Lithium disilicates are commercially important and among the most widely studied and well-characterized glass-ceramics, but their toughening mechanism – and those of most glass-ceramics – is still ...unknown. In this work, stoichiometric lithium disilicate glasses were used as a model system and crystallized using carefully designed and controlled two-stage heat treatments to give different crystallized volume fractions while maintaining a constant grain size of approximately 12μm. This original procedure allowed us to separately control the effects of these two microstructural parameters on the mechanical properties of the glass-ceramic. The hardness, elastic modulus, four-point bending strength, indentation fracture toughness and double-torsion fracture toughness were measured for samples with different crystallized volume fractions, ranging from the parent glass to fully crystallized samples. We found that the bending strength increases rapidly with crystallization at crystal volume fractions below 10% and reaches a value 2.5 times greater than that of the original glass. For a fully crystallized sample, the fracture toughness increases almost fivefold, from 0.75 to 3.5MPa.m1/2. Laser confocal microscopy was used to reveal the topography of the fracture surfaces. Three mechanisms that contribute to toughening – crack deflection, crack bowing and trapping, and crack bridging – were evaluated. A model incorporating the elastic modulus, crystal fracture toughness and crystallized volume fraction was proposed and successfully tested to explain the increased fracture toughness with crystallized volume fraction for the full range of crystallization in LS2 glass-ceramics.
The objective of this study was to compare the efficacy of Biosilicate and Duraphat in the treatment of dentin hypersensitivity (DH).
This clinical trial was conducted with young adults presenting ...DH. A visual analogue scale (VAS) was used to assess the level of pain, using volatile and tactile tests. Forty participants presenting two teeth with DH were included, and these teeth were divided into two groups according to the treatment: Biosilicate or Duraphat. Each product was randomly applied on one tooth per participant once a week for 4 weeks and evaluated every 15 days for 60 days after the last application.
The mean and standard deviation (SD) of VAS values for the initial volatile sensitivity evaluation were 6.18 (1.99) and 6.08 (1.98) for the Biosilicate and Duraphat groups, respectively, and at the fourth week 0.48 (1.5) and 0.83 (1.58). After 60 days, the volatile sensitivity showed the following values: 0.63 (1.19) for Biosilicate and 1.03 (1.07) for Duraphat. The intragroup comparison showed a significant reduction of mean VAS values for DH-related pain assessed by volatile testing for both groups (p<0.001), and the assessment at the 60-day follow-up showed mean values statistically similar to those obtained at the end of treatment. Initial tactile sensitivity observed was 1.48 (2.39) for the Biosilicate and 1.4 (2.2) for the Duraphat group and at the 60-day follow-up 0.23 (0.73) and 0.15 (0.36), respectively, with significant statistical difference (p<0.002). When the reduction in tactile and volatile sensitivities between both groups was compared, no statistically significant difference was observed.
This study indicated that both products were able to promote an important reduction in dentin hypersensitivity with similar results within a 60-day follow-up.
The main purpose of the present work was to evaluate if low laser level therapy (LLLT) can improve the effects of Biosilicate®/PLGA (BS/PLGA) composites on cell viability and bone consolidation using ...a tibial defects of rats. The composites were characterized by scanning electron microscope (SEM) and reflection Fourier transform infrared spectrometer (FTIR). For the in vitro study, fibroblast and osteoblast cells were seeded in the extract of the composites irradiated or not with LLLT (Ga-Al-As, 808nm, 10J/cm2) to assess cell viability after 24, 48 and 72h. For the in vivo study, 80 Wistar rats with tibial bone defects were distributed into 4 groups (BS; BS+LLLT; BS/PLGA and BS/PLGA+LLLT) and euthanized after 2 and 6weeks. Laser irradiation Ga-Al-As (808nm, 30J/cm2) in the rats was performed 3 times a week. The SEM and FTIR results revealed that PLGA were successfully inserted into BS and the microparticles degraded over time. The in vitro findings demonstrated higher fibroblast viability in both BS/PLGA groups after 24h and higher osteoblast viability in BS/PLGA+LLLT in all periods. As a conclusion, animals treated with BS/PLGA+LLLT demonstrated an improved material degradation and an increased amount of granulation tissue and newly formed bone.
•The microparticles of PLGA inserted into BS degraded over time, leaving pores into the material.•Biosilicate®/PLGA composites irradiated with LLLT improve the osteoblasts viability.•Biosilicate®/PLGA associated to LLLT were effective in stimulating bone formation in an experimental model of tibial defect.
This study evaluated effects of Bioglass 45S5 (BG) and Biosilicate (BS) remineralization on the chemical composition and bond strength of control dentin (CD) and bleached dentin (BD) surfaces.
Dentin ...bleaching treatment was performed using the walking bleaching technique with 0.01 g of sodium perborate and 0.5 mL of 3% hydrogen peroxide for 14 days. Remineralization treatment was carried out by rubbing a remineralization solution (0.015 g of BG or BS diluted in 1.35 mL of distilled water) on the etched dentin surface for 30 seconds. Micro-Raman spectroscopy (MRS) was used to quantitatively analyze the mineral matrix ratios of CD and BD (n=5) after remineralization treatment with BG and BS over 15 days of incubation in artificial saliva. The CD and BD discs (n=10) with and without remineralization treatment with BG and BS were restored using a two-step etch-and-rinse adhesive system (Optibond S, Kerr) and five layers of 1-mm-thick composite resin (Filtek Z250, 3M ESPE). The restored dentin discs were sectioned into nine bonded beams with cross-sectional areas of approximately 0.9 mm
and tested for microtensile bond strength (μTBS). The dentin surface of one fractured beam per tooth was submitted to MRS to characterize the physicochemical composition (n=10) at the interface. The data were analyzed using one-way analysis of variance and the Tukey-Kramer post hoc test (
<0.005).
MRS bioactive analyses revealed that both BG and BS promoted increased mineral matrix ratios in the CD and BD. Significantly higher μTBS values were found after CD treatment with BG (CD: 57 MPa±11; CD-BG: 78 MPa±15) and when BG and BS were applied to the BD (BD: 42 MPa±5; BD-BG: 71 MPa±14; BD-BS: 64 MPa±11) (
<0.005). The MRS analysis of the fractured dentin beam showed that the remineralization treatment significantly increased the dentin relative mineral concentration and promoted the appearance of new interface peaks, indicating a chemical interaction (
<0.005).
Remineralization of BD is an effective therapy to restore damage caused by dentin bleaching and acid conditioning. This approach not only increases dentin mineral compounds but also improves dentin's ability to interact chemically with the adhesive system.
Glass-forming ability (GFA) is the easiness to vitrify a liquid on cooling, while glass stability (GS) is the glass resistance against devitrification on heating; but it is questionable if there is ...any direct relationship between these two parameters. Therefore, to test this possibility, we assess and compare GFA and several GS parameters through quantitative criteria. GFA and GS were calculated for six stoichiometric glass forming oxides that only present surface (heterogeneous) crystallization in laboratory time scales: GeO2, Na2O·2SiO2, PbO·SiO2, CaO·Al2O3·2SiO2, CaO·MgO·2SiO2 and 2MgO·2Al2O3·5SiO2; plus Li2O·2SiO2 and Li2O·2B2O3 that, in addition to surface nucleation, also present homogeneous (internal) crystallization. We gauge GFA by the critical cooling rate, qcr, which was calculated from an estimated number of heterogeneous nucleation sites per unit surface, Ns, and from experimental crystal growth rates, u(T), assuming a detectable surface crystallized fraction Xc=0.001. We define GS parameters by fourteen different combinations of the following characteristic differential thermal analysis (DTA) or differential scanning calorimetry (DSC) temperatures: the glass transition temperature (Tg), the onset crystallization temperature on heating (Txh), the peak crystallization temperature on heating (Tch), and the melting point (Tm). To obtain the experimental GS parameters for each glass we carried out DSC runs using coarse and fine powders, and completed the necessary data with literature values for Tm. The results for fine and coarse particles were quite similar. Most of the GS parameters that consist of three characteristic DSC temperatures show excellent correlation with GFA, however, rather poor correlations were observed for parameters that use only two characteristic temperatures. We thus demonstrated that certain, but not all GS parameters can be used to infer GFA.
•Fabrication of waveguides in Transparent Glass-Ceramic (TGC) via fs-laser writing.•Buried waveguides in Magnesium Aluminum Silicate (MAS) TGC and its precursor glass.•Single mode (precursor glass) ...and ring mode (MAS-TGC) were obtained.•Femtosecond laser writing technique.•Strengthened photonic devices.
Transparent glass-ceramics (TGC) have been investigated to replace hard, mechanically strong, scratch resistant materials in ballistic armor applications and smart phone displays. Certain types of TGC have superior performance than borosilicate and soda-lime glasses, and are much easier to produce, especially large parts, than transparent mono or polycrystalline ceramics. Thereupon, transparent glass-ceramics could be feasible in other applications, such as stronger photonic devices. In this work, we used femtosecond laser pulses to inscribe optical waveguides inside a magnesium aluminum silicate (MAS) precursor glass and glass-ceramic, which has shown satisfactory mechanical properties to be applied as ballistic armor. Single mode waveguides for the precursor glass and ring mode for MAS-TGC were obtained and characterized (total insertion loss, mode profile, and threshold energy for heat diffusion at different fabrication depths). Micro-Raman measurements on the microfabricated waveguide core and on the pristine material surface show some difference for the TGC, but none for the glass. Particularly, we found that the threshold energy for heat diffusion is higher in the MAS glass-ceramic than in its parent glass. Its good optical waveguiding and mechanical properties indicate that this new TGC might be adequate for photonic devices that require mechanically competent materials.
Abstract The characterization and conservation of castor accessions in germplasm bank are essential in order to breeding programs achieve its goals. Despite Brazil having the 4th largest castor ...germplasm bank in the world, castor diversity in Brazil remains little explored. Thus, this study aimed at characterize castor accessions collected in different Brazilian regions by means of 31 morphoagronomic traits and gray mold reaction. Forty accessions of the Universidade do Estado de São Paulo (UNESP), Botucatu, SP, Brazil, germplasm bank were evaluated. Genetic parameters were estimated for the quantitative traits, and the accessions were grouped by Ward method using the standardized Euclidean distance and the simple coincidence index for quantitative and qualitative data, respectively. Qualitative and quantitative traits were important to understand and differentiate castor accessions. The accessions showed a high variation regarding the castor gray mold reaction. The accessions assessed in this study have been preserved and can be used as a source for genetic variability in the development of new castor varieties in breeding programs.
The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission ...electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between
T
g (742°C) and the DSC crystallization peak (
T=1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt
3Fe, detected by EDS and SAD–TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite.
Updated definition of glass-ceramics Deubener, J.; Allix, M.; Davis, M.J. ...
Journal of non-crystalline solids,
12/2018, Letnik:
501
Journal Article
Recenzirano
Odprti dostop
Glass-ceramics are noted for their unusual combination of properties and manifold commercialized products for consumer and specialized markets. Evolution of novel glass and ceramic processing routes, ...a plethora of new compositions, and unique exotic nano- and microstructures over the past 60 years led us to review the definition of glass-ceramics. Well-established and emerging processing methods, such as co-firing, additive manufacturing, and laser patterning are analyzed concerning the core requirements of processing glass-ceramics and the performance of the final products. In this communication, we propose a revised, updated definition of glass-ceramics, which reads “Glass-ceramics are inorganic, non-metallic materials prepared by controlled crystallization of glasses via different processing methods. They contain at least one type of functional crystalline phase and a residual glass. The volume fraction crystallized may vary from ppm to almost 100%”.
•An updated definition of glass-ceramics (GCs) is provided.•GCs are prepared by controlled crystallization of glasses via different processing methods.•GCs contain at least one type of functional crystalline phase and a residual glass.•The volume fraction crystallized of a GC may vary from ppm to almost 100%.
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