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1.
Clin Oral Investig ; 26(5): 3939-3947, 2022 May.
Article in English | MEDLINE | ID: mdl-35039941

ABSTRACT

OBJECTIVES: This study aims to evaluate the effects of cyclic loading on the bending moments and the developed stress state of austenitic and R-phase endodontic files through finite element analysis. MATERIALS AND METHODS: The mechanical properties of two groups of NiTi wires, austenite and R-phase, were measured in samples at two different conditions: uncycled and cycled. The cycled condition was achieved by subjecting samples of the two groups to 80% of the corresponding fatigue life under rotating bending efforts. The measured mechanical properties were then used in the finite element analysis, where the boundary and loading conditions were set to replicate a standard bending test. RESULTS: The results showed that mechanical cycling leads to decreasing stress levels and bending moments in the simulated files, especially in the austenitic ones. In comparison with austenite, R-phase presented a more stable mechanical behavior during cycling. CONCLUSIONS: The results show that the moment and stress calculated for an instrument under bending can be considerably decreased after some cyclic work. CLINICAL RELEVANCE: The fatigue related to the clinical use of an endodontic file decreases the moment (as well as the forces) imposed by the instrument during the shaping of a curved root canal. This decrease is directly related to the type of atomic array present in the alloy.


Subject(s)
Dental Alloys , Titanium , Equipment Design , Fatigue , Finite Element Analysis , Humans , Materials Testing , Root Canal Preparation , Stress, Mechanical
2.
Front Plant Sci ; 10: 916, 2019.
Article in English | MEDLINE | ID: mdl-31354779

ABSTRACT

Photosynthesis involves the conversion of sunlight energy into stored chemical energy, which is achieved through electron transport along a series of redox reactions. Excess photosynthetic electron transport might be dangerous due to the risk of molecular oxygen reduction, generating reactive oxygen species (ROS) over-accumulation. Avoiding excess ROS production requires the rate of electron transport to be coordinated with the capacity of electron acceptors in the chloroplast stroma. Imbalance between the donor and acceptor sides of photosystem I (PSI) can lead to inactivation, which is called PSI photoinhibition. We used a light-inducible PSI photoinhibition system in Arabidopsis thaliana to resolve the time dynamics of inhibition and to investigate its impact on ROS production and turnover. The oxidation state of the PSI reaction center and rates of CO2 fixation both indicated strong and rapid PSI photoinhibition upon donor side/acceptor side imbalance, while the rate of inhibition eased during prolonged imbalance. PSI photoinhibition was not associated with any major changes in ROS accumulation or antioxidant activity; however, a lower level of lipid oxidation correlated with lower abundance of chloroplast lipoxygenase in PSI-inhibited leaves. The results of this study suggest that rapid activation of PSI photoinhibition under severe photosynthetic imbalance protects the chloroplast from over-reduction and excess ROS formation.

3.
J Exp Bot ; 70(2): 627-639, 2019 01 07.
Article in English | MEDLINE | ID: mdl-30312463

ABSTRACT

Retrograde signalling pathways that are triggered by changes in cellular redox homeostasis remain poorly understood. Transformed rice plants that are deficient in peroxisomal ascorbate peroxidase APX4 (OsAPX4-RNAi) are known to exhibit more effective protection of photosynthesis against oxidative stress than controls when catalase (CAT) is inhibited, but the mechanisms involved have not been characterized. An in-depth physiological and proteomics analysis was therefore performed on OsAPX4-RNAi CAT-inhibited rice plants. Loss of APX4 function led to an increased abundance of several proteins that are involved in essential metabolic pathways, possibly as a result of increased tissue H2O2 levels. Higher photosynthetic activities observed in the OsAPX4-RNAi plants under CAT inhibition were accompanied by higher levels of Rubisco, higher maximum rates of Rubisco carboxylation, and increased photochemical efficiencies, together with large increases in photosynthesis-related proteins. Large increases were also observed in the levels of proteins involved in the ascorbate/glutathione cycle and in other antioxidant-related pathways, and these changes may be important in the protection of photosynthesis in the OsAPX4-RNAi plants. Large increases in the abundance of proteins localized in the nuclei and mitochondria were also observed, together with increased levels of proteins involved in important cellular pathways, particularly protein translation. Taken together, the results show that OsAPX4-RNAi plants exhibit significant metabolic reprogramming, which incorporates a more effective antioxidant response to protect photosynthesis under conditions of impaired CAT activity.


Subject(s)
Ascorbate Peroxidases/metabolism , Catalase/metabolism , Oryza/metabolism , Oxidative Stress , Photosynthesis , RNA Interference
4.
Dent Mater ; 29(12): e318-24, 2013 Dec.
Article in English | MEDLINE | ID: mdl-24183054

ABSTRACT

OBJECTIVE: Comparison of physical and mechanical properties of one conventional and a new NiTi wire, which had received an additional thermomechanical treatment. METHODS: Specimens of both conventional (NiTi) and the new type of wire, called M-Wire (MW), were subjected to tensile and three-point bending tests, Vickers microhardness measurements, and to rotating-bending fatigue tests at a strain-controlled level of 6%. Fracture surfaces were observed by scanning electron microscopy and the non-deformed microstructures by transmission electron microscopy. RESULTS: The thermomechanical treatment applied to produce the M-Wire apparently increased the tensile strength and Vickers microhardness of the material, but its apparent Young modulus was smaller than that of conventionally treated NiTi. The three-point bending tests showed a higher flexibility for MW which also exhibited a significantly higher number of cycles to failure. SIGNIFICANCE: M-Wire presented mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed NiTi wires.


Subject(s)
Endodontics/instrumentation , Materials Testing , Nickel , Titanium , Microscopy, Electron, Scanning , Microscopy, Electron, Transmission , Tensile Strength
5.
Article in English | MEDLINE | ID: mdl-16997104

ABSTRACT

OBJECTIVE: Evaluate the effect of 5.25% NaOCl on the surface characteristics and fatigue resistance of ProFile. STUDY DESIGN: Eighty new ProFile instruments were divided into 1 control group (CG) and 3 experimental groups (EG1, EG2, EG3). Instruments of EG1 were immersed in 5.25% NaOCl for 24 hours. Instruments of EG2 and EG3 shaped 10 curved root canals, using, respectively, deionized water and 5.25% NaOCl as irrigants. Surface characteristics were observed by scanning electron microscopy. All instruments were then submitted to fatigue tests. Two-way ANOVA tests were employed to compare the results. RESULTS: Surface characteristics showed no alteration after the immersion tests. The fatigue resistance of instruments in EG2 and EG3 was significantly lower than in CG and EG1. CONCLUSIONS: Immersion of ProFile in 5.25% NaOCl for 24 hours had no influence on surface characteristics and fatigue resistance. Simulated clinical use was a decisive factor in the decrease of fatigue life.


Subject(s)
Dental Alloys , Dental Instruments , Nickel , Root Canal Irrigants , Root Canal Preparation/instrumentation , Sodium Hypochlorite , Titanium , Analysis of Variance , Corrosion , Dental Stress Analysis , Equipment Failure , Equipment Reuse , Humans , Materials Testing , Microscopy, Electron, Scanning , Surface Properties
6.
Arch Inst Cardiol Mex ; 61(1): 75-8, 1991.
Article in Spanish | MEDLINE | ID: mdl-2048915

ABSTRACT

We describe the case of a patient aged 64 with aortic valve disease and pericardial effusion. Echocardiographic evaluation showed an intrapericardial mass of about 7 cm of diameter with clotted appearance, adhered to the visceral leaf, at the level of the atrio-ventricular function. Because of this finding we performed color codified Doppler echocardiography, observing that this mass acquired a blue hue during diastole and mosaic hue at the end of the systole, realizing that this phenomenon was due to fluid retention. There are many publications about the value of echocardiography for the identification of pericardial masses and some of them show how an effusion can hide a tumor. The interest of this particular case lies in that the effusion simulated a tumor and by means of the color codified Doppler we could demonstrate that it corresponded to the stream of the pericardial fluid. During the surgical procedure the absence of the mass was corroborated.


Subject(s)
Echocardiography, Doppler , Heart Neoplasms/diagnostic imaging , Pericardial Effusion/diagnostic imaging , Aortic Valve Insufficiency/complications , Aortic Valve Insufficiency/diagnostic imaging , Calcinosis/complications , Calcinosis/diagnostic imaging , Diagnosis, Differential , Humans , Male , Middle Aged , Pericardial Effusion/etiology , Pericardium/diagnostic imaging
7.
Arch Inst Cardiol Mex ; 59(1): 55-61, 1989.
Article in Spanish | MEDLINE | ID: mdl-2486735

ABSTRACT

Thirty healthy individuals with no history of cardiovascular disease were studied to determine the electrocardiographic effects of maximal exercise immediately followed by ingestion of ice water. The subjects were subgrouped according to their training into (A) high (N = 5), (B) moderate (N = 14) and (C) low (N = 11) levels. Electrocardiograms (ECGs) were taken at rest and at rest with ingestion of ice water followed by maximal stress tests. Maximal stress tests were repeated followed by ingestion of ice water at the beginning of and at 2, 3, 6 and 9 minutes of recuperation. The stress test combining maximal effort and ice water ingestion was positive in all members of Group A, in 4 from Group B and in 1 from Group C. A stress test associating maximal effort with ice water ingestion is a useful method of detecting subjects susceptible to changes in ECG which appear to be secondary to coronary spasm. It has a low cost it is simple to perform and represents minimal risk.


Subject(s)
Drinking , Electrocardiography , Exercise Test/methods , Adult , Cold Temperature , Female , Humans , Male
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