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Background: While the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling. Methods: One-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05). Results: The study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114). Conclusions: One-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss. [ABSTRACT FROM AUTHOR]

Statement of the Problem: Monolithic zirconia restoration has been introduced to overcome the porcelain chipping. Different factors can affect the color of monolithic zirconia, so achieving the desired color in the restorations is considered as a challenge. Purpose: The purpose of this in vitro study was to determine the effect of different foundation materials on the color of monolithic zirconia at different thicknesses. Materials and Method: In this experimental study, thirty ceramic disks in three thicknesses (i.e. 0.6mm, 1.1mm and 1.5mm) were fabricated from high translucency shade A2 monolithic zirconia block. Disk shaped foundation materials were fabricated from nickel chromium alloy (Ni-Cr), non-precious gold alloy (NPG), zirconia, and shade A2 composite resin. The color was measured by a spectrophotometer. The color differences (ΔE) in the control and the test groups were calculated. The data were analyzed using two way ANOVA and compared with the post-hoc Tukey test (a=0.05). Results: ceramic thickness and foundation materials had a significant effect on the mean values of ΔE of monolithic zirconia ceramics (p= 0.001). The highest amount of ΔE value was observed in NPG, while Ni-Cr resulted in the lowest ΔE. Unacceptable results (ΔE>2.25) were observed for monolithic zirconia ceramics on NPG foundation material with a thicknesses of 0.6 and 1.1mm. The mean L* values of all foundation materials were higher than those of the control group except for Ni-Cr. The highest a* was seen in NPG and the mean b* values of all tested foundation materials were higher than those of the control group except for Ni-Cr. Conclusion: Increasing the thickness of monolithic zirconia decreased the color mismatch. High translucent monolithic zirconia could mask the color of Ni-Cr and zirconia in all three thicknesses (ΔE˂2.25), while it could not mask the color of NPG under thickness of 1.5mm. [ABSTRACT FROM AUTHOR]

Background: The flexural strength (FS) of a denture base material is of great concern, and many approaches have been used to strengthen the denture acrylic resins. The present study aimed to evaluate the effect of high-performance polymer (BioHPP) and metal mesh reinforcement on the FS of a heat-cured poly methyl methacrylate (PMMA) acrylic resin. Materials and Methods: This experimental study was done on 30 rectangular specimens (64 mm x 13 mm x 3 mm) of a heat-cured PMMA resin. The specimens were divided into three groups (n = 10) to be reinforced with either metal mesh or BioHPP mesh; one group was left nonreinforced, serving as the control group. The FS of specimens was assessed through a 3-point bending test by using a universal testing machine at a crosshead speed of 2 mm/min. Kruskal--Wallis H and Dunn's post hoc tests were used to compare the FS among the groups (alpha = 0.05). Results: The FS in the metal-reinforced group was statistically significantly higher than the two other groups (P < 0.001). However, the FS of the BioHPP-reinforced samples was not statistically significantly higher than the nonreinforced ones (P = 0.614). Conclusion: Reinforcing the PMMA with metal mesh significantly enhances its FS while BioHPP has no significant effect on the PMMA FS. [ABSTRACT FROM AUTHOR]

Statement of the Problem: Retrieval of cement-retained implant-supported restorations is challenging in cases of screw loosening or periodontal problems. Purpose: The purpose of this study was to evaluate the effect of the screw access hole on the fracture resistance of zirconia-based cement-retained restorations with and without an access opening. Materials and Method: In this in vitro study thirty-three cement-retained implantsupported zirconia-based molar crowns were fabricated and divided into 3 groups (n=11). As the control group, group 1 consisted of conventional cement-retained crowns. Group 2 comprised conventional cement-retained crowns in which a hole was created in the location of the screw. Group 3 consisted of cement-retained crowns in which a ledge was created in the location of the screw access channel. The specimens were cemented to their abutments and their access openings were filled with composite resin. A compressive load was applied to the specimens using a universal testing machine until they fractured. The mean fracture resistance values of the samples were compared by using the one-way ANOVA and Tamhane post-hoc test (a=0.05). Results: The mean fracture resistance values were 1270.18± 12.67 N in group 1 (the control group), 960.09±210.67 N in group 2 (conventional), and 1357.81±361.68 N in group 3 (the special design). The fracture resistance value was higher in the special design group than that of the conventional design (p= 0.018) and the fracture resistance value of the conventional design group was less than that of the control group (p= 0.042). No statistically significant difference was detected between the control group and the special design group in fracture resistance values. Conclusion: Preparing a screw access hole in cement-retained implant-supported zirconiabased crowns decreased the fracture resistance of the restoration. Designing a ledge in the zirconia framework around the access hole may increase the fracture resistance of the restoration. [ABSTRACT FROM AUTHOR]

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 x 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 (α= 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. [ABSTRACT FROM AUTHOR]

Statement of the Problem: There is not enough information available about the effect of thickness reduction and the coloring method on the color of new monolithic zirconia ceramic system. Purpose: This study aimed to evaluate the effect of varying thickness reductions and number of coloring liquid applications on the final color of anatomic contour monolithic zirconia ceramics. Materials and Method: In this experimental in-vitro study, 48 disk-shaped monolithic zirconia specimens (10×2mm) were divided into three groups (Group I to III) according to the number of A2-coloring liquid applications (n=16). Each group was then divided into 4 subgroups (n=4) by reducing the thickness of 2 to 0.5 mm in increments of 0.5 mm on the colored surface. Color measurement was done through CIELab (l*, a*, b*) on a reflection spectrophotometer on five different areas of each specimen. Color differences (ΔE) were calculated. Data were analyzed by using two-way ANOVA and Tukey's HSD test (α=0.05). Results: The number of coloring liquid applications and reducing the thickness of monolithic zirconia disks had significant effects on CIE L* a* and b* values. The CIEL*, a* and b* values increased as the thickness decreased (p< 0.05), whereas, increasing the number of coloring liquid applications resulted in decreased CIE L* value and increased CIE a* and b* values (p< 0.05). Conclusion: Decreasing the thickness of monolithic zirconia increases the lightness and reddish, yellowish appearance. Meanwhile, increasing the number of coloring liquid applications reduces the lightness and makes it seem more reddish and yellowish. [ABSTRACT FROM AUTHOR]