The Experts below are selected from a list of 20883 Experts worldwide ranked by ideXlab platform
Socrates Dokos - One of the best experts on this subject based on the ideXlab platform.
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a multiphysics biventricular cardiac model simulations with a left ventricular assist device
Frontiers in Physiology, 2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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Data_Sheet_1_A Multiphysics Biventricular Cardiac Model: Simulations With a Left-Ventricular Assist Device.pdf
2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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a multiphysics biventricular cardiac model simulations with a left ventricular assist device
Frontiers in Physiology, 2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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Video_5_A Multiphysics Biventricular Cardiac Model: Simulations With a Left-Ventricular Assist Device.AVI
2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
Jack L Ferracane - One of the best experts on this subject based on the ideXlab platform.
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kinetics of polymerization and Contraction Stress development in self adhesive resin cements
Dental Materials, 2012Co-Authors: A Frassetto, Jack L Ferracane, Giulio Marchesi, Lorenzo Breschi, Chiara Ottavia Navarra, Gianluca Turco, R Di Lenarda, Milena CadenaroAbstract:Abstract Objectives The aim of the study was to evaluate the Contraction Stress, microhardness and polymerization kinetics of three self-adhesive cements vs. conventional dual-cure resin cement. Methods Cements tested were: RelyX Unicem (3M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Clearfil SA Cement (Kuraray, Tokyo, Japan) and Duolink (Bisco Inc., Schaumburg, IL, USA). Cements were irradiated with a LED-curing unit (bluephase, IvoclarVivadent) for 20 or 40 s and the Contraction forces (N) generated during polymerization were continuously recorded for 6 h with a universal testing machine. Polymerization kinetics were monitored using micro-Raman spectroscopy and degree of conversion was calculated. Vickers microhardness was also recorded. All measurements were performed at 10 min and 6 h. Data were statistically analyzed by three-way ANOVA with repeated measures and Tukey's post hoc test ( α = 0.05). Results Irrespective of exposure time, Stress analysis ranked in the following order: Clearfil SA Cement p p Significance The conventional resin-based cement showed higher Stress values than the self-adhesive cements. The results were material-dependent and probably correlated to the composition of each material.
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effect of shrinkage strain modulus and instrument compliance on polymerization shrinkage Stress of light cured composites during the initial curing stage
Dental Materials, 2010Co-Authors: Sun Hong Min, Jack L Ferracane, Inbog LeeAbstract:Abstract Objectives The aim of this study was to investigate the influence of shrinkage strain, modulus, and instrument compliance on the polymerization shrinkage Stress measurement of light-cured composites, and to determine whether the silorane-based low-shrinkage composite shows a low-polymerization shrinkage Stress. Methods A universal hybrid; Z250 (Z2), a flowable; Z350 (Z3), and a silorane-based; P90 (P9) composite was examined. A modified “bonded disc method” was used to measure the axial shrinkage strain of the composite. For the measurement of the initial modulus development of composites during light curing, a dynamic oscillatory shear test was undertaken using a custom-made oscillation rheometer. A frequency of 6 Hz and strain amplitude of 0.0091 rad for 20 s was employed and the complex shear modulus ( G * ) was determined. A newly designed Stress–strain analyzer was made to measure the shrinkage Stress of the composites with two modes: (1) high compliance, or (2) low compliance. The shift between the two modes was controlled by an On–Off switch of a negative feedback circuit. Theoretical shrinkage Stress was calculated from the shrinkage strain and modulus measured above, and compared with experimentally measured Stress. Data were analyzed with one-way ANOVA and Tukey's post hoc test ( α = 0.05), and correlation analysis was done to investigate the relationship between measured Stress and shrinkage strain, modulus, and theoretical Stress. Results The shrinkage strain of Z3 (4.12%) at 10 min was the highest, followed by Z2 (2.31%) and P9 (0.77%). At 10 s after light curing, Z2 showed the highest modulus (466.2 MPa), Z3 (154.1 MPa), and P9 the lowest (130.7 MPa). The measured Stresses with low compliance were much higher than those with high compliance. With high compliance, the Contraction Stress of Z3 was the highest (2.75 MPa), followed by Z2 (1.54 MPa) and P9 (0.48 MPa). In low-compliance mode, the Stresses of Z3 (7.93 MPa) and Z2 (7.48 MPa) were similar ( p = 0.323) while the Stress of P9 (3.23 MPa) was much lower. A strong correlation was observed between the theoretical Stress and the measured Stress with low compliance ( R = 0.996). In high-compliance mode, the shrinkage strain also showed a near-linear relationship with the Stress measured ( R = 0.937), but the modulus showed a low correlation with the measured Stress ( R = 0.398). Significance Depending on the instrument compliance, polymerization shrinkage Stress showed significant differences for each material. In high-compliance shrinkage strain played a greater role, while in low-compliance shrinkage strain and elastic modulus contributed comparably in determining the shrinkage Stress. The low-shrinkage silorane-based composite demonstrated considerable reduction in shrinkage strain and Stress.
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Contraction Stress of low shrinkage composite materials assessed with different testing systems
Dental Materials, 2010Co-Authors: Giulio Marchesi, Jack L Ferracane, Lorenzo Breschi, Francesca Antoniolli, Roberto Di Lenarda, Milena CadenaroAbstract:Objectives. The Contraction Stress of a silorane-based material and a new low-shrinkage nanohybrid composite were compared to three conventional dimethacrylate-based resin composites using two different measuring systems. It was hypothesized that the silorane-based material and the low-shrinkage nanohybrid composite would exhibit lower Contraction Stress than dimethacrylate-based composites irrespective of measuring system. Methods. The materials tested were Filtek Silorane LS (3M ESPE), Venus Diamond (Heraeus Kulzer), Tetric EvoCeram (Ivoclar Vivadent), Quixfil (Dentsply DeTrey), and Filtek Z250 (3M ESPE). Shrinkage Stress was assessed using a Stress–strain analyzer consisting of two opposing attachments, one connected to a load sensor and the other fixed to the device, or a system fixed to a universal testing machine with an extensometer as a feedback system. All specimens were light-cured with 20 J/cm 2
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determination of the optimal photoinitiator concentration in dental composites based on essential material properties
Dental Materials, 2009Co-Authors: L Musanje, Jack L Ferracane, R L SakaguchiAbstract:Abstract Objectives The aim of this study was to determine the concentrations of the photosensitizer (camphoroquinone, CQ) and coinitiator (ethyl-4-dimethylaminobenzoate, EDMAB) that resulted in maximum conversion but generated minimum Contraction Stress in experimental composites. Methods Experimental composites were prepared with an identical resin formulation [TEGDMA:UDMA:bis-GMA of 30.25:33.65:33.65]. Five groups of resin were prepared at varied CQ concentrations (0.1, 0.2, 0.4, 0.8 and 1.6 wt% of the resin). Five subgroups of resin were prepared at each level of CQ concentration, by adding EDMAB at 0.05, 0.1, 0.2, 0.4 and 0.8 wt% of the resin, resulting in 25 experimental resins. Finally, strontium glass (∼3 μm) and silica (0.04 μm) were added at 71.5 and 12.6 wt% of the composite, respectively. Samples ( n = 3) were then evaluated for Knoop hardness (KHN), degree of conversion (DC), depth of cure (DoC) and Contraction Stress (CS). Results There was an optimal CQ and EDMAB concentration that resulted in maximum DC and KHN, beyond which increased concentration resulted in a decline in those properties. KHN testing identified two regions of maxima with best overlaps occurring at CQ:EDMAB ratio of 1.44:0.42 and 1.05:1.65 mol%. DC evaluation showed one region of maximum, the best overlap occurring at CQ:EDMAB ratio of 2.40:0.83 mol%. DoC was 4 mm. Overall, maximum CS was attained before the system reached the maximum possible conversion and hardness. Significance (1) Selection of optimal photoinitiator/amine concentration is critical to materials’ formulation, for excessive amounts can compromise materials’ properties. (2) There was no sufficient evidence to suggest that Contraction Stress can be reduced by lowering CQ/EDMAB concentration without compromising DC and KHN.
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effect of irradiance and light source on Contraction Stress degree of conversion and push out bond strength of composite restoratives
American Journal of Dentistry, 2009Co-Authors: Leonardo Goncalves Cunha, Jack L Ferracane, Roberta Caroline Bruschi Alonso, Carmem S Pfeifer, Mario Fernando De Goes, Mario Alexandre Coelho SinhoretiAbstract:Purpose To evaluate the influence of five curing methods on Contraction Stress, Stress rate, and degree of conversion (DC) of a composite and on bond strength of composite restoratives. Methods For the Stress test, composite was applied between two 5-mm diameter glass rods, mounted in a servohydraulic machine. Stress rates were calculated as the change in Stress vs. time. DC was measured by FTIR. Bond strength testing was performed using a push-out test in bovine incisors. The C-factor was 3.0 for all tests. Five methods were evaluated: High Intensity LED (LED HI), Continuous Halogen Light (QTH CL), Medium Intensity LED (LED MI), Low Intensity LED (LED LI), and Pulse Delay Halogen Light (QTH PD). Results were analyzed by ANOVA and Tukey's test (alpha = 0.05). Results Stress values ranged from 9.25 MPa (QTH PD) to 10.46 MPa (LED MI). No statistical difference was observed among the methods. Bond strength values ranged from 24.6 MPa (LED HI) to 35.4 MPa (QTH PD), with the QTH PD presenting a statistically higher value compared to the other methods. Stress rate and bond strength presented an inverse linear correlation (r2 = 0.79). LED HI presented the highest maximum Stress rate, followed by LED MI, QTH CL, LED LI, and QTH PD. The reduction in Stress rate observed for the low intensity groups was associated with a general increase in bond strength, with no adverse effect on the degree of conversion of the restorative composite.
Azam Ahmad Bakir - One of the best experts on this subject based on the ideXlab platform.
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a multiphysics biventricular cardiac model simulations with a left ventricular assist device
Frontiers in Physiology, 2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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Data_Sheet_1_A Multiphysics Biventricular Cardiac Model: Simulations With a Left-Ventricular Assist Device.pdf
2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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a multiphysics biventricular cardiac model simulations with a left ventricular assist device
Frontiers in Physiology, 2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
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Video_5_A Multiphysics Biventricular Cardiac Model: Simulations With a Left-Ventricular Assist Device.AVI
2018Co-Authors: Azam Ahmad Bakir, Amr Al Abed, Michael C Stevens, Nigel H Lovell, Socrates DokosAbstract:Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-Contraction equations were adapted to trigger myocardial Contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) Contraction Stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.
Ning Liu - One of the best experts on this subject based on the ideXlab platform.
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mechanism of post weld heat treatment cracking in rene 80 nickel based superalloy
Materials Science and Technology, 2002Co-Authors: L C Lim, Ning LiuAbstract:AbstractMicrostructural studies carried out on Rene 80 (approximate composition 60Ni–14Cr–9.5Co–4Mo–5Ti–3Al–0.17C–Zr–B, wt-%) weldments before and after post-weld heat treatment (PWHT) revealed abundant evidence of constitutionally liquated and resolidified grain boundaries extending from the mushy zone into the heat affected zone (HAZ). While total dissolution of γ' occurred along such grain boundaries, a much lesser degree of γ' dissolution was noted in the adjacent material. During the PWHT, a high density of γ' precipitated out both within the mushy zone and in the constitutionally liquated and resolidified grain boundary regions in the HAZ. As the dissolution and reprecipitation of γ' occurred fairly uniformly throughout the mushy zone, the ensuing aging Contraction Stress/ strain was fairly uniformly distributed in the region. In contrast, in the adjacent part of the HAZ, an extreme volume of γ' precipitation occurred locally along the grain boundary regions, a result of the highest concentration of...
Albert J. Feilzer - One of the best experts on this subject based on the ideXlab platform.
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Contraction Stress and bond strength to dentinfor compatible and incompatible combinations of bonding systems and chemical and light cured core build up resin composites
Dental Materials, 2006Co-Authors: Peter B Bolhuis, Anton J De Gee, Cornelis J Kleverlaan, Ahmed El A Zohairy, Albert J. FeilzerAbstract:Summary Objective Recent studies have shown that adhesives containing acidic monomers combined with composites can adversely effect the polymerization reaction producing low bond strengths. This phenomenon may also occur in making composite build-ups, jeopardizing one of the key factors for a successful core build-up restoration. The aim of this study was to investigate the Contraction Stress development and bond strength to dentin of core build-up resin composites combined with adhesives of various acidities. In addition the hypothesis tested was that light irradiation through chemical-cured composites during curing does not influence Contraction Stress or bond strength to dentin. Methods The chemical-cured (Clearfil Core) and light-cured (Clearfil Photo Core) core build-up resin composites were combined with two light-cured adhesives, Clearfil SE Bond (pH=1.8) and One-Step Bond (pH=4.3) and two dual-cured adhesives, Clearfil Photo Bond (pH=2.5) and All-Bond 2 (pH=6.1). Contraction Stress development (at C =3) was determined for a period of 30 min in a universal testing machine where the opposing bonding surfaces were glass and dentin. After the 30 min period, the specimens were loaded in tension to determine the bond strength to dentin. To test the hypothesis, the combinations of the chemical-cured composites with the four bonding systems were also light irradiated for 40 s right at the start of curing. Results For all composite-adhesive combinations tested, the adhesion to dentin resisted the developing polymerization Contraction Stresses. Both, dentin as a substrate to bond at and the use of adhesives, were showed to play an important role in keeping the Contraction Stresses low. The chemical-cured composite (Clearfil Core) combined with the light-cured adhesive SE Bond (pH=1.8) showed for both Contraction Stress and bond strength significant lower values than the other combinations. The hypothesis was accepted for combinations of the chemical-cured composite with All-Bond 2 and One-Step Bond, but was not supported by combinations with Clearfil SE Bond or Clearfil Photo Bond, as a significant increase in Contraction Stress was found. The higher values found for bond strength were not significant. Significance Besides combinations of chemical-cured core build-up composites with light or dual-cured adhesives as recommended by the manufacturer, also combinations with adhesives of other manufacturers are compatible, provided that the pH is higher than approximately 4.3. Chemical-cured core build-up composites combined with light-cured adhesives with a pH as low as 1.8 lead to a significantly lower Stress and bond strength compared to other combinations. Light irradiation during curing through a combination of a chemical-cured composite and a low pH adhesive reactivates polymerization.
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polymerization shrinkage and Contraction Stress of dental resin composites
Dental Materials, 2005Co-Authors: Cornelis J Kleverlaan, Albert J. FeilzerAbstract:Summary Objective The aim of this study was to evaluate the shrinkage, Contraction Stress, tensile modulus, and the flow factor of 17 commercially available dental resin composites. Method The volumetric shrinkage measurements were performed by mercury dilatometry, and the Contraction Stress and tensile modulus were determined by means of Stress–strain analysis. The statistical analysis was conducted by ANOVA and Tukey's post hoc test, and linear regression. Results Strong linear correlation for most resin composites were found for (i) Contraction Stress and shrinkage (ii) Contraction Stress and tensile modulus, and (iii) shrinkage and tensile modules. For most of the materials the unpolymerized resin content determines the amount of shrinkage, Contraction Stress and tensile modules. The pre-polymerized clusters in Heliomolar results in improved shrinkage/Contraction Stress properties. The shrinkage/Contraction Stress for Filtek Z100, Aelite Flo, and Flow-it was too high for the amount of resin in the resin composite. This was rationalized by high polymerization rates, a flow factor, and the nature of the resin. Significance High shrinkage and/or high Contraction Stress may lead to failure of the bond between the resin composites and the tooth structure. This study shows that the unpolymerized resin content determines the amount of shrinkage, Contraction Stress and tensile modules. Therefore, using pre-polymerized clusters will improve shrinkage/Contraction Stress properties, as was shown in Heliomolar, while high polymerization rates, and low flow factors have a deteriorative effect on the shrinkage/Contraction Stress properties.
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polymerization Contraction Stress in thin resin composite layers as a function of layer thickness
Dental Materials, 1997Co-Authors: Darja Alster, Albert J. Feilzer, Anton J De Gee, C L DavidsonAbstract:Objectives. In the present study, the effect of layer thickness on the curing Stress in thin resin composite layers was investigated. Since the value of the Contraction Stress is dependent on the compliance of the measuring equipment (especially for thin films), a method to determine the compliance of the test apparatus was tested.
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the influence of water sorption on the development of setting shrinkage Stress in traditional and resin modified glass ionomer cements
Dental Materials, 1995Co-Authors: Albert J. Feilzer, A J De Gee, Afrodite Kakaboura, C L DavidsonAbstract:Abstract Objectives . The aim of this study was to determine the setting Stress development for some traditional and resin-modified glass ionomer cements and to assess the effect of early water exposure to this Stress. Methods . The development of the setting Stress of the glass ionomer cements was determined in a tensilometer set-up as described earlier by Feilzer et al. (1987). Results . The results of this study show the influence of water sorption on the development of setting shrinkage Stress in bonded glass ionomer cements. When curing took place under isolated conditions (no hydration or dehydration), all the traditional glass ionomer cements investigated fractured spontaneously, either adhesively and/or cohesively, due to the developing Stress. Early exposure to water led to Stress relief and prevented spontaneous fracturing. For the light-cured products, no spontaneous failures were observed under isolated conditions. Stress relief due to water sorption reversed the Contraction Stress into an expansion Stress. Significance . Exposure of traditional glass ionomer cements to water at an appropriate time by the use of permeable matrix systems is advised. Whether the conversion of Contraction Stresses into expansion Stresses, as observed for the resin-modified products, is beneficial for a restoration requires further study.
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the dependence of shrinkage Stress reduction on porosity concentration in thin resin layers
Journal of Dental Research, 1992Co-Authors: D Alster, Albert J. Feilzer, A J De Gee, A Mol, C L DavidsonAbstract:The development of polymerization Contraction Stress was determined as a function of the surface area of porosity, so that the contribution of voids in resin composite to Stress relief could be investigated. Experiments were carried out on 200-um-thick layers of resin bonded from wall to wall in a restrained condition. The resin samples were divided into three groups: Group A was without porosity, group B contained a small number of pores, and group C contained a large number of pores in comparison with group B. For each group, porosity area, maximal Stress, and Stress development rate were determined. The mean maximal Stress and Stress development rate were inversely proportional to the mean porosity surface. These characteristics differed significantly (p < 0.01) between group A and C. For determination of whether shrinkage Stress reduction has to be ascribed to flow from the outer surfaces of the voids or to inhibition of the setting reaction by oxygen in the voids, resin containing only nitrogen bubbl...