Direct and Transdentinal (Indirect) Antibacterial Activity of Commercially Available Dental Gel Formulations against Streptococcus mutans

**Objective** To evaluate the direct and transdentinal (indirect) agar diffusion antibacterial activity of different commercially available antibacterial dental gel formulations against Streptococcus mutans. Materials and **Methods** The commercially available dental gel formulations were Corsodyl® (COG, 1% chlorhexidine), Cervitec® (CEG, 0.2% chlorhexidine + 0.2% sodium fluoride), Forever Bright® (FOB, aloe vera), Gengigel® (GEG, 0.2% hyaluronic acid), 35% phosphoric acid gel and distilled water (control). Direct agar diffusion was performed by isolating three wells from brain-heart infusion agar plates using sterile glass pipettes attached to a vacuum pump and adding 0.1 ml of the gels to each well. Transdentinal (indirect) agar diffusion was performed by applying gel to 0.2- and 0.5-mm-thick human dentin discs previously etched with phosphoric acid and rinsed with distilled water. Zones formed around the wells and the dentin discs were measured and analyzed using Kruskal-Wallis and Mann-Whitney U tests with Bonferroni correction (p 0.01). COG and CEG exhibited higher antibacterial effects compared to FOB and GEG (p < 0.01) in both direct and transdentinal (indirect) testing procedures. GEG did not show any antimicrobial activity in transdentinal (indirect) testing. **Conclusion** Commercially available dental gels inhibited S. mutans, which may indicate their potential as cavity disinfectants

Enhanced thermoelectric performance in Mg_3+xSb_1.5Bi_0.49Te_0.01 via engineering microstructure through melt-centrifugation

N-type Zintl phases with earth-abundant and non-toxic constituent elements have attracted intense research interest thanks to their high thermoelectric efficiencies in the mid-temperature range, exemplified by the recently discovered Mg3Sb2 material. In this study, the liquid phase is expelled from the microstructure of the optimized n-type phase Mg3+xSb1.5Bi0.49Te0.01 by applying a melt-centrifugation technique leading to the formation of lattice dislocations, grain boundary dislocations and increasing porosity. Additional phonon scattering mechanisms were introduced in the microstructure through this manufacturing method, resulting in a significant 50% reduction in the total thermal conductivity from ∼1 W m−1 K−1 to ∼0.5 W m−1 K−1 at 723 K. Combined with high power factors, this reduced heat transport leads to a dimensionless thermoelectric figure of merit, zT, value of ∼1.64 at 723 K, 43% higher than the value obtained in untreated Mg3+xSb1.5Bi0.49Te0.01 (zT ∼ 1.14 at 723 K). This peak zT value yields a predicted device ZT of 0.95, and a promising theoretical thermoelectric efficiency of about 12%. These results further underline the great potential of the lightweight Mg3Sb2 material for mid-temperature energy harvesting via thermoelectric effects

Synthesis, crystal structure and magnetic properties of Li_0.44Eu₃[B₃N₆]

Li0.44Eu3[B3N6] was synthesized from the metathesis reaction of Li-3[BN2] and EuCI3 at 850 degrees C. Li0.44EU3-[B3N6] crystallizes in the trigonal space group R (3) over barc (No. 167) with a=12.0225(2) angstrom, c=6.8556(2) angstrom and Z=6. In the crystal structure, isolated, planar cyclic [B3N6](9-) units are charge-balanced by the mixed-valence Eu3+/Eu2+ and Li+ cations. Li+ occupies partially (44%) the Wyckoff site 6b and is sandwiched between the [B3N6](9-) anions. Mossbauer spectroscopy results show the resonance lines of Eu2+ and Eu3+, respectively, indicating the heterogeneous mixed valency of the Eu atoms. X-Band ESR investigations between 5 and 300 K reveal an intense signal over the whole temperature range originating from Eu2+. Magnetic susceptibility measurements indicate a Curie-Weiss behavior with an experimental effective magnetic moment of (mu eff)=8.28 (mu B) per formula unit. (C) 2013 Elsevier Inc. All rights reserved

Phase-Transition-Enhanced Thermoelectric Transport in Rickardite Mineral Cu_3−xTe₂

The binary copper chalcogenides Cu2−δX (X = S, Se, and Te) have recently gained significant interest due to their high thermoelectric performance at moderate temperatures. In an effort to unveil new Cu-based compounds with promising thermoelectric potential, Cu3−xTe2 rickardite mineral emerged as a candidate based on a purely text mining approach applied by a machine learning method. Polycrystalline samples of Cu3−xTe2 within the homogeneity range (x = 0.1, 0.2) were successfully synthesized from the raw elements by a solid-state method. High-temperature powder X-ray diffraction combined with differential scanning calorimetry and specific heat measurements showed several reversible phase transitions at around 458, 640, and 647 K. Signatures of these transitions were observed on the electronic and thermal transport properties, measured over a broad range of temperatures (5−733 K). The transition undergone by this compound at 647 K results in a crossover from metallic-like to semiconducting-like properties. The combination of high power factor and low thermal conductivity in the high-temperature phase results in improved thermoelectric performances with a peak dimensionless thermoelectric figure-of-merit zT of ∼0.14 at 733 K. The synthetic rickardite mineral is an exciting candidate to be used as a phase change material in broad application areas such as in waste heat harvesting and photovoltaic systems. © XXXX American Chemical Societ

Second Black Sea Symposium For Young Scientists In Biomedicine March 27-30, 2014, Varna, Bulgaria

Варненски медицински форум (Varna Medical Forum) V. 3, Suppl 1(2014