Fatigue strength of tungsten inert gas-repaired weld joints in airplane critical structures

In this work the effect of Gas Tungsten Arc Welding (GTAW) repairs on the axial fatigue strength of an AISI 4130 steel welded joint used in airframe critical to the flight-safety was investigated. Fatigue tests were performed at room temperature on 0.89 mm thick hot-rolled plates with constant amplitude and load ratio of R = 0.1, at 20 Hz frequency. Monotonic tensile tests, optical metallography and microhardness, residual stress and weld geometric factors measurements were also performed. The fatigue strength decreased with the number of GTAW repairs, and was related to microstructural and microhardness changes, as well as residual stress field and weld profile geometry factors, which gave origin to high stress concentration at the weld toe. (C) 2011 Elsevier B.V. All rights reserved.

Biocompatibility in vitro tests of mineral trioxide aggregate and regular and white Portland cements

Mineral trioxide aggregate (MTA) and Portland cement are being used in dentistry as root end-filling materials. However, biocompatibility data concerning genotoxicity and cytotoxicity are needed for complete risk assessment of these compounds. In the present study, genotoxic and cytotoxic effects of MTA and Portland cements were evaluated in vitro using the alkaline single cell gel (comet) assay and trypan blue exclusion test, respectively, on mouse lymphoma cells. The results demonstrated that the single cell gel (comet) assay failed to detect DNA damage after a treatment of cells by MTA and Portland cements for concentrations up to 1000 mu g/ml. Similarly, results showed that none of the compounds tested were cytotoxic. Taken together, these results seem to indicate that MTA and Portland cements are not genotoxins and do not induce cellular death.

Evaluation of genetic damage in human peripheral lymphocytes exposed to mineral trioxide aggregate and Portland cements

Mineral trioxide aggregate (MTA) and Portland cement are being used in dentistry as root-end-filling material for periapical surgery and for the sealing of communications between the root canal system and the surrounding tissues. However, genotoxicity tests for complete risk assessment of these compounds have not been conducted up to now. In the present study, the genotoxic effects of MTA and Portland cements were evaluated in peripheral lymphocytes from 10 volunteers by the alkaline single cell gel (comet) assay. The results pointed out that the single cell gel (comet) assay failed to detect the presence of DNA damage after a treatment of peripheral lymphocytes by MTA and Portland cements for concentrations up to 1000 mu g mL(-1). In summary, our results indicate that exposure to MTA or Portland cements may not be a factor that increases the level of DNA lesions in human peripheral lymphocytes as detected by single cell gel (comet) assay.

Mineral trioxide aggregate stimulates macrophages and mast cells to release neutrophil chemotactic factors: role of IL-1 beta, MIP-2 and LTB4

Objective. In the present study, the role of macrophages and mast cells in mineral trioxide aggregate (MTA)-induced release of neutrophil chemotactic factor was investigated.Study design. MTA suspension (50 mg/mL) was plated over inserts on macrophages or mast cells for 90 minutes. Untreated cells served as controls. Cells were washed and cultured for 90 minutes in RPMI without the stimuli. Macrophages and mast cell supernatants were injected intraperitoneally (0.5 mL/cavity), and neutrophil migration was assessed 6 hours later. In some experiments, cells were incubated for 30 minutes with dexamethasone (DEX, 10 mu M/well), BWA4C (BW, 100 mu M/well) or U75302 (U75, 10 mu M/well). The concentration of Leukotriene B-4 (LTB4) in the cell-free supernatant from mast cells and macrophage culture was measured by ELISA.Results. Supernatants from MTA-stimulated macrophages and mast cells caused neutrophil migration. The release of neutrophil chemotactic factor by macrophages and mast cells was significantly inhibited by DEX, BW, or U75. Macrophages and mast cells expressed mRNA for interleukin-1 (IL-1)beta and macrophage inflammatory protein-2 (MIP-2) and the pretreatment of macrophages and mast cells with DEX, BW, or U75 significantly altered IL-1 beta and MIP-2 mRNA expression. LTB4 was detected in the MTA-stimulated macrophage supernatant but not mast cells.Conclusions. MTA-induces the release of neutrophil chemotactic factor substances from macrophages and mast cells with participation of IL-1 beta, MIP-2, and LTB4. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010; 109: e135-e142)

Reaction of the lateral periodontium of dogs' teeth to contaminated and noncontaminated perforations filled with mineral trioxide aggregate

It has been shown that the mineral trioxide aggregate (MTA) used to seal lateral/furcal perforations stimulates the deposition of newly formed cementum. Nevertheless, when the site of the perforation is contaminated, the healing process might occur under less favorable conditions. This study evaluated the repair healing process of noncontaminated and contaminated lateral perforations filled with MTA and the effect of previously filling the contaminated perforations with a bactericidal agent. Thirty lateral root perforations were prepared in endodontically treated dog's teeth, thus forming 3 groups with 10 specimens each. In group 1 the perforations were immediately sealed with MTA. In group 2 the perforations were left open for 7 days and thereafter sealed with MTA. In group 3 the perforations were left open for 7 days, filled temporarily with a calcium hydroxide-based paste for 14 days, and then sealed with MTA. The animals were killed after 90 days, and the pieces were prepared for histomorphologic and histomicrobiologic evaluations. The statistical analysis showed that group 1 had significantly better repair than groups 2 (P <.05) and 3 (P <.05), which validates the superior results obtained when MTA was immediately used to seal root perforations. Groups 2 and 3 had statistically similar repair to each other (P >.05). There were a larger number of cases of complete or partial biologic seal in group 1 compared with the contaminated groups. It might be concluded that the lateral root perforations sealed with MTA after contamination presented worse repair than the noncontaminated, immediately sealed perforations. The temporary filling with a bactericidal agent (calcium hydroxide-based paste) did not improve the repair of perforations exposed to contamination, and the contaminated groups presented similar results to each other.

Influence of the type of vehicle and limit of obturation on apical and periapical tissue response in dogs' teeth after root canal filling with mineral trioxide aggregate

The purpose of this study was to investigate the influence of the type of vehicle (distilled water or propyleneglycol) on the response of apical tissues of dogs' teeth after root canal filling with mineral trioxide aggregate (MTA) at two different limits. Forty roots of incisors and premolars of two adult dogs were used. After pulpectomy, the root canals were prepared biomechanically, and the roots had the apical cemental barrier penetrated with a #15 K-file and widened to a #25 K-file. The root canals were assigned to four groups according to the vehicle used for MTA (ProRoot-MTA; Tulsa Dental, Tulsa, OK) preparation and the limit of root canal filling: group 1, filling with MTA/distilled water to the limit of the cemental canal; group 2, overfilling with MTA/distilled water, group 3, filling with MTA/propyleneglycol to the limit of the cemental canal; and group 4, overfilling with MTAlpropyleneglycol. The animals were killed by anesthetic overdose 90 days after endodontic treatment and the anatomic pieces were prepared for histomorphological analysis. The sections were stained with hematoxylin and eosin and Brown and Brenn techniques. The results showed that MTA pastes prepared with either distilled water or propyleneglycol as vehicles had similar biological behavior (p > 0.05); root fillings placed at the cemental canal limit showed better results than the overfillings (p = 0.01), and MTA/propyleneglycol paste was more easily placed into the root canals than MTA/distilled water paste.

Evaluation of Rat Alveolar Bone Response to Angelus MTA or Experimental Light-cured Mineral Trioxide Aggregate Using Fluorochromes

Introduction: The aim of this study was to evaluate the rat alveolar bone response after the implantation of experimental light-cured mineral trioxide aggregate (MTA) or Angelus MTA (Angelus, Londrina, Parana, Brazil) by histological and fluorescence analysis. Methods: Thirty Wistar Albino rats were divided into three groups. In the control group, empty polyethylene tubes were inserted into the rat alveolar sockets immediately after extraction. In the other groups, the tubes were filled with light-cured MTA or Angelus MTA. Five animals from each group were injected with calcein on day 7, alizarin on day 14, and oxytetracycline on day 21. on day 30, these animals were killed, and the right hemimaxillas were removed and histologically processed. Half of the maxillas were processed and stained with hematoxylin and eosin. The remaining maxillas were processed for fluorescence analysis and stained with Stevenel blue and alizarin red. New bone was histomorphometrically evaluated using a Merz grid. Results: The light-cured MTA presented a similar response when compared with Angelus MTA; it was characterized by a mild inflammatory response and complete bone healing. In the light-cured MTA group, the fluorescence areas were more evident at 21 days, showing an increase in bone formation. However, dystrophic mineralization was observed only with Angelus MTA. Conclusions: It was concluded that both materials present a similar inflammatory response and bone healing, but dystrophic mineralization was observed only with Angelus MTA. (J Endod 2011;37:250-254)

Evaluation of mineral trioxide aggregate and calcium hydroxide cement as pulp-capping agents in human teeth

This study evaluated the histomorphologic response of human dental pulps capped with mineral trioxide aggregate (MTA) and Ca(OH)(2) cement (CH). Pulp exposures were performed on the occlusal floor of 40 human permanent premolars. After that, the pulp was capped either with CH or MTA and restored with composite resin. After 30 and 60 days, teeth were extracted and processed for histologic exam and categorized in a histologic score system. The data were subjected to Kruskal-Wallis and Conover tests (alpha = .05). All groups performed well in terms of hard tissue bridge formation, inflammatory response, and other pulpal findings. However, a lower response of CH30 was observed for the dentin bridge formation, when compared with MTA30 and MTA60 groups. Although the pulp healing with calcium hydroxide was slower than that of MTA, both materials were successful for pulp capping in human teeth.

Mineral trioxide aggregate but not light-cure mineral trioxide aggregate stimulated mineralization

The purpose of this study was to evaluate the subcutaneous response of rat connective tissue to light-cure MTA and Angelus MTA. These materials were placed in polyethylene and dentin tubes and implanted into dorsal connective tissue of Wistar rats for 30 and 60 days. The specimens were prepared to be stained with hematoxylin-eosin, Von Kossa, and without stain for polarized light and evaluated in an optic microscope. The Angelus MTA showed a mild inflammatory response at 30 days and none at 60 days, characterized by organized connective tissue, presence of some chronic inflammatory cells, and induction of mineralized tissue formation. Light-cure MTA presented a moderate chronic inflammatory response at 30 days that decreased at 60 days but was more intense than with Angelus MTA and without dystrophic calcifications. It was possible to conclude that light-cure MTA was similar to MTA at 60 days, but it did not stimulate mineralization.

A Mineral Trioxide Aggregate Sealer Stimulated Mineralization

The aim of this study was to evaluate the rat subcutaneous tissue response to implanted polyethylene tubes filled with Endo-CPM-Sealer (Portland Cement Modified Sealer) (EGEO S.R.L., Buenos Aires, Argentina) compared with Sealapex (SybronEndo, Glendora, CA) and Angelus MTA (Angelus, Londrina, Brazil). These materials were placed in polyethylene and dentin tubes and implanted into dorsal connective tissue of Wistar rats for 7, 15, 30, 60, and 90 days. The specimens were prepared to be stained with hematoxylin and eosin or Von Kossa or not stained for polarized light. Qualitative and quantitative evaluations of the reaction were performed. Both materials caused mild to moderate reactions at 7 days that decreased with time. The response was similar to the control on the 30th day with Endo-CPM-Sealer and Angelus MTA and on the 60th day with Sealapex. Mineralization and granulations birefringent to the polarized light were observed with all materials. it was possible to conclude that Endo-CPM-Sealer was biocompatible and stimulated mineralization. (J Endod 2009;35:256-260)

Mineral Trioxide Aggregate-based Endodontic Sealer Stimulates Hydroxyapatite Nucleation in Human Osteoblast-like Cell Culture

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Scanning electron microscopy evaluation of the hard tissue barrier after pulp capping with calcium hydroxide, mineral trioxide aggregate (MTA) or ProRoot MTA

The aim of this study was to investigate the morphology and localisation of calcium hydroxide- and mineral trioxide aggregate (MTA)-induced hard tissue barriers after pulpotomy in dogs' teeth. Pulpotomies were performed on maxillary and mandibular premolars of five dogs. The teeth were assigned into three groups according to the pulp-capping agent used. The pulpal wounds were capped with calcium hydroxide (Ca(OH)(2) - control), MTA or ProRoot MTA, and the cavities were restored with amalgam. After a 90-day follow-up period, the dogs were euthanised and the teeth were examined under scanning electron microscopy (SEM). An image-processing and analysis software was used to delimit the perimeters of the root canal area and the hard tissue barrier to determine the percentage of root canal obliteration. SEM data were used to assess the morphology, localisation and extension of the reparative hard tissue barriers. ProRoot MTA was statistically different from MTA and Ca(OH)(2) (P < 0.05) regarding tissue barrier morphology. Localisation data showed that ProRoot MTA was significantly different from Ca(OH)(2) (P < 0.05) and similar to MTA (P > 0.01; P > 0.05). No statistically significant difference (P > 0.01; P > 0.05) was observed between MTA and Ca(OH)(2). A larger number of complete (centroperipheral) hard tissue barriers with predominance of dentinal tubules was observed to the ProRoot MTA when compared with the Ca(OH)(2) group.

Cytotoxic effects and pulpal response caused by a mineral trioxide aggregate formulation and calcium hydroxide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

pH, Calcium Ion Release, and Setting Time of an Experimental Mineral Trioxide Aggregate-based Root Canal Sealer

Introduction: An experimental mineral trioxide aggregate sealer (MTAS) has been developed for use as a root canal sealer. The aim of this study was to evaluate the setting time, pH, and calcium ion release of MTAS compared with white Portland cement (CPB-40; Votorantin Cimentos, Camargo Correa SA, Pedro Leopoldo, MG, Brazil), white MTA Angelus (MTA; Angelus, Londrina, PR, Brazil), and AH Plus (Dentsply DeTrey, Konstanz, Germany). Methods: For the evaluation of setting time, each material was analyzed using Gilmore-type needles. Polyethylene tubes with the materials were immersed in distilled water for the measurement of pH (digital pH meter) and calcium release (atomic absorption spectrophotometry). The evaluations were performed at 3, 6, 12, 24, and 48 hours and 7, 14, and 28 days. Data were analyzed by analysis of variance and the Tukey test at 5% significance level. Results: MTAS showed higher calcium release at all experimental periods, a greater increase in pH up to 48 hours and the longest setting time. Conclusions: MTAS presented favorable properties for its indication as a root canal sealer. (J Endod 2011;37:844-846)

The use of calcium hydroxide and mineral trioxide aggregate on apexification of a replanted tooth: a case report

To report the outcome of the endodontic treatment of a reimplanted central maxillary incisor with open apex after 8 years and 7 months of follow-up.This case report presents the treatment of a right central maxillary incisor of an 8-year old white male patient with history of traumatic avulsion and immediate replantation. The endodontic therapy consisted of periodical changes of calcium hydroxide dressing and a definitive root canal filling with mineral trioxide aggregate (MTA). The treatment was successful without pathologies up to 7 years of follow-up. After the institution of orthodontic treatment a localized and late root resorption was noticed at the last radiographic examination (8 years and 7 months postoperative follow-up). Moreover, the use of MTA promoted a mild crown grey discoloration.