Effects of Remineralizing Agents Based on Calcium Phosphate, Sodium Phosphate, or Sodium Fluoride on Eroded Cervical Dentin

SUMMARY Objectives: To evaluate the effect of remineralizing agents on collagen matrix pattern, precipitate formation, and dentinal tubule obliteration in eroded cervical dentin. Methods and Materials: One hundred bovine cervical dentin specimens were previously eroded (0.6% hydrochloric acid, pH 2.3, 5 minutes) and then randomized into five groups (n=20): G1, control (without treatment); G2, Desensibilize Nano P (FGM); G3, MI Paste Plus (Recaldent); G4, Regenerate (NR-5); and G5, Desensibilize KF 2% (FGM). These treatments were applied in four sessions with 7-day intervals. During this period, the samples were subjected to an erosive challenge with orange juice (pH 3.8, 5 minutes). The specimens were analyzed by polarized light microscopy with picrosirius red staining, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Results: The G3 showed a higher concentration of type I collagen than G2 and G5 (p<0.05). The G3 showed greater formation of surface precipitates than that of G1 and G5 (p<0.05). In addition, G4 and G5 showed a greater number of open dentinal tubules than that of G3 (p<0.05). Conclusions: Calcium phosphate-based remineralizing agents have shown to be a promising alternative treatment for preventing deleterious effects on the eroded dentin collagen matrix. In addition, they promoted precipitate formation and dentinal tubule obliteration on the eroded dentin.

A safe way of performing dangerous experiments. III. The safety box. 2. Demonstrating the reactions of alkali metals with concentrated oxoacids

A way to conciliate one of the most dangerous reactions and at the same time, a way of a systematic approach towards studying the reaction of the alkali metals and acids, has been offered. Explanation of the observed phenomena considering the extent of how vigorous the reaction is and the circumstances contributing to the rate of reaction due to the precipitate formation or water presence, are discussed. In this paper, the reaction between some concentrated aqueous solutions of oxoacids (HNO3, H3PO4, H2SO4, HClO4) and alkali metals (Li, Na, K) are considered. Video clips of the experiments were prepared as an aid for those instructors that lack experience and/or the necessary materials. This publication is a continuation of the previously published article about the reaction of alkali metals with hydrohalic acids and is part of the series of publications under the general title “A Safe Way of Performing Dangerous Experiments”.

THE ROLE OF INTERMEDIATE IRRIGANTS IN THE PREVENTION OF THE FORMATION OF ORANGE-BROWN PRECIPITATE, FORMED DUE TO INTERACTION BETWEEN SODIUM HYPOCHLORITE AND CHLORHEXIDINE: A SPECTROPHOTOMETRIC ANALYSIS.

This study aimed to assess the efciency of intermediate irrigants in the prevention of formation of precipitate, formed due to the interaction of sodium hypochlorite and chlorhexidine when used as root canal irrigants.The formation of orange brown precipitate, due to the reaction of 3% sodium hypochlorite and 2% chlorhexidine was assessed using spectrophotometric analysis. Three intermediate irrigants were then assessed for their capabilities to prevent the formation of the precipitate. Group A- 6.25% sodium metabisulphite, Group B- 10% sodium ascorbate and Group C- saline were used at different volumes and the values were recorded by measuring their optical density. An invitro analysis was further carried out on single rooted teeth, to verify the efcacy of intermediate irrigants. The teeth which were subjected to the tests were sectioned and observed under stereomicroscope for the presence of remnants of orange brown precipitate in the root canals. Results: The spectrophotometric analysis showed peak value at 450nm and the precipitate formation was found at 60µl of 2% chlorhexidine and 1 ml of sodium hypochlorite. There was statistical difference in the optical density values between the groups, with saline having highest optical density values followed by 6.25% sodium metabisulphite and 10% sodium ascorbate group. Wherein 10% sodium ascorbate solution prevented the formation of orange brown precipitate than other two group. It was concluded that 10% sodium ascorbate played a vital role in the reduction of formation of parachloro-aniline, when used as an intermediate irrigant. 6.25% Sodium metabisulphite also prevented the precipitate formation, to a lesser extent than sodium ascorbate. However, saline did not eliminate the formation of the precipitate.

Effect of microstructure and precipitate formation on mechanical and corrosion behavior of friction stir processed AA6061 alloy using different cooling media

The present work studies the effect of microstructure and precipitate formation on mechanical and corrosion characteristics of friction stir processed AA6061 alloy using different cooling technologies (cryogenic and water cooling). The results revealed that recrystallized fine grains formed in all friction stir processing samples (grain size within a range of 2–6 µm) as a result of dynamic recovery and recrystallization, while samples processed in cooling-assisted friction stir processing resulted in better grain refinement in the stir zone than in air-cooled friction stir processing. Three kinds of precipitates (Fe-based needle-shaped precipitates, Si-based round-shaped precipitates, and chain of small round-shaped Si-based precipitates) were identified in base material and friction stir processing samples. Compared to air-cooled friction stir processing, in cooling-assisted friction stir processing, the hardness and tensile strength increased but remained lower than for the base alloy due to the presence of high density Fe-based needle-shaped precipitates. The ductility after friction stir processing greatly improved due to thermal softening and dissolution of precipitates. The corrosion results demonstrated that the corrosion resistance greatly enhanced after friction stir processing due to uniform distribution of grain structure and discontinuous chain of small round-shaped Si-based precipitates in stir zone. Moreover, cooling-assisted friction stir processing resulted in improved corrosion resistance compared to air-cooled friction stir processing due to the formation of fine precipitates.