Multimethod analysis of large- and low-tapered single file reciprocating instruments: Design, metallurgy, mechanical performance, and irrigation flow

AIM

To compare eight large- and low-tapered heat-treated reciprocating instruments regarding their design, metallurgy, mechanical properties, and irrigation flow through an in silico model.

METHODOLOGY

A total of 472 new 25-mm E-Flex Rex (25/.04 and 25/.06), Excalibur (25/.05), Procodile (25/.06), Reciproc Blue R25 (25/.08v), WaveOne Gold Primary (25/.07v), and Univy Sense (25/.04 and 25/.06) instruments were evaluated regarding their design (stereomicroscopy, scanning electron microscopy, and 3D surface scanning), metallurgy (energy-dispersive X-ray spectroscopy and differential scanning calorimetry), and mechanical performance (cyclic fatigue, torsional resistance, cutting ability, bending and buckling resistance). Computational fluid dynamics assessment was also conducted to determine the irrigation flow pattern, apical pressure, and wall shear stress in simulated canal preparations. Kruskal-Wallis and one-way anova post hoc Tukey tests were used for statistical comparisons (α = 5%).

RESULTS

Instruments presented variations in blade numbers, helical angles, and tip designs, with all featuring non-active tips, symmetrical blades, and equiatomic nickel-titanium ratios. Cross-sectional designs exhibited an S-shaped geometry, except for WaveOne Gold. Univy 25/.04 and Reciproc Blue displayed the smallest and largest core diameters at D3. Univy 25/.04 and E-Flex Rec 25/.04 demonstrated the longest time to fracture (p < .05). Reciproc Blue and Univy 25/.04 exhibited the highest and lowest torque to fracture, respectively (p < .05). Univy 25/.04 and Reciproc Blue had the highest rotation angles, whilst E-Flex Rec 25/.06 showed the lowest angle (p < .05). The better cutting ability was observed with E-Flex Rec 25/.06, Procodile, Excalibur, and Reciproc Blue (p > .05). Reciproc R25 and E-Flex Rec showed the highest buckling resistance values (p < .05), with WaveOne Gold being the least flexible instrument. The impact of instruments' size and taper on wall shear stress and apical pressure did not follow a distinct pattern, although Univy 25/.04 and E-Flex Rec 25/.06 yielded the highest and lowest values for both parameters, respectively.

CONCLUSIONS

Low-tapered reciprocating instruments exhibit increased flexibility, higher time to fracture, and greater angles of rotation, coupled with reduced maximum bending loads and buckling strength compared to large-tapered instruments. Nevertheless, low-tapered systems also exhibit lower maximum torque to fracture and inferior cutting ability, contributing to a narrower apical canal enlargement that may compromise the penetration of irrigants in that region.

Epidemiology and outcomes of carbapenem-resistant Klebsiella pneumoniae bacteriuria in kidney transplant recipients

BACKGROUND

Little is known about the epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) bacteriuria following kidney transplantation. We determined the incidence of post-transplant CRKP bacteriuria in adults who underwent kidney transplant from 2007 to 2010 at 2 New York City centers.

METHODS

We conducted a case-control study to identify factors associated with CRKP bacteriuria compared with carbapenem-susceptible K. pneumoniae (CSKP) bacteriuria, assessed whether CRKP bacteriuria was associated with mortality or graft failure, and compared outcomes of treated episodes of CRKP and CSKP bacteriuria.

RESULTS

Of 1852 transplants, 20 (1.1%) patients developed CRKP bacteriuria. Factors associated with CRKP bacteriuria included receipt of multiple organs (odds ratio [OR] 4.7, 95% confidence interval [CI] 1.1-20.4), deceased-donor allograft (OR 5.9, 95% CI 1.3-26.8), transplant admission length of stay (OR 1.1 per day, 95% CI 1.0-1.1), pre-transplant CRKP infection or colonization (OR 18.3, 95% CI 2.0-170.5), diabetes mellitus (OR 2.8, 95% CI 1.0-7.8), and receipt of antimicrobials other than trimethoprim-sulfamethoxazole (OR 4.3, 95% CI 1.6-11.2).

CONCLUSION

Compared to CSKP bacteriuria, CRKP bacteriuria was associated with increased mortality (30% vs. 10%, P = 0.03) but not graft failure. Treated episodes of CRKP bacteriuria were less likely to achieve microbiologic clearance (83% vs. 97%; P = 0.05) and more likely to recur within 3 months (50% vs. 22%, P = 0.02) than CSKP episodes. CRKP bacteriuria after kidney transplant is associated with mortality and antimicrobial failure after treatment.

Barium titanate thin films deposited by electrophoresis on p-Doped Si (001) substrates

Barium titanate (BaTiO3) thin films have been prepared by electrophoretic deposition on p-doped and platinum covered silicon (Si) substrates. Their structure, nanostructure and dielectric properties were characterized. The as-deposited films were polycrystalline and composed by barium titanate nanograins with an average grain size approximately 9 nm. Annealing at high temperatures promoted grain growth, so that the samples annealed at 600 degrees C presented average grain sizes approximately 24 nm. From Raman spectroscopy measurements it was found that the tetragonal (ferroelectric) BaTiO3 phase was stabilized on the films. Also, at higher annealing temperatures, cation disorder was reduced on the films. From measurements of the temperature dependence of the dielectric permittivity the corresponding paraelectric-ferroelectric phase transition was determined. The observed transition temperature (approximately 100 degrees C) was found to be below the BaTiO3 bulk or thick film values, due to the small nanosized grains composing the films.

Adsorption of bovine serum albumin on template-polymerized chitosan/poly(methacrylic acid) complexes

Particulate systems composed of polyelectrolyte complexes (PEC) based on chitosan and poly(methacrylic acid) were obtained via template polymerization. The resultant particles were characterized as having regions with different charge densities: chitosan predominating in the core and poly(methacrylic acid) at the surface, the particles being negatively charged, as a consequence. Albumin was adsorbed on these particles (after cross-linking with glutardialdehyde), and pH was controlled to obtain two conditions: (i) adsorption of positively charged albumin and (ii) adsorption of albumin at its isoelectric point. Adsorption isotherms and zeta-potential measurements showed that albumin adsorption was controlled by hydrogen bonding/van der Waals interactions and that brush-like structures may enhance the adsorption of albumin on these particles. It was also found that shearing can induce desorption of albumin from the PEC surface, depending on the continuous phase albumin concentration.

Effect of Molecular Weight and Ionic Strength on the Formation of Polyelectrolyte Complexes Based on Poly(methacrylic acid) and Chitosan

Chitosan/poly(methacrylic acid) complexes, CS/PMAA, were prepared via dropwise addition of a solution of PMAA to a solution of chitosan in acetic acid 2 wt %. The increase in molecular weight of PMAA inhibited the formation of insoluble complexes, while the increase in ionic strength first favored the formation of the complex followed by inhibiting it at higher concentrations. These observations were related to a description of polyelectrolyte complexation that was strongly dependent on macromolecular dimensions, both in terms of molecular weight and of coil expansion/contraction driven by polyelectrolyte effect.

Permeability studies in chitosan membranes. Effects of crosslinking and poly(ethylene oxide) addition

Pure chitosan, glutaraldehyde crosslinked chitosan, and a blend of chitosan with poly(ethylene oxide) (PEO) membranes were prepared. The three membranes were characterized in terms of their swelling capacities as well as their permeabilities to a drug model (sulfamerazine sodium salt). For the permeation experiments, the variables analyzed were the type of membrane and the initial drug concentration in the liquid phase (from 0.1% to 1.5%). Permeability coefficients were calculated using UV spectroscopy. The results showed that for the three analyzed membranes, the permeability did not change with time (over the studied time interval). An increase in the permeability for CHI/PEO membranes compared to those made of pure chitosan was also observed, possibly due to microporous region formation and/or crystallinity reduction. For the crosslinked membrane, an even higher increase in the permeability coefficient was observed. In this case, the increase was attributed to free volume variation.

Characterization of Vibrio fluvialis-like strains implicated in limp lobster disease

Studies were undertaken to characterize and determine the pathogenic mechanisms involved in a newly described systemic disease in Homarus americanus (American lobster) caused by a Vibrio fluvialis-like microorganism. Nineteen isolates were obtained from eight of nine lobsters sampled. Biochemically, the isolates resembled V. fluvialis, and the isolates grew optimally at 20 degrees C; none could grow at temperatures above 23 degrees C. The type strain (1AMA) displayed a thermal reduction time (D value) of 5.77 min at 37 degrees C. All of the isolates required at least 1% NaCl for growth. Collectively, the data suggest that these isolates may embody a new biotype. Pulsed-field gel electrophoresis (PFGE) analysis of the isolates revealed five closely related subgroups. Some isolates produced a sheep hemagglutinin that was neither an outer membrane protein nor a metalloprotease. Several isolates possessed capsules. The isolates were highly susceptible to a variety of antibiotics tested. However, six isolates were resistant to erythromycin. Seventeen isolates harbored plasmids. Lobster challenge studies revealed that the 50% lethal dose of a plasmid-positive strain was 100-fold lower than that of a plasmid-negative strain, suggesting that the plasmid may enhance the pathogenicity of these microorganisms in lobsters. Microorganisms that were recovered from experimentally infected lobsters exhibited biochemical and PFGE profiles that were indistinguishable from those of the challenge strain. Tissue affinity studies demonstrated that the challenge microorganisms accumulated in heart and midgut tissues as well as in the hemolymph. Culture supernatants and polymyxin B lysates of the strains caused elongation of CHO cells in tissue culture, suggesting the presence of a hitherto unknown enterotoxin. Both plasmid-positive and plasmid-negative strains caused significant dose-related intestinal fluid accumulations in suckling mice. Absence of viable organisms in the intestinal contents of mice suggests that these microorganisms cause diarrhea in mice by intoxication rather than by an infectious process. Further, these results support the thermal reduction data at 37 degrees C and suggest that the mechanism(s) that led to fluid accumulation in mice differs from the disease process observed in lobsters by requiring neither the persistence of viable microorganisms nor the presence of plasmids. In summary, results of lobster studies satisfy Koch's postulates at the organismal and molecular levels; the findings support the hypothesis that these V. fluvialis-like organisms were responsible for the originally described systemic disease, which is now called limp lobster disease.

Profile of alveolar gases during periodic and regular breathing in preterm infants

To determine the changes in alveolar PCO2 (PACO2) and PO2 (PAO2) during periodic and regular breathing epochs in the same infants, we studied 11 preterm infants during quiet sleep (birth weight 1,630 +/- 94 g; gestational age 31 +/- 1 weeks; postnatal age 32 +/- 3 days). A total of 94 breathing/apneic cycles were analyzed and compared with regular periods. During periodic and regular breathing epochs, there were negative correlations of PAO2 on PACO2. Short (< or = 5 s) and long (> 5 s) apneas for individual infants occurred along the regression line for that infant. There was not a single overall critical PACO2 below which apnea occurred, but for individual infants the PACO2 and the PAO2 of the breath preceding apnea varied within a limited range. Apneas occurred in clusters of PACO2 and PAO2 along the average regression line of PAO2 on PACO2. Analysis of the data showed that apnea occurred at the lowest PACO2 and highest PAO2 levels if allowance was made for circulation time. During apnea, 'the best fit' for the increase in PACO2 and the decrease in PAO2 was linear, rather than logarithmic. The findings suggest the following. (1) There is not a single overall critical level of PACO2 for apnea to occur, but in a given infant this level varies within a limited range. This indicates that these infants are likely breathing near the apnea threshold. (2) Short and long apneas appear to occur randomly along the regression of PAO2 on PACO2 for a particular infant. (3) The changes in alveolar gases are linear during apnea.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparative study of the use of nifedipine and captopril in hypertensive emergencies]

Forty patients with hypertensive crises, whose pressure levels had not satisfactorily decreased after intravenous furosemide 20 mg, were selected in the Emergency Ward. These patients were divided in two groups. The ones in group A received sublingual nifedipine 10 mg and the others in group B received oral captopril 50 mg. These drugs were repeated after 30 minutes to the maximum of three doses or until obtaining diastolic blood pressure less than 115 mmHg. Most patients (77.5%) had their blood pressure reduced to the proposed values after the first dose, and the remaining ones (22.5%) reacted to the therapy only after the administration of the subsequent doses. No side effects were observed. All patients were discharged from the emergency unit and were sent for follow-up in the outpatient service. The use of nifedipine and captopril has proved to be an effective treatment for hypertensive crises.

Assessing levels of airborne bioallergens in New York City

Sampling of airborne ragweed and other pollen grains in the City of New York is described as it took place during the months of August and September 1973. Three sampling stations participated in the program. This effort was meant to serve as the forerunner of a citywide volunteer pollen sampling network based on the cooperation of existing health care providing institutions, schools, and stations of the operational sampling network of the New York City Department of Air Resources. Monitoring stations were set up on the roof of Cooper Union School of Engineering at 51 Astor Place in downtown Manhattan, at the Boyce Thompson Institute for Plant Research, Inc. at Yonkers, N.Y. and use was made of the data supplied by Middlesex General Hospital, New Brunswick, N.J. Seasonal results of ragweed pollen sampling, undertaken at the downtown New York City location of Cooper Union with the swing-shield intermittant rotoslide sampler, are similar to those of studies undertaken in the 1940's and 1950's with the Durham slide sampler in the New York metropolitan area. Comparison of the collected data with converted data obtained in 1979 at Long Island Jewish-Hillside Medical Center with the aid of a Durham gravity slide sampler shows the trend similarity of the data collected by us in 1973 and those obtained in 1979. Collected data of the 1973 ragweed season were supplied to the New York City news media on a daily basis, as a much appreciated service to the public.

Broadcast of microbial aerosols by stacks of sewage treatment plants and effects of ozonation on bacteria in the gaseous effluent

In the aeration basins of sewage treatment plants, compressed air is supplied to diffusers near the bottom of tanks to aid in the conversion by aerobic bacteria of dissolved and suspended solids of sewage into particles that will settle. Air bubbles breaking at the air-water interface will aerosolize bacteria that concentrate in the uppermost microlayer. The microbiological output of a plant in New York City with such a system was monitored. Samples of the gaseous effluent were collected inside the aeration building, inside the building's stack, 300 meters upwind (background sampler), and 300 meters downwind (test sampler), using Andersen samplers. Among the genera identified in the atmosphere in and around the plant were Mycobacterium, Klebsiella, and Streptococcus, all potentially pathogenic. The disinfection power of ozone, which is generally used for odor control, was also tested. Samples were taken from the ozone mixing chamber in the stack of the thickentng tank building. No significant difference in general bacterial counts could be detected at different levels of ozone production. It appears that in the air, ozone is an ineffective bactericidal agent. Results in this preliminary study demonstrate the need to evaluate the hazard of microbial aerosols generated by sewage treatment plants similar to the one studied. The possibility of such hazards is of special interest where facilities are located upwind of populations especially susceptible to infections, because of age of debility. Correlations with epidemiologic data are indicated.