Triantafyllia T. Zorba

Influence of strontium for calcium substitution on the glass-ceramic network and biomimetic behavior in the ternary system SiO2-CaO-MgO

Strontium (Sr) enhances bone formation both in vitro and in vivo, while it reduces bone resorption. Thus, Sr incorporation in bioactive glass–ceramic scaffolds for bone tissue regeneration could further enhance osteogenesis. The aim of this work was the synthesis, characterization and investigation of the apatite-forming ability in inorganic environment of two sol–gel-derived bioactive Sr-containing glass–ceramic materials with 5 and 10% of SrO. The thermal properties of the synthesized materials were studied using differential thermal analysis (TG–DTA). The apatite-forming ability test was conducted in SBF for various immersion times for both thermally treated and untreated samples. The characterization of the samples before and after immersion in SBF was performed with Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy with associated energy-dispersive spectroscopy. FTIR spectra revealed that all synthesized glass–ceramic materials presented the characteristic bands of silicate glasses, while XRD identified various crystalline phases, mostly calcium silicates. Strontium is present in the form of strontium silicate in both as-received and thermally treated specimens, and Sr-diopside in the thermally treated specimens. The apatite-forming ability of the glass–ceramic materials was confirmed by the formation of a hydroxyapatite layer after 3 and 5xa0days of immersion in SBF on the surface of the untreated and thermally treated samples, respectively. The apatite layer, also, became thicker as the immersion time increased.

Color stability of lithium disilicate ceramics after aging and immersion in common beverages

Statement of problem: The color of an esthetic restoration and its color stability are important for long‐term success. However, the impact of common beverages on lithium disilicate ceramic is not well known. Purpose: The purpose of this in vitro study was to investigate color variations of lithium disilicate ceramics after thermocycling (TC) and immersion in commonly consumed beverages. Material and methods: A total of 288 specimens (1×10×10 mm) were fabricated from IPS e‐max computer‐aided design (CAD) (n=72), IPS e‐max CERAM ([CER] n=72), IPS e‐max Press with glazing ([PG] n=72), and IPS e‐max Press without glazing ([PNG] n=72) according to the manufacturers instructions. Each group was divided into 4 subgroups (n=18): TC, coffee, black tea, and red wine. Thermocycling was performed at 21 900 cycles at 5°C, 37°C, 55°C, and 37°C (3 years’ clinical simulation), whereas the specimens were soaked in the staining solutions for up to 54 hours (3 years’ clinical simulation). Color parameters L*, a*, and b* were assessed with an ultraviolet‐visible spectroscopy recording spectrophotometer. Color difference (&Dgr;E) was calculated using the equation [&Dgr;E= [(&Dgr;L*)2 + (&Dgr;a*)2 + (&Dgr;b*)2]½]. Intraexaminer reliability was assessed by using the intraclass correlation coefficient. Two‐way analysis of variance was used for the analysis of &Dgr;E, and the parameters L*, a*, and b* were analyzed with linear mixed models for repeated measurements and the Bonferroni pair‐wise comparison test (&agr;=.05). Results: Parameters &Dgr;E, L*, a*, and b* were significantly affected by the interaction between material and treatment (P<.001). A &Dgr;E >1 was recorded for PG with tea, wine, and coffee, PG after TC and CER after TC. For L*, greater reduction was observed for PNG with tea and CER after TC, whereas for a* significant changes were positive (to red shades), except for PNG with TC, where PNG with wine showed the greatest positive change. For b*, significant changes were negative (to blue shades) except for PNG with tea and coffee and CAD with tea. Conclusions: All groups demonstrated color changes below the clinically perceptible level (&Dgr;E<3.7), except PNG in tea which showed statistically significant color differences (&Dgr;E>4). CAD presented higher color stability compared with the nonglazed Press specimens.

Aging of 3Y-TZP dental zirconia and yttrium depletion

OBJECTIVEnYttrium-stabilized zirconia is susceptible to low temperature degradation after interaction with water. Various mechanisms by which water molecules destabilize the tetragonal phase have been proposed, while the concept of yttrium depletion by the incorporation of hydroxyl ions in the crystalline structure either through the formation of YOH/ZrOH bonds or small α-Y(OH)3 crystallites, is prevailing. The present study was performed to investigate the surface alterations on a 3Y-TZP dental ceramic during the process of in-vitro aging and to further explore the yttrium depletion mechanism that occurs upon interaction with water.nnnMETHODSnSurface structural changes of zirconia specimens where investigated before and after in-vitro aging with X-ray diffraction analysis, Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, fluorescence microscopy and scanning electron microscopy.nnnRESULTSnHigh luminescence generated from the non-aged specimen was explained by the high amount of oxygen vacancies. The phase transformation from the t-ZrO2 to the m-ZrO2 phase after aging was accompanied by a significant loss of yttrium, a clear decrease of oxygen vacancies and a profound decrease of luminescence. Surface oxygen vacancies either migrated into the inner of the specimens or/and/engaged oxygen from the ZrO2 and formed the metallic phase of Y2O3 on the surface after aging.nnnSIGNIFICANCEnAn ideal amount of oxygen vacancies that could stabilize the tetragonal phase in Y-TZP zirconia ceramics, without compromising esthetics and LTD resistance, is still a matter of further research and different susceptibilities to LTD among various dental zirconia ceramics are based on the amount of oxygen vacancies that can be annihilated by water molecules.

Unraveling the materials and techniques of post-Byzantine wall paintings: Is there a sole pictorial phase at the catholicon of Stomion, Central Greece?

Saint Demetrius of Stomion is a historical monastery placed in the geographical area of Larissa town, Greece, with a remarkable presence from its founding until nowadays. The monasterys present catholicon (main church) has been dated in the 16th century and its surviving wall paintings were constructed in 1758. In addition to the characterization of the materials applied, the purpose of this study is to determine the existence of a sole pictorial phase, that of the mid-18th century, or the occurrence of overpaintings. Additionally, the present study aims to begin the establishment of the documentation of materials and techniques of the late post-Byzantine iconographic guilds, which acted in Central and Northern Greece. The collected samples were analyzed by means of microscopic, spectroscopic and thermogravimetric methods. The use of fresco technique is implied by the major participation of calcium carbonate in all of the painting layers, its main contribution in the plaster layers and the microstratigraphic analysis of the samples cross-sections, while the scarce and local presence of a proteinaceous material implies the limited use of egg-tempera technique for the highlights. The pigment analysis shows that mostly traditional pigments were used, including cinnabar, ferrous pigments (ochre, sienna, umber), minium, Naples yellow, massicot/litharge, green earth (celadonite), malachite, carbon and bone black, calcite, kaolinite and lead white. The absence of modern pigments, the consistency of all samples regarding microstratigraphy and applied materials, and the lack of the extensive use of an organic medium, strongly suggest the lack of overpaintings.

Lead Telluride Doped with Au as a Very Promising Material for Thermoelectric Applications

PbTe single crystals doped with monovalent Au or Cu were grown using the Bridgman method. Far infrared reflectivity spectra were measured at room temperature for all samples and plasma minima were registered. These experimental spectra were numerically analyzed and optical parameters were calculated. All the samples of PbTe doped with Au or Cu were of the “” type. The properties of these compositions were analyzed and compared with PbTe containing other dopants. The samples of PbTe doped with only 3.3u2009at% Au were the best among the PbTe

Infrared properties of sintered α-MnSe

Abstract Far-infrared reflection spectra of sintered α-MnSe were measured at room temperature. The measured spectrum had one pronounced peak in accordance with literature data and group theory estimation and one smaller peak resulting from the applied sintering procedure. The measured reflection spectrum was analyzed using Kramers–Kronig analysis and a three-component effective medium model based on Bruggemans theory assuming the presence of a small amount of pores, dominant crystalline grains and intergranular material. In the model the crystalline grains were modeled as a single oscillator appropriate to the single crystal and the intergranular material was also defined as a single ionic oscillator.

Far Infrared Properties of BaTiO3 Ceramics

Far infrared and mid infrared reflectivity measurements have been made at BaTiO3 ceramics at room temperature in the range between 10 μm and 200 μm. The Kramers-Kronig analysis and a fitting procedure, based on a four parameter model of the spectrum, determined the infrared active transverse and longitudinal optical modes, their damping factors and the values of dielectric permittivity. Group theory analysis has been done and the number of experimentally observed infrared active modes was compared with the theoretical prediction. The calculated values of the parameters were compared for samples produced with different technology treatment. The high frequency dielectric permittivity (at 1013 Hz) decreases from 5.13 to 1.88, for the BaTiO3 samples sintered at 1320°C for ten and two hours, respectively. Similarly, the change of other parameters provides some information about densification of BaTiO3 ceramics. It was also concluded that infrared optical reflectivity measurements could give reliable results at the boundary cases, when it is difficult to distinguish if a material has either cubic or tetragonal structure.