Pull-out strength of patient-specific template-guided vs. free-hand fluoroscopically controlled thoracolumbar pedicle screws: a biomechanical analysis of a randomized cadaveric study.

PURPOSE: To assess the pull-out strength of thoracolumbar pedicle screws implanted via either a patient-specific template-guided or conventional free-hand fluoroscopically controlled technique in a randomized cadaveric study, and to evaluate the influence of local vertebral bone density, quantified by Hounsfield units (HU), on pedicle screw pull-out strength. METHODS: Thoracolumbar pedicles of three spine cadavers were instrumented using either a free-hand fluoroscopically controlled or a patient-specific template-guided technique. Preoperative bone density was quantified by HU measured on CT. Pedicle perforation was evaluated on postoperative CT scans by an independent and blinded radiologist. After dissected vertebrae were embedded in aluminum fixation devices, pull-out testing was initiated with a preload of 50 N and a constant displacement rate of 0.5 mm/s. Subgroup analyses were performed excluding pedicle screws with a pedicle breach (n = 47). RESULTS: Pull-out strength was significantly different with 549 ± 278 and 441 ± 289 N in the template-guided (n = 50) versus fluoroscopically controlled (n = 48) subgroups (p = 0.031), respectively. Subgroup analysis limited to screws with an intrapedicular trajectory revealed a tendency toward a higher pull-out strength in the template-guided (n = 30) versus fluoroscopically controlled screws (n = 21) with 587 ± 309 and 454 ± 269 N (p = 0.118), respectively. There was a trend toward a higher pull-out strength (709 ± 418 versus 420 ± 149 N) in vertebrae with a bone density of (>171 HU) versus (<133 HU), respectively (p = 0.061). CONCLUSIONS: There was a significantly higher pull-out strength of thoracolumbar pedicle screws when inserted via a patient-specific template-guided versus conventional free-hand fluoroscopically controlled technique, potentially associated with screw trajectory.

Differences between reported and actual restored caries lesion depths: results from The Dental PBRN.

OBJECTIVE: The objectives of this research were to: (1) quantify the discordance between the caries lesion depth at which dentists restored initial lesions during a clinical study ("actual depth") and the lesion depth that they reported during a hypothetical clinical scenario ("reported depth"); (2) test the hypothesis that certain practitioner, practice, patient, and caries lesion characteristics are significantly associated with this discordance. METHODS: Practitioner-investigators who perform restorative dentistry in their practices completed an enrollment questionnaire and participated in 2 consecutive studies on caries diagnosis and treatment. The first study was a survey asking about caries treatment. The second study collected data on restorations placed in routine clinical practice due to caries in patients over 19 years of age on occlusal surfaces only or proximal surfaces only. We report results on 2,691 restorations placed by 205 dentists in 1,930 patients with complete data. RESULTS: Discordance between actual depth and reported depth occurred in only about 2% of the restorations done due to proximal caries, but about 49% of the restorations done due to occlusal caries. Practice type, restorative material used and the diagnostic methods used were significantly associated with discordance. CONCLUSION: Dentists frequently restored occlusal caries at a shallower depth as compared to their reported depth, but the discordance was very small for proximal lesions. Discordance for occlusal caries was more common when radiographs were not taken or if a resin restoration was placed.

Differences between reported and actual restored caries lesion depths: results from The Dental PBRN.

OBJECTIVE: The objectives of this research were to (1) quantify the discordance between the caries lesion depth at which dentists restored initial lesions during a clinical study ("actual depth") and the lesion depth that they reported during a hypothetical clinical scenario ("reported depth"); (2) test the hypothesis that certain practitioner, practice, patient, and caries lesion characteristics are significantly associated with this discordance. METHODS: Practitioner-investigators who perform restorative dentistry in their practices completed an enrollment questionnaire and participated in two consecutive studies on caries diagnosis and treatment. The first study was a survey asking about caries treatment. The second study collected data on restorations placed in routine clinical practice due to caries in patients over 19 years of age on occlusal surfaces only or proximal surfaces only. We report results on 2691 restorations placed by 205 dentists in 1930 patients with complete data. RESULTS: Discordance between actual depth and reported depth occurred in only about 2% of the restorations done due to proximal caries, but about 49% of the restorations done due to occlusal caries. Practice type, restorative material used and the diagnostic methods used were significantly associated with discordance. CONCLUSION: Dentists frequently restored occlusal caries at a shallower depth as compared to their reported depth, but the discordance was very small for proximal lesions. Discordance for occlusal caries was more common when radiographs were not taken or if a resin restoration was placed.

Phase transitions in K2Cr2O7 and structural redeterminations of phase II.

Crystals of phase II K2Cr2O7, potassium dichromate, space group P1 , grown from aqueous solution undergo a first-order transition to phase I, space group reportedly P21/n, at a phase-transition temperature, TPT, of 544 (2) K on first heating; the corresponding transition on cooling is at 502 (2) K. The endotherm on subsequent heatings occurs reproducibly at TPT = 531 (2) K. Mass loss between ca 531 and 544 K, identified as included water, is rapid and continues more slowly to higher temperatures for a total loss of ca 0.20%. The higher TPT on first heating is associated with the increasing pressure of superheated water occupying inclusion defects. The latent diagonal glide plane in phase II allows the structure of phase I to be inferred. The triclinic structure at 296 K has been independently redetermined. Normal probability analysis shows high consistency between the resulting and previous atomic coordinates, but with uncertainties reduced by a factor of ca 2. The earlier uncertainties are systematically underestimated by a comparable factor. The structure of phase IIb, space group A2/a on transposing axes, was determined at ca 300 K by Krivovichev et al. [Acta Cryst. (2000), C56, 629-630]. The first-order transition between phases I and II arises from the ca 60 degrees relative rotation of terminal O atoms in each tetrahedron as the n glide plane is gained or lost. A transition between phases IIb and I, also of first order, is likely but not between phases II and IIb. An intermediate phase may exist between phases IIb and I.

Bis[aminoguanidinium(1+)] hexafluorozirconate(IV): redeterminations and normal probability analysis.

The crystal structure of bis[aminoguanidinium(1+)] hexafluorozirconate(IV), (CH(7)N(4))(2)[ZrF(6)], originally reported by Bukvetskii, Gerasimenko & Davidovich [Koord. Khim. (1990), 16, 1479-1484], has been redetermined independently using two different samples. Normal probability analysis confirms the reliability of all refined parameter standard uncertainties in the new determinations, whereas systematic error detectable in the earlier work leads to a maximum difference of 0.069 (6) A in atomic positions between the previously reported and present values of an F-atom y coordinate. Radiation-induced structural damage in aminoguanidinium polyfluorozirconates may result from minor displacements of H atoms in weak N-H...F bonds to new potential minima and subsequent anionic realignment.

Aminoguanidinium(1+) pentafluorozirconate: multiple redetermination and comparisons.

The structure of CN(4)H(7)ZrF(5) reported by Bukvetskii et al. [Koord. Khim. (1992). 18, 576-579] has been independently redetermined on the basis of measurements on three different crystals. Assuming all four resulting structures are drawn from a normal distribution, normal probability analysis of the atomic coordinates taken in pairs reveals joint standard uncertainties that are underestimated by factors as large as 16.5 for the x(Zr) coordinate. Unit-cell parameters in the four crystals similarly have joint uncertainties, under the same assumption, that are underestimated by factors as large as 83.0 for the b axis. The variations in axial lengths from crystal to crystal and the declines in standard reflection intensities by 13-15% in at least two of the crystals measured are consistent with the inference that the distribution is not normal. Rather, the differences observed may be assumed to be caused by small but highly significant radiation-induced structural changes. The large underestimations hence reflect physical differences among the four irradiated crystals. The determinations show that the CN(4)H(7)(+1) cation is exactly planar except for the two H atoms bonded to the terminal N atom; the plane of this NH(2) group is normal to that of the cation. The average length of the three independent C-N bonds is 1.318 (11) A; the N-N bond length is 1.397 (3) A. Distorted ZrF(7) pentagonal bipyramids share edges, forming chains linked by N-H...F bonds to the CN(4)H(7)(+1) ions.

Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer.

We investigated key factors controlling mass and energy exchange by a young (6-year-old) ponderosa pine (Pinus ponderosa Laws.) plantation on the west side of the Sierra Nevada Mountains and an old-growth ponderosa pine forest (mix of 45- and 250-year-old trees) on the east side of the Cascade Mountains, from June through September 1997. At both sites, we operated eddy covariance systems above the canopy to measure net ecosystem exchange of carbon dioxide and water vapor, and made concurrent meteorological and ecophysiological measurements. Our objective was to understand and compare the controls on ecosystem processes in these two forests. Precipitation is much higher in the young plantation than in the old-growth forest (1660 versus 550 mm year-1), although both forests experienced decreasing soil water availability and increasing vapor pressure deficits (D) as the summer of 1997 progressed. As a result, drought stress increased at both sites during this period, and changes in D strongly influenced ecosystem conductance and net carbon uptake. Ecosystem conductance for a given D was higher in the young pine plantation than in the old-growth forest, but decreased dramatically following several days of high D in late summer, possibly because of xylem cavitation. Net CO2 exchange generally decreased with conductance at both sites, although values were roughly twice as high at the young site. Simulations with the 3-PG model, which included the effect of tree age on fluxes, suggest that, during the fall through spring period, milder temperatures and ample water availability at the young site provide better conditions for photosynthesis than at the old pine site. Thus, over the long-term, the young site can carry more leaf area, and the climatic conditions between fall and spring offset the more severe limitations imposed by summer drought.

Anhydrous ammonioguanidinium(2+) and dihydrated bis[aminoguanidinium(1+)] hexafluorosilicates: new co-products of preparing ferroelectric ammonioguanidinium(2+) hexafluorozirconate.

Ammonioguanidinium hexafluorosilicate, CH8N4(2+).SiF6(2-), and bis(aminoguanidinium) hexafluorosilicate dihydrate, 2CH7N4+.SiF6(2-).2H2O, are new materials formed as by-products in course of preparing ferroelectric CH8N4ZrF6 in the presence of glassware. Their structures were determined for comparison with the corresponding hexafluorozirconates. All atoms including the eight H atoms in the CH8N4(2+) cation and the seven H atoms in the CH7N4+ cation have been located and refined with wR(F2) = 0.0653, R = 0.0255, S = 1.146 and wR(F2) = 0.0745, R = 0.0301, S = 1.065, respectively. The N2C-N-N backbone of the 2+ cation is close to planarity, while that of the 1+ cation does not differ significantly from planarity. The SiF6(2-) octahedron is nearly ideally regular in both materials, with < Si-F > = 1.684 (unbiassed estimator of standard uncertainty = 0.016) A in the anhydrous hexafluorosilicate and 1.6801 (unbiassed estimator of standard uncertainty = 0.0006) A in the dihydrate. The combination of coulombic and NH...F interactions in CH8N4SiF6 results in a relatively dense variant of the NaCl structure. In addition to similar forces, the dihydrate is also characterized by the role of the water molecule with its strong NH...O interactions; its packing efficiency is, however, appreciably less than that of the anhydrous hexafluorosilicate with an approximately 8% increase in void space. Cleaved crystals of the dihydrate are frequently twinned across the (001) composition plane, with a twofold rotation about the b axis as the twin operation.

A nonprimate animal model applicable to zidovudine pharmacokinetics in humans: inhibition of glucuronidation and renal excretion of zidovudine by probenecid in rats.

The monkey is considered the best animal model to study the pharmacokinetics of zidovudine (azidothymidine, AZT) because humans and monkeys eliminate 60 to 75% of AZT by metabolism to the 5'-O-glucuronide (GAZT), in contrast to other experimental animals, which excrete most of the drug unchanged in the urine. It has become increasingly difficult and costly to use monkeys in research. Therefore, we undertook studies to determine the suitability of the rat as an alternative animal model to study the pharmacokinetics of AZT. In the initial experiments, [3H]AZT was administered i.v. at doses of 19, 60 and 187 mumol/kg to male Sprague-Dawley rats with intact bile ducts. The respective values (mean +/- S.D.) for total clearance of AZT were 2.4 +/- 0.2, 2.3 +/- 0.3 and 1.8 +/- 0.4 l/hr/kg and for renal clearance were 1.7 +/- 0.2, 1.8 +/- 0.4 and 1.5 +/- 0.4 l/hr/kg. The renal clearance of AZT was approximately equal to renal plasma flow of rats (1.5 l/hr/kg), suggesting that in addition to filtration, AZT is also efficiently secreted in the kidney of the rat. The respective values for volume of distribution at steady state were 1.3 +/- 0.2, 1.0 +/- 0.2 and 0.84 +/- 0.19 l/kg (P less than .05) and elimination half-life were (harmonic mean) 0.55, 0.44 and 0.46 hr. Urinary excretion of AZT as unchanged drug in intact rats accounted for 70 +/- 6, 79 +/- 6, and 83 +/- 12% of the dose, whereas only 0.7 to 0.8% of the dose was recovered in the urine as GAZT. Rats with exteriorized bile ducts, the proposed alternative animal model, were given an i.v. dose of 60 mumol/kg of [3H]AZT. To test the effect of a concurrently administered drug on the elimination of AZT in the model, some rats with bile duct cannulas were pretreated with probenecid, a known inhibitor of AZT elimination in humans. Urine and bile were collected to quantify the formation of GAZT. GAZT was identified by fast atom bombardment mass spectrometry as the major metabolite of AZT in the rat. GAZT excretion in the bile and urine accounted for 11 +/- 3% of the dose in saline-treated rats, compared to only 1.4 +/- 0.3% in rats treated with probenecid (P less than .001).(ABSTRACT TRUNCATED AT 400 WORDS)

[Caring for the cancer patient: how can nurses face this challenge?]. / Assistir o paciente oncológico: como as enfermeiras poderão enfrentar este desafio?

This paper presents a report of the experience the authors had in taking care of 103 hospitalized oncology patients based on a particular framework. They reflect upon the nursing care provided to those patients, and also emphasizing patient's statements regarding their lived experience.