Comparative study of physico-chemical properties of MTA-based and portland cements

The purpose of this investigation was to evaluate the physicochemical properties of gray and white structural and nonstructural Portland cement, gray and white ProRoot MTA and MTA BIO. The water/powder ratio, setting time, solubility and pH (hydrogen-ion potential) changes of the materials were evaluated. Tests followed specification #57 from the American National Standard Institute/ American Dental Association (2000) for endodontic sealing materials and pH was determined by a digital pHmeter. The test results were statistically analyzed by variance analyses for global comparison and by the complementary Tukey's test for pairwise comparisons (5%). Considering the water/powder ratio, no significant difference (p>0.05) was observed among the cements. MTA BIO (33.10±2.30) had the lowest setting time (p<0.05), gray Pro- Root MTA (10.10±2.70) had the highest (p<0.05). White nonstructural Portland cement (2.55±0.08) had the highest solubility (p<0.05), while gray ProRoot MTA (1.03±0.12) had the lowest (p<0.05), although all materials showed solubility values in compliance to ANSI/ADA. No difference (p>0.05) was observed among materials when considering pH evaluation. The pH levels were highly alkaline immediately after immersion in solution, remaining stable throughout the test period. The authors conclude that the cements had similar water/powder proportions. MTA BIO had the shortest setting time and gray ProRoot MTA had the lowest solubility. All cements had similar behavior in the pH analysis.

A proposta desse trabalho foi de avaliar as propriedades fisicoquimicas dos cimentos Portland cinza e branco estrutural e nao estrutural, do ProRoot MTA cinza e branco e do MTA BIO. Foram avaliadas a proporcao po-liquido, tempo de endurecimento, solubilidade e variacao do pH dos cimentos. Os testes seguiram as normas que determinam a especificacao numero 57 da ANSI/ ADA para cimentos obturadores e a variacao de pH foi analisada por meio de pHmetro digital. Os resultados dos testes foram analisados estatisticamente por meio de teste de analise de variancia e pelo teste de Tukey para comparacao entre pares, com nivel de significancia de 5%. Nao foram evidenciaram diferencas estatisticamente significantes (p>0,05) entre os cimentos no que se refere a proporcao po-liquido. O MTA BIO (33,10±2,30) mostrou os menores valores de tempo de endurecimento (p<0,05), enquanto o ProRoot MTA cinza (102,10±2,70) mostrou os maiores resultados (p<0,05). Todos os materiais mostraram valores de solubilidade dentro dos padroes da ANSI/ADA, sendo que o cimento ProRoot MTA cinza (1,03±0,12) apresentou a menor solubilidade (p<0,05) e o Portland branco nao estrutural (2,55±0,08), a maior (p<0,05). No que se refere a variacao do pH, nao foram determinadas diferencas significantes entre os materiais (p>0,05). Os niveis de pH mostraram-se altamente alcalinos, imediatamente apos a imersao em agua, mantendo-se estavel ao longo do periodo de teste. Concluiu-se, que os cimentos estudados tiveram proporcoes po-liquido similares. O MTA BIO apresentou tempo de endurecimento mais curto e a menor solubilidade foi apresentada pelo ProRoot MTA cinza. Todos os cimentos tiveram comportamento semelhante na analise do pH.

Comparative study of physico-chemical properties of MTA-based and Portland cements.

The purpose of this investigation was to evaluate the physicochemical properties of gray and white structural and nonstructural Portland cement, gray and white ProRoot MTA and MTA BIO. The water/powder ratio, setting time, solubility and pH (hydrogen-ion potential) changes of the materials were evaluated. Tests followed specification #57 from the American National Standard Institute/American Dental Association (2000) for endodontic sealing materials and pH was determined by a digital pH meter. The test results were statistically analyzed by variance analyses for global comparison and by the complementary Tukey's test for pairwise comparisons (5%). Considering the water/powder ratio, no significant difference (p > 0.05) was observed among the cements. MTA BIO (33.10 +/- 2.30) had the lowest setting time (p < 0.05), gray ProRoot MTA (10.10 +/- 2.70) had the highest (p < 0.05). White nonstructural Portland cement (2.55 +/- 0.08) had the highest solubility (p < 0.05), while gray ProRoot MTA (1.03 +/- 0.12) had the lowest (p < 0.05), although all materials showed solubility values in compliance to ANSI/ADA. No difference (p > 0.05) was observed among materials when considering pH evaluation. The pH levels were highly alkaline immediately after immersion in solution, remaining stable throughout the test period. The authors conclude that the cements had similar water/powder proportions. MTA BIO had the shortest setting time and gray ProRoot MTA had the lowest solubility. All cements had similar behavior in the pH analysis.

Determination of lead content in medicinal plants by pre-concentration flow injection analysis-flame atomic absorption spectrometry.

INTRODUCTION: Although medicinal plants are widely used throughout the world, few studies have been carried out concerning the levels of heavy metal contaminants present. Such metals are highly toxic to living organisms even in low concentrations owing to their cumulative effect. The present paper describes the the development of a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. OBJECTIVE: To develop a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. METHODOLOGY: A pre-concentration flow system was coupled to a flame atomic absorption spectrometer. The plant samples were analysed after nitroperchloric digestion. The proposed system was optimised by evaluating the following parameters: nature, concentration and volume of the eluent solution, elution flow rate, elution efficiency, pre-concentration flow rate and pre-concentration time. RESULTS: The proposed system exhibited good performance with high precision and repeatability (RSD < or = 2.36%), excellent linearity (r = 0.9999), low sample consumption (10.5 mL per determination) and an analytical throughput of 55 samples/h. Lead concentrations ranged from 3.37 + or - 0.25 to 7.03 + or - 0.51 microg/g in dry material. This concentration interval is greater than that previously published in the literature. CONCLUSION: The inclusion of a pre-concentration column in the flow manifold improved the sensitivity of the spectrometer. Thus, it was possible to determine the analyte at the ng/mL level in sample solutions of medicinal plants. This is a very important accomplishment, especially when the cumulative effect of heavy metals in living organisms is considered.

An improved flow-injection system for spectrophotometric determination of molybdenum and tungsten in tool steels.

A flow-injection procedure for simultaneous spectrophotometric determination of tungsten and molybdenum in steel alloys is proposed. The method exploits the catalytic effects of Mo(VI) and W(VI) on the rate of iodide oxidation by hydrogen peroxide under acidic conditions. A novel strategy for ion-exchange separation of the potential interfering species is proposed, and an AG50W-X8 cationic resin mini-column is used. The sample is injected twice, originating two sequential plugs, citrate being added to one of them in order to suppress the W(VI) catalytic activity thus providing the kinetic discrimination. The system handles 70 samples per hour and requires 1.6mg KI per determination. A linear response is verified up to 10mgl(-1) Mo (or W) in the injectate, and signal additivity is 98-103%. Results are precise (R.S.D.<0.04) and in agreement with ICP-OES. Running a standard reference material (IPT-50) assessed also accuracy.

Identification of a metallothionein in Synechococcus by capillary electrophoresis hyphenated with inductively coupled plasma mass spectrometry.

A home-made system hyphenating capillary electrophoresis with an inductively coupled plasma mass spectrometer (CE-ICP-MS) for cadmium speciation of protein-binding and free cadmium ions in solution is presented. The CE-ICP-MS interface consisted of an acrylic block with an internal volume ca. 20 microL in which a platinum electrode, a capillary column, and a connection to an ICP nebulizer were inserted. A make-up electrolyte solution containing 50 mmol L(-1) Tris-HCl buffer solution (pH 9.0) was continuously flowed through the interface to the ICP nebulizer. The separation of free Cd ions, Cd-cysteine, and Cd bounded to metallothionein (MT) isoforms from rabbit liver was carried out by capillary electrophoresis, and the analytes were detected by ICP-MS. The feasibility to isolate metallothionein compounds extracted from the cyanobacterium Synechococcus PCC7942 was demonstrated. The Cd binding proteins were induced in Synechococcus PCC7942 and further analyzed by CE ICP-MS.