Methyl(2-mercapto-4-methylpyrimidinato)mercury(II): A methylmercury(II) derivative with an unusual metal-metal interaction

4-Methylpyrimidine-2-thione reacts with methylmercury hydroxide to give the thiolate derivative HgMe(SC4H2N2Me-2), the X-ray structure of which reveals pairs of molecules with a mercury-mercury distance of 3.10 Å.

Soluble phosphate accumulation by Aspergillus niger from fluorapatite

In order to determine conditions that may provide greater solubilization of insouluble phosphate, the fungus Aspergillus niger was grown in a stationary culture containing modified citrate medium supplemented with 800 mg fluorapatite per litre. Solubilization of insouluble phosphate increased with fungal growth, reaching a maximum after 11 days of culture. Soluble phosphate levels were correlated with pH of the culture medium but not with titratable acidity values, probably due to the metabolic activity of the fungus resulting from consumption of sugar in the culture medium. Fructose, glucose, xylose, and sucrose were the carbohydrates that favoured fluorapatite solubilization the most when compared with galactose and maltose. Although increasing fructose concentrations in the culture medium favoured mycelial growth, increased total acidity and a fall in pH, soluble phosphate levels were reduced, probably owing to consumption by the rapidly growing fungus. Among the nitrogen sources tested, ammonium salts favoured the production of larger amounts of soluble phosphate than organic nitrogen (peptone or urea) or nitrate, corresponding to the lowest pH and highest titratable acidity values obtained. © 1988 Springer-Verlag.

Comportamento dos tecidos periapicais de dentes de cães após a obturação de canal com Sealapex acrescido ou não de iodoformio.

Some endodontists use iodoform in Sealapex in order to rend it more radiopac. This procedure is empiric and for this reason we decided to observe, histologically, if the iodoform introduces some modification in the biological properties of Sealapex. Thirty root canals of dogs' teeth were overinstrumented and filled, by lateral condensation technique, with gutta percha points and Sealapex, with or without iodoform. The iodoform was added in two different proportions: 30 mg or 112 mg for one centimeter of the base and one centimeter of the catalyst of Sealapex. The pieces were removed for histological studies, 6 months after the treatment. The histological results showed that Sealapex encourages apical closure by cementum deposition and that the addition of iodoform does not change that biological property.

Estudo da penetração de agentes ácidos para o condicionamento do esmalte dental em cimentos à base de hidróxido de cálcio.

It was verified the penetration of phosphoric acid into 3 commercial calcium hydroxide-based cements (Life, Renew and Prisma VLC Dycal). The colorimetric method employed permitted the identidication of phosphorus amount in representative samples of 6 successive layers 0.1 mm thick of each material. The acid etching used were the commercial products Scotchbond Etching Gel--3M at 36.114% by weight and Solução Condicionadora--Johnson & Johnson at 36.054% by weight. The contact time was 60 seconds. The result showed that layers 0.1 mm tick for Life and Prisma VLC Dycal and 0.2 mm thick for Renew were able to block the penetration of phosphoric acid solution whereas layers 0.1 mm thick for the 3 cements were able to block the penetration of phosphoric acid gel.

Radiographic and microbiologic evaluation of posttreatment apical and periapical repair of root canals of dogs' teeth with experimentally induced chronic lesion

The objective of the present study was to evaluate radiographically and bacteriologically apical and periapical repair in dogs' teeth with induced chronic periapical lesions with the use of two different operative techniques (techniques 1 and 2). The study was conducted on 40 root canals of upper and lower premolars from two dogs aged approximately 12 months. Periapical lesions were induced by leaving the root canals exposed to the oral environment for 5 days and then sealing them with zinc oxide-eugenol for 45 days. After this period, radiographic examination revealed the occurrence of a radiolucent lesion and endodontic treatment was started. The two techniques did not differ in terms of chemomechanical preparation, final filling, or type of cement, but differed in terms of irrigating solution and the presence of an antibacterial dressing. Thus 4% to 6% hypochlorite and hydrogen peroxide (10 volumes) were used in technique 1 during chemomechanical preparation and an antibacterial dressing based on calcium hydroxide was applied between sessions, whereas Dakin's fluid (0.5% sodium hypochlorite solution) and a final filling with no antibacterial dressing were used in technique 2. After chemomechanical preparation, the root canals were filled with gutta-percha cones and Sealapex (Sealapex-Sybron, Kerr, Sao Paulo, Brazil), and the animals were killed 270 days after the final filling. Blocks were cut into 6-μm sections and stained by the Brown and Brenn method. Radiographic, histomicrobiologic and statistical analysis permitted us to conclude the following: radiographically there was a marked reduction or even the disappearance of the radiolucent area present before treatment with greater success in the group treated with technique 1 (group I) than in the group treated with technique 2 (group II); the extent of bacterial invasion of dentinal tubules was greater and more intense in group II than in group I; and the amount of microorganisms detected in the ramifications of the apical delta and in the lumen of the root canal was intense in group II and mild or absent in group I. © 1994.

Hydrothermal treatment of gadolinium oxide in presence of silica

Hydrothermal and solvothermal (isopropanol) treatments of gadolinium oxide and silica were investigated under different pressure and temperature conditions. Products were examined by infrared vibrational spectroscopy (IR), x-ray powder diffraction (XRD) and thermal analysis (DTA, TG). Hexagonal gadolinium hydroxide was obtained in hydrothermal conditions, even in presence of silica, while no change was observed from isopropanolic medium treatment. Hydrothermally treated samples are more reactive as precursors for solid state reactions in inorganic synthesis.

Effect of dentine surface treatment on leakage of root fillings with a glass ionomer sealer.

The purpose of this study was to observe the quality of seal of the glass ionomer cement, Ketac-Endo, after treatment of the root canal wall. The root canals of 140 extracted human teeth were prepared biomechanically. The root canals were treated with either EDTA or received an intracanal dressing of calcium hydroxide or camphorated paramonochlorphenol. The root canals were filled by the lateral condensation technique with gutta-percha points and the sealer Ketac-Endo, or zinc oxide-eugenol cement or Sealapex. The teeth were placed into a 2% methylene blue dye solution inside a flask, which was attached to a vacuum pump. Leakage was measured linearly. Sealapex exhibited significantly less leakage than Ketac-Endo or zinc oxide-eugenol cement (P<0.01). The use of EDTA and intermediary dressings reduced significantly (P<0.01) the leakage observed with the zinc oxide-eugenol sealer and Ketac-Endo.

Specific components found in circulating immune complexes (CIC) in paracoccidioidomycosis

Circulating immune complexes (CIC) from 15 paracoccidioidomycosis (PCM) patient sera and from 20 healthy control sera were analysed. After CIC precipitation, solubilization and acid treatment, only a little reactivity to P. brasiliensis antigens was found in the free antibodies from PCM-CIC. This result has suggested that there were antibodies with a high affinity bound to fungus components. Dissociated CIC were fractionated in a column of Sephacryl S300 and the fractions that probably contained antigens were pooled and applied to an affinity column, prepared with mouse anti-gp43 monoclonal antibody. Using ECL-Western blotting assay two polypeptide with apparent mass of 43 and 62 kDa were found.

Structural changes induced by ultrasound during aging of the boehmite phase

Structural changes induced by ultrasound during the aging of the aluminum monohydroxide (boehmite) were studied by means of X-ray diffraction (XRD) and nitrogen adsorption. The BET surface area and the pore volume of the ultrasound stimulated hydroxide (HU) are about 40% less than those of the non-stimulated one (HS). The mean pore size practically does not change, while the mean crystallite size (L) is about 25% greater in the HU system. The increase of L alone is not enough to account for the surface area diminution, suggesting that the sonication also induces compaction by elimination of some porosity. The sonication of the precursor hydroxide does not seem to play an apparent role in the structural properties of the resulting calcinated γ-alumina. © 1997 Elsevier Science B.V.

Effect of different root canal sealers on periapical repair of teeth with chronic periradicular periodontitis

Teeth with induced chronic periradicular periodontitis in dogs were root canal treated. After the biomechanical preparation, using K files and 5.25% sodium hypochlorite as the irrigant solution, all root canals were dressed with an antibacterial dressing based on calcium hydroxide, which was left in place for 7 days. After this time, the root canals were obturated with lateral condensation of cold gutta-percha with either a calcium hydroxide root canal filling material (Sealapex) or a zinc oxide-eugenol sealer (Fill Canal). After 270 days, histopathological analysis showed better apical and periapical repair in the teeth obturated with Sealapex (P < 0.05).

Monolithic diphasic gels of mullite by sol-gel process under ultrasound stimulation

Diphasic gel in the mullite composition was prepared from a colloidal sol of boehmite mixed with a hydrolyzed tetraethoxisilane (TEOS) solution. The boehmite sol was obtained by peptization of a poorly crystallized or very small mean crystallite size (∼34 Å) precipitate, resulting from the reaction between solutions of aluminum sulfate and sodium hydroxide. Ultrasound was utilized in the processes of the TEOS hydrolysis and the boehmite peptization, and also for complete homogenization of the mixture to gel. The wet gel is almost clear and monolithic. The gel transparency is lost on drying, when syneresis has ended, so that the interlinked pore structure starts to empty and is recovered upon water re-absorption. Cracking closely accompanies this critical drying process. Differential thermal analysis (DTA) and X-ray diffraction (XRD) show that the solid structure of the gel is composed of an amorphous silica phase, as a matrix, and a colloidal sized crystalline phase of boehmite. Upon heat treatment, the boehmite phase within the gel closely follows the same transition sequence as in pure alumina shifted towards higher temperatures. Orthorhombic mullite formation was detected at 1300°C. © 1998 Elsevier Science B.V. All rights reserved.

Biocompatibility of an adhesive system applied to exposed human dental pulp

Human pulp tissue was directly capped with All Bond 2, or calcium hydroxide and evaluated 7, 30, or 60 days after the procedures. Histological analysis was performed to assess the inflammatory cell response, tissue disorganization, dentin bridging, and the presence of bacteria. At 7 days, with All Bond 2 capping, there was a large area of neutrophilic infiltrate underlying the pulp capping material, and the death of adjacent odontoblasts, was observed. However, with time, the neutrophilic reaction was replaced by fibroblastic proliferation with macrophages and giant cells surrounding globules of resin scattered in the coronal pulp tissue. The persistent inflammatory reaction and hyaline alteration of extracellular matrix inhibited complete pulp repair or dentin bridging. In contrast, at 7 days, the pulp tissue capped with calcium hydroxide exhibited odontoblast-like cells organized underneath coagulation necrosis. Pulp repair evolved into apparent complete dentin bridge formation at 60 days. All Bond 2 did not appear to allow any pulp repair and does not appear to be indicated for direct pulp capping of human teeth. Copyright © 1999 by The American Association of Endodontists.

Oxidative dissolution of covellite by Thiobacillus ferrooxidans

Oxidation of research-grade covellite was investigated in respirometric and growth experiments with Thiobacillus ferrooxidans. Covellite was directly oxidized by T. ferrooxidans in respirometric experiments, but the pH of mineral salts medium increased to prohibitively high values because of high sulfide concentrations. In glycine-H 2SO 4 buffered medium the pH remained steady and the oxygen uptake activity of T. ferrooxidans was not inhibited. In cultures growing with covellite as the sole source of energy, the pH increased to about 4. Redox potential increased to 500-600 mV during bacterial oxidation of covellite in the presence and absence of additional Fe 2+, whereas it remained mostly at about 350 mV in abiotic control. Jarosite was a major solid-phase product in T. ferrooxidans cultures. The solubilization of copper from covellite in inoculated flasks was higher than that obtained in control flasks and was not enhanced in the presence of additional Fe 2+.The sample also contained bornite (Cu 5FeS 4) which released iron in solution under all experimental conditions. Accumulation of S 0 was apparent only in inoculated covellite samples. © 1997 Elsevier B.V. All rights reserved.

Evaluation of cell culture cytotoxicity of five root canal sealers

The cytotoxicity of four calcium hydroxide-based root canal sealers (Sealapex, CRCS, Apexit, and Sealer 26) and one zinc oxide-eugenol-based sealer (Fill Canal) was evaluated microscopically for morphological changes in rat peritoneal macrophages. The least cytotoxic sealer was Fill Canal, followed in increasing order of cytotoxicity by CRCS, Sealer 26, Apexit, and Sealapex. Copyright © 2000 by The American Association of Endodontists.

Biocompatibility of two current adhesive resins

The purpose of the study was to evaluate the biocompatibility of two current adhesive resins and a calcium hydroxide cement. Fifty-four polyethylene tubes were filled with these dental materials, which were hand-mixed or light-cured according to the manufacturer's directions: group 1-Clearfill Liner Bond 2 (Kuraray); group 2-Single Bond (3M); and group 3-calcium hydroxide cement (Dycal-Dentsply). The materials were implanted into dorsal connective tissue of rats, which were killed 7, 30, and 60 days after the implantation procedure. The implant sites were excised, immersed in buffered Karnovsky's fixative, and processed using routine histological techniques. Sections of 6 μm thickness were stained with hematoxylin and eosin and assessed under light microscopy. Both adhesive resins at 7 days elicited a moderate/intense inflammatory reaction that decreased over time. Fibrous capsules surrounding the tubes were observed at 30 days. Half of the samples in groups 1 and 2 showed thin fibrous capsule formation containing macrophages, capillaries, lymphocytes, fibroblasts, and collagen fibers. Connective tissue healing was observed even though many specimens exhibited a persistent inflammatory reaction mediated by macrophages and giant cells at the 60-day evaluation. Dycal allowed complete healing at 30 days with only a thin fibrous capsule. In conclusion, all experimental materials were successfully walled off by the connective tissue of the rat. However the adhesive resins may release particulates that may, in turn, induce a persistent local inflammatory reaction. Consequently, in this specific condition, these materials cannot be regarded as biocompatible. Dycal was less irritating than the adhesive resins and was better tolerated by the connective tissue. Copyright © 2000 by The American Association of Endodontists.