242 research outputs found
Thermocycling effects on resin bond to silicatized and silanized zirconia
Various techniques have been introduced to create a durable resin composite bond to sintered zirconia (Y-TZP). Shear bond strength values achieved through tribochemical treatment have been investigated in numerous studies, but less is reported about long-term durability. The objective here was to evaluate the effects of thermocycling and silane on shear bond strength of a composite luting cement to silicatized Y-TZP. Two groups of Y-TZP (Procera Zirconia, Nobel Biocare), both consisting of 40 specimens were prepared. The specimen surfaces were air particle abraded with silica-coated aluminum trioxide particles (particle size 110 Οm, duration 15 s, air pressure 300 kPa, nozzle distance 10 mm). The silica-coated surfaces in group ZA were silanized with an acrylate-functional silane (Experimental laboratory-made acrylate silane, Toray Dow Corning Silicone) and in the other group ZM with a pre-activated methacrylate silane (ESPE Sil, 3M ESPE). The surfaces were coated with adhesive system (Scotchbond 1, 3M ESPE) and photo-polymerized for 10 s. Resin composite luting cement (RelyX ARC, 3M ESPE) stubs were bonded to substrates and photo-polymerized for 40 s. The test specimens were thermocycled for 0, 1000, 3000, 8000 or 15 000 times (temperature 5-55°C, exposure time 20 s). The shear bond strengths of luting cement to ceramics were measured with a crosshead speed of 1.0 mm/min. ANOVA was used for statistical analysis. ANOVA revealed that both silane and thermocycling affected significantly (p < 0.001) the shear bond strength. Short term hydrolytic stability of acrylate silane was superior. It was concluded that evaluation of bonding requires extended thermocycling. Š 2009 VSP.postprin
Effect of primers and resins on the shear bond strength of resin composite to zirconia
Objective. To evaluate the effects of various surface conditioning methods and agents. Methods. The intaglio zirconia substrates were air particle abraded with Al2O3 (Ă 50âÎźm) for 10âs. An air pressure of 450âkPa and a nozzle distance of 10âmm were used. Surface conditioning by groups: Aâ=âsilane coupling agent â+âorganophosphate adhesive; Bâ=âorganophosphate primer + silane coupling agent + organophosphate adhesive; Câ=âorganophosphate primer; Dâ=âmethacrylate adhesive; Eâ=âthiophosphate primerâ+âmethacrylate adhesive. Composite stubs were bonded to substrates and photo-polymerized. The specimens were thermocycled 8000 times 55Âą1âC and 5Âą1âC and kept in distilled water for 14âd. The shear bond strengths were measured with a universal testing machine. Results. Shear bond strengths (MPa Âą SD): Group A 25.8Âą6.7, Group B 26.5Âą8.6, Group C 16.7Âą8.5, Group D 2.6Âą0.7, and Group E 4.2Âą1.2. ANOVA: significant differences among groups (P<.05). Groups A and B: mainly cohesive fractures, Group C: mixed or adhesive fractures, Groups D and E: adhesive fractures. Conclusions. A value of 10â13âMPa is the minimum acceptable shear bond strength. Groups A, B, and C exceeded this limit, Groups D and E could not achieve the limit.published_or_final_versio
Fracture strength and fractographic analysis of zirconia copings treated with four experimental silane primers
This study evaluated and compared the effect of new four experimental silane coupling agents on the fracture strength of zirconia copings. The findings were supported with fractographic and finite element analyses. All together 125 zirconia copings with a ?wall thickness of 0.6mm were fabricated on identical nickel-chromium master dies and then divided randomly into five groups (n=25). Four test groups were prepared according the experimental silane primer (labeled: OIWA1, OIWA2, OIWA3 and OIWA4) ?and one control group without silanization. The silane monomers used were: ?3-methacryloxypropyltrimethoxysilane (in OIWA1), ?3-acryloxypropyltrimethoxysilane (in OIWA2), ?3-?isocyanatopropyltriethoxysilane (in OIWA3) and styrylethyltrimethoxysilane (in OIWA4). Tribochemical sandblasting (silica-coating) treatment was performed to the inner surface of the copings in the ?test groups. All the specimens were silanized at the inner surfaces of the zirconia copings. Self-?adhesive universal resin cement was used to cement the copings to ?the underlying master die. Zirconia copings were vertically loaded on the ?cusp ?area until the first crack failure was occurred using Precision Universal Tester ?at a ?constant crosshead speed of 1mm/min. Then, the machine ?was manually controlled to cause more failure ?to further determine the texture of fracture. Three dimensional finite element analysis and fractography were performed to support the fracture strength findings. Based on the finite element analysis results, zirconia silanized with ?3-acryloyloxypropyltrimethoxysilane showed the highest fracture strength with a mean of ?963.75?N (SD 4.5N), while zirconia copings silanized with ?3-methacryloyloxypropyltrimethoxysilane showed a mean fracture strength value of ?925.65N (SD 2.4N). Styrylethyltrimethoxysilane-silanised zirconia showed mean fracture strength of 895.95N (SD 3.5N). Adding silane coupling agents to the resin-zirconia interface increased the fracture strengths significantly (ANOVA, p<0.05). Silanization with four new experimental silane primers in vitro produced significantly ?greater fracture strength than the control group not treated with the test silane.
Characterization of Conventional and High-Translucency Y-TZP Dental Ceramics Submitted to Air Abrasion
Protein Phosphatase 2A Mediates Dormancy of Glioblastoma Multiforme-Derived Tumor Stem-Like Cells during Hypoxia
The hypoxic microenvironment of glioblastoma multiforme (GBM) is thought to increase resistance to cancer therapies. Recent evidence suggests that hypoxia induces protein phosphatase 2A (PP2A), a regulator of cell cycle and cell death. The effects of PP2A on GBM tumor cell proliferation and survival during hypoxic conditions have not been studied.Expression of PP2A subunits and HIF-Îą proteins was measured in 65 high-grade astrocytoma and 18 non-neoplastic surgical brain specimens by western blotting. PP2A activity was measured by an immunoprecipitation assay. For in vitro experiments, GBM-derived tumor stem cell-like cells (TSCs) were exposed to severe hypoxia produced by either CoClâ or 1% Oâ. PP2A activity was inhibited either by okadaic acid or by shRNA depletion of the PP2A C subunit. Effects of PP2A activity on cell cycle progression and cell survival during hypoxic conditions were assessed using flow cytometry.In our patient cohort, PP2A activity was positively correlated with HIF-1â protein expression (Pâ=â0.002). Patients with PP2A activity levels above 160 pMP had significantly worse survival compared to patients with levels below this threshold (Pâ=â0.002). PP2A activity was an independent predictor of survival on multivariable analysis (Pâ=â0.009). In our in vitro experiments, we confirmed that severe hypoxia induces PP2A activity in TSCs 6 hours after onset of exposure. PP2A activity mediated G1/S phase growth inhibition and reduced cellular ATP consumption in hypoxic TSCs. Conversely, inhibition of PP2A activity led to increased cell proliferation, exhaustion of intracellular ATP, and accelerated P53-independent cell death of hypoxic TSCs.Our results suggest that PP2A activity predicts poor survival in GBM. PP2A appears to reduce the metabolic demand of hypoxic TSCs and enhances tumor cell survival. Modulation of PP2A may be a potential target for cancer therapy
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
Azimuthal anisotropy of charged particles at high transverse momenta in PbPb collisions at sqrt(s[NN]) = 2.76 TeV
The azimuthal anisotropy of charged particles in PbPb collisions at
nucleon-nucleon center-of-mass energy of 2.76 TeV is measured with the CMS
detector at the LHC over an extended transverse momentum (pt) range up to
approximately 60 GeV. The data cover both the low-pt region associated with
hydrodynamic flow phenomena and the high-pt region where the anisotropies may
reflect the path-length dependence of parton energy loss in the created medium.
The anisotropy parameter (v2) of the particles is extracted by correlating
charged tracks with respect to the event-plane reconstructed by using the
energy deposited in forward-angle calorimeters. For the six bins of collision
centrality studied, spanning the range of 0-60% most-central events, the
observed v2 values are found to first increase with pt, reaching a maximum
around pt = 3 GeV, and then to gradually decrease to almost zero, with the
decline persisting up to at least pt = 40 GeV over the full centrality range
measured.Comment: Replaced with published version. Added journal reference and DO
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