A method of determining the corrosive properties of dental amalgams.

The purpose of this study was to determine the corrosive properties of 5 dental amalgams, using a modified rotating disk electrode method described by Van der Merwe, De Wet and Mc Crindle (1991). Ten cylindrical specimens of each amalgams were prepared according to the ISO guidelines. The amount of gamma-2 present was determined by the method employed by Sarkar and Greener (1972), while the corrosion rates were calculated from the Tafel slopes of the polarisation diagrams. All data were analysed statistically. Results showed that at day one Silvalloy contained the most gamma-2, followed by Amalgaphase (previous formulation) and Amalgaphase (new formulation). Dispersalloy and Amalga Sphere contained no gamma-2 at day one. At day nine none of the amalgams tested contained gamma-2 phase. The corrosion rates of the different groups of amalgam varied significantly (p < 0.01) as tested by ANOVA. The spherical amalgam, Amalga Sphere, showed a better corrosion resistance (p < 0.01) than the other amalgams. The method used for evaluating the corrosive properties of dental amalgam proved to be precise, rapid and simple.

Clinical evaluation of four dental amalgams over a three year period.

The aim of this study was to compare the clinical durability of four dental amalgams. In each of eighty-two patients one class 2 cavity was restored with Dispersalloy (Johnson and Johnson) which served as the control and all the other class 2 cavities were randomly restored with one of the following amalgams: Amalgaphase, Amalga 43 (Amalgam Alloys-South Africa) or Permite C (Southern Dental Industries). Matrix bands were placed and Kalzinol bases and Polyvar varnishes applied in all cavities. The amalgams were mixed according to the manufacturers' instructions, the cavities overpacked with amalgam, condensed by hand, carved and then burnished with a ball burnisher. Twenty-four hours later all restorations were polished and colour photographs taken. The restorations were evaluated using the Ryge and Snyder (1973) evaluation system, as well as comparison of the colour photographs. The Fisher's Exact Test was used for the statistical analysis. The two South African manufactured amalgams compared well with the two imported amalgams. However, at the end of the third year the score for the marginal integrity of Amalgaphase, one of the local products, was significantly different (p < 0.083) and inferior to that of the control, Dispersalloy. Evidence is produced to suggest that over a three year period Amalgaphase performed better than Dispersalloy, Amalga 43 and Permite C.

Clinical evaluation of four dental amalgams over a two year period.

The aim of this study was to determine the clinical durability of two locally manufactured amalgams. In each of eighty-two patients one class II cavity was restored with Dispersalloy (Johnson and Johnson) which served as the control and all the other class II cavities were randomly restored with one of the following amalgams: Amalgaphase, Amalga 43 (Amalgam Alloys-South Africa) or Permite C (Southern Dental Industries). Matrix bands were placed. Kalzinol bases and Polyvar varnish were applied in all cavities. All amalgams were mixed according to the manufacturers' instructions. The cavities were overpacked with amalgam, and the amalgam condensed by hand, carved and then burnished with a ball burnisher. Twenty-four hours later all restorations were polished with a Shofu polishing system and colour photographs were taken. The restorations were evaluated using the Ryge and Snyder (1973) evaluation system, as well as comparison of the colour photos. The Fisher's Exact Test was used for the statistical analysis. During the second year there were no significant (p < 0.05) differences between the four brands of amalgam restorations except as regards the gloss category. The two South African manufactured amalgams compared well with the two imported amalgams. During the second year the marginal integrity and surface texture of Amalgaphase compared well with that of Permite C. Dispersalloy and Permite C showed more deterioration in anatomic form than the two South African amalgams. Amalgaphase was the only amalgam to show no bulk fracture within a period of two years. Amalgaphase performed better in the gloss category than the other three amalgams during the second year evaluation. According to the weighted product calculation Amalgaphase was the best amalgam followed by Dispersalloy, Amalga 43 and Permite C.

Corrosion of five different dental amalgams.

The purpose of this study was to determine the gamma-2 presence in two South African amalgams (Amalgaphase and Silvalloy) and to compare this data with that obtained from tests on a well-known gamma-2 containing amalgam (Amalcap) and on two products with a reportedly low gamma-2 content (Dispersalloy and Permite-C). Samples were prepared according to standard ISO procedures in special sample holders. The rotating disc electrode technique (similar to the technique described by Gal-Or, Bruckenstein and Carter, 1978) was used to determine the presence of gamma-2. All samples were evaluated after one and again after nine days. Results indicated that only Dispersalloy displayed no reaction at day one; in other words no gamma-2 could be detected after 24 hours. All other amalgams showed a definite peak on the polarization plot between -200 and -250 mV indicating electrochemical activity (corrosion) in that region. On day nine, only Amalcap (the gamma-2 containing amalgam) still exhibited a reaction peak. Thorough clinical studies will have to be undertaken to evaluate the durability of the South African products.

Aerospora of an Eragrostis curvula pasture in South Africa.

A qualitative and quantitative survey was made of the aerospora above an Eragrostis curvula (Schrad.) Nees pasture. The pasture, which lay adjacent to a field of Panicum coloratum L. where an outbread of ovine photosensitivity had occurred, was not grazed during the survey. A Burkard volumetric spore trap was used to sample the aerospora continuously for 10 months. Twenty components of the aerospora were recognized: spores of 9 genera of fungi (Cladosporium, Alternaria, Epicoccum, Drechslera, Pithomyces chartarum (Berk. & Curt.) M. B. Ellis, Nigrospora, Sporormia, Curvularia, Spegazzinia); 8 recognizable but unidentified spore types; hyphal fragments and pollen grains. Cladosporium conidia comprised 83,37% of the total aerospora. Conidia of Pithomyces chartarum formed a small (0,29%) but significant component of the aerospora, since this fungus is known to cause hepatogenous photosensitivity.