Flexural strength and translucency characterization of aesthetic monolithic zirconia and relevance to clinical indications: A systematic review.

The fatigue behaviours were evaluated on a novel zirconia dental restoration known as self-glazed zirconia (SG), prepared by a precision additive 3D gel deposition approach, compared with a conventional zirconia (CZ) restoration, shaped by CNC milling of zirconia blanks made by cold isostatic pressing. Eight fixed partial dentures made by each method were subjected to fracture test, without or with the application of 5-million fatigue cycles, respectively. The processing defects, grain size, and t–m phase transformation were examined by SEM and XRD. The results revealed that the fracture force of the SG restorations was higher than that of the CZ restorations in both cases, which ascribed to the fact that more voids and larger grains in the conventional versus in the SG restorations. The t–m phase transformation was observed only on the fracture surfaces of both materials subjected to fatigue test. Both zirconia restorations meet the clinical requirement.

Fatigue behaviours of the zirconia dental restorations prepared by two manufacturing methods

Statement of problem Anatomic contour zirconia crowns are widely used in clinical dental practice because of their mechanical reliability and improved appearance. However, few studies have performed clinical evaluations of the esthetics of these crowns in terms of color and translucency gradient. Purpose The purpose of this clinical trial was to compare the esthetic effect and color-matching behaviors of anatomic contour zirconia crowns manufactured with 3-dimensional (3D) gel deposition and dry milling methods. Material and methods Twenty-seven premolar teeth of 27 participants received 2 identical anatomic contour zirconia crowns fabricated by additive 3D gel deposition or dry milling. Color differences (ΔE) between the crown and natural control teeth were measured by a dental shade-matching device. Subjective color matching was rated by professionals using an extended visual rating scale for appearance match (EVRSAM) and by participants using a visual analog scale (VAS). Data were analyzed by using repeated measures ANOVA, the Bonferroni test, paired Student t test, Pearson chi-square test, and Wilcoxon test (α=.05). Results Significant differences were found in ΔE between zirconia crown and core types (P .05). The average ΔE of crowns made by wet deposition and dry milling were 2.45 ±1.60 and 4.55 ±1.54 (P Conclusions Anatomic contour zirconia crowns fabricated by additive wet deposition were better matched to adjacent teeth and had excellent esthetics in terms of color and translucency gradient.

Esthetic appearances of anatomic contour zirconia crowns made by additive wet deposition and subtractive dry milling: A self-controlled clinical trial

The grinding and polishing efficiency of self-glazed zirconia and Zenostar zirconia, prepared by wet and dry approaches, respectively, were evaluated. Each sample was divided into two subgroups (n = 5). One was ground, and the other was polished by following the clinical adjustment protocol. Statistics were analysed by independent t-test to a significance level of p   .05). The polishing efficiency of the whole and of the fine polishing procedure of the two kinds of zirconia was significantly different (p < .05). It thus can be concluded that grinding and polishing efficiency of a novel self-glazed zirconia is significantly higher than that of the conventional Zenostar zirconia.

https://www.tandfonline.com/doi/pdf/10.1080/17436753.2018.1472904

Grinding and polishing efficiency of a novel self-glazed zirconia versus the conventional dry-pressed and sintered zirconia ceramics

The effects of microstructures on the mechanical properties of lithium disilicate (Li2Si2O5:LS2) glass-ceramics (GCs) were carefully investigated for the SiO2–Li2O–P2O5–K2O–ZnO system. The microstructures of GC samples, having three different compositions but the same total 6 mol% of additives (P2O5, ZnO, K2O), could be controlled by varying heat treatment conditions of glass samples. In addition to major LS2 crystalline phase, two other minor crystalline phases of Li3PO4 (LP) and cristobalite were detectable. Average crystal sizes of GC samples were in the region of 0.3–10 μm, and the volume fractions of crystalline phases were in the region of 0.70–0.73. The biaxial flexural strength was improved with decreasing the average crystal size from ~10 to ~1 μm by following the Hall-Petch relation, and the maximum flexural strength of 445.8 ± 7.2 MPa was obtainable from the GC samples with the additive compositions of 1.5 mol% P2O5, 2.75 mol% K2O and 2 mol% of ZnO which were nucleated at 540 °C for 1 h and grown at 850 °C for 4 h. When 8.4 vol% cristobalite was incorporated into the sample, however, there was a severe scattering in flexural strength data due to the formation of microcracks induced by the beta-to-alpha transition of cristobalite and also due to a micro tensile stress in the residual glassy phase induced by a large difference in thermal expansion coefficients between crystal and residual glassy phases. Meanwhile, the Vickers hardness was increased with decreasing the average crystal size down to ~0.3 μm, indicating that the factors for the deterioration of flexural strength have a negligible effect on hardness.

Effects of microstructures on the mechanical properties of lithium disilicate glass-ceramics for the SiO2–Li2O–P2O5–K2O–ZnO system

The fractography of a new grade of zirconia ceramics, known as self-glazed zirconia, was investigated. The as-sintered intact top surface was made with superior smoothness that mimicked the optical appearances of the natural teeth enamel. The beneath surface opposite to this was made hierarchically rough with microscopic pits of the size up to 60 μm together with grain-level roughness of about 2 μm. The three-point bending test of the samples made with the hierarchically rough surface being tensile one demonstrated an average bending strength of 1120 ± 70 MPa and a Weibull modulus of as high as 18 ascribed to the improved structural homogeneity. Surface topography was found the main origins of crack initiation leading to fracture. The observed unusually predominant transgranular fracture mode of submicron-sized grains disclosed a possible toughening mechanism of disassembling of mesocrystalline grains that differs significantly from the commonly quoted phase transformation toughening of this category of ceramics.

Jing Zhao

Papers

Fractography of self-glazed zirconia with improved reliability