Effect of the root canal final rinse protocols on the debris and smear layer removal and on the push‐out strength of an epoxy‐based sealer

The aim of the present study was to evaluate the efficacy of QMiX, SmearClear, and 17% EDTA for the debris and smear layer removal from the root canal and its effects on the push‐out bond strength of an epoxy‐based sealer by scanning electron microscopy (SEM). Forty extracted human canines (n = 10) were assigned to the following final rinse protocols: G1‐distilled water (control), G2–17% EDTA, G3‐SmearClear, and G4‐QMiX. The specimens were submitted to a SEM analysis to evaluate the presence of debris and smear layer, respectively, in the apical or cervical segments. In sequence, forty extracted human maxillary canines with the root canals instrumented were divided into four groups (n = 10) similar to the SEM analysis study. After the filling with AH Plus, the roots were transversally sectioned to obtain dentinal slices. The specimens were submitted to a push‐out bond strength test using an electromechanical testing machine. The statistical analysis for the SEM and push‐out bond strength studies were performed using the Kruskal–Wallis and Dunn tests (α = 5%). There was no difference among the G2, G3, and G4 efficacy in removing the debris and smear layer (P > 0.05). The efficacy of these groups was superior to the control group. The push‐out bond strength values of G2, G3, and G4 were superior to the control group. The ability to remove the debris and smear layer by SmearClear and QMiX was as effective as the 17% EDTA. The final rinse with these solutions promoted similar push‐out bond strength values. Microsc. Res. Tech. 76:533–537, 2013. © 2013 Wiley Periodicals, Inc.     

Limitations of pulsed MIG‐MAG welding for obtaining welded joints with constant penetration and bead shape

Summary

This article presents a study of the MIG‐MAG welding process with pulsed‐arc transfer applied to joints in motor vehicle exhaust pipes and silencers for which the mean thickness of the base material is approximately 2 mm, and the ratio of the latter to the workpiece diameter is about 0.04. It is shown that, for this type of welded joint, constraints on the maximum and minimum values for penetration into the base metal are incompatible with those relating to the shape and size of the weld bead due to progressive heating of the workpieces during the process.     

LASER PROCESSING OF HIGH TEMPERATURE SUPERCONDUCTING THIN FILMS

High quality thin films of high temperature superconductors (HTS) have been fabricated using pulsed or cw lasers as physical vapor deposition sources. There is current interest in scaling the pulsed laser deposition (PLD) technique to coat 3-in. wafers with HTS. Process control and diagnostics relevant to achieving the required scaling and reproducibility will be reviewed.     

Imaging of metal-coated biological samples by scanning tunneling microscopy

A method for imaging biological samples by scanning tunneling microscopy (STM) is presented. There are two main difficulties in imaging biological samples by STM: (1) the low conductivity of biological material and (2) finding a method of reliably depositing the sample on a flat conducting surface. The first of these difficulties was solved by coating the samples with a thin film of platinum-carbon. The deposition problem was solved by a method similar to a procedure used to deposit biological molecules onto field ion microscope (FIM) tips. STM images of bacteriophage T7 and filamentous phage fd are shown. The substrate on which the samples were absorbed was atomically flat gold. The images do not show molecular detail due to the metal coating, but the gross dimensions and morphology are correct for each type of virus. Also, the surface density of virus particles increases and decreases in the way expected when the conditions of deposition are changed. These methods allow reliable and reproducible STM imaging of biological samples.     

Food surveillance in the Basque country (Spain) I. The design of a total diet study.

A total diet study has been initiated in the Basque country (Spain), the purpose of which is to provide estimates of the average intake of both food contaminants and certain nutrients. The types and quantities of foods that make up the average Basque 'Total Diet' are based on the results of surveys carried out between 1988 and 1990. These surveys have identified the major items in the national diet (91 categories of foods) which are combined for the total diet study, for analysis, into 16 groups of similar foods. Each group is being analysed for selected contaminants of concern which initially are: heavy metals (mercury, lead, cadmium and arsenic), organochlorine pesticides (HCB, HCH (alpha, beta, gamma, delta), DDT (DDE, TDE), dieldrin, aldrin, endrin, heptachlor, heptachlor epoxide, endosulfan and methoxychlor) and selected trace element nutrients (zinc, selenium and iron). In the milk and dairy products groups an assessment of aflatoxin M1 contamination is also being carried out.     

Properties of poly(ethylene terephthalate)–poly(ethylene naphthalene 2,6‐dicarboxylate) blends with montmorillonite clay

The production and properties of blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) with three modified clays are reported. Octadecylammonium chloride and maleic anhydride (MAH) are used to modify the surface of the montmorillonite–Na⁺ clay particles (clay–Na⁺) to produce clay–C18 and clay–MAH, respectively, before they are mixed with the PET/PEN system. The transesterification degree, hydrophobicity and the effect of the clays on the mechanical, rheological and thermal properties are analysed. The PET–PEN/clay–C18 system does not show any improvements in the mechanical properties, which is attributed to poor exfoliation. On the other hand, in the PET–PEN/clay–MAH blends, the modified clay restricts crystallization of the matrix, as evidenced in the low value of the crystallization enthalpy. The process‐induced PET–PEN transesterification reaction is affected by the clay particles. Clay–C18 induces the largest proportion of naphthalate–ethylene–terephthalate (NET) blocks, as opposed to clay–Na⁺ which renders the lowest proportion. The clay readily incorporates in the bulk polymer, but receding contact‐angle measurements reveal a small influence of the particles on the surface properties of the sample. The clay–Na⁺ blend shows a predominant solid‐like behaviour, as evidenced by the magnitude of the storage modulus in the low‐frequency range, which reflects a high entanglement density and a substantial degree of polymer–particle interactions. Copyright © 2005 Society of Chemical Industry     

Green composites of organic materials and recycled post‐consumer polyethylene

Addition of organic fillers to post‐consumer recycled plastics can give rise to several advantages. First of all, the cost of these fillers is usually very low, the organic fillers are biodegradable contributing to an improved environmental impact and, last but not least, some mechanical and thermomechanical properties can be enhanced. Organic fillers are not widely used in the plastic industry although their use is increasing. Bad dispersion into the polymer matrix at high‐level content and poor adhesion with the matrix are the more important obstacles to this approach. In this work various organic fillers have been used with a post‐consumer plastic material originating from films for greenhouses. The properties of these green composites have been compared with those of materials filled with a conventional inorganic filler. The organic fillers cause slightly worse processability, due to an increase of viscosity, an enhancement of the rigidity and of the thermomechanical resistance similar to that measured for the inorganic filler, while a reduction of the impact strength is observed. Copyright © 2004 Society of Chemical Industry