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Aim. The study evaluated the in vitro effects of 30% carbamide peroxide on human enamel by microhardness tests. Materials and method. 20 enamel slices were obtained from recently extracted premolars. To determine the microhardness index, the dental crowns were sectioned longitudinally into two mesial and distal halves. Sections were embedded in a self-polymerising epoxy resin, leaving open the enamel surface subjected to analysis. Enamel samples were randomly divided into two equal groups (n = 10), as follows: control group 1 - sections without whitening procedures, experimental group 2 - sections bleached with 30% carbamide peroxide for 15 min per day, along 14 days. After removing the bleaching gel, the specimens were stored in 250 ml artificial saliva at 37°C, an operation repeated twice a day. Enamel microhardness evaluation was performed using Vicker's microhardness test, applied in the beginning and end of treatment. Results. In the control group (1), the registered enamel hardness values ranged between 312 and 328 Mpa, with a mean value of 320.20 (p = 0.3>0.05); in the experimental group (2), the enamel hardness values ranged between 254 and 301 Mpa, with a mean value of 278.40 (p = 0.09>0.05). Intergroup comparison of microhardness values showed a statistically significant difference (p = 0.001 < 0.05). Conclusions. The results obtained demonstrated a significant decrease of enamel microhardness, induced by the action of the carbamide peroxide whitening product tested in the study. [ABSTRACT FROM AUTHOR]

The purpose of the investigation was to study the process, by which protoplasts derived from callus tissue overcome the hydrolysis of membrane phospholipids, which is induced by the isolation. Dividing protoplasts from Petunia hybrida L. (line SFIa) and non-dividing protoplasts from Parthenocissus tricuspidata L. crown gall (Morel strain) were fed with sodium [1-14C]-acetate for 1 h. The incorporation was carried out at protoplast isolation and after 1, 2, 4 and 7 days of culture. The rates of fatty add and lipid synthesis were then followed. Isolation stress induced diversions in the utilization of the precursor via triacylglycerol (Petunia) or diacylglycerol (Parthenocissus) and a decrease in the synthesis of oleic acid (Parthenocissus). During the first 2 days of culture, the rate of phospholipid synthesis was similar in both systems. Later on, an increase in the rate and in the efficiency of phospholipid synthesis was observed in dividing Petunia protoplasts. The accelerated rate of lipid synthesis allowed them to recover the same partitioning and content in membrane phospholipids as the reference cells in the callus. This process seemed to be related to cell division, since it was not observed in the non-dividing protoplasts of Parthenocissus. [ABSTRACT FROM AUTHOR]

Protoplasts isolated from callus cells of Petunia hybrida L. and Parthenocissus tricuspidata L. crown gall were used in order to correlate the fatty acid and lipid contents and composition during culture with the ability or unability of the cells to divide. Freshly isolated protoplasts were characterized by a decrease in fatty acids, galactoli‐pids and phospholipids, an increased saturation of the fatty acids of the phospholipids and higher weight percentages of neutral lipids and phosphatidic acid. During culture, fatty acids and phospholipid increased in dividing protoplast of Petunia but not in non‐dividing protoplasts of Parthenocissus. The findings may imply a two‐stage response to isolation stresses: the first step being lipid degradation and the second lipid biosynthesis. [ABSTRACT FROM AUTHOR]

In this work is presented the impact assess of metallurgical specific activities on the environment through global pollution index calculation. The pollution index value calculated for environmental components: air, water, soil, vegetation, noise, waste, population health status indicated an environment subject to human effect within acceptable limits. [ABSTRACT FROM AUTHOR]

The main objective of this paper was to establish how the thickness of welded pieces influences the metallographic structure of welded joints. Thus were made a total of 6 samples, and from each sample were taken test specimens for metallographic analysis of the base material, the filler material respective heat affected zone (HAZ). The samples were carried out by welding process: metal active gases (MAG) using a steel E 36-4, and the welded pieces had a thickness between 10 and 24 mm. The welding regime was characterized by parameters IW = 200 / A, Uw = 24 / V. The joint by welding pieces was "T" form and both piece used as the base and the piece used as heart for welded joint were made of sheets with different thicknesses. [ABSTRACT FROM AUTHOR]