Microstructural changes and fracture resistance of nano-crystalline monolithic zirconia restorations upon aging

Abstract

To assess the effect of nano-modification of two CAD/CAM monolithic Zirconia systems (wet and dry-milled) on microstructural changes and fracture resistance upon aging. Twenty monolithic Zirconia discs (10mm x1.5mm) were divided into 2 groups (n=10) according to fabrication system;wet-milled (Incoris TZI) and dry-milled (CeramillZolid). Each group was subdivided into two subgroups (n=5), whether subjected to aging or not. Aging proceduresincluded accelerated hydrothermal aging and cyclic loading. Microstructural changes were assessed quantitatively and qualitatively using x-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Discs were subjected to fracture resistance test usinguniversal testing machine. Meansandstandard deviations were recorded for phase transformation (t-m)of Zirconia and repeated ANOVA was used to correlate phase transformation with fracture resistance results (p≤0.05). For aged subgroups, XRD analysis revealed significantly higher phase transformation of wet-milled than dry-milled (p≤0.05) and SEM analysis revealed wide zone phase transformation for wet-milled zirconia and minimal zone for dry-milled. For both systems, no significant difference between the mean flexural strength values ofnon-agedand aged zirconia (p≤0.05). Nanocrystalline microstructure of monolithic zirconia improved its resistance to aging. The fracture resistance of the two systems was not affected by aging.

The Effect of Hydrothermal Aging on The Color Stability of Gradient Zirconia. In Vitro Study

“…to Kamel et al 18 They found that after aging procedure in wet milling system, peaks of monoclinic phase appeared significantly. While, minimal peaks of monoclinic phase appeared in dry milling system.…”

Effect of two Blocking Reverse Taper Preparation Methods on the Internal Fit of CAD/CAM Monolithic Zirconia Crowns (An In-vitro study)

“…These volumetric changes may affect the fit of zirconia crowns, especially when constructed over reverse-tapered preparation. 9 Die printing was accomplished by the Halot 3D Sky printer. The printer has a resolution accuracy of 0.034mm and XY axis accuracy of 0.05mm, making it capable of providing high quality dies with high precision.…”

“…Also, the process of sintering of zirconia after milling results in shrinkage rates of 30% for zirconia, which affects the accuracy of fit of Zirconia restorations. 9,10 One of the factors which affects the internal fit of the fixed restorations is the preparation angle. 11 The term 'angulation' refers to the angle of preparation or to the total occlusal convergence (TOC).…”

“…23 Many researchers [24][25][26][27][28] have used this approach because it is a very simple, low-cost method that allows measurements to be taken both directly in the mouth cavity and in vitro studies since it does not need specimen destruction. 9 Silicone replica technique is carried out in the same way that a prosthesis is cemented.…”

Surface Roughness and Bacterial Colonization Of Two Types Of Zirconia (Cubic And Gradient) After Accelerated Hydrothermal Aging. (Comparative In-Vitro Study)

“…35 To simulate further of oral conditions, samples were subjected to accelerated hydrothermal aging. 56 Standardization of aging procedure was done according to standard aging protocol of ISO13356 by autoclaving zirconia samples of both groups at temperature of 134 o C and 2 bar pressure for 5 hours simulating 15 years serviceability. 57 This strategy was in accordance with another studies that mentioned the reliability of using autoclave to simulate oral conditions.…”