Semiconducting Aluminum Compounds

Two aluminum metal matrix composites (MMC) reinforced with 13 vol.% of SiC or B4C particles were made by stir casting followed by hot extrusion. Effects of sliding velocity on the wear, friction and tribochemistry of the worn surfaces of both composites sliding against a commercial phenolic brake pad have been investigated under dry condition. The wear tests were carried out using a pin-on-disc type apparatus at two linear sliding speeds: 1.62 and 4.17 m s-1 under a constant contact pressure of 0.75 MPa for a sliding distance of 5832 m. The coefficient of friction was recorded and wear rate of the MMC pins calculated from mass loss measurement. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was used to investigated the worn surface. It is observed that higher sliding velocity leads to lower wear rate and lower friction coefficient for both MMCs. Formation of a compact transfer layer has been identified in the matrix region of the worn surface of the MMCs. The transfer layer mostly consists of constituents of the phenolic pad material which acted as counterbody. The amount of the constituents of the counterbody in the transfer layer is seen to increase as sliding velocity increases. It is suggested that the transfer layer on MMC acts as a protective cover and helps reduce both wear rate and friction coefficient.

Aim  To compare the major constituents present in ProRoot mineral trioxide aggregate (MTA), ProRoot MTA (tooth coloured formula), ordinary Portland cement and white Portland cement using powder X-ray diffractometery.Methodology  X-ray diffractometery of the four materials was carried out with the divergence and scatter slits set at 1° and the receiving slit at 0.10 mm. The scan range was set at 5–70° and continuous scans for the θ–2θ range were run with a scan speed of 2° min−1. The patterns obtained were then compared with the Powder Diffraction Files (PDF) found in the International Centre for Diffraction Data database. The three strongest peaks were used for the identification of the constituents. The relative intensities were plotted against the angle 2θ and compared with the plots in the PDF.Results  The main constituents were found to be tricalcium silicate, tricalcium aluminate, calcium silicate, and tetracalcium aluminoferrite in all the four cements with the additional presence of Bi2O3 in ProRoot MTA and ProRoot MTA (tooth coloured formula).Conclusions  The four cements had similar major constituents. Data on Portland cement may be used for the further development or modification of ProRoot MTA in order to improve its physical characteristics and expand its scope of clinical applications.

The aim of this study was to compare mineral trioxide aggregate (MTA) with calcium hydroxide [Ca(OH)2] clinically and radiographically as materials used to induce root-end closure in necrotic permanent teeth with immature apices (apexification). Fifteen children, each with at least 2 necrotic permanent teeth requiring root-end closure (apexification), were selected for this study. All selected teeth were evenly divided into 2 test groups. In group 1, the conventional calcium hydroxide apexification (control) was performed, whereas in group 2, the MTA apexification (experimental) was done. The children were recalled for clinical and radiographic evaluations after 3, 6, and 12 months. The follow-up evaluations revealed failure due to persistent periradicular inflammation and tenderness to percussion detected at 6 and 12 months postoperative evaluation in only 2 teeth treated with Ca(OH)2. The remaining 13 teeth appeared to be clinically and radiographically successful 12 months postop...

Parents increasingly request esthetic restorations for their children's teeth. This split mouth, randomized controlled trial compared primary molars treated with white MTA pulpotomies and restored with either multi-surface composites (MSC) or stainless steel crowns (SSC). Forty matched, contra-lateral pairs of molars received MTA pulpotomies and were randomly assigned to MSC or SSC restorations and evaluated clinically and radiographically at 6 and 12 months. Two calibrated, blinded examiners evaluated and scored radiographs. Thirty-seven matched pairs were evaluated at 6 months, and 31 were available at 12 months. All teeth in both groups were radiographically and clinically successful at 6 and 12 months. Dentin bridge formation was noted in 20% of the primary molars by 12 months. Although not significant, the composite group exhibited fewer intact clinical margins than the SSC group. The vast majority (94%) of teeth restored with composite displayed gray discoloration at follo...

The purpose of this study was to report the success rate of using mineral trioxide aggregate (MTA) and zinc oxide eugenol (ZOE) as vital pulp therapy agents in immature permanent teeth with carious or traumatic pulp exposure. Subjects were children with permanent teeth requiring pulpotomy (apexogenesis) and without systemic diseases. Both ZOE and MTA treatments as pulpotomy agents showed clinical and radiographic success in immature permanent teeth. Although MTA was more successful, it is more expensive, and dentin bridges may develop over canal orifices, complicating future root canal therapy.

To evaluate the clinical, radiographical and histological findings in human third molars in which mechanical pulp exposures were capped with white ProRoot mineral trioxide aggregate (WMTA). Forty-eight human third molars, caries-free or with incipient caries, scheduled to be extracted, were used and randomly divided into two groups: Group A: (n= 24) received WMTA and control Group B: (n= 24) received chemical set calcium hydroxide (Dycal). The teeth were isolated with rubber dam and Class I cavities prepared. Pulp exposure was performed using a sterile diamond bur and confirmed by frank bleeding. A sterile cotton pellet dipped in saline solution was placed over the exposure for 60 seconds. The preparation was then lightly rinsed with water and gently air-dried. WMTA or CH was placed over the exposure site followed by a small amount of a light-cured compomer. After etching with 35% phosphoric acid gel for 15 seconds, rinsing and blot drying, Prime and Bond NT adhesive was applied and...

Purpose: The purpose of this study was to compare mineral trioxide aggregate (MTA) with calcium hydroxide (Ca(OH)2) clinically and radiographically as a pulpotomy agent in immature permanent teeth (apexogenesis). Methods: Fifteen children, each with at least 2 immature permanent teeth requiring pulp- otomy (apexogenesis), were selected for this study. All selected teeth were evenly divided into 2 test groups. In

A carbonated hydrocalumite was synthesized by the microwave method for being used as antacid. The gel was formed using Ca and Al nitrate solutions in a basic medium (NaOH+Na2CO3), then, this gel was aged and heated in a domestic microwave for 2.5min (1250W). The obtained white solid was washed with distilled water, dried in an oven at 100°C for 18h and characterized by different techniques such as: X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), BET surface area measurements, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Finally, the carbonated hydrocalumite was tested as antacid by using a synthetic gastric juice and its activity was compared with a commercial antacid formulated with hydrotalcite. Results showed that the carbonated hydrocalumite was more effective than that commercial antacid.

Kaolin suspensions were coagulated with AlCl3 and a high-basicity PACl at pH 7, at dosages that gave zeta potentials close to zero. The actions of the two coagulants were completely different. With AlCl3, the formation of an amorphous hydroxide precipitate played a dominant role. When the coagulant was added to the suspension, flocs grew rapidly and incorporated most of the kaolin particles within the hydroxide precipitate. When the suspension was added some time after the coagulant, the clay particles were found to be mainly on the outer floc surfaces, although the floc size was about the same. The light scattering properties of the flocs were very dependent on the number and location of particles in the precipitate. With PACl, delaying the addition of kaolin had no influence on the final floc properties. In further tests, different suspensions over a range of concentrations were coagulated with alum at pH 7. Monitoring by a 'turbidity fluctuation' technique showed an appar...

Polyene cyclization of the titled compounds under catalysis with AlCl(3)/SnCl(4) gave rise to the corresponding polycyclic products, many of which were structurally highly unexpected, and thus, individual X-ray analysis was required to finalize the structural identification. Mechanistically, an unusual 1,2-hydride shift is proposed to elucidate the product formation.

The aim of this study was to compare the in vitro sealing ability of ProRoot MTA, ProRoot MTA (Tooth-Coloured Formula), ordinary Portland cement and white Portland cement when used as root-end filling materials. Twenty-four single-rooted human premolars were prepared and obturated using standard techniques, then retrofilled with the test materials. The prepared teeth were immersed in 1% methylene blue dye for 72 hours and then assessed for dye leakage. The depth of dye penetration was measured and expressed as a percentage of the length of the retrofilling. Data was analysed using ANOVA and Fisher's Least Significant Test (LSD) (p < 0.05). None of the teeth in any of the test groups showed leakage beyond the retrofillings. Given the low cost and apparently similar sealing ability of the cements, it is reasonable to consider Portland cement as a possible substitute for MTA as a root-end filling material. However, further tests, especially in vivo biocompatibility tests, need to be conducted before Portland cement can be recommended for clinical use.