Fracture resistance of endodontically treated teeth with different heights of crown ferrule restored with prefabricated carbon fiber post and composite resin core by intermittent loading

This study evaluated the fracture resistance of endodontically treated teeth restored with prefabricated carbon fiber posts and varying quantities of coronal dentin. Sixty freshly extracted upper canines were randomly divided into groups of 10 teeth each. The specimens were exposed to 250,000 cycles in a controlled chewing simulator. All intact specimens were subjected to a static load (N) in a universal testing machine at 45 degrees to the long axis. Data were analyzed by 1-way analysis of variance and Tukey test (alpha = .05). Significant differences (P < .001) were found among the mean fracture forces of the test groups (positive control, 0 mm, 1 mm, 2 mm, 3 mm, and negative control groups: 1022.82 N, 1008.22 N, 1292.52 N, 1289.19 N, 1255.38 N, and 1582.11, respectively). These results suggested that the amount of coronal dentin did not significantly increase the fracture resistance of endodontically treated teeth restored with prefabricated carbon fiber post and composite resin core. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:e52-e57)

The Relationship between Blood and Serum Lead Levels in Peripartum Women and their Respective Umbilical Cords

Foetal exposure to lead (Pb) during pregnancy is a major problem. However, no previous study has examined whether Pb concentrations in blood (Pb-B) and in serum (Pb-S) from pregnant women correlate with Pb-B and Pb-S in the foetuses. This hypothesis was tested in the present study. We measured Pb-B and Pb-S in 120 healthy pregnant women (more than 38 weeks of gestation) and their respective umbilical cord samples. The analyses were carried out with an inductively coupled plasma mass spectrometer. We found higher Pb-B levels in the women compared with their respective umbilical cord samples (1.736 +/- 0.090 mu g/dL and 1.194 +/- 0.062 mu g/dL, respectively; p < 0.05). In parallel, we found higher Pb-S levels in the women compared with their respective umbilical cord samples (0.042 +/- 0.003 mu g/dL and 0.032 +/- 0.003 mu g/dL, respectively; p < 0.05). However, similar %Pb-S/Pb-B ratios were found in the women compared with their respective umbilical cord samples (2.414 +/- 0.210% and 2.740 +/- 0.219%, respectively; p > 0.05). Interestingly, we found positive correlations between Pb-B in the umbilical cords and Pb-B in the respective pregnant women (rs = 0.5714; p < 0.0001), and between Pb-S in the umbilical cords and Pb-S in the respective pregnant women (rs = 0.3902; p < 0.0001) as well as between %Pb-B/Pb-S in the umbilical cords and %Pb-B/Pb-S in the respective pregnant women (rs = 0.3767; p < 0.0001). These results indicate that the assessment of Pb-B and Pb-S in pregnant women provides relevant indexes of foetal exposure to Pb. Moreover, the similar %Pb-S/Pb-B in pregnant women and in the umbilical cords shows that the foetuses are directly exposed to the rapidly exchangeable Pb fraction found in their mothers.

Vitamin D receptor haplotypes affect lead levels during pregnancy

Pregnant women are particularly susceptible to toxic effects associated with lead (Pb) exposure. Pb accumulates in bone tissue and is rapidly mobilized from bones during pregnancy, thus resulting in fetal contamination. While vitamin D receptor (VDR) polymorphisms modify bone mineralization and affect Pb biomarkers including blood (Pb-B) and serum (Pb-S) Pb concentrations, and %Pb-S/Pb-B ratio, the effects of these polymorphisms on Pb levels in pregnant women are unknown. This study aimed at examining the effects of three (Fokl, Bsml and Apal) VDR polymorphisms (and VDR haplotypes) on Pb levels in pregnant women. Pb-B and Pb-S were determined by inductively coupled plasma mass spectrometry in samples from 256 healthy pregnant women and their respective umbilical cords. Genotypes for the VDR polymorphisms were determined by PCR and restriction fragment length digestion. While the three VDR polymorphisms had no significant effects on Pb-B, Pb-S or %Pb-S/Pb-B ratio, the haplotype combining the f, a, and b alleles for the Fokl, Apal and Bsml polymorphisms, respectively, was associated with significantly lower Pb-S and %Pb-S/Pb-B (P<0.05). However, maternal VDR haplotypes had no effects on Pb levels in the umbilical cords. To our knowledge, this is the first study showing that a combination of genetic polymorphisms (haplotype) commonly found in the VDR gene affects Pb-S and %Pb-S/Pb-B ratios in pregnant women. These findings may have major implications for Pb toxicity because they may help to predict the existence of a group of subjects that is genetically less prone to Pb toxicity during pregnancy. (C) 2010 Elsevier B.V. All rights reserved.

Should we measure serum or plasma lead concentrations?

Project: Serum samples may not be appropriate to assess lead (Pb) concentrations because they may contain artificially higher Pb concentrations compared with those measured in plasma samples. Here, we compared Pb concentrations in serum versus heparin plasma separated from blood collected with or without vacuum. We have also examined the effects of sample standing time on Pb concentrations measured in serum, heparin plasma, and EDTA plasma. Procedure: We studied plasma and serum samples from twelve healthy subjects. Blood samples were collected via venous drainage phlebotomy with and without vacuum into trace metal free tubes containing no anticoagulants (serum), or lithium heparin, or EDTA (to obtain plasma). Variable sample standing times (0, 5, and 30 min) prior to centrifugation were allowed. Plasma and serum Pb and iron concentrations were determined by inductively coupled plasma mass spectrometry. Plasma and serum cell-free hemoglobin concentrations were measured. Results: Pb concentrations in serum and in heparin plasma from blood samples collected with or without vacuum were similar and not associated with significant changes in iron or hemoglobin concentrations. The sample standing time (up to 30 min) did not affect Pb concentrations in serum or in heparin plasma, which were approximately 50% lower than those found in EDTA plasma. Conclusions: Serum or heparin plasma separated from blood samples collected via venous phlebotomy with or without vacuum are appropriate medium to assess Pb concentrations, independently of the sample standing time. (C) 2010 Elsevier GmbH. All rights reserved.

Human Alveolar Bone-Derived Cell-Culture Behaviour on Biodegradable Poly(L-lactic Acid)

Poly(L-lactic acid) (PLA) is a polymer of great technological interest, whose excellent mechanical properties, thermal plasticity and bioresorbability render it potentially useful for environmental applications, as a biodegradable plastic and as a biocompatible material in biomedicine. The interactions between an implant material surface and host cells play central roles in the integration, biological performance and clinical success of implanted biomedical devices. Osteoblasts from human alveolar bone were chosen to investigate the cell behaviour when in contact with PLA discs. Cell morphology and adhesion through osteopontin (OPN) and fibronectin (FN) expression were evaluated in the initial osteogenesis, as well as cell proliferation, alkaline phosphatase activity and bone nodule formation. It was shown that the polymer favoured cell attachment. Cell proliferation increased until 21 days but in a smaller rate when compared to the control group. On the other hand, ALP activity and bone mineralization were not enhanced by the polymer. It is suggested that this polymer favours cell adhesion in the early osteogenesis in vitro, but it does not enhance differentiation and mineralization. (C) Koninklijke Brill NV, Leiden, 2009

End-of-life practices in seven Brazilian pediatric intensive care units

Objective: To evaluate the incidence of life support limitation and medical practices in the last 48 hrs of life of children in seven Brazilian pediatric intensive care units (PICUs). Design. Cross-sectional multicenter retrospective study based on medical chart review. Setting: Seven PICUs belonging to university and tertiary hospitals located in three Brazilian regions: two in Porto Alegre (southern region), two in Sao Paulo (southeastern region), and three in Salvador (northeastern region). Patients. Medical records of all children who died in seven PICUs from January 2003 to December 2004. Deaths in the first 24 hrs of admission to the PICU and brain death were excluded. Interventions: Two pediatric intensive care residents from each PICU were trained to fill out a standard protocol (K = 0.9) to record demographic data and all medical management provided in the last 48 hrs of life (inotropes, sedatives, mechanical ventilation, full resuscitation maneuvers or not). Student`s t-test, analysis of variance, chi-square test, and relative risk were used for comparison of data. Measurements and Main Results. Five hundred and sixty-one deaths were identified; 97 records were excluded (61 because of brain death and 36 due to <24 hrs in the PICU). Thirty-six medical charts could not be found. Cardiopulmonary resuscitation was performed in 242 children (57%) with a significant difference between the southeastern and northeastern regions (p =.0003). Older age (p = .025) and longer PICU stay (p = .001) were associated with do-not-resuscitate orders. In just 52.5% of the patients with life support limitation, the decision was clearly recorded in the medical chart. No ventilatory support was provided in 14 cases. Inotropic drug infusions were maintained or increased in 66% of patients with do-not-resuscitate orders. Conclusions. The incidence of life support limitation has increased among Brazilian PICUs but with significant regional differences. Do-not-resuscitate orders are still the most common practice, with scarce initiatives for withdrawing or withholding life support measures.

Serological response of guinea pigs to oily and aqueous inactivated vaccines containing a Brazilian isolate of the Bovine Viral Diarrhea Virus (BVDV)

Bovine Viral Diarrhea Virus (BVDV) is widespread in cattle in Brazil and research shows its large antigenic variability. Available vaccines are produced with virus strains isolated in other countries and may not be effective. In this study, inactivated vaccines containing the Brazilian BVDV-Ib IBSP11 isolate were developed and tested on 6 groups of 10 guinea pigs (Cavia porcellus). Animals in groups A and C received an aqueous vaccine (aluminum hydroxide); B and D groups received an oily vaccine (Montanide ISA50); Group E positive-control animals were given an imported commercial vaccine with BVDV-la Singer; Group F animals were sham vaccinated (negative control). Groups A, B and E received two doses, and Groups C and D, three, every 21 days. Twelve blood samples were taken, at 21-day intervals over 231 days, and evaluated for antibody titer through virus-neutralization (VN), using a homologous strain (IBSP11), and a heterologous strain (BVDV-la NADL). Most animals, 42 days following the first dose, seroconverted to both strains and, after the second dose, there was a significant increase of titers in all groups. The oily formulation induced greater response after the third administration. This increase was not observed with the aqueous vaccines, regardless of the virus used in the VN. Antibody decline was more rapid in animals that received aqueous vaccines. The results showed the importance of studying the influence of endemic strains of commercial vaccines, to improve the efficacy of BVD vaccination. Use of the endemic strain in vaccine formulation presented promising results, as well as the use of guinea pigs as a laboratory model. (C) 2011 Elsevier Ltd. All rights reserved.

Tokamak magnetic field lines described by simple maps

The magnetic field line structure in a tokamak can be obtained by direct numerical integration of the field line equations. However, this is a lengthy procedure and the analysis of the solution may be very time-consuming. Otherwise we can use simple two-dimensional, area-preserving maps, obtained either by approximations of the magnetic field line equations, or from dynamical considerations. These maps can be quickly iterated, furnishing solutions that mirror the ones obtained from direct numerical integration, and which are useful when long-term studies of field line behavior are necessary (e.g. in diffusion calculations). In this work we focus on a set of simple tokamak maps for which these advantages are specially pronounced.

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Four aluminas were used as Supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between Support and modifier. The Supports were impregnated with different concentrations Of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount Of Surface modifier Oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide Should be identified above this limit when a complete coating is reached. The results obtained From XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide oil the Surface of alumina Support reached the coating in the limit of 15 Zr nm(-2), without the formation of the ZrO(2) phase. (c) 2009 Elsevier Inc. All rights reserved.

Tectonic implications of a paleomagnetic study of the Sarmiento Ophiolitic Complex, southern Chile

A paleomagnetic study was carried out on the Late Jurassic Sarmiento Ophiolitic Complex (SOC) exposed in the Magallanes fold and thrust belt in the southern Patagonian Andes (southern Chile). This complex, mainly consisting of a thick succession of pillow-lavas, sheeted dikes and gabbros, is a seafloor remnant of the Late Jurassic to Early Cretaceous Rocas Verdes basin that developed along the south-western margin of South America. Stepwise thermal and alternating field demagnetization permitted the isolation of a post-folding characteristic remanence, apparently carried by fine grain (SD?) magnetite, both in the pillow-lavas and dikes. The mean ""in situ"" direction for the SOC is Dec: 286.9 degrees, Inc: -58.5 degrees, alpha-95: 6.9 degrees, N: 11 (sites). Rock magnetic properties, petrography and whole-rock K-Ar ages in the same rocks are interpreted as evidence of correlation between remanence acquisition and a greenschist facies metamorphic overprint that must have occurred during latest stages or after closure and tectonic inversion of the basin in the Late Cretaceous. The mean remanence direction is anomalous relative to the expected Late Cretaceous direction from stable South America. Particularly, a declination anomaly over 50 degrees is suggestively similar to paleomagnetically interpreted counter clockwise rotations found in thrust slices of the Jurassic El Quemado Fm. located over 100 km north of the study area in Argentina. Nevertheless, a significant ccw rotation of the whole SOC is difficult to reconcile with geologic evidence and paleogeographic models that suggest a narrow back-arc basin sub-parallel to the continental margin. A rigid-body 30 degrees westward tilting of the SOC block around a horizontal axis trending NNW, is considered a much simpler explanation, being consistent with geologic evidence. This may have occurred as a consequence of inverse reactivation of old normal faults, which limit both the SOC exposures and the Cordillera Sarmiento to the East. The age of tilting is unknown but it must postdate remanence acquisition in the Late Cretaceous. Two major orogenic events of the southern Patagonian Andes, in the Eocene (ca. 42 Ma) and Middle Miocene (ca. 12 Ma), respectively, could have caused the proposed tilting. (C) 2008 Elsevier B.V. All rights reserved.

Sampling, WLS, and Mixed Models

Mixed models may be defined with or without reference to sampling, and can be used to predict realized random effects, as when estimating the latent values of study subjects measured with response error. When the model is specified without reference to sampling, a simple mixed model includes two random variables, one stemming from an exchangeable distribution of latent values of study subjects and the other, from the study subjects` response error distributions. Positive probabilities are assigned to both potentially realizable responses and artificial responses that are not potentially realizable, resulting in artificial latent values. In contrast, finite population mixed models represent the two-stage process of sampling subjects and measuring their responses, where positive probabilities are only assigned to potentially realizable responses. A comparison of the estimators over the same potentially realizable responses indicates that the optimal linear mixed model estimator (the usual best linear unbiased predictor, BLUP) is often (but not always) more accurate than the comparable finite population mixed model estimator (the FPMM BLUP). We examine a simple example and provide the basis for a broader discussion of the role of conditioning, sampling, and model assumptions in developing inference.

Performance of balanced two-stage empirical predictors of realized cluster latent values from finite populations: A simulation study

Predictors of random effects are usually based on the popular mixed effects (ME) model developed under the assumption that the sample is obtained from a conceptual infinite population; such predictors are employed even when the actual population is finite. Two alternatives that incorporate the finite nature of the population are obtained from the superpopulation model proposed by Scott and Smith (1969. Estimation in multi-stage surveys. J. Amer. Statist. Assoc. 64, 830-840) or from the finite population mixed model recently proposed by Stanek and Singer (2004. Predicting random effects from finite population clustered samples with response error. J. Amer. Statist. Assoc. 99, 1119-1130). Predictors derived under the latter model with the additional assumptions that all variance components are known and that within-cluster variances are equal have smaller mean squared error (MSE) than the competitors based on either the ME or Scott and Smith`s models. As population variances are rarely known, we propose method of moment estimators to obtain empirical predictors and conduct a simulation study to evaluate their performance. The results suggest that the finite population mixed model empirical predictor is more stable than its competitors since, in terms of MSE, it is either the best or the second best and when second best, its performance lies within acceptable limits. When both cluster and unit intra-class correlation coefficients are very high (e.g., 0.95 or more), the performance of the empirical predictors derived under the three models is similar. (c) 2007 Elsevier B.V. All rights reserved.

Inferential Implications of Over-Parametrization: A Case Study in Incomplete Categorical Data

P>In the context of either Bayesian or classical sensitivity analyses of over-parametrized models for incomplete categorical data, it is well known that prior-dependence on posterior inferences of nonidentifiable parameters or that too parsimonious over-parametrized models may lead to erroneous conclusions. Nevertheless, some authors either pay no attention to which parameters are nonidentifiable or do not appropriately account for possible prior-dependence. We review the literature on this topic and consider simple examples to emphasize that in both inferential frameworks, the subjective components can influence results in nontrivial ways, irrespectively of the sample size. Specifically, we show that prior distributions commonly regarded as slightly informative or noninformative may actually be too informative for nonidentifiable parameters, and that the choice of over-parametrized models may drastically impact the results, suggesting that a careful examination of their effects should be considered before drawing conclusions.Resume Que ce soit dans un cadre Bayesien ou classique, il est bien connu que la surparametrisation, dans les modeles pour donnees categorielles incompletes, peut conduire a des conclusions erronees. Cependant, certains auteurs persistent a negliger les problemes lies a la presence de parametres non identifies. Nous passons en revue la litterature dans ce domaine, et considerons quelques exemples surparametres simples dans lesquels les elements subjectifs influencent de facon non negligeable les resultats, independamment de la taille des echantillons. Plus precisement, nous montrons comment des a priori consideres comme peu ou non-informatifs peuvent se reveler extremement informatifs en ce qui concerne les parametres non identifies, et que le recours a des modeles surparametres peut avoir sur les conclusions finales un impact considerable. Ceci suggere un examen tres attentif de l`impact potentiel des a priori.

Comparing diagnostic tests with missing data

When missing data occur in studies designed to compare the accuracy of diagnostic tests, a common, though naive, practice is to base the comparison of sensitivity, specificity, as well as of positive and negative predictive values on some subset of the data that fits into methods implemented in standard statistical packages. Such methods are usually valid only under the strong missing completely at random (MCAR) assumption and may generate biased and less precise estimates. We review some models that use the dependence structure of the completely observed cases to incorporate the information of the partially categorized observations into the analysis and show how they may be fitted via a two-stage hybrid process involving maximum likelihood in the first stage and weighted least squares in the second. We indicate how computational subroutines written in R may be used to fit the proposed models and illustrate the different analysis strategies with observational data collected to compare the accuracy of three distinct non-invasive diagnostic methods for endometriosis. The results indicate that even when the MCAR assumption is plausible, the naive partial analyses should be avoided.

Leverage analysis for linear mixed models

We consider a generalized leverage matrix useful for the identification of influential units and observations in linear mixed models and show how a decomposition of this matrix may be employed to identify high leverage points for both the marginal fitted values and the random effect component of the conditional fitted values. We illustrate the different uses of the two components of the decomposition with a simulated example as well as with a real data set.