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High strength of Yttria stabilized tetragonal zirconia polycrystal (Y-TZP) zirconia ceramics are sensitive to low temperature degradation (LTD) that leads to exaggerated tetragonal to monoclinic transformation and a surface to depth propagating degradation that diminishes their mechanical properties. In vitro tests for accelerating ageing have been proposed for the prediction of zirconia ceramics clinical performance. The aim of the present work was to investigate the in vitro ageing of a cold isostatic-pressed zirconia ceramic for all ceramic restorations. Bar-shaped specimens milled from a zirconia block (Ivoclar IPS e.max ZirCAD) were sintered to full density, mirror-polished and cut into two equal pieces. One piece was used as control while the other was subsequently aged (steam 134°C / 2 bars / 10 hours). Atomic Force Microscopy (AFM) was used to evaluate the surface profile and the micro-structural features before and after ageing. Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction Analysis (XRD) were used to determine the degree of the m-ZrO2 transformation. Ageing resulted in an increase of the surface roughness, while the formation of monoclinic spots on the surface of the specimens was verified by surface uplifts in the AFM images. The peaks of the m-phase were clearly observed in the FTIR spectra while an average increase of 16% w.t. of the m-ZrO2 phase was recorded by XRD. Although, no sound lifetime predictions can be made from accelerated tests, based on the ISO standard that imposes that the m-phase should not exceed 25% wt after 5h at 134 °C and 2 bar pressure, it can be concluded that the tested ceramic resisted an extreme transformation that could negatively affect its clinical performance.

the core and lead to total failure of the construction. Chipping rates concerning zirconia restorations are higher compared to metal ceramic prostheses [4,5], which raised questions about the veneering procedure and the quality of the core-veneer interface. Furthermore, the chemical bonding aspects between veneer layers and metals are distinct from those between veneer layers and zirconia, due to different chemical-, mechanical-, and thermal properties [6]. The chemical structure of the zirconia core and the feldspathic veneer are completely different, while the differences in thermal expansion coefficients may affect the stability of the tetragonal phase of Y-TZP ceramic at the interface [7]. To overcome these problems monolithic J Prosthodont Res. 2021; **(**):

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The bioactivity of a glass ionomer luting cement (Ketac®-cem, ESPE, Germany), which was modified by Bioglass® (PerioGlas® Synthetic Bone Graft Particulate, US Biomaterials) in different bioglass/powder weight ratios, and the biocompatibility of the produced mixtures were evaluated in this study using different cell lines. The incorporation of Bioglass® in the cement structure resulted in the formation of sparsely located biological apatite aggregations. However, although Bioglass® incorporation seemed to enhance cell proliferation, the materials became eventually brittle and highly soluble depending on Bioglass® amount.

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