Determination of Phase Transitions in Gutta-Percha by Differential Thermal Analysis
Pure gutta-percha was heat-treated in a differential thermal analyzer. The high melting form crystallized on cooling when gutta-percha was heated to 70 C or less. Above 74 C, crystallization into the low melting form predominated. Either polymorph can be selectively crystallized by control of the heat-treatment temperature before cooling.
An in-vitro evaluation of the influence of temperature of plasticization on the sealing ability of Thermafil.
The effect of temperature of plasticization on the sealing ability of Thermafil obturators was evaluated. Forty-eight canals in roots of extracted human mandibular molar teeth were divided into four groups of 12. The root canals had curvatures of less than 25 degrees, as determined using the Schneider technique. Four canals were used as positive and negative controls. All canals were prepared using a step-back technique to size 30 at the working length. Roth's sealer was used in all canals. In one group the Thermafil obturators were thermoplasticized in an open flame, as recommended by the manufacturer. In the remaining three groups the obturators were thermoplasticized by immersion in water-baths maintained at constant temperatures of 60, 75 and 90 degrees C respectively. After immersion in Indian ink, the teeth were cleared and the depth of penetration of dye through the apical foramen was measured. In all specimens there was extrusion of sealer and sometimes gutta-percha beyond the apical stop. Sometimes, there was leakage up to the apical stop but not beyond. In view of this the measurements were divided into leakage from the apical foramen to the apical stop and from the apical stop coronally. It was found that in the zone between the apical foramen and the apical stop the Thermafil obturators plasticized at 60 degrees C produced a significantly better seal than those obturators plasticized in an open flame (P < 0.05). In the zone coronal to the apical stop there were no significant differences in leakage between the groups.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.