. The internal staining method can create a rougher surface for some of the surface treatment methods.
Of all the available restorations, all-ceramic crowns are among the options that offer the most desirable esthetic outcome. Compared with other restorations, the color and translucency of all-ceramic crowns more easily mimic the natural tooth structure. Clinicians believe that the zirconia-based ceramics are the most preferable choice of all-ceramic systems, as they meet the biomechanical needs such as chemical and dimensional stability, high mechanical strength, and fracture toughness. All-ceramic crowns and fixed dental prostheses (FDPs) have long benefited from the highly stable material of yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics as the core material. What makes them so favorable is their great strength and superb fracture resistance against the inherent transformation-toughening mechanism.
To meet the esthetics needs, glass ceramic or translucent feldspathic materials are used to veneer the zirconia frameworks. Besides the unclear bonding mechanism between Y-TZP and the veneering ceramic, there is another undeniable weak point to these restorations, which is the core-veneer interface that expose them to the risk of ceramic chipping. Such breakdowns can be due to the incongruent coefficient of thermal expansion between the zirconia and the veneered porcelain. Attempts to overcome these failures led to development of highly sintered monolithic or anatomically contoured zirconia crowns. Zirconia restorations went clinically more successful and reliable as the veneering porcelain layer was excluded.
Sometimes, diamond rotary instruments are used for modification and intraoral...