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Ceramic thin films are used in various applications for their structural or functional properties. Below a thickness of approximately 25 μm, ceramic films are typically deposited, sintered, and used on a supporting substrate due to their fragility. Here, we present a set of easy and versatile green film deposition and sintering techniques that allow the fabrication of free-standing micrometer-thin alumina and yttria-stabilized zirconia foils. Because of their extremely low thickness, the foils were transparent and flexible but still strong enough that they were self-supporting and could be handled manually. The presented concepts are not limited to the materials used here and can potentially be extended to most ceramic materials and glasses. So prepared free-standing ultrathin ceramic foils allow new assembly and fabrication methods of devices and novel materials that contain thin ceramic membranes.

All-ceramic dental restorations exhibit enhanced esthetics and biocompatibility as compared to traditional metal-based prosthesis. However, long-term fatigue and subcritical crack growth in the presence of water and cyclic loading can decrease the strength of ceramic components over time. We investigated the cyclic fatigue in water of three dental materials currently used as frameworks in all-ceramic restorations: a 3 mol%-yttria partially stabilized zirconia (3Y-TZP, Cercon, Degudent GmbH), a Al 2 O 3 –ZrO 2 –Glass composite (Inceram-Zirconia, Vita Zahnfabrik GmbH) and a Li 2 O·2SiO 2 glass ceramic (Empress 2, Ivoclar Vivadent AG). Fatigue and fast fracture tests were performed to determine the Weibull distribution of lifetime and initial mechanical strength for each framework component. In spite of its noticeable susceptibility to fatigue in water, the 3Y-TZP material was found to be particularly suitable for the preparation of posterior all-ceramic bridges due to its high initial mechanical strength. Guidelines are provided for the selection of materials and the design of all-ceramic posterior bridges exhibiting lifetime longer than 20 years under severe wet and cyclic loading conditions.

Objectives Ceramic materials applied in dentistry may exhibit significant subcritical crack growth due to the severe cyclic loading in the aqueous environment encountered in the mouth during mastication. The authors report on the subcritical crack growth behavior of three dental restoration systems (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) under cyclic loading in water, in order to establish guidelines for the use and design of long-lifetime all-ceramic posterior bridges. Methods Inert strength and lifetime tests under cyclic loading in an aqueous environment were performed in a mechanical bending apparatus and evaluated with Weibull statistics. Results Subcritical crack growth occurred predominantly in the outer veneer layer of the veneer–framework composites. The apatite-based veneer (IPS Eris) was more susceptible to subcritical crack propagation compared to the feldspathic glass veneers (Cercon S and Vita VM7). Significance Dental restoration systems containing apatite-based veneers and weak frameworks (Empress 2/IPS Eris) are not recommended for the fabrication of all-ceramic bridges in the molar region. Conversely, veneer–framework systems consisting of feldspathic glass veneers and tough zirconia-based frameworks (TZP/Cercon S and Inceram-Zirconia/Vita VM7) may exhibit lifetimes longer than 20 years if the bridge connector is properly designed.

The aim of this study was to evaluate the cyclic fatigue behavior of zirconia (3Y-TZP) in water and derive guidelines for the design of zirconia-based dental bridges with extended lifetime.The subcritical crack growth parameters under aqueous and cyclic loading conditions were determined from Weibull distributions of the initial mechanical strength and of the lifetime of TZP specimens. The strength and lifetime data were obtained using a specially designed bending machine under simple and oscillatory loading conditions, respectively.The TZP components submitted to cyclic loading in water exhibited subcritical crack propagation at stress levels significantly ( approximately 50%) lower than the critical stress intensity factor (K(IC)=5.6 MPam(1/2)). In spite of this susceptibility to subcritical crack growth, calculations based on the fatigue parameters and on the stress applied on the prosthesis indicate that posterior bridges with zirconia frameworks can exhibit lifetimes longer than 20 years if the diameter of the bridge connector is properly designed.This in vitro study indicates that partially stabilized zirconia (3Y-TZP) can withstand the severe cyclic loading and wet conditions typically applied in the molar region of the mouth and is therefore an appropriate material for the fabrication of all-ceramic multi-unit posterior bridges.

ZnO-based varistor ceramics were sintered under various conditions to optimize their mechanical strength. For highest strength, the optimum sintering temperature was 1070°C or below. At higher maximum temperature, the strength decreased because of grain coarsening and the increasingly inhomogeneous distribution of secondary phases thereby induced. Fracture typically started from holes associated with hollow or poorly compacted sprayed granules. All series contained the same type of critical flaws, but, depending on the sintering temperature, the fracture toughness changed, which led to different strengths. At sintering temperatures above 1050°C, the density started to decrease slightly because of swelling attributed to the pressure of gas entrapped in closed pores.

High-strength ceramics are required in dental posterior restorations in order to withstand the excessive tensile stresses that occur during mastication. The aim of this study was to investigate the fracture behavior and the fast-fracture mechanical strength of three veneer-framework composites (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) for all-ceramic dental bridges.The load bearing capacity of the veneer-framework composites were evaluated using a bending mechanical apparatus. The stress distribution through the rectangular-shaped layered samples was assessed using simple beam calculations and used to estimate the fracture strength of the veneer layer. Optical microscopy of fractured specimens was employed to determine the origin of cracks and the fracture mode.Under fast fracture conditions, cracks were observed to initiate on, or close to, the veneer outer surface and propagate towards the inner framework material. Crack deflection occurred at the veneer-framework interface of composites containing a tough framework material (TZP/Cercon S and Inceram-Zirconia/Vita VM7), as opposed to the straight propagation observed in the case of weaker frameworks (Empress 2/IPS Eris).The mechanical strength of dental composites containing a weak framework (K(IC)3 MPam(1/2)) is ultimately determined by the low fracture strength of the veneer layer, since no crack arresting occurs at the veneer-framework interface. Therefore, high-toughness ceramics (K(IC)5 MPam(1/2)) should be used as framework materials of posterior all-ceramic bridges, so that cracks propagating from the veneer layer do not lead to a premature failure of the prosthesis.