Publications by authors named "Lambrini Papadopoulou"

30 Publications

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Correction to: Effect of brominated flame retardant on the pyrolysis products of polymers originating in WEEE.

Environ Sci Pollut Res Int 2021 Aug 11. Epub 2021 Aug 11.

Laboratory of Polymers and Dyes Chemistry and Technology, Department of Chemistry, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece.

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http://dx.doi.org/10.1007/s11356-021-15862-7DOI Listing
August 2021

Effect of brominated flame retardant on the pyrolysis products of polymers originating in WEEE.

Environ Sci Pollut Res Int 2021 Jul 26. Epub 2021 Jul 26.

Laboratory of Polymers and Dyes Chemistry and Technology, Department of Chemistry, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece.

Chemical recycling is an environmentally friendly method, which is often used for the recycling of plastics included in waste electric and electronic equipment (WEEE), since fuels and secondary valuable materials can be produced. Brominated flame retardants (BFRs) are usually added into these plastics to reduce their flammability; but they are toxic substances. The aim of this work is to examine the thermal behaviour and the products obtained after pyrolysis of polymer blends that consist of acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), polycarbonate (PC) and polypropylene (PP) with composition that simulates real WEEE, in the absence and presence of a common BFR, tetrabromobisphenol A (TBBPA), in order to investigate its effect on pyrolysis products. Blends were prepared via the solvent casting method and the melt-mixing in an extruder; it was revealed that the latter method may be a better choice for blends preparation, since it did not affect the products obtained. The chemical structure of each polymeric blend was identified by Fourier transform infrared spectroscopy (FTIR). Thermal degradation of the blends was evaluated by thermogravimetric (TG) experiments performed using a thermal analyser (TGA) and a pyrolyser for evolved gas analysis (EGA). It was observed that blends had a similar behaviour during their thermal degradation; and in most cases, they followed a one-step mechanism. Pyrolysis products were identified by the pyrolyser combined with a gas chromatographer/mass spectrometer (GC/MS), and comprised various useful compounds, such as monomers, aromatic hydrocarbons and phenolic compounds that could be used as chemical feedstock. Furthermore, it was found that TBBPA affected products distribution by enhancing the formation of phenolic compounds and on the other hand by resulting in brominated compounds, such as dibromophenol.
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http://dx.doi.org/10.1007/s11356-021-15489-8DOI Listing
July 2021

Novel Femto Laser Patterning of High Translucent Zirconia as an Alternative to Conventional Particle Abrasion.

Dent J (Basel) 2021 Feb 8;9(2). Epub 2021 Feb 8.

School of Dentistry, National and Kapodistrian University of Athens, 2 Thivon Str, Goudi, 11527 Athens, Greece.

Background: currently applied surface treatments for zirconia bonding may create undesired microcracks and surface flaws. The aim of the present study was to evaluate the efficacy of alternative surface treatments on the shear bond strength of high translucency zirconia to 10-Methacryloyloxydecyl dihydrogen phosphate (MDP)-containing resin-based cement.

Methods: fifty disk-shaped specimens (10 mm × 5 mm) were fabricated from a commercial yttria-stabilized zirconia with 5 mole% yttrium oxide tetragonal zirconia polycrystal (5Y-TZP), and underwent air-abrasion with alumina particles (50 μm-AL50 and 90 μm-AL90), glass beads (GB 10-60 μm), and ablation with femtosecond laser (FEMTO). Shear bond strength was evaluated with a universal testing machine under a crosshead speed of 0.5 mm/min until fracture. Fracture type was evaluated with an optical stereomicroscope. Differences among groups were evaluated by one-way ANOVA and Bonferroni pairwise comparison tests ( < 0.05).

Results: the highest shear bond strength values were presented by the laser treated group (23.97 ± 3.7 MPa). No statistically significant differences were found among the Cl, Al50, Al90 and FEMTO groups. The lowest mean value was presented by the glass-beads treated group (11.93 ± 2.88 MPa) which was significantly lower compared to all other groups ( < 0.001).

Conclusions: under the limitations of this in vitro study, femtosecond laser treatment of High-translucent monolithic zirconia (HTZ) ceramics is a promising alternative method for the mechanical retention of resin cements.
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http://dx.doi.org/10.3390/dj9020020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915195PMC
February 2021

Synthesis and Characterization of Mesoporous Mg- and Sr-Doped Nanoparticles for Moxifloxacin Drug Delivery in Promising Tissue Engineering Applications.

Int J Mol Sci 2021 Jan 8;22(2). Epub 2021 Jan 8.

School of Dentistry, Faculty of Health Sciences, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.

Mesoporous silica-based nanoparticles (MSNs) are considered promising drug carriers because of their ordered pore structure, which permits high drug loading and release capacity. The dissolution of Si and Ca from MSNs can trigger osteogenic differentiation of stem cells towards extracellular matrix calcification, while Mg and Sr constitute key elements of bone biology and metabolism. The aim of this study was the synthesis and characterization of sol-gel-derived MSNs co-doped with Ca, Mg and Sr. Their physico-chemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectroscopy (XRF), Brunauer Emmett Teller and Brunauer Joyner Halenda (BET/BJH), dynamic light scattering (DLS) and ζ-potential measurements. Moxifloxacin loading and release profiles were assessed with high performance liquid chromatography (HPLC) cell viability on human periodontal ligament fibroblasts and their hemolytic activity in contact with human red blood cells (RBCs) at various concentrations were also investigated. Doped MSNs generally retained their textural characteristics, while different compositions affected particle size, hemolytic activity and moxifloxacin loading/release profiles. All co-doped MSNs revealed the formation of hydroxycarbonate apatite on their surface after immersion in simulated body fluid (SBF) and promoted mitochondrial activity and cell proliferation.
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http://dx.doi.org/10.3390/ijms22020577DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7827177PMC
January 2021

The effect of different aging protocols on the flexural strength and phase transformations of two monolithic zirconia ceramics.

J Appl Biomater Funct Mater 2020 Jan-Dec;18:2280800020982677

Laboratory of Prosthodontics, Dentistry Department, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Introduction: The aim of the present study was to investigate how different aging protocols can affect the flexural strength and phase transformations of yttrium-stabilized zirconia ceramics (Y-TZP) for monolithic restorations.

Materials And Methods: Bar-shaped specimens from two zirconia ceramics bars were divided into three groups: a. no treatment (c), b. aging in an autoclave (a), and c. thermal cycling (t). The flexural strength was determined by the 3-point bending test and statistical analysis was performed to determine significant differences (< 0.05). Weibull statistics was used to analyze the dispersion of strength values while surface microstructural analysis was performed through X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

Results: Aging did not significantly affect the flexural strength but differences were recorded between the two groups, with group A presenting higher strength values and m-phase percentages.

Conclusions: The observed differences between the two ceramics could be attributed to variations in composition and processing.
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http://dx.doi.org/10.1177/2280800020982677DOI Listing
December 2020

Mechanical and thermal properties of PMMA resin composites for interim fixed prostheses reinforced with calcium β-pyrophosphate.

J Mech Behav Biomed Mater 2020 12 17;112:104094. Epub 2020 Sep 17.

Laboratory of Polymers Chemistry and Technology, Department of Chemistry, Faculty of Sciences, Aristotle University of Thessaloniki, GR-54124, Macedonia, Greece.

Interim restorations are essential in fixed prosthodontics as they provide temporary protection of teeth before the insertion of the permanent restoration. Poly(methyl methacrylate) (PMMA) is widely used in the fabrication of interim-fixed restorations as it is a biocompatible material with a lot of convenient properties. However, it exhibits low impact and tensile strength and therefore it is necessary to be reinforced. Calcium β-pyrophosphate (β-CPP) is considered a promising reinforcing material for dental applications, especially for enamel regeneration due to its stability at low pH and its low wear rate. The aim of this study was to manufacture PMMA/β-CPP composites suitable for fixed-interim restorations and to study their mechanical and thermal properties. In order to enhance β-CPP dispersion into PMMA matrix, ball-milling was performed for 1 or 6 h. Three-point bending test was performed to study flexural strength, Dynamic Mechanical Analysis (DMA) to reveal the elastic and viscous moduli along with T, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction Analysis (XRD) to investigate the structure of the materials and SEM for the morphological evaluation of both composite powders and polymerized specimens. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) experiments were performed to study their thermal properties. A statistically significant increase in flexural strength was found in the 0.5, 0.75 and 1% composite groups after 6 h ball-milling, relative to the control, with the 6 h ball milling mixed specimens, presenting the highest flexural strength values. The brittle fracture type was common to all groups. An obvious improvement of the mechanical properties and a slight improvement in the thermal stability of the composite materials values were also observed as β-CPP content was increased, while T values were statistically not-affected.
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http://dx.doi.org/10.1016/j.jmbbm.2020.104094DOI Listing
December 2020

Design, characterisation and drug release study of polymeric, drug-eluting single layer thin films on the surface of intraocular lenses.

IET Nanobiotechnol 2020 Aug;14(6):501-507

Second Ophthalmology Department, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece.

To design, develop and study a novel drug delivery system for intraocular applications. The spin coating technique was applied to develop a polymeric, drug-eluting thin film consisting of a blend of organic polymers [poly (D, L lactide coglycolide) lactide: glycolide 75: 25, PLGA and polycaprolactone, PCL] and dexamethasone on the surface of intraocular lenses (IOLs). The initial durability of the IOLs during spinning was assessed. Information about the structural and optical properties of the modified IOLs was extracted using atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry. A drug release study was conducted for 8 weeks. The IOLs were durable in spinning speeds higher than the ones used to develop thin films. Single-layer thin films were successfully developed on the optics and the haptics of the lenses. The films formed nanopores with encapsulated aggregates of dexamethasone. The spectroscopic ellipsometry showed an acceptable optical transparency of the lenses regardless of the deposition of the drug-eluting films on their surface. The drug release study demonstrated gradual dexamethasone release over the selected period. In conclusion, the novel drug-eluting IOL system exhibited desired properties regarding its transparency and drug release rate. Further research is necessary to assess their suitability as an intraocular drug delivery system.
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http://dx.doi.org/10.1049/iet-nbt.2020.0005DOI Listing
August 2020

Morphological and geochemical characterization of the particulate deposits and the black crust from the Triumphal Arch of Galerius in Thessaloniki, Greece: Implications for deterioration assessment.

Sci Total Environ 2020 Sep 15;734:139455. Epub 2020 May 15.

Department of Solid State, Faculty of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.

In the present study, 12 particulate deposits and one black crust sample were collected from the Triumphal Arch of Galerius in Thessaloniki, Greece and characterized by employing a multi-analytical approach including chemical analysis of trace elements and ionic species, as well as scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS) to gain information about the micromorphology and the chemical composition in terms of major elements. In addition, one unaltered marble sample, e.g. the marble directly beneath the black crust, was examined by microscopic and isotopic methods to characterize its texture and origin. The particulate deposits consist mainly of calcite, quartz, aluminosilicate mineral phases, several metal oxides of Fe, Ti and FeCr with Mn and Cu. They also include bird droppings enriched in P and S, and plant residuals. The black crust has a similar mineral composition and is dominated by calcite with traces of quartz and halite, whereas P- and S-enriched particles are common. In both cases a coating on calcite crystals with a thin crust rich in Ca, Ba and S is commonly observed and is attributed to the previous conservation works. Concentrations of As, Zn, Pb, Cu, nitrate, sulfate, chloride and acetate were significantly higher in particle deposits than in the black crust as opposed to Fe, Co, Ni and formates that were at the same level. The traffic-related trace elements Pb, Zn and Cu and most ions were significantly higher in low-altitude deposition samples. The current marble deterioration is induced by a combination of factors, including mechanical, physico-chemical and biological processes.
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http://dx.doi.org/10.1016/j.scitotenv.2020.139455DOI Listing
September 2020

Concentration, fractionation, and ecological risk assessment of heavy metals and phosphorus in surface sediments from lakes in N. Greece.

Environ Geochem Health 2020 Sep 13;42(9):2747-2769. Epub 2020 Jan 13.

Environmental Pollution Control Laboratory, Chemistry Department, Aristotle University of Thessaloniki, 54124, Thessaloníki, Greece.

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, were investigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index I values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as "unpolluted," while many sediments in lakes Volvi and Kerkini were characterized as "moderately to heavily polluted" with regard to Cd. The descending order of potential ecological risk [Formula: see text] was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.
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http://dx.doi.org/10.1007/s10653-019-00509-xDOI Listing
September 2020

In vitro assessment of oral and respiratory bioaccesibility of trace elements of environmental concern in Greek fly ashes: Assessing health risk via ingestion and inhalation.

Sci Total Environ 2020 Feb 30;704:135324. Epub 2019 Nov 30.

GEOBIOTEC, Department of Geoscience, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.

Fly ash engender significant environmental and human health problems due to enhanced contents of potentially harmful trace elements (TrElems). This study aims to evaluate human exposure to TrElems via a combined ingestion (i.e., oral bioaccessibility) and inhalation (i.e., respiratory bioaccessibility) pathway. Five fly ash samples were collected from power plants operating in the main lignite basins of Greece, while the ingestible (<250 μm) and inhalable (<10 μm) particle size fractions were utilized. The Unified Bioaccessibility Method (UBM) was utilized to assess the oral bioaccessibility, while the respiratory bioaccessible fractions were extracted using the Artificial Lysosomal Fluid (ALF). All studied FAs exhibited significantly higher contents in Ba, Cr, Ni, V and Zn. Cadmium was presented relative enriched in the finer size fraction (<10 μm), while Ba, Co, Cr, Cu, Mn, Ni and V were depleted. The UBM-extractable concentrations fluctuated greatly among the studied FAs, while notably lower bioaccessible contents were recorded in the gastrointestinal phase. On the other hand, ALF-extractable concentrations were surprisingly higher than the corresponding UBM-extractable ones in the gastric phase. The oral bioaccessibility of the studied TrElems ranged from 12.5 to 100%, while respiratory bioaccessibility presented high values exceeding 45% on average. A significant effect of fly ash type on human bioaccessibility was revealed. Thus, high-Ca FAs exhibited significantly higher bioaccessibility of the studied TrElems via ingestion, while a relatively higher bioaccessibility via inhalation was observed for high-Si FAs. Regarding non-carcinogenic health risk via ingestion and inhalation, Cr and Co exhibited the highest HQ and HQ values, however there were significantly lower than safe level (HQ < 1). On the contrary, Cr was the dominant contributor to carcinogenic risk with CR values being well above threshold or even tolerable risk levels.
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http://dx.doi.org/10.1016/j.scitotenv.2019.135324DOI Listing
February 2020

Effect of ethanol/TEOS ratios and amount of ammonia on the properties of copper-doped calcium silicate nanoceramics.

J Mater Sci Mater Med 2019 Aug 22;30(9):98. Epub 2019 Aug 22.

School of Physics, Faculty of Sciences, Aristotle University of Thessaloniki, 54124, Thessaloníki, Greece.

Calcium magnesium silicate glasses could be suggested for the synthesis of scaffolds for hard tissue regeneration, as they present a high residual glassy phase, high hardness values and hydroxyapatite-forming ability. The use of trace elements in the human body, such as Cu, could improve the biological performance of such glasses, as Cu is known to play a significant role in angiogenesis. Nano-bioceramics are preferable compared to their micro-scale counterparts, because of their increased surface area, which improves both mechanical properties and apatite-forming ability due to the increased nucleation sites provided, their high diffusion rates, reduced sintering time or temperature, and high mechanical properties. The aim of the present work was the evaluation of the effect of different ratios of Ethanol/TEOS and total amount of the inserted ammonia to the particle size, morphology and bioactive, hemolytic and antibacterial behavior of nanoparticles in the quaternary system SiO-CaO-MgO-CuO. Different ratios of Ethanol/TEOS and ammonia amount affected the size and morphology of bioactive nanopowders. The optimum materials were synthesized with the highest ethanol/TEOS ratio and ammonia amount as verified by the enhanced apatite-forming ability and antibacterial and non-hemolytic properties.
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http://dx.doi.org/10.1007/s10856-019-6297-8DOI Listing
August 2019

In vitro evaluation of the shear bond strength and bioactivity of a bioceramic cement for bonding monolithic zirconia.

J Prosthet Dent 2019 Aug 17;122(2):167.e1-167.e10. Epub 2019 Jul 17.

Professor and Head, Laboratory of Prosthodontics, Department of Dentistry, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece. Electronic address:

Statement Of Problem: Adhesive cementation is the most common bonding strategy for zirconia restorations. Although cementation with a bioactive luting agent has been proposed as an alternative, how the bond strength compares is unclear.

Purpose: The purpose of this in vitro study was to evaluate shear bond strength after cementing a monolithic zirconia ceramic to human dentin with a bioceramic cement, compare it with a traditional cement, and evaluate its bioactive properties.

Material And Methods: A total of 120 dentin specimens and 120 yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) (BruxZir) cylindrical specimens were used. Zirconia and dentin specimens were randomly divided into 8 study groups (n=15) based on 2 luting cement types (a bioceramic cement or glass ionomer cement as control), 2 airborne-particle abrasion protocols (50 μm or 110 μm), and 2 water storage durations (24 hours or 30 days). After the shear bond strength test using a universal machine at a crosshead speed of 1 mm/min, fracture patterns were evaluated under a stereomicroscope and a scanning electron microscope. Strength values were statistically analyzed with a 3-factor ANOVA model (α=.05). Bioactivity was evaluated in simulated body fluid (SBF).

Results: The control glass ionomer cement achieved significantly greater shear bond strength compared with the tested bioceramic cement. Mean bond strength values ranged from 2.52 MPa to 5.23 MPa for the bioceramic cement tested and from 4.20 MPa to 6.61 MPa for the control cement. The duration of water storage played a significant role in the bond strength, with groups stored for 30 days reaching higher bond strength values, whereas the particle size of airborne-particle abrasion did not have a significant effect. Failure types were primarily mixed. No apatite formation was recorded on the surface of the specimens even after 30 days of immersion in SBF.

Conclusions: The evaluated cement did not develop apatite in SBF, and its bond strength values were below the control glass ionomer cement.
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http://dx.doi.org/10.1016/j.prosdent.2019.04.016DOI Listing
August 2019

Evaluation of the biological behaviour of various dental implant abutment materials on attachment and viability of human gingival fibroblasts.

Dent Mater 2019 07 3;35(7):1053-1063. Epub 2019 May 3.

Department of Prosthodontics, School of Dentistry, Faculty of Health Sciences, Aristotle University of Thessaloniki (A.U.Th), GR-54124, Thessaloniki, Greece. Electronic address:

Objective: This study aimed to investigate the biological effects of yttria-stabilized zirconia (Y-TZP) compared to other dental implant abutment materials, i.e. lithium disilicate (LS2) and titanium alloy (Ti), as well as the effects of aging of Y-TZP on viability/proliferation and attachment properties of Human Gingival Fibroblasts (HGFs).

Methods: Cylindrical specimens of each material were prepared as per manufacturer's instructions. Y-TZP specimens were divided into three groups: 1. no aging (Zr0), 2. aging for 5 h, 134 °C, 2 bars, 100% humidity (Zr5), 3. aging for 10 h under the same conditions (Zr10). Surface roughness was evaluated by optical profilometry; cell metabolic activity/viability by MTT assay, morphological changes by Scanning Electron Microscopy (SEM) and ratio of live/dead cells by confocal microscopy.

Results: Results showed statistically significant reduction of HGF metabolic activity/viability in contact with Y-TZP after aging. Nevertheless, non-aged zirconia showed no significant differences compared with LS2, Ti and control cultures. In contrast, significant stimulation of cell metabolic activity/viability was observed in HGFs exposed to LS2 eluates. Differential morphological patterns were observed for HGF in contact with different materials/treatments, with obviously increased number of dead cells and sparser distribution of HGFs cultured on Zr10 specimens. These effects were not correlated with surface topography, since Y-TZP aging did not alter surface micro-roughness.

Significance: These findings indicate that Y-TZP shows comparable biological properties to Ti and LS2 as implant abutment material. Nevertheless, Y-TZP aging might influence gingival cell attachment and proliferation properties, providing an alert to a potentially negative effect on the long-term maintenance of gingival architecture.
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http://dx.doi.org/10.1016/j.dental.2019.04.010DOI Listing
July 2019

Natural radioactivity studies in a paleontology site and paleoclimate interpretation of the last 8 Mya.

J Environ Radioact 2018 Oct 30;193-194:1-14. Epub 2018 Aug 30.

Department of Geology, School of Geology, AUTH, Thessaloniki, 54124, Greece.

Fossil bones and sediments from different horizons of the Upper Miocene paleontological site of Platania, Drama-Greece were studied using U, U, Th series and K measurements obtained by γ-spectroscopy. Additionally, SEM and XRF analysis was applied to bone and sediment samples while a lithological analysis of the sediments was also carried out. The Ra/U ratios in the fossilization layers are attributed to the U depletion from the sediment and its incorporation into the fossils. The Ra/Pa ratio indicates that the absorption of the isotopes started long before 4.2 Ma ago. The Th/K profile demonstrate two distinct geological substrates, the lower corresponding to the Upper Miocene whereas the upper to the Upper Pleistocene-Holocene. Among them mediates a Mn-rich layer associated with the "Zanclean flood" during Pliocene. One layer above the "Glacial maximum event" during the Early Pleistocene was recorded. The natural radioactive sedimentary profile obtained reproduces the paleo-climatic conditions in Southeast Europe, which could be useful for the future.
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http://dx.doi.org/10.1016/j.jenvrad.2018.08.012DOI Listing
October 2018

Evaluation of the micro-mechanical and bioactive properties of bioactive glass-dental porcelain composite.

J Mech Behav Biomed Mater 2018 10 26;86:77-83. Epub 2018 Jun 26.

School of Health Sciences, Dentistry Department, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece. Electronic address:

The aim of this study was to evaluate microhardness and elastic modulus of a novel sol-gel derived dental ceramic - 58S bioactive glass composite (BP67: Bioactive Glass:33.3%, Dental Ceramic:66.7%) BP67 material by micro-indentation and to investigate its microstructure and bioactivity. The research hypotheses were that the values of microhardness (1) and elastic modulus (2) of the novel bioceramic composite and the commercial dental ceramic will be of the same order. The experimental sol-gel derived ceramics showed similar microstructural characteristics to a commercial feldspathic porcelain, and presence of additional calcium phosphate phases, which contributed its bioactivity. The formation of an apatite-like layer on the materials' surface observed by Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) techniques after 12 days of maintenance in Conventional Simulated Body Fluid (cSBF) solution. The BP67 exhibited values of microhardness and modulus of elasticity which were not statistically significant different compared to dental ceramic, indicating the adequate mechanical integrity of the material. The results of this study suggest that the novel bioactive composite could be potentially applied in prosthetic dentistry, while its thermal and optical properties should be investigated in future studies.
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http://dx.doi.org/10.1016/j.jmbbm.2018.06.019DOI Listing
October 2018

Bactericidal and Bioactive Dental Composites.

Front Physiol 2018 16;9:103. Epub 2018 Feb 16.

Department of Orthodontics and Pediatric Dentistry, University of Michigan, Ann Arbor, MI, United States.

Antimicrobial and bioactive restorative materials are needed to develop a bacteria free environment and tight bond with the surrounding tissue, preventing the spread of secondary caries and thus extending the lifetime of dental restorations. The characteristic properties of new dental bioactive and antibacterial composites are presented in this work. The new composites have been microstructurally characterized and both long and short term properties have been studied. The Ag-doped sol-gel derived bioactive glass (Ag-BG) was incorporated into resin composite in concentrations 5, 10, and 15 wt.%, to fabricate new Ag-doped bioactive and antibacterial dental composites (Ag-BGCOMP). The microstructural properties and elemental analysis of the developed Ag-BGCOMP was observed. The total bond strength (TBS) was measured immediately and after long term of immersion in medium using microtensile testing. The capability of Ag-BGCOMPs to form apatite layer on their surface after immersion in Simulated Body Fluid (SBF) as well as the bacteria growth inhibition in a biofilm formed by () were evaluated. Homogeneous distribution of Ag-BG particles into the resin composite was observed microstructurally for all Ag-BGCOMPs. The TBS measurements showed non-statistically significant difference between control samples (Ag-BG 0 wt.%) and Ag-BGCOMP specimens. Moreover, the total bond strength between the surrounding tooth tissue and the material of restoration does not present any statistically significant change for all the cases even after 3 months of immersion in the medium. The bioactivity of the Ag-BGCOMPs was also shown by the formation of a calcium-phosphate layer on the surface of the specimens after immersion in SBF. Antibacterial activity was observed for all Ag-BGCOMPs, statistically significant differences were observed between control samples and Ag-BGCOMPs. Accordingly, the number of dead bacteria in the biofilm found to increase significantly with the increase of Ag-BG concentration in the Ag-BGCOMPs. New resin composites with antibacterial and remineralizing properties have been manufactured. Characterization of these materials provides a rationale for future clinical trials to evaluate clinical benefits and outcomes in comparison with currently used dental materials. The new developed composites could ultimately prevent restoration failure and could advance patients' wellbeing.
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http://dx.doi.org/10.3389/fphys.2018.00103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5820345PMC
February 2018

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

J Prosthet Dent 2018 Apr 18;119(4):632-642. Epub 2017 Sep 18.

Professor, Department of Fixed Prosthesis & Implant Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki, Greece. Electronic address:

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 manufacturer's 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 (ΔE) was calculated using the equation [ΔΕ= [(ΔL*) + (Δa*) + (Δb*)]½]. Intraexaminer reliability was assessed by using the intraclass correlation coefficient. Two-way analysis of variance was used for the analysis of ΔΕ, and the parameters L*, a*, and b* were analyzed with linear mixed models for repeated measurements and the Bonferroni pair-wise comparison test (α=.05).

Results: Parameters ΔΕ, L*, a*, and b* were significantly affected by the interaction between material and treatment (P<.001). A ΔΕ >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 (ΔΕ<3.7), except PNG in tea which showed statistically significant color differences (ΔΕ>4). CAD presented higher color stability compared with the nonglazed Press specimens.
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http://dx.doi.org/10.1016/j.prosdent.2017.04.031DOI Listing
April 2018

Magnetic signature, geochemistry, and oral bioaccessibility of "technogenic" metals in contaminated industrial soils from Sindos Industrial Area, Northern Greece.

Environ Sci Pollut Res Int 2017 Jul 4;24(20):17041-17055. Epub 2017 Jun 4.

Department of Mineralogy-Petrology-Economic Geology, Faculty of Geology, School of Geology, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece.

The objective of this study was to assess the contamination level of potentially harmful elements (PHEs) in industrial soils and how this relates to environmental magnetism. Moreover, emphasis was given to the determination of the potential mobile fractions of typically "technogenic" metals. Therefore, magnetic and geochemical parameters were determined in topsoils (0-20 cm) collected around a chemical industry in Sindos Industrial Area, Thessaloniki, Greece. Soil samples were presented significantly enriched in "technogenic" metals such Cd, Pb, and Zn, while cases of severe soil contamination were observed in sampling sites north-west of the industrial unit. Contents of Cd, Cr, Cu, Ni, Pb, Mo, Sb, Sn, and Zn in soils and pollution load index (PLI) were highly correlated with mass specific magnetic susceptibility (χ ). Similarly, enrichment factor (EF) and geoaccumulation index (I ) for "technogenic" Pb and Zn exhibited high positive correlation factors with χ . Principal component analysis (PCA) classified PHEs along with the magnetic variable (χ ) into a common group indicating anthropogenic influence. The water extractable concentrations were substantially low, while the descending order of UBM (Unified BARGE Method) extractable concentrations in the gastric phase was Zn > Pb > As > Cd, yet Cd showed the highest bioaccessibility (almost 95%).
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http://dx.doi.org/10.1007/s11356-017-9355-0DOI Listing
July 2017

Reinforcement of a PMMA resin for interim fixed prostheses with silica nanoparticles.

J Mech Behav Biomed Mater 2017 05 9;69:213-222. Epub 2017 Jan 9.

School of Health Sciences, Department of Dentistry, Section of Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece. Electronic address:

Purpose: Fractures in long span provisional/interim restorations are a common complication. Adequate fracture toughness is necessary to resist occlusal forces and crack propagation, so these restorations should be constructed with materials of improved mechanical properties. The aim of this study was to investigate the possible reinforcement of neat silica nanoparticles and trietoxyvinylsilane-modified silica nanoparticles in a PMMA resin for fixed interim restorations.

Materials And Methods: Composite PMMA-Silica nanoparticles powders were mixed with PMMA liquid and compact bar shaped specimens were fabricated according to the British standard BS EN ISO 127337:2005. The single-edge notched method was used to evaluate fracture toughness (three-point bending test), while the dynamic thermomechanical properties (Storage Modulus, Loss Modulus, tanδ) of a series of nanocomposites with different amounts of nanoparticles (0.25%, 0.50%, 0.75%, 1% w.t.) were evaluated. Statistical analysis was performed and the statistically significant level was set to p<0.05.

Results: The fracture toughness of all experimental composites was remarkably higher compared to control. There was a tendency to decrease of fracture toughness, by increasing the concentration of the filler. No statistically significant differences were detected among the modified/unmodified silica nanoparticles. Dynamic mechanical properties were also affected. By increasing the silica nanoparticles content an increase in Storage Modulus was recorded, while Glass Transition Temperature was shifted at higher temperatures.

Conclusions: Under the limitations of this in-vitro study, it can be suggested that both neat silica nanoparticles and trietoxyvinylsilane-modified silica nanoparticles, especially at low concentrations, may enhance the overall performance of fixed interim prostheses, as can effectively increase the fracture toughness, the elastic modulus and the Glass Transition Temperature of PMMA resins used in fixed provisional restorations.
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http://dx.doi.org/10.1016/j.jmbbm.2017.01.013DOI Listing
May 2017

An experimental bioactive dental ceramic for metal-ceramic restorations: Textural characteristics and investigation of the mechanical properties.

J Mech Behav Biomed Mater 2017 02 28;66:95-103. Epub 2016 Oct 28.

Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece. Electronic address:

The aim of this study was the evaluation of the textural characteristics of an experimental sol-gel derived feldspathic dental ceramic, which has already been proven bioactive and the investigation of its flexural strength through Weibull Statistical Analysis. The null hypothesis was that the flexural strength of the experimental and the commercial dental ceramic would be of the same order, resulting in a dental ceramic with apatite forming ability and adequate mechanical integrity. Although the flexural strength of the experimental ceramics was not statistically significant different compared to the commercial one, the amount of blind pores due to processing was greater. The textural characteristics of the experimental ceramic were in accordance with the standard low porosity levels reported for dental ceramics used for fixed prosthetic restorations. Feldspathic dental ceramics with typical textural characteristics and advanced mechanical properties as well as enhanced apatite forming ability can be synthesized through the sol-gel method.
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http://dx.doi.org/10.1016/j.jmbbm.2016.10.019DOI Listing
February 2017

Enrichment and oral bioaccessibility of selected trace elements in fly ash-derived magnetic components.

Environ Sci Pollut Res Int 2017 Jan 4;24(3):2337-2349. Epub 2016 Nov 4.

Institute of Nanoscience and Nanotechnology, NCRS "Demokritos", 15310 Aghia Paraskevi, Athens, Greece.

The mineralogy, morphology, and chemical composition of magnetic fractions separated from fly ashes (FAs) originating from Greek lignite-burning power plants was investigated. The oral bioaccessibility of potentially harmful elements (PHEs) from the fly ash magnetic fractions (FAMFs) was also assessed using in vitro gastrointestinal extraction (BARGE Unified Bioaccessibility Method, UBM). The FAMFs isolated were in the range 4.6-18.4%, and their mass specific magnetic susceptibility ranged from 1138 × 10 to 1682 × 10 m/kg. XRD analysis and Mossbauer spectroscopy indicated that the dominant iron species were Fe-rich aluminosilicate glass along with magnetite, hematite, and maghemite (in decreasing order). The raw FAs exhibited differences in their chemical composition, indicating the particularity of every lignite basin. The elemental contents of FAMFs presented trends with fly ash type; thus, the FAMFs of high-Ca FAs were enriched in siderophile (Cr, Co, Ni) and lithophile (Cs, Li, Rb) elements and those separated from low-Ca FAs were presented depleted in chalcophile elements. Based on UBM extraction tests, the PHEs were more bioaccessible from the non-magnetic components of the FAs compared to the magnetic ones; however, the bioaccessible fractions estimated for the FAMFs were exceeding 40 % in many cases. Arsenic was found to be significantly bioaccessible (median ~ 80 %) from FAMFs despite the lower As contents in the magnetic fraction.
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http://dx.doi.org/10.1007/s11356-016-7967-4DOI Listing
January 2017

Odontogenic differentiation and biomineralization potential of dental pulp stem cells inside Mg-based bioceramic scaffolds under low-level laser treatment.

Lasers Med Sci 2017 Jan 26;32(1):201-210. Epub 2016 Oct 26.

Department of Fixed Prosthesis and Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, GR-54124, Greece.

This study aimed to investigate the potential of low-level laser irradiation (LLLI) to promote odontogenic differentiation and biomineralization by dental pulp stem cells (DPSCs) seeded inside bioceramic scaffolds. Mg-based, Zn-doped bioceramic scaffolds, synthesized by the sol-gel technique, were spotted with DPSCs and exposed to LLLI at 660 nm with maximum output power of 140 mw at fluencies (a) 2 and 4 J/cm to evaluate cell viability/proliferation by the MTT assay and (b) 4 J/cm to evaluate cell differentiation, using real-time PCR (expression of odontogenic markers) and a p-nitrophenylphosphate (pNPP)-based assay for alkaline phosphatase (ALP) activity measurement. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used for structural/chemical characterization of the regenerated tissues. Exposure of the DPSCs/scaffold complexes to the proposed LLLI scheme was associated with statistically significant increase of odontogenesis-related markers (bone morphogenetic protein 2 (BMP-2): 22.4-fold, dentin sialophosphoprotein (DSPP): 28.4-fold, Osterix: 18.5-fold, and Runt-related transcription factor 2 (Runx2): 3.4-fold). ALP activity was significantly increased at 3 and 7 days inside the irradiated compared to that in the non-irradiated SC/DPSC complexes, but gradually decreased until 14 days. Newly formed Ca-P tissue was formed on the SC/DPSC complexes after 28 days of culture that attained the characteristics of bioapatite. Overall, LLLI treatment proved to be beneficial for odontogenic differentiation and biomineralization of DPSCs inside the bioceramic scaffolds, making this therapeutic modality promising for targeted dentin engineering.
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http://dx.doi.org/10.1007/s10103-016-2102-9DOI Listing
January 2017

Inducing bioactivity of dental ceramic/bioactive glass composites by Nd:YAG laser.

Dent Mater 2016 11 24;32(11):e284-e296. Epub 2016 Sep 24.

Department of Fixed Prosthesis and Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece. Electronic address:

Objectives: Aims of this study were to investigate the optimal conditions of laser irradiation of a novel Bioactive Glass/Dental Ceramic-BP67 composite for acceleration of hydroxyapatite-HA formation and to assess cellular responses on the precipitated HA region.

Methods: BP67 (Bioactive Glass: 33.3%, Dental Ceramic: 66.7%) was fabricated by the sol-gel method. A laser assisted biomimetic-LAB process was applied to BP67 sintered specimens immersed in 1.5-times concentrated simulated body fluid-1.5×-SBF. The effect of various energy densities of pulsed nanosecond Nd-YAG (1064nm) laser and irradiation exposure times (30min, 1 and 3h) were evaluated for HA precipitation. The HA film was characterized by FTIR, XRD, SEM and micro Raman techniques. ICP-AES was used for revealing changes in chemical composition of the 1.5×-SBF during irradiation. Cell viability and morphological characteristics of periodontal ligament fibroblasts-PDLFs, human gingival fibroblasts-HGFs and SAOS-2 osteoblasts on the HA surface were evaluated by MTT assays and SEM.

Results: At optimal energy fluence of 1.52J/cm and irradiation time for 3h followed by immersion in 1.5×-SBF at 60°C, a dense HA layer was formed on laser-irradiated BP67 within 7 days. The resulting HA film was tightly bonded to the underlying substrate and had mineral composition similar to cementum. MTT assay showed a consistent reduction of cell proliferation on the HA layer in comparison to conventional control ceramic and BP67 for all 3 cell lines studied.

Significance: These findings suggest LAB is an effective method for acceleration of HA formation on materials with low bioactivity, while cellular responses need further investigation.
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http://dx.doi.org/10.1016/j.dental.2016.09.029DOI Listing
November 2016

Human treated dentin matrices combined with Zn-doped, Mg-based bioceramic scaffolds and human dental pulp stem cells towards targeted dentin regeneration.

Dent Mater 2016 08 11;32(8):e159-75. Epub 2016 Jun 11.

Department of Fixed Prosthesis & Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece. Electronic address:

Objective: This study aimed to investigate the potential of Mg-based bioceramic scaffolds combined with human treated-dentin matrices (hTDMs) and dentinogenesis-related morphogens to promote odontogenic differentiation and dentin-like tissue formation by Dental Pulp Stem Cells-DPSCs.

Methods: DPSC cultures were established and characterized by flow cytometry. Experimental cavities were prepared inside crowns of extracted teeth and demineralized by EDTA (hTDMs). Zn-doped, Mg-based bioceramic scaffolds, synthesized by the sol-gel technique, were hosted inside the hTDMs. DPSCs were spotted inside the hTDMs/scaffold constructs with/without additional exposure to DMP-1 or BMP-2 (100ng/ml, 24h). Scanning Electron Microscopy-SEM, live/dead fluorescence staining and MTT assay were used to evaluate cell attachment and viability; Real time PCR for expression of osteo/odontogenic markers; Inductively Coupled Plasma-Atomic Emission Spectrometry-ICP/AES for scaffold elemental release analysis; ELISA for hTDM growth factor release analysis; SEM and X-ray Diffraction-XRD for structural/chemical characterization of the regenerated tissues.

Results: Scaffolds constantly released low concentrations of Mg(2+), Ca(2+), Zn(2+) and Si(4+), while hTDMs growth factors, like DMP-1, BMP-2 and TGFβ-1. hTDMs/scaffold constructs supported DPSC viability, inducing their rapid odontogenic shift, indicated by upregulation of DSPP, BMP-2, osteocalcin and osterix expression. Newly-formed Ca-P tissue overspread the scaffolds partially transforming into bioapatite. Exposure to DMP-1 or BMP-2 pronouncedly enhanced odontogenic differentiation phenomena.

Significance: This is the first study to validate that combining the bioactivity and ion releasing properties of bioceramic materials with growth factor release by treated natural dentin further supported by exogenous addition of key dentinogenesis-related morphogens (DMP-1, BMP-2) can be a promising strategy for targeted dentin regeneration.
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http://dx.doi.org/10.1016/j.dental.2016.05.013DOI Listing
August 2016

Characterization, heavy metal content and health risk assessment of urban road dusts from the historic center of the city of Thessaloniki, Greece.

Environ Geochem Health 2017 Jun 30;39(3):611-634. Epub 2016 May 30.

Environmental Pollution Control Laboratory, Chemistry Department, Aristotle University of Thessaloniki, 54124, Thessaloníki, Greece.

In the present study, an investigation of the mineralogy and morphology, the heavy metal content and the health risk of urban road dusts from the second largest city of Greece was conducted. For this reason road dust samples from selected sites within the city core area were collected. No differences were observed in the mineralogy of road dusts coming from different sampling sites, and they were mainly consisted of quartz and calcite, while an elevated amorphous content was detected. Morphologically road dusts presented Ca-rich, Fe-rich and silicates particles with various shapes and sizes. The mean concentrations of Cd, Cr, Cu, Mn, Ni, Pb and Zn in road dust were 1.76, 104.9, 662.3, 336.4, 89.43, 209 and 452.8 μg g, respectively. A series of spatial distribution patterns revealed that the hotspot areas were tended to associate with major road junctions and regions with high traffic. Combination of pollution indexes and statistical analyses (correlation analysis, cluster analysis and principal component analysis) revealed that road dusts have a severe influence by anthropogenic activities. In attempt to identify the source of metals through geostatistical and multivariate statistical analyses, it was concluded as follows: Cr, Cu, Fe and Zn mainly originated from tire/break wear and vehicle abrasions, while Cd, Mn and Pb were mainly related to fuel/oil leakage from automobiles along with oil lubricants and vehicle abrasion. Hazard quotient values for children based on total metal concentrations for the road dust ingestion route were lower than safe level (=1). However, the fact that the Hazard Index value for Pb (0.459) which is a particularly toxic metal, was close to safe level, renders essential further investigation in order to provide more reliable characterizations of potential health risks.
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http://dx.doi.org/10.1007/s10653-016-9836-yDOI Listing
June 2017

Sol-Gel Derived Mg-Based Ceramic Scaffolds Doped with Zinc or Copper Ions: Preliminary Results on Their Synthesis, Characterization, and Biocompatibility.

Int J Biomater 2016 14;2016:3858301. Epub 2016 Feb 14.

Dentistry Department, Laboratory of Fixed Prosthesis and Implant Prosthodontics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.

Glass-ceramic scaffolds containing Mg have shown recently the potential to enhance the proliferation, differentiation, and biomineralization of stem cells in vitro, property that makes them promising candidates for dental tissue regeneration. An additional property of a scaffold aimed at dental tissue regeneration is to protect the regeneration process against oral bacteria penetration. In this respect, novel bioactive scaffolds containing Mg(2+) and Cu(2+) or Zn(2+), ions known for their antimicrobial properties, were synthesized by the foam replica technique and tested regarding their bioactive response in SBF, mechanical properties, degradation, and porosity. Finally their ability to support the attachment and long-term proliferation of Dental Pulp Stem Cells (DPSCs) was also evaluated. The results showed that conversely to their bioactive response in SBF solution, Zn-doped scaffolds proved to respond adequately regarding their mechanical strength and to be efficient regarding their biological response, in comparison to Cu-doped scaffolds, which makes them promising candidates for targeted dental stem cell odontogenic differentiation and calcified dental tissue engineering.
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http://dx.doi.org/10.1155/2016/3858301DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4769780PMC
March 2016

Study of road dust magnetic phases as the main carrier of potentially harmful trace elements.

Sci Total Environ 2016 May 27;553:380-391. Epub 2016 Feb 27.

Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.

Mineralogical and morphological characteristics and heavy metal content of different fractions (bulk, non-magnetic fraction-NMF and magnetic fraction-MF) of road dusts from the city of Thessaloniki (Northern Greece) were investigated. Main emphasis was given on the magnetic phases extracted from these dusts. High magnetic susceptibility values were presented, whereas the MFs content of road dust samples ranged in 2.2-14.7 wt.%. Thermomagnetic analyses indicated that the dominating magnetic carrier in all road dust samples was magnetite, while the presence of hematite and iron sulphides in the investigated samples cannot be excluded. SEM/EDX analyses identified two groups of ferrimagnetic particles: spherules with various surface morphologies and textures and angular/aggregate particles with elevated heavy metal contents, especially Cr. The road dusts (bulk samples) were dominated by calcium, while the mean concentrations of trace elements decreased in the order Zn > Mn > Cu > Pb > Cr > Ni > V > Sn > As > Sb > Co > Mo > W > Cd. MFs exhibited significantly higher concentrations of trace elements compared to NMFs indicating that these potentially harmful elements (PHEs) are preferentially enriched in the MFs and highly associated with the ferrimagnetic particles. Hazard Index (HI) obtained for both adults and children through exposure to bulk dust samples were lower or close to the safe level (=1). On the contrary, the HIs for the magnetic phases indicated that both children and adults are experiencing potential health risk since HI for Cr was significantly higher than safe level. Cancer risk due to road dust exposure is low.
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http://dx.doi.org/10.1016/j.scitotenv.2016.02.149DOI Listing
May 2016

Effect of heat treatment and in vitro aging on the microstructure and mechanical properties of cold isostatic-pressed zirconia ceramics for dental restorations.

Dent Mater 2014 Oct 17;30(10):e272-82. Epub 2014 Jun 17.

Department of Fixed Prosthesis and Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, Greece. Electronic address:

Objectives: The temperature variations during the veneering firing cycles of a zirconia dental ceramic can negatively affect its mechanical properties. A possible synergistic effect of both heat-treatment and aging while exposed to the oral environment could result to catastrophic failure. The aim of the present study was to investigate the effect of heat treatment followed during veneering and in vitro aging on the mechanical and microstructural properties of zirconia dental ceramics.

Methods: Three specimens from each of two zirconia blocks (Ivoclar IPS e.max ZirCAD (IV) and Wieland ZENO Zr (WI)) were cut by CAD/CAM technology, fully sintered and polished. Each one was cut in four equal parts. One part was used as control (C), one was heat-treated (H), one was aged (A) (134°C, 2bar, 10h) and one was heat-treated and subsequently aged (HA). The mechanical properties (nano-hardness (H) and elastic modulus (E*)) were investigated by nano-indentation tests while the surface characterization was carried out with XRD, FTIR and SEM.

Results: Different treatments on IV and WI samples resulted in a reduction of both H and E* values, however the differences were not statistically significant (p>0.05). The combination of treatments imposes an overall effect (p<0.001), enhancing the influence on both H and E* values. This reduction in mechanical properties was followed by an increase of monoclinic content. Greater variations in both H and E* values were recorded for WI samples.

Significance: The clinical performance of zirconia dental ceramics may be affected during firing and aging resulting in increased probability of failure.
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http://dx.doi.org/10.1016/j.dental.2014.05.017DOI Listing
October 2014

Flexural strength and the probability of failure of cold isostatic pressed zirconia core ceramics.

J Prosthet Dent 2012 Aug;108(2):84-95

Department of Fixed Prosthesis and Implants Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Statement Of Problem: The flexural strength of zirconia core ceramics must predictably withstand the high stresses developed during oral function. The in-depth interpretation of strength parameters and the probability of failure during clinical performance could assist the clinician in selecting the optimum materials while planning treatment.

Purpose: The purpose of this study was to evaluate the flexural strength based on survival probability and Weibull statistical analysis of 2 zirconia cores for ceramic restorations.

Material And Methods: Twenty bar-shaped specimens were milled from 2 core ceramics, IPS e.max ZirCAD and Wieland ZENO Zr, and were loaded until fracture according to ISO 6872 (3-point bending test). An independent samples t test was used to assess significant differences of fracture strength (α=.05). Weibull statistical analysis of the flexural strength data provided 2 parameter estimates: Weibull modulus (m) and characteristic strength (σ(0)). The fractured surfaces of the specimens were evaluated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The investigation of the crystallographic state of the materials was performed with x-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR) spectroscopy.

Results: Higher mean flexural strength (P<.001) and σ(0) were recorded for WZ ceramics. However IZ ceramics presented a higher m value and a microstructure with fewer voids and pores. The fractured surfaces presented similar fractographic properties (mirror regions followed by hackle lines zones). Both groups primarily sustained the tetragonal phase of zirconia and a negligible amount of the monoclinic phase.

Conclusions: Although both zirconia ceramics presented similar fractographic and crystallographic properties, the higher flexural strength of WZ ceramics was associated with a lower m and more voids in their microstructure. These findings suggest a greater scattering of strength values and a flaw distribution that are expected to increase failure probability.
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http://dx.doi.org/10.1016/S0022-3913(12)60112-7DOI Listing
August 2012

Microstructural characterization and comparative evaluation of physical, mechanical and biological properties of three ceramics for metal-ceramic restorations.

Dent Mater 2008 Oct 16;24(10):1362-73. Epub 2008 Apr 16.

School of Dentistry, Geology Department, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Objectives: A wide variety of dental ceramics compositions have been introduced in dental clinical practice in order to combine desired aesthetics with superior mechanical performance. The aim of the present study was to investigate the microstructural changes in three dental ceramics after their sintering according to manufacturers' instructions and to comparatively evaluate some of their physical, mechanical and biological properties.

Methods: The analysis of the phases present in each material before and after sintering was performed with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). The thermal properties of ceramic specimens were evaluated with differential thermal and thermogravimetric analysis (TG-DTA). The mechanical properties evaluated were fracture toughness, Young's modulus and microhardness with the Vickers indentation method. MTT assay was used for cell proliferation assessment. One-way analysis of variance (ANOVA) with Bonferroni multiple comparisons tests was used to determine statistically significant differences (significance level of p<0.05).

Results: Results showed a remarkable variation among the three ceramic compositions of leucite content in the starting unheated ceramic powders ranging between 14 and 32 wt.% and in the respective sintered powders ranging between 15 and 41 wt.% The low fusing glass-ceramic and the high fusing leucite-based ceramic presented significantly higher fracture toughness (p<0.001) and microhardness and lower modulus of elasticity (p<0.05) compared to the low fusing feldspathic ceramic. The three ceramics were almost equivalent concerning their in vitro biological behavior.

Significance: Variations in crystal structure, distribution and composition are related to differences concerning mechanical properties of dental ceramics.
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http://dx.doi.org/10.1016/j.dental.2008.03.002DOI Listing
October 2008
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