Three-Dimensional Finite Element Analysis of Stress Distribution on Different Bony Ridges With Different Lengths of Morse Taper Implants and Prosthesis Dimensions

This finite element analysis (FEA) compared stress distribution on different bony ridges rehabilitated with different lengths of morse taper implants, varying dimensions of metal-ceramic crowns to maintain the occlusal alignment. Three-dimensional FE models were designed representing a posterior left side segment of the mandible: group control, 3 implants of 11 mm length; group 1, implants of 13 mm, 11 mm and 5 mm length; group 2, 1 implant of 11 mm and 2 implants of 5 mm length; and group 3, 3 implants of 5 mm length. The abutments heights were 3.5 mm for 13- and 11-mm implants (regular), and 0.8 mm for 5-mm implants (short). Evaluation was performed on Ansys software, oblique loads of 365N for molars and 200N for premolars. There was 50% higher stress on cortical bone for the short implants than regular implants. There was 80% higher stress on trabecular bone for the short implants than regular implants. There was higher stress concentration on the bone region of the short implants neck. However, these implants were capable of dissipating the stress to the bones, given the applied loads, but achieving near the threshold between elastic and plastic deformation to the trabecular bone. Distal implants and/or with biggest occlusal table generated greatest stress regions on the surrounding bone. It was concluded that patients requiring short implants associated with increased proportions implant prostheses need careful evaluation and occlusal adjustment, as a possible overload in these short implants, and even in regular ones, can generate stress beyond the physiological threshold of the surrounding bone, compromising the whole system.

Plasma corticosterone elevation inhibits the activation of nuclear factor kappa B (NFKB) in the Syrian hamster pineal gland

We evaluated how the mild stress-induced increase in endogenous corticosterone affected the pineal gland in Syrian hamsters (Mesocricetus auratus). The animals were maintained under constant light for 1 day, instead of a cycle of 14:10-h, to increase the circulating corticosterone levels during the daytime. The nuclear translocation of nuclear factor kappa B (NFKB), which is the pivotal transcription factor for stress and injury, presented a daily rhythm in normal animals. NFKB nuclear content increased linearly from the onset of light [Zeitgeber Time 0 (ZT0)] until ZT11 and decreased after ZT12 when the plasma corticosterone peak was detected in normal animals. However, the 24-h profiles of the two curves were different, and they did not clearly support an exclusive relationship between corticosterone levels and NFKB content. Therefore, we tested the effect of increased endogenous corticosterone through inducing mild stress by maintaining daytime illumination for one night. This stressful condition, which increased daytime corticosterone levels, resulted in a daytime decrease in NFKB nuclear content, and this was inhibited by mifepristone. Overall, this study shows that NFKB has a daily rhythm in Syrian hamster pineal glands and, by increasing endogenous corticosterone with a stressful condition, NFKB activity is regulated. Therefore, this study suggests that the pineal gland in the Syrian hamster is a sensor of stressful conditions.

Describing fatigue crack growth and load ratio effects in Al 2524 T3 alloy with an enhanced exponential model

The fatigue crack behavior in metals and alloys under constant amplitude test conditions is usually described by relationships between the crack growth rate da/dN and the stress intensity factor range Delta K. In the present work, an enhanced two-parameter exponential equation of fatigue crack growth was introduced in order to describe sub-critical crack propagation behavior of Al 2524-T3 alloy, commonly used in aircraft engineering applications. It was demonstrated that besides adequately correlating the load ratio effects, the exponential model also accounts for the slight deviations from linearity shown by the experimental curves. A comparison with Elber, Kujawski and "Unified Approach" models allowed for verifying the better performance, when confronted to the other tested models, presented by the exponential model. (C) 2012 Elsevier Ltd. All rights reserved.

Fatigue crack growth assessments in welded components including crack closure effects: Experiments and 3-D numerical modeling

This work provides a numerical and experimental investigation of fatigue crack growth behavior in steel weldments including crack closure effects and their coupled interaction with weld strength mismatch. A central objective of this study is to extend previously developed frameworks for evaluation of crack clo- sure effects on FCGR to steel weldments while, at the same time, gaining additional understanding of commonly adopted criteria for crack closure loads and their influence on fatigue life of structural welds. Very detailed non-linear finite element analyses using 3-D models of compact tension C ( T ) fracture spec- imens with center cracked, square groove welds provide the evolution of crack growth with cyclic stress intensity factor which is required for the estimation of the closure loads. Fatigue crack growth tests con- ducted on plane-sided, shallow-cracked C ( T ) specimens provide the necessary data against which crack closure effects on fatigue crack growth behavior can be assessed. Overall, the present investigation pro- vides additional support for estimation procedures of plasticity-induced crack closure loads in fatigue analyses of structural steels and their weldments

Extracytoplasmic function (ECF) sigma factor sigma(F) is involved in Caulobacter crescentus response to heavy metal stress

Background: The alpha-proteobacterium Caulobacter crescentus inhabits low-nutrient environments and can tolerate certain levels of heavy metals in these sites. It has been reported that C. crescentus responds to exposure to various heavy metals by altering the expression of a large number of genes. Results: In this work, we show that the ECF sigma factor sigma(F) is one of the regulatory proteins involved in the control of the transcriptional response to chromium and cadmium. Microarray experiments indicate that sigma(F) controls eight genes during chromium stress, most of which were previously described as induced by heavy metals. Surprisingly, sigma(F) itself is not strongly auto-regulated under metal stress conditions. Interestingly, sigma(F)-dependent genes are not induced in the presence of agents that generate reactive oxygen species. Promoter analyses revealed that a conserved sigma(F)-dependent sequence is located upstream of all genes of the sigma(F) regulon. In addition, we show that the second gene in the sigF operon acts as a negative regulator of sigma(F) function, and the encoded protein has been named NrsF (Negative regulator of sigma F). Substitution of two conserved cysteine residues (C131 and C181) in NrsF affects its ability to maintain the expression of sigma(F)-dependent genes at basal levels. Furthermore, we show that sigma(F) is released into the cytoplasm during chromium stress and in cells carrying point mutations in both conserved cysteines of the protein NrsF. Conclusion: A possible mechanism for induction of the sigma(F)-dependent genes by chromium and cadmium is the inactivation of the putative anti-sigma factor NrsF, leading to the release of sigma(F) to bind RNA polymerase core and drive transcription of its regulon.

Low-level laser therapy (808 nm) reduces inflammatory response and oxidative stress in rat tibialis anterior muscle after cryolesion

Background and Objective Muscle regeneration is a complex phenomenon, involving coordinated activation of several cellular responses. During this process, oxidative stress and consequent tissue damage occur with a severity that may depend on the intensity and duration of the inflammatory response. Among the therapeutic approaches to attenuate inflammation and increase tissue repair, low-level laser therapy (LLLT) may be a safe and effective clinical procedure. The aim of this study was to evaluate the effects of LLLT on oxidative/nitrative stress and inflammatory mediators produced during a cryolesion of the tibialis anterior (TA) muscle in rats. Material and Methods Sixty Wistar rats were randomly divided into three groups (n?=?20): control (BC), injured TA muscle without LLLT (IC), injured TA muscle submitted to LLLT (IRI). The injured region was irradiated daily for 4 consecutive days, starting immediately after the lesion using a AlGaAs laser (continuous wave, 808?nm, tip area of 0.00785?cm2, power 30?mW, application time 47?seconds, fluence 180?J/cm2; 3.8?mW/cm2; and total energy 1.4?J). The animals were sacrificed on the fourth day after injury. Results LLLT reduced oxidative and nitrative stress in injured muscle, decreased lipid peroxidation, nitrotyrosine formation and NO production, probably due to reduction in iNOS protein expression. Moreover, LLLT increased SOD gene expression, and decreased the inflammatory response as measured by gene expression of NF-k beta and COX-2 and by TNF-a and IL-1 beta concentration. Conclusion These results suggest that LLLT could be an effective therapeutic approach to modulate oxidative and nitrative stress and to reduce inflammation in injured muscle. Lasers Surg. Med. 44: 726735, 2012. (c) 2012 Wiley Periodicals, Inc.

Extracytoplasmic function (ECF) sigma factor σF is involved in Caulobacter crescentus response to heavy metal stress

Background The α-proteobacterium Caulobacter crescentus inhabits low-nutrient environments and can tolerate certain levels of heavy metals in these sites. It has been reported that C. crescentus responds to exposure to various heavy metals by altering the expression of a large number of genes. Results In this work, we show that the ECF sigma factor σF is one of the regulatory proteins involved in the control of the transcriptional response to chromium and cadmium. Microarray experiments indicate that σF controls eight genes during chromium stress, most of which were previously described as induced by heavy metals. Surprisingly, σF itself is not strongly auto-regulated under metal stress conditions. Interestingly, σF-dependent genes are not induced in the presence of agents that generate reactive oxygen species. Promoter analyses revealed that a conserved σF-dependent sequence is located upstream of all genes of the σF regulon. In addition, we show that the second gene in the sigF operon acts as a negative regulator of σF function, and the encoded protein has been named NrsF (Negative regulator of sigma F). Substitution of two conserved cysteine residues (C131 and C181) in NrsF affects its ability to maintain the expression of σF-dependent genes at basal levels. Furthermore, we show that σF is released into the cytoplasm during chromium stress and in cells carrying point mutations in both conserved cysteines of the protein NrsF. Conclusion A possible mechanism for induction of the σF-dependent genes by chromium and cadmium is the inactivation of the putative anti-sigma factor NrsF, leading to the release of σF to bind RNA polymerase core and drive transcription of its regulon.

The tale of a person and a peptide: Wylie W. Vale Jr. and the role of corticotropin- releasing factor in the stress response

The studies reviewed in this article certainly do not constitute the entire body of research conducted by Wylie Vale's group and his collaborators, they might constitute turning points in CRF research. In addition, the studies reviewed here show that, over the course of 31 years (from 1981 to 2012), Wylie tirelessly pursued the answers to fundamental questions regarding CRF. He was a man whose drive never seemed to falter