Key Engineering Materials Vols. 493-494

Abstract: Results of the present study provide strong indications towards the effective application of the 110oC Thermoluminescence (TL) peak in discriminating between different bioactive responses for the case of the 58S bioactive glass. The in vitro bioactivity of this glass in the form of powder in SBF solution was tested for various immersion times, ranging between 0 and 6 days. This TL peak is ubiquitously present in all 58S samples, for all immersion times. The intensity of the110oC TL peak was proven to be very sensitive to the different bioactive responses, indicating a strongly decreasing pattern with increasing immersion time in SBF, easily identifying thus the loss of silica. This loss is reflected to the decrease of the 110oC TL peak intensity, which appears to be fast even for the shorter immersion times. The 110oC TL glow peak intensity and sensitization could also be yielding a time scale regarding the beginning of some among the several stages included in the bioactivity sequence.

Abstract: Bioactive glasses not only can bond to hard tissues of the body, are also able to release ions that have stimulatory effects on cells and so are regarded as promising candidate materials for gene activating purposes in tissue engineering applications. In this research the effect of co-substitution of Magnesium and Zinc for Calcium on bioactivity of binary sol-gel derived glass 70S30C (70 mol. % SiO₂, 30 mol. % CaO) was investigated. Calcium phosphates forming ability tests and investigation of glass degradation products in simulated body fluid (SBF) were performed as follows.After sol-gel synthesis of glass powders of comparable and under 38 μm particle size distributions, their state of being amorphous was investigated using X-ray diffraction. Then for in vitro investigation of bioactivity, ion release, pH change and Calcium phosphate formation during immersion of glass powders in SBF at 37 ͦ C up to 2 weeks were studied. Infrared spectroscopy was performed on the reacted glass powders.Results indicate that substitution of Zinc for Calcium suppresses crystalline apatite formation more effectively than substitution of Magnesium for Calcium and help us design modified compositions of magnesium and zinc containing bioactive glasses that can find applications in bone and also cartillage tissue engineering.

Abstract: Modification of surface morphology and composition of niobophosphate glass and glass-ceramic in the system P₂O₅-CaO-Nb₂O₅-Na₂O was investigated. Amorphous, partly crystalline and crystalline samples were prepared in shape of pellet with diameter 10 mm. Samples were treated in 1 and 5 days in citric acid at 37°C and 3h in boiling HCl. Surface morphology before and after treatment was investigated by scanning electron microscopy (SEM), phase composition by X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Glass sample was smooth, after treatment in citric acid it had cracks and pit-holes on the surface. Partly crystalline sample was smooth and contained inclusions of crystalline Ca₃(PO₄)₂ and Ca₂P₂O₇. Platy crystals of Ca₃(PO₄)₂ dissolved first, than bulky Ca₂P₂O₇. Crystalline samples contained Na₄Nb₈P₄O₃₂ and calcium phosphate phases; surface was rough before and after treatment. EDX showed that amount of phosphorous is proportional to amount of calcium and inversely proportional to amount of sodium and niobium in glass-ceramic samples.

Abstract: In this study, it was aimed to produce bioactive glasses (SiO₂-CaO-P₂O₅-Na₂O-SrO) with the substitution of strontium in different weight percentages. Physical, thermal, and in vitro biological properties of the glasses were studied and compared to each other. In vitro simulated body fluid studies were performed to investigate the bioactivity of the produced glass samples. Scanning electron microscopy, X-ray diffraction, ultraviolet spectroscopy and inductively coupled plasma techniques were used to monitor changes in the glass surface and SBF composition. The results showed that all glasses favored precipitation of calcium phosphate layer when they were soaked in SBF; however bioactivity of the glasses increased with the increase of strontium content in the glasses.

Abstract: Human beings are often infected by microorganisms in the living environment. Among various natural and inorganic substances, silver or silver ions have a powerful antibacterial activity. In the present study, the bioactivity and antibacterial activity of the SiO₂–CaO–P₂O₅–Ag₂O was compared with that of its ternary counterpart glass system (as a control sample) in vitro. The molar ratio of silver oxide in the bioactive glass composition was considered as different amount (0.5%, 1% and 2%). The surface characterization was evaluated after soaking in simulated body fluid (SBF). The sharpest apatite peak in X-ray diffraction (XRD) analyse after 7 days soaking in SBF was observed for 2% Ag sample (2%Ag-BG). Hence, the antibacterial effects of 2%Ag-BG sample against 2 gram negatives bacterium were examined by agar plate test. The result showed that the amount of silver did not prevent the HAp formation. Also, the antibacterial properties of 2%Ag-BG sample indicated near 100% bactericidal ratio (according to the width of antibacterial halo).

Abstract: End temperature of the firing cycle, during processing of dental ceramics, directs the interaction of both sintering and crystallization pathways, tailoring physicochemical properties and bioactivity. Thus, the purpose of the present study was to investigate the influence of end temperature over the structural properties and composition, along with the bioactive behavior of dental porcelain, modified by bioactive glass. Sol-gel derived specimens of bioactive glass (58S)- commercial dental porcelain composites synthesized (BP) and underwent firing cycles at the crystallization temperature (Tc=1040oC) and the temperature just below the melting range (Tm=1080oC), as the composite material. The recommended temperature for the commercial porcelain (Ta=930oC) was examined, too. All specimens were characterized using X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM). The assessment of bioactivity was performed in vitro, via the detection of apatite layer development. The well-defined particles, observed by SEM, at 930oC, developed contact formation during the stage of neck growth at 1040oC and 1080oC, indicating the initiation of sintering process. Increasing temperature, the complex porei network became smoother, while spherical and closed porei were evident. FTIR revealed the predominance of wollastonite at the increased temperatures, along with the appearance of cristobalite, while XRD confirmed the results. Finally, the in vitro tests evidenced the bioactivity of the specimens independently of the final temperature, though the increased temperature caused delayed apatite layer formation on their surface. The, microstructural and chemical evolution of the studied composite is temperature-dependent. Increased temperature favored the sintering process initiation, along with the surface crystallization, which delays bioactivity.

Abstract: Lime phosphosilicate and soda lime phosphosilicate glasses prepared by sol-gel method were precursors of bioactive glass-ceramics. The structure of the samples and the distribution of the [SiO₄] units was investigated by X-ray diffraction and infrared spectroscopy. Human osteosarcoma cell line (MG63) was used for the in vitro cellular response. DNA staining (Hoechst 33258) assay was performed for assessing samples colonization.

Abstract: The purpose of this study was to evaluate the effects of various root canal treatment methods on bonding strength of a glass-fıber post to root canal dentin. 60 human maxillary anterior teeth were prepared with ParaPost (Coltène) up to diameter of 1.75 mm with drills of 1.14, 1.25, 1.40, 1.50 and 1.75 mm from 1 mm coronal level of apices. The upper surfaces of polished areas were ground to acquire correct angle with the long axis of drills and the specimens were divided into 6 groups (n=10). Glass-fiber posts (1.5mm) (everStick POST, StickTech) were cemented with a dual-cure composite resin cement (ParaCem, Coltène) after following treatment methods. (Group 1) 0.9% isotonic NaCl solution (control), (Group 2) 2.5% NaOCl + Er:YAG Laser (Kavo K-E-Y), (Group 3) 2% Chlorhexidine + Er:YAG Laser , (Group 4) Slurry Bioactive Glass Granules (Vivoxid), (Group 5) Silane-based Primer (3M, ESPE, RelyX) + Er:YAG Laser, (Group 6) Slurry Bioactive Glass Granules + Silane-based Primer + Er:YAG Laser. From each root, two disks of 2 mm thickness was obtained. The push-out test was carried out by using a universal testing device (Lloyd LRX) with a loading tip (diameter 1.7 mm, crosshead speed of 1.0 mm/min) until loosening of the post. Statistical analysis was performed using ANOVA followed by post-hoc comparisons (Tukey B, p<0.05). Root canals were evaluated by SEM. Bond strength of fiber posts were significantly affected by the type of treatment (p<0.05). The highest bond strength was observed in Group 5, whereas the lowest bond strength values were recorded with the Group 3. Bond strength of glass-fiber post to root canal dentin was affected by treatment method. Treatment with laser and Bioactive Glass Granules in combination of using silane yielded the highest bond strength.

Abstract: The purpose of this study was to evaluate the effects of silanization of the glass on denture base materials and to evaluate different types of glasses. A total of 136 Poly(methyl methacrylate) (PMMA) (Palapress – Heraeus Kulzer) blocks were prepared in dimensions of 65mm x 10mm x 3mm. PMMA blocks were modified by different ratios of non-silanized and silanized Bioactive Glass Granules (BAG) (Vivoxid) and Inert Glass Granules (IG) (Vivoxid). The blocks were polished under water cooling and divided into 17 groups. (Group 1) No glass (control), (Group 2-5) 3-6-9-12% non-silanized BAG, (Group 6-9) 3-6-9-12% silanized BAG, (Group 10-13) 3-6-9-12% non-silanized IG, (Group 14-17) 3-6-9-12% silanized IG. The specimens were stored in distilled water and weighed (Mettler, Toledo) in days of 1, 2, 3, 7, 14, 21, 30, 45, 60. After water sorption test, the specimens were dried under 80°C and weighed in days of 0, 1, 2, 3, 5, 7, 9 for calculating the solubility values. Statistical analysis was performed using analysis of variance (ANOVA) followed by post-hoc comparisons (Dunnett T3, p<0.05). Water sorption and solubility values were significantly affected by the type and silanizaion of the glass (p<0.05). The highest water sorption value was observed in 12% silanized IG group (1,83±0,04%), whereas the lowest sorption values were recorded with 12% non-silanized BAG group (1,21±0,07%). Contrarily, The highest solubility value was observed in 12% non-silanized BAG group (0,98±0,03%), whereas the lowest solubility values were recorded with 12% non-silanized BAG group (0,34±0,03%). Water sorption and solubility values were affected by the type and silanization of the glass. Silanization improved the physical properties of the glass as well as the properties of the denture base material.

Abstract: It has been reported that there is a slight equilibrium between calcite and apatite precipitation from SBF solution during typical bioactivity assays, once it is supersaturating in both ionic precursors. In order to better understand this mechanism, we have proposed here to evaluate the role of three different aqueous medium (water, SBF and McCoy), under equilibrium (agitation) and out of equilibrium (no agitation).