Effect of indenter material on reliability of all-ceramic crowns

Porous Talcum-Based Steatite Ceramics Fabricated by the Admixture of Organic Particles: Experimental Characterization and Effective Medium/Field Modeling of Thermo-Mechanical Properties

In this paper, an experimental campaign, as regards the thermo-mechanical properties (heat capacity, thermal conductivity, Young's modulus, and tensile (bending) strength) of talcum-based steatite ceramics with artificially introduced porosity, is presented. The latter has been created by adding various amounts of an organic pore-forming agent, almond shell granulate, prior to compaction and sintering of the green bodies. The so-obtained porosity-dependent material parameters have been represented by homogenization schemes from effective medium/effective field theory. As regards the latter, thermal conductivity and elastic properties are well described by the self-consistent estimate, with effective material properties scaling in a linear manner with porosity, with the latter in the range of 1.5 vol-%, representing the intrinsic porosity of the ceramic material, to 30 vol-% in this study. On the other hand, strength properties are, due to the localization of the failure mechanism in the quasi-brittle material, characterized by a higher-order power-law dependency on porosity.

Two-body wear resistance and fatigue survival of new Y-TZP and ATZ ceramics made with a new slip-casting method

BACKGROUND

Dental zirconium oxide restorations are milled from pre-sintered blocks or disks which are produced either with high isostatic pressure (HIP) or, simpler, a slurry technique. The objective was to perform a fatigue test and an in vitro wear simulation of two ceramics, yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramic and a hybrid zirconium oxide-aluminum oxide ceramic, (ATZ) both produced either the classical way using high isostatic pressure (HIP, control) or with a slurry technique.

MATERIALS AND METHODS

Ten discs/group were subjected to a cyclic biaxial fatigue test using a staircase approach under water at 37 °C in a dynamic universal testing machine. The 2-body wear test was performed on eight lapped 12 mm thick cylindrical samples subjected to spherical (ø 6 mm) leucite ceramic antagonists in a CS-4 chewing simulator at 49 N force and 0.7 mm lateral movement for 600 k cycles and 4167 thermal cycles (5-55 °C). Volumetric wear was calculated based on laser-scanned surfaces. Selected samples of both tests were viewed in SEM.

RESULTS

All the ceramic specimens produced using the HIP method survived up to 1.2 M cycles with the maximum load of the equipment (1000 N) loading the specimens up to 1527 MPa. The fatigue limit stress at 1.2 M cycles for the Slurry ATZ samples was 946 MPa. For the Slurry Y-TZP samples the fatigue limit stress at 1.2 M cycles was 658 MPa. At 600 k cycles, all zirconium oxide ceramics showed no measurable wear and had a highly polished appearance. The leucite ceramic antagonists wear developed in a linear way. There was no difference between the materials produced with the slurry and the HIP process. ATZ ceramic produced significantly more wear than 3Y- TZP ceramic.

CONCLUSIONS

The HIP method provided higher fatigue strength than the Slurry manufacturing method. All HIP ceramics surpassed the limit threshold (1527 MPa) of the testing machine. The tested ceramics did not show any measurable wear but had worn the leucite reinforced glass ceramic antagonists for a considerable amount.

Influence of CAD/CAM milling, sintering and surface treatments on the fatigue behavior of lithium disilicate glass ceramic

This paper reports on the process-fatigue relation of lithium disilicate glass ceramic (LDGC) using low-cycle, high-load Hertzian indentations with a rigid indenter to simulate teeth grinding/clenching of LDGC restorations with different surface asperities obtained in CAD/CAM milling, sintering, polishing and glazing. The maximum contact stresses were evaluated as functions of the number of load cycles and surface treatments using the Hertzian model. Indentation-induced surface damage was viewed using scanning electron microscopy (SEM) to understand the relationships among microstructures, surface asperities, crack morphology and propagation. Different processes and surface treatments significantly affected the maximum contact stresses of indented LDGC surfaces (ANOVA, p < 0.05), which were all significantly reduced with the number of cycles (ANOVA, p < 0.05). Quasi-plastic deformation was dominant in single-cycle indentation of all processed and treated surfaces. In higher cycle indentations, inner cone cracks were formed on all surfaces; median and transverse cracks were formed on the roughest surfaces processed by CAD/CAM milling and sintering. Ring cracks, fretting, pulverization, micro-bridges, surface smearing and wedging, and edge chippings were also propagated on all surfaces. The process-fatigue relation provides an understanding of the mechanical functions of surface asperities produced in different processes and treatments. It indicates that the mechanically assisted growth of surface asperities with different roughness strongly affected the indentation-induced surface damage. Finally, the smoothest surfaces produced by CAD/CAM milling, polishing and sintering sustained the highest contact stresses and the least fatigue damage at higher cycles, ensuring their superior fatigue performance compared to other processed LDGC surfaces.