Particle size analysis of amalgam powder and handpiece generated specimens.

OBJECTIVES: The increasing interest in the elimination of amalgam particles from the dental waste (DW) stream, requires efficient devices to remove these particles. The major objective of this project was to perform a comparative evaluation of five basic methods of particle size analysis in terms of the instrument's ability to quantify the size distribution of the various components within the DW stream. METHODS: The analytical techniques chosen were image analysis via scanning electron microscopy, standard wire mesh sieves, X-ray sedigraphy, laser diffraction, and electrozone analysis. The DW particle stream components were represented by amalgam powders and handpiece/diamond bur generated specimens of enamel; dentin, whole tooth, and condensed amalgam. RESULTS: Each analytical method quantified the examined DW particle stream components. However, X-ray sedigraphy, electrozone, and laser diffraction particle analyses provided similar results for determining particle distributions of DW samples. These three methods were able to more clearly quantify the properties of the examined powder and condensed amalgam samples. Furthermore, these methods indicated that a significant fraction of the DW stream contains particles less than 20 microm. SIGNIFICANCE: The findings of this study indicated that the electrozone method is likely to be the most effective technique for quantifying the particle size distribution in the DW particle stream. This method required a relative small volume of sample, was not affected by density, shape factors or optical properties, and measured a sufficient number of particles to provide a reliable representation of the particle size distribution curve.

Determination of spatial continuity of soil lead levels in an urban residential neighborhood.

This study uses geostatistical techniques to model and estimate soil lead levels in an urban, residential neighborhood. Sixty-two composite soil samples (median 1773 ppm; range 175 to 7953 ppm) in a four-block area of brick and stone homes were obtained. The spatial continuity of soil lead levels was modeled with a semi-variogram, which was then used to estimate lead levels at unsampled locations, a process called kriging. Because soil lead levels were spatially correlated, it is likely that a "nonrandom" process generated the lead distribution found. This finding signifies the existence of lead sources which were tentatively identified on historical maps of the area and from past traffic volume patterns. The distribution of kriged estimates of soil lead levels provides an explanatory tool for exploring and identifying potential sources and may be useful for targeting urban soil abatement efforts.

Influence of pH, nitrogen and phosphorus sources on the production of hepatitis B virus pre-S2 antigen by Hansenula polymorpha.

Experimental design techniques were used to study the influence of the composition of the culture medium on the production of hepatitis B virus pre-S2 antigen by the methylotrophic yeast Hansenula polymorpha. pH, phosphoric acid, ammonium chloride and yeast extract concentrations were selected as experimental factors and their influence was investigated using Central Composite design techniques. The results indicated that antigen yield was maximized at high pH and in a culture medium containing both ammonium chloride and yeast extract. Phosphoric acid was found to have a detrimental effect on antigen production. This study allowed a 50% increase in antigen production in a medium in which the yeast extract concentration was decreased to 32 g/l. These optimal conditions have been confirmed with an octagonal design experiment. Moreover, it was shown that the antigen produced was very stable up to at least 8 days after induction and that the yeast extract concentration could be lowered to 22 g/l without appreciable effect on antigen yield. The increase in antigen production was not due to an increase in cell biomass, since no correlation could be found between these two parameters. The newly defined culture medium should allow a greatly increased antigen production at the fermentor level, at a lower cost and with minimal operational problems.

Some factors influencing the proportion of periplasmic hepatitis B virus pre-S2 antigen in the recombinant yeast Hansenula polymorpha.

A central composite design (CCD) was used to evaluate, for the purpose of future process optimization, the influence of pH, yeast extract and ammonium chloride concentrations on the proportion of periplasmic hepatitis B pre-S2 antigen in the recombinant yeast Hansenula polymorpha. Each factor was tested at five levels, and a second order polynomial model for the proportion of periplasmic antigen was fitted to the treatment combinations. pH showed the greatest effect: the proportion of periplasmic antigen was greatly increased at the higher pH levels. At the higher pH levels used, the proportion of periplasmic antigen was enhanced by a high concentration of ammonium chloride. Additional experiments have confirmed both the validity of the selected model and the optimal conditions found. A significant correlation was found between the proportion of periplasmic antigen and the total yield of antigen. These results indicated that it should be possible to modulate the distribution of the pre-S2 antigen between the periplasm and the cytoplasm of the yeast.