AC impedance measurements on high copper dental amalgams.

In recent years alloys with a high copper content were developed to improve the corrosion resistance of dental amalgam by elimination of the gamma 2 (Sn-Hg) phase. The purpose of the present investigation was to compare the electrochemical behaviour of high copper amalgams obtained from single composition amalgam alloys (Indiloy; Shofu, Dental Corp., Menlo Park, USA) with those that used the additive mode of copper alloying (Dispersalloy; Johnson & Johnson, East Windsor, USA).

Compressive strength of some polyalkenoates with or without dental amalgam alloy incorporation.

The present study compares the compressive strength after one week of some conventional glass-ionomer restorative materials with that of glass ionomers reinforced by the addition of ceramic-coated silver or dental amalgam alloy particles to the aluminosilicate glass powder. Apart from the commercially available Ketac Silver and Miracle Mix, experimental mixtures of Fuji II glass-ionomer powder, the old as well as the new version, with various amounts of either a spherical or lathe-cut amalgam alloy were investigated. For the conventional glass ionomers, the mean compressive strength based on all measurements amounts to 159.9 +/- 4.5 MPa. Both formulations of Fuji II have a comparable strength after one-week maturation. The compressive strength of Ketac Silver does not differ significantly from that of Ketac Fill or from that of the conventional glass ionomers investigated. The effect of admixing amalgam alloy on the compressive strength is found to be determined by the shape and the amount of the alloy particles. Moreover, both parameters are interactive with the formulation of the Fuji glass ionomer used for preparation of the mixture. The results indicate that when dental amalgam alloy is added to the glass ionomer, lathe-cut particles are to be preferred but only in an amount up to 20% by weight.

An application of impedance techniques to corrosion research on dental amalgam.

AC impedance techniques are finding increasing application in corrosion research. It was our aim to introduce them as a method for the evaluation of the electrochemical behaviour of dental amalgam. The complex plane plots are large depressed semicircles representing the frequency dependence of the impedance and measured at the corrosion potential. Conventional dental amalgams, in a chloride medium, exhibit a current peak in the proximity of -250 mV (vs. SCE). The corresponding impedance spectra are rather complex and difficult to interpret. The high frequency part, however, can be fitted to a semicircle with its centre lying below the real axis. An evaluation of the corresponding 'charge transfer resistance' shows that it is inversely proportional to the corrosion current density.

A mechanistic study of the electrochemical corrosion of the gamma 2 phase in dental amalgams. I. Evaluation of the measurements.

Conventional dental amalgams are prone to corrosion of the gamma 2 phase. In an anodic polarization experiment the presence of gamma 2 causes a current peak in the proximity of -250mV vs. SCE. Electrochemical impedance measurements carried out at this potential indicate the occurrence of an impedance curve in two parts. The high frequency part is a semi-circle with its centre below the real axis. Apart from the faradaic impedance and the double layer capacitance, the high frequency part is dominated by the behaviour of the corrosion products layer on the amalgam surface. The low frequency part has the form of a diffusion-like curve. However, since the phase angle is smaller for the above-mentioned case than for a free diffusion, this phenomenon is ascribed to diffusion in a porous layer at the interface between amalgam solution.

A mechanistic study of the electrochemical corrosion of the gamma 2 phase in dental amalgams. II. Introduction of a model.

Electrochemical impedance measurements on conventional dental amalgams at an anodic polarization potential of -250 mV vs. SCE were performed. An initial evaluation was given in part I of this study; in the second part the results are interpreted in terms of a model. The latter, characterized by an equivalent circuit, is a parallel combination of a flat surface and a pore. The selection of appropriate values for the elements of the equivalent circuit leads to a better insight into the corrosion process. Although no simple relationship exists between the circuit elements and the impedance curves, an explanation was found for some typical features of these curves. As an application, the influence of the anodic polarization potential on the impedance curves was studied. Evaluation by means of the model demonstrated the importance of the characteristics of the corrosion products.

A model for the corrosion behavior of dental amalgams.

At high frequencies, electrochemical impedance behavior for corroding dental amalgams cannot be interpreted in terms of a simple Randles equivalent circuit. This may often be ascribed to the imperfect cell geometry resulting in a nonuniform current distribution. However, the insertion of a constant phase element (CPE) in the non-faradaic branch of the equivalent circuit offers a new scope for interpretation as the circuit provides an m-parameter corresponding to the degree of distortion. The decrease of m as a function of time was explained by a mathematical model reflecting an increasing number of pores. Moreover, that same model allows a better understanding of the passivating effect of NaHCO3 and of the differences between conventional and Cu-rich dental amalgams.

A method for the measurement of dimensional change of dental amalgam.

A dimensional change occurs during the setting of a dental amalgam. A measurement circuit, which makes it possible to register these changes, is introduced. To this purpose strain gages were used. The registration instrument is tested by comparing different dental amalgam products.

[Comparative studies between various amalgams]. / Een vergelijkende studie tussen een aantal amalgamen.

A number of dental amalgam products have been compared in the context of a thesis. Four products, each of them possessing different characteristics, have been selected. Six Eighty Amalgam Alloy is a conventional product; Fluor Alloy contains a quantity of SnF2; Amalcap non gamma2 belongs to the group of the so-called non gamma2-alloys; Indiloy is spherical and contains indium. Each product was subjected to a series of tests and investigations: structure, dimensional changes after condensation, compressive strength, behaviour during a relaxation-test and resistance to corrosion. Indiloy was the product with the most interesting structure and it could be ascertained the mercury especially attacked silver and indium of the original alloy. Thus a sort of matrix is formed. The measuring of the dimensional changes was done by introducing a new method. Fluor Alloy and Indiloy present a behaviour that differs a lot from the expected one: at first a contraction followed by a more important expansion. A relaxation-test is an alternative to the creep-test and the connection between both is demonstrated. Combining the results of the resistances to the compressive forces with those of the relaxation-tests shows Indiloy possesses superior mechanical properties while those of Six Eighty Amalgam Alloy are rather inferior. A final series of tests concerns the resistance to corrosion. Amalcap non gamma2 and Indiloy have a much greater rough resistance to corrosion than the two other ones.

Iohexol in patients undergoing urography: a comparison of polypropylene containers (Unique Soft Pack) and glass vials.

The purpose of the present phase IV multicentre trial was to evaluate general patient tolerance to Omnipaque 350 mgI/ml (iohexol) supplied in polypropylene containers compared to that of the same product supplied in routinely used glass vials, with emphasis on allergy-like adverse events. Polypropylene is a pure plastic material with practically no additives, and has been tested in vitro as a contrast medium packaging material for several years. Handling of these containers is easier and safer than handling of glass vials. Iohexol was administered to 1481 patients undergoing urography (741 patients in the glass vial group, 740 in the polypropylene container group), all of whom successfully participated in the trial. Six centres, representing four European countries, participated. Patients were randomized to receive iohexol from either polypropylene containers or traditional glass vials according to a double blind, parallel design. Pre-established inclusion and pre-admission exclusion criteria were followed, as well as routine procedures for preparation of the patients and conduct of the urography examinations at each hospital. Patient tolerance was assessed by recording all adverse events experienced over a period of up to 1 h after the procedure. Allergy-like events were defined as coughing, sneezing, nausea, vomiting, urticaria or itching. No adverse events were experienced by 56.5% of the patients in the glass vial group, nor by 58.0% of those in the polypropylene group. Discomfort (mainly a sensation of warmth) was reported by 39.4% and 38.6% of the patients, and adverse events other than discomfort by 7.4% and 5.9% of the patients, respectively. There seemed to be a correlation between the speed of injection and the frequency of discomfort (an increase with increasing speed), both of which varied a lot between centres. There was no significant difference in the incidence of allergy-like events between the two groups. Such reactions were seen in 2.0% of patients in the glass vial group and 1.9% of those in the polypropylene container group. There was no significant difference between the patients' tolerance to iohexol supplied in traditional glass vials or in polypropylene containers. Therefore, the new polypropylene container can be recommended as a container for Iohexol.

[Risk of bone disease as a result of fluoride intake in chronic renal insufficiency]. / Risque osseux de l'apport fluoré chez l'insuffisant rénal chronique.

Four cases of osteosclerosis were observed in patients with renal failure. All subjects presented with moderate reduction in renal function which had been stabilized for several years. Osteosclerosis appeared progressively but was clinically symptomatic in only one patient. Fluoride intoxication was ascertained on the basis of X-ray examination and bone biopsy. In addition, the source of fluoride intoxication was easily recognized as the drinking water (2 to 3 1/day), "Vichy Saint Yorre" commercial mineral water (fluoride concentration 9 mg/l) in 3 cases, and tap water in the fourth case. These observations emphasize the risk of high chronic fluoride intake in patients with renal failure, even with mild reduction of glomerular filtration rate.