Papers by Author: Xanthippi Chatzistavrou

Abstract: In most biphasic composite systems consisting of sol-gel derived bioactive glass and a second system that is usually used as a reinforcing agent, thorough stirring is necessary to prevent the precipitation of the grains of the second system. Consequently, the aim of this work is to investigate the impact of various stirring rates on the crystallinity and bioactivity of a bioactive glass in the system 58S. Sol-gel-derived bioactive glass (58S) was produced as described in literature. During the gelation, stirring rates of 0, 200, 400, 600 and 800 rpms were applied producing, respectively, the corresponding glass powders. The in vitro bioactivity of the powders was tested in Simulated Body Fluid (SBF) for various immersion times, while the solution was renewed after 6h, 24h and then every 2 days. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffractometry (XRD) were used to characterize all materials before and after immersion in SBF solution. FTIR and XRD measurements of all powders revealed mainly the formation of an amorphous glass, while the main crystalline phase was identified to be Ca2SiO4. After immersion in SBF solution for 12h, SEM microphotographs revealed apatite formation on the surface of all samples, while FTIR and XRD confirmed the aforementioned findings. Furthermore, since EDS analysis proved a mean molar Ca/P ratio of about1.7 after 6 days of immersion of all samples- besides those stirred at 400 and 600rpm- it can be assumed that a thick apatite layer was formed covering the whole surface.

Abstract: Scaffold-based tooth engineering is currently the most popular approach towards replacing dental tissues or even engineering a bio-tooth. Although, various scaffold materials have been employed in tooth regeneration, the scaffold-based tooth design has, until now, achieved only limited success. Recently, bioactive Mg-based ceramics have attracted interest as Mg plays an important role on skeletal metabolism and affects the quality and structure of hard dental tissues. Mg has been reported to improve the mechanical properties of calcium phosphate ceramics, control biodegradation rate and stabilize the cell-material interface improving cell attachment and growth. The aim of this study was the development of an experimental Mg-based ceramic material, with enhanced bioactivity and adequate mechanical properties, in order to be potentially used in dental tissue regeneration. The Mg-based ceramic was prepared by the sol-gel method, while the stabilization was performed at 1300, 1400 and 1450oC in order a fully crystalline material to be obtained. The characterization of the materials -before and after immersion is Simulated Body Fluid (SBF)- was performed by Fourier Tranform Infrared Spectroscopy (FTIR), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy associated with an EDS analyzer (SEM-EDS), while the flexural strength of uniaxially pressed pellets was measured using a universal testing machine for 3- point bending tests (Instron 3344). FTIR spectra and XRD patterns of all powder samples before immersion in SBF solution confirmed the presence of three crystalline phases; akermanite, merwinite and diopside. The onset of apatite formation on the surface of all powders was observed even after three days of immersion, while the apatite formation on the surface of the sintered pellets was slightly delayed. Flexural strength values were in the range of 30Mpa. In conclusion, Mg-based glass-ceramics attain adequate mechanical integrity and high rate of bioactivity and could be potentially used in the construction of ceramic scaffolds for dental tissue regeneration.

Abstract: The aim of this work was to improve a newly developed family of glass-ceramic composite materials by incorporating silver ions in the ceramic structure, thus developing new Ag-doped materials with the ability of showing antibacterial activity for dental applications. Two different sol-gel methodologies were applied for the fabrication of colorless, homogenous and chemically durable materials which can slowly release silver ion for relatively long periods. Both methods led to the successful development of Ag-doped glass-ceramics with silver ions incorporated in the structure that can slowly release in buffer solution, during a period of 45 days. The potential, application of these materials involve the development of bioactive surfaces on dental substrates which can seal the marginal gap creating a bacterial free environment finally supporting the success of dental restorations.

Abstract: The aim of this study was the fabrication using a sol-gel technique of a new glass-ceramic with potential use in dental applications. The characterization of the composition and microstructural properties of the produced material confirmed the similarity between the new sol-gel derived glass-ceramic and a commercial leucite based fluorapatite dental glass-ceramic. The produced material has potential application in dental restorations and it is expected to exhibit better control of composition, microstructure and properties due to the intrinsic advantages of the sol-gel preparation method.

Abstract: Thermal treatment of bioactive glasses can affect their microstructure and thus their bioactivity. The aim of this study was the characterization of the thermally treated sol-gel-derived bioactive glass 58S at characteristic temperatures and the dependence of its bioactive behavior on the specific thermal treatment. The thermal behavior of the bioactive glass was studied by thermal analysis (TG/DTA). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffractometry (XRD) were used for the characterization of the bioactive glass. The bioactive behavior in Simulated Body Fluid (SBF) was examined by Scanning Electron Microscopy (SEM-EDS) and FTIR. The major crystal phases after thermal treatment were Calcium Silicates, Wollastonite and Pseudowollastonite, while all thermally treated samples developed apatite after 48 hours in SBF. A slight enhancement of bioactivity was observed for the samples heated at the temperature range 910-970oC.

Abstract: Sol-gel derived glasses have been reported to express considerably higher bioactivity than melt-derived ones. The use of the sol-gel method for the fabrication of dental ceramic bioactive glass composites has resulted in composites consisting of an amorphous glassy network into which crystals of Calcium Silicate (CS), Wollastonite (W), leucite (Lt) and Fluorapatite (FAp) are dispersed. Thus, the aim of the present study was the investigation of the bioactivity of sol-gel derived dental ceramic/bioactive glass composites, in the form of powders and in thermally treated disk shaped specimens. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to characterize the reacted products. The sol-gel derived dental glass ceramic composites present high bioactivity compared to the respective melt-derived ones, which is attributed to the higher CaO content and the crystallization of bioactive W and CS crystal phases during the fabrication process. However, the powdered samples presented faster HCAp formation compared to the respective specimens, due to their higher surface energy.

Abstract: In this study new ternary bioactive mixtures were investigated, which are appropriate for applications as coatings on the surface of dental ceramics. The fabrication of mixtures based on the combination of dental ceramic, hydroxyapatite and bioactive glass was demonstrated. The mixtures were characterized by FTIR, XRD and SEM and their bioactive behavior was investigated by immersion in Simulated Body Fluid (SBF). The ternary mixture consisted of a high fusing leucite-feldspathic dental ceramic which exhibited the highest bioactive behavior assigned to the characteristic crystal phases occurring under the specific heat treatment investigated.

Abstract: In this study the fabrication and characterization of a novel sol-gel derived HAp-CaO composite material is investigated. The bioactive behavior of the fabricated composite was assessed by immersion studies in SBF. A brittle and weakly crystalline carbonate hydroxyapatite (HCAp) layer was found to develop few hours after the immersion in SBF confirming high bioactivity. The presence of CaO accelerates the formation of HCAp phase.

Abstract: Melt derived bioactive glass- porcelain system is reported to be bioactive but with a slow rate of bioactivity. The aim of this work is to fabricate and characterize bioactive glass/dental porcelain composites produced by the sol-gel method. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffractometry (XRD) were used to characterize the fabricated materials. The FTIR spectra and the XRD patterns confirm the presence of both constituents in the mixtures, while the dominant crystal phases in bioactive glass/dental porcelain specimens are leucite and wollastonite.

Abstract: Dental ceramic-bioactive glass composites support the attachment and proliferation of human periodontal ligament cells, while their immersion in a simulated body fluid (SBF) results in the precipitation of biological hydroxyapatite further supporting cell proliferation [1]. The aim of the present study was the comparative evaluation of three dental ceramic-bioactive glass composites’ crystal structure relative to bioactive glass amount and the evaluation of their bioactivity. All composites consisted of leucite and Na2CaSi3O9 crystals dispersed in amorphous glassy matrix. Leucite and Na2CaSi3O9 crystals decreased significantly in all composites with the highest amount of dental ceramic, which did not precipitated apatite during the examined immersion time in SBF. An increase of Na2CaSi3O9 crystals in the composites with the highest amount of bioactive glass resulted in faster apatite formation. Increased bioactivity was linearly correlated to increased amount of bioactive glass.