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At least 613 records · Page 34Linked to original sources
PubMed1995

Comparison of clinical and angiographic outcomes after saphenous vein graft angioplasty using coronary versus 'biliary' tubular slotted stents.

BACKGROUND: Saphenous vein graft (SVG) angioplasty using 15-mm articulated, tubular slotted stents results in low (0% to 20%) residual diameter stenoses and infrequent (< 5%) major complications. A "biliary" stent design with greater radial compressive strength, enhanced visibility, and more variable sizing (diameter and length) has been approved for noncoronary indications. A comparison of outcomes after coronary versus biliary stent placement in SVG stenoses has not been performed. The purpose of this study was to compare the angiographic and clinical results after SVG angioplasty using these two balloon-expandable, tubular slotted stent designs. METHODS AND RESULTS: During a 3-year period, 231 patients with 305 SVG lesions were treated using Palmaz-Schatz coronary (n = 108) or biliary (n = 123) stents. Cineangiograms were reviewed using qualitative morphological and quantitative angiographic methods. Time-dependent clinical outcome (freedom from death, Q-wave myocardial infarction, or the need for repeat coronary bypass surgery or SVG angioplasty) was assessed using Kaplan-Meier life-table methods. Unstable angina (P < .001) and recent myocardial infarction (P = .001) were present more often in patients undergoing biliary stent versus coronary stent placement. Biliary stent-treated SVG lesions were more frequently de novo (P = .001), ostial in location (P = .002), > or = 10 mm in length (P = .009), thrombus containing (P = .001), and ulcerated (P < .001) than coronary stent-treated SVG lesions. Angiographically, biliary stent-treated lesions had larger reference vessel diameter (3.43 +/- 0.59 mm versus 3.10 +/- 0.64 mm, P < .001), higher balloon-to-artery ratio (1.15 +/- 0.16 mm versus 1.07 +/- 0.19, P = .0001), and lower residual diameter stenosis (6 +/- 17% versus 14 +/- 11% in coronary stent-treated patients; P < .001). Procedural success rates were high (95%), in-hospital major complications were uncommon (< 3%), and follow-up clinical outcomes were favorable (6-month event-free survival approximately 80%) in both groups. CONCLUSIONS: Despite frequent short-term ischemic syndromes and unfavorable lesion characteristics, both biliary and coronary cohorts have similarly favorable short-term procedural results and long-term clinical outcomes. The increased strut thickness of the biliary stent confers greater fluoroscopic visibility and radial compressive strength in exchange for decreased stent flexibility and added technical demand in stent deployment. Extreme caution is recommended with biliary stent placement in the treatment of SVG lesions as clinical results are highly operator dependent.

Aged↗
PubMed1994

Mechanical properties of vacuum-mixed acrylic bone cement.

The thrust of the present work was the experimental determination of the uniaxial static compressive and fully reversed tension-compression fatigue properties of CMW 3 acrylic bone cement whose constituents were mixed in a proprietary chamber while simultaneously subjected to a vacuum. Selected indices of performance in this material are: mean static compressive strength, 81.4 MPa; mean compressive modulus of elasticity, 1.95 GPa; endurance limit, 8.1 MPa; and characteristic fatigue life (using a three-parameter Weibull fit to the fatigue test data obtained at a stress of +/- 10 MPa), 238,712 cycles. The difficulties in comparing results obtained using different cement formulations, preparation conditions, and test conditions are detailed. With this in mind, it is suggested that the present results are within the range of values reported by previous workers for other formulations mixed using a variety of methods. The clinical significance of the present results is discussed.

Acrylates↗
PubMed1996

New aspects of the effect of size and size distribution on the setting parameters and mechanical properties of acrylic bone cements.

The effect of the size and the size distribution of poly(methyl methacrylate) (PMMA) beads on the classical kinetic parameters, peak temperature and setting time, for acrylic bone cement formulations prepared with PMMA particles in the range 10-60 microns of average diameter and a relatively wide size distribution is analysed. In addition, the combined effects of the concentration of the free radical initiator benzoyl peroxide and the activator N, N-dimethyl-4-toluidine for the different particle sizes are studied and compared with those commercially available formulations like CMW or Rostal. The results obtained indicated that the use of PMMA particles with average diameter of 50-60 microns, and a relatively wide size distribution (10-140 microns diameter), significantly changes the curing parameters (peak temperature and setting time) of the cement formulations in comparison with the classical behaviour of the commercial systems of CMW and Rostal, without any noticeable loss in the mechanical properties, such as tensile strength, elastic moduli, and compressive strength and plastic strain.

Benzoyl Peroxide↗
PubMed2004

Effects of the steroidal aromatase inhibitor exemestane and the nonsteroidal aromatase inhibitor letrozole on bone and lipid metabolism in ovariectomized rats.

PURPOSE: Exemestane (EXE) and letrozole (LET) are third-generation aromatase inhibitors currently prescribed for postmenopausal hormone-dependent breast cancer. The impact on end organs of estrogen depletion in menopausal women is of significant clinical importance. We studied the effects of EXE, its principal metabolite, 17-hydroexemestane (17-H-EXE), and LET on bone and lipid metabolism in ovariectomized (OVX) rats. EXPERIMENTAL DESIGN: OVX rats were treated by weekly intramuscular injection for 16 weeks with 20, 50, and 100 mg/kg EXE, 20 mg/kg 17-H-EXE, and daily oral gavage of 1 mg/kg LET. At the end of the treatment period, bone mineral density (BMD), the bone resorption marker serum pyridinoline, the bone formation marker serum osteocalcin, bone mechanical properties, histomorphometry, and serum lipid concentrations were determined. RESULTS: Lumbar vertebral and femoral BMD, bending strength of the femur, compressive strength of the fifth lumbar vertebra, and trabecular bone volume were significantly higher in OVX animals given EXE and 17-H-EXE than in OVX controls. EXE and 17-H-EXE significantly reduced an ovariectomy-induced increase in serum pyridinoline and serum osteocalcin. EXE and 17-H-EXE given to OVX rats caused significant reductions of serum cholesterol and low-density lipoprotein cholesterol. In contrast, OVX rats treated with LET had BMD, bone biomarkers, mechanical failure properties, and lipid levels similar to those of OVX controls. CONCLUSIONS: EXE and 17-H-EXE significantly prevent bone loss, enhance bone mechanical strength, and lower serum cholesterol and low-density lipoprotein levels in OVX rats. These protective effects on end-organ function are not seen with the nonsteroidal inhibitor LET.

Amino Acids↗
PubMed2002

In vitro study of drug-loaded bioresorbable films and support structures.

Bioresorbable films can serve simultaneously as anatomic support structures and as drug delivery platforms. In the present study, bioresorbable poly(L-lactic acid) (PLLA) films containing dexamethasone were prepared by solution processing methods. Their in vitro studies focused on the mechanical properties with respect to morphology and degradation and erosion processes. Novel expandable support devices (stents) developed from these films were studied. Such a stent would support conduits, such as the neonatal trachea to treat tracheal malacia, until the airway matures, and would then be totally resorbed, obviating the need for a removal operation. The PLLA films showed good initial mechanical properties. They can accommodate drug incorporation on the film surface and also in the bulk. Water incubation of the films results in a decrease in their tensile mechanical properties, due to chain scission and morphological changes. These changes can vary from degradation and small changes in morphological features to erosion, leading to a microporous structure, depending on the polymer. The cumulative release of dexamethasone from the films is linear. The rate of release is determined by the film's structure (drug location/dispersion). The stents demonstrated good mechanical properties. The initial radial compression strength of the stent is determined mainly by the polymer structure. Drug incorporation has a minor effect on the initial stent strength. Exposure to radial compression stress results in elastic reversible deformation or a sudden brittle fracture, depending on the polymer. A 20-week in vitro study of the stents showed that they are applicable for supporting body conduits, such as the trachea.

Absorbable Implants↗
PubMed2006

Age- and sex-specific differences in the factor of risk for vertebral fracture: a population-based study using QCT.

UNLABELLED: We used QCT scans obtained in 687 men and women, 21-97 years of age, to estimate the factor of risk for vertebral fracture, Phi(vert), defined as the ratio of spinal loading to vertebral strength. With age, vertebral strength declined and Phi(vert) increased significantly more in women than men. Age- and sex-specific differences in Phi(vert) closely resembled previously reported vertebral fracture incidence. INTRODUCTION: Despite the high prevalence of vertebral fractures, little is known about the interaction between spinal loading and vertebral fragility. MATERIALS AND METHODS: We assessed the ratio of spinal loading to vertebral strength (i.e., the factor of risk, Phi(vert)) in an age- and sex-stratified population-based sample of 700 women and men 21-97 years of age. We measured volumetric BMD (vBMD, mg/cm3) and cross-sectional area (CSA, cm2) of the midvertebral bodies of L1-L3 using QCT and computed vertebral compressive strength from these data using engineering beam theory. A biomechanical model of the trunk was used to estimate compressive forces applied to the L3 vertebral body during standing, bending forward, and bending forward while lifting 10 kg. The factor of risk for fracture, Phi(vert), was computed as the ratio of spinal compressive force to vertebral strength for each activity. RESULTS: Men had a higher vertebral strength at all ages, largely because of their greater CSA. Whereas both sexes exhibited a marked decline in vertebral compressive strength with age (p < 0.001), the decline was greater in women than men (-43% versus -31%, p = 0.008). Compressive forces on L3 were greater in men than women, because of their greater body weight and height. For both sexes, forces during bending and lifting were 8-fold higher than those experienced during upright standing. For all activities, Phi(vert) increased with age, but significantly more so in women than men (p < 0.001). For bending and lifting, Phi(vert-bending) exceeded 1.0 in 30% of women and 12% of men > or =50 years of age, values that are similar to the reported frequency of vertebral fracture. CONCLUSION: These findings illustrate potential mechanisms underlying vertebral fractures and provide strong rationale for further evaluation of this QCT-based biomechanical approach for assessment of fracture risk.

Adult↗
PubMed1993

Mechanical properties of direct and post-cured composites.

Surface mechanical properties (diametral tensile strength, Knoop hardness, and Rockwell Superficial indentation and recovery) and bulk mechanical properties (compressive strength and modulus of elasticity in compression) of seven composites were measured in vitro under two curing conditions (light-curing only and light-curing plus manufacturer's recommended post-curing). Post-curing improved the Knoop hardeness by 7 to 46% and diametral tensile strength by 15 to 39% of some of the composites. None of the composites had improved compressive strength and only two had an improved modulus of elasticity.

Analysis of Variance↗
PubMed2004

Oyster shell as substitute for aggregate in mortar.

Enormous amounts of oyster shell waste have been illegally disposed of at oyster farm sites along the southern coast of Korea. In this study to evaluate the possibility of recycling this waste for use as a construction material, the mechanical characteristics of pulverized oyster shell were investigated in terms of its potential utilization as a substitute for the aggregates used in mortar. The unconfined compressive strengths of various soil mortar specimens, with varying blending ratios of cement, water and oyster shell, were evaluated by performing unconfined compression tests, and the results were compared with the strengths of normal cement mortar made with sand. In addition, the effect of organic chemicals on the hardening of concrete was evaluated by preparing ethyl-benzene-mixed mortar specimens. The long-term strength improvement resulting from the addition of fly ash was also examined by performing unconfined compression tests on specimens with fly-ash content. There was no significant reduction in the compressive strength of the mortars containing small oyster shell particles instead of sand. From these test data, the possible application of oyster shells in construction materials could be verified, and the change in the strength parameters according to the presence of organic compounds was also evaluated.

Animals↗
PubMed2002

Mechanical properties and bond strength of glass-ionomer cements.

PURPOSE: The objective of this study was to evaluate the mechanical properties and bond strength of glass-ionomer cements (GICs) and resin-modified GICs (RM-GICs) that are indicated as restorative materials for the Atraumatic Restorative Treatment (ART) technique. MATERIALS AND METHODS: Fifteen disk specimens for the diametral tensile strength (DTS) test and fifteen cylindrical specimens for the compressive strength (CS) test were made of each GIC: Ketac-Fil, Ketac-Molar (ESPE), Fuji IX and Fuji PLUS (GC). Forty human molars were sectioned and embedded in resin with either buccal or lingual surfaces exposed for the tensile bond strength (TBS) test. The surface was ground until a flattened area of enamel or dentin was obtained. After conditioning, inverted truncated cones of GICs were prepared on the flat tooth surfaces. The powder:liquid ratio of Fuji PLUS was adjusted for restorative purposes. Prior to testing, specimens were stored for 24 h (TBS test) and for 1 h, 24 h, and 7 days (CS and DTS tests) in deionized water at 37 degrees C. They were then loaded at a crosshead speed of 1.0 mm/min for CS and 0.5 mm/min for DTS and TBS tests until failure occurred. The data were submitted to two-way ANOVA at 0.05 level of significance, followed by a Tukey-Kramer test for multiple comparisons. RESULTS: The mean CS values ranged from 90.27 to 170.73 MPa and DTS means from 6.21 to 22.32, with test periods from 1 h to 7 days. The means for TBS ranged from 4.90 to 11.36 MPa and from 2.52 to 5.55 MPa in enamel and dentin, respectively. No differences were found between materials with the CS test except at 1 hour. The resin-modified GIC (RM-GIC) had the highest DTS, with no changes between the test periods, and the highest TBS for both enamel and dentin. CONCLUSION: Among the GICs tested, RM-GIC showed higher values of DTS and TBS.

Analysis of Variance↗
PubMed2003

Modelling heavy metal and anion effects on physical and mechanical properties of portland cement by means of factorial experiments.

The aim of the present work was to investigate the influence of a number of heavy metals (Cd, Cr(III), Cu, Pb and Zn), as well as anions (Cl-, SO4(2-)) on the physical and mechanical properties of cementitious pastes, including setting time, bulk density and unconfined compressive strength. The above mentioned species and their concentrations were selected in order to simulate addition of 20% municipal solid waste incinerator ash to Portland cement. Spiking experiments were performed according to a 2IV(7-3) fractional factorial design by addition of pure compounds containing the contaminants of interest to Portland cement. The results from the experimental campaign, which were interpreted using statistical analysis techniques, showed that the investigated contaminants variously affected the hydration process of cement. The ranking for final setting time values was Zn(NO3)2 > K2SO4 > NaCl > mean response > Cr(NO3)3 > NaCl+Cr(NO3)3, Cd(NO3)2+Pb(NO3)2 or CuCl2+Zn(NO3)2 interaction, whereas the ranking for UCS values during hardening was Zn(NO3)2 > CuCl2 > NaCl+K2SO4, CuCl2+Pb(NO3)2 or Cd(NO3)2+Zn(NO3)2 interaction > mean response. Conversely, none of the selected contaminants was found to significantly influence ultimate strength.

Anions↗
PubMed1989

[Evaluation of the effectiveness of ion exchange on strengthening of dental porcelain].

This study evaluated the effectiveness of ion exchange on strengthening of porcelain used in metal ceramic. The paste for ion exchange was painted directly on the porcelain surface, dried, and heated at 450 degrees C in the porcelain furnace. The bending strength of porcelain test samples (6.5 x 1.5 x 20 mm), the compressive strength of porcelain-fused-to-metal (PFM) crowns, which were cemented on the metal dies of upper central incisor by an adhesive luting resin 'Panavia EX', and the color change of porcelain test samples (phi 10 x 4 mm) were measured before and after ion exchange. The conclusions were: 1. It was confirmed by X-ray analysis that the compressive stress layer generated by ion exchange for 30 minutes was 150-200 microns in thickness. However, further elongation of time of ion exchange elicited no significant argumentation in the strength. 2. 34 or 57 percent increase of the mean compressive strength of PFM crowns was observed after ion exchange for 30 minutes when the load was applied in the direction of 45 degrees lingually to the tooth long axis or of the tooth long axis, respectively. 3. No significant decrease was found when parts of the incisal edge or the lingual surface of PFM crowns which were strengthened by ion exchange for 30 minutes were reduced by 200 microns. 4. There was so slight difference in the color of dental porcelain before and after ion exchange that the influence seemed to be negligible in its clinical application.

Dental Porcelain↗