Glucose 6-phosphate isomerase was extracted from cells of Actinomyces viscosus strain RF-7. The enzyme, with a pH optimum of about 7.6 in HEPES buffer, exhibited Michaelis-Menten kinetics and the apparent Km values for glucose 6-phosphate and fructose 6-phosplate were 4.88 mM and 0.28 mM, respectively. Erythrose 4-phosphate was a strong inhibitor of the enzyme reaction, and 6-phosphogluconate and ribulose 5-phosphate were also competitive with fructose 6-phosphate. The apparent Ki values were 2 μM for erythrose 4-phosphate, 0.11 mM for 6-phosphogluconate and 0.56 mM for ribulose 5-phosphate; the other phosphorylated intermediates were without effect. The enzyme had a molecular weight of 115, 000 as estimated by gel filtration chromatography on Sephadex G-150.

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The authors, using an NIN apparatus, examined the dimensional changes occurring in dental plaster during the setting process from its slurry state immediately after being mixed to its solid state, and the following results were obtained : 1) Linear shrinkage that can be seen in the initial stage of the setting process shows a tendency to become larger when the water/powder ratio is increased, and the length of the specimen is shorter. 2) Expansion initiation time shows a tendency to be quickened when the water/powder ratio is reduced, but little difference due to the length of the specimen is recognizable. 3) The apparent linear expansion shows a tendency to become larger when the water/powder ratio is smaller, and when the length of the specimen is shorter. 4) Velocity (time constant) from the beginning of expansion to the maximum expansion is almost constant, being little influenced by the water/powder ratio and the length of the specimen.

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Correlation between natural background radiation exposure rates and cancer mortality rates in 46 Japanese prefectures was statistically studied over the period between 1968 and 1978. With regard to the correlation between natural background radiation exposure rates and cancer mortality rates, statistically significant positive correlation coefficients were observed in most cases of cancers with only a few exceptions.

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Three different types of dies (straight, tapered and undercut) obtained using three types of impression materials (alginate, polysulfide and addition-curing silicone) were measured for height and the dimension of the diameter with a three-dimensional digitizer. Assuming that the value obtained by adding the amount of free-setting expansion of the die material to the dimension of the original represents the highest accuracy, the difference in dimension according to the types of impression material used would be as follows :
1. The die made with alginate : In the case of the straight type, both the height and diameter increased somewhat uniformly. In the case of the tapered type, the height was correct but the diameter was slightly larger, especially in the upper portion. In the case of the undercut type, the height was fairly large and the diameter was large in all portions, especially in the lower portion as though spreading had occurred.
2. The die made with polysulfide : In the case of the straight type, the height was particularly large but the diameter was correct. In the case of the tapered type, the height was slightly larger, and the diameter was a little larger in the upper portion, correct in the central portion, but slightly smaller in the lower portion. In the case of the undercut type, the height was almost as large as that of the die made with alginate and the diameter was large on the whole, showing a form swollen in the middle.
3. The die made with addition-curing silicone : In the case of the straight type, the height was slightly large and the diameter was correct in the upper portion but was slightly small in the lower portion. In the case of the tapered type, both the height and diameter were accurate but the diameter became slightly small in the lower portion. In the case of the undercut type, both the height and diameter were almost uniformly larger, although only slightly. However, in the case of the die made with silicone, the undercut recovery was found to be better than that of the dies made with the two other impression materials.

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A new method for analyzing the fluoride content of the surface layer of human enamel was devised and used in a comparative study, along with methods which have hitherto been reported. The results obtained showed a high correlation between the decalcified depth (X) and the cumulative amount of fluoride in the region from the enamel surface (Y) to the deeper layers, as expressed by the regression power curve (Y=aX^b).
Furthermore, it was confirmed that the cumulative amount of fluoride from the enamel surface as calculated from this graph was of a value extremely close to the determined value and it was thus possible to obtain better results than in the cases where other methods were used, irrespective of the amount of fluoride contained in the enamel. The regression power curve thus produced was then differentiated by any depth (X) and the result divided by the surface area (mm²) ×2.95×10-⁶ to obtain the estimated fluoride concentration of the enamel at anydepth. Consequently, it was suggested that this would provide an extremely effective and expedient method for determining the distribution of fluoride concentration in human enamel in the future.

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