An Improved Method for the Preparation of "Serial" Sections of Undecalcified Dental Tissues
INCE our previous report' various improvements on the existing methods bJof sectioning undecalcified dental tissues have come to our knowledge. Lefkowitz2 used a rapidly revolving large diameter phosphobronze disc, the circumference of which was charged with diamond powder. The width of the cuts produced by his apparatus is not given, but it cannot have been less than 0.150 mm., this being the thickness of the disc. As the thickness of the sections is stated to vary from 0.250 to 0.400 mm., this method can at best have yielded an average of 2 sections per mm. Sognnaes3 cuts a number of sections simultaneously with a set of circular steel saws each 0.250 mm. thick. Only one 0.750 mm. section is produced per mm. But, as in the case of Lefkowitz' apparatus, comparatively large sections can be obtained (e.g., complete longitudinal sections of human molars). His introduction of methyl methacrylate as an embedding medium constitutes an important improvement of the technic. In a very simple arrangement Atkinson4' 5 employed bonded carborundum discs from 0.8 to 0.125 mm. in thickness, but it is not stated how many sections per mm. can be obtained. In this case too, large sections can apparently be made. In 1946 we1 reported on a method producing small sections at the rate of 5 sections per 2 mm. The number of sections per mm. and the size of the sections seemed capable of improvement. A large and very thin circular saw blade is capable of cutting large sections and at the same time causing small losses of material as narrow saw cuts can be made with it. The unstability of its cutting edge calls for an allowance in the distance of the successive saw cuts (i.e., in the thickness of the slabs) which precludes an approach to serial sectioning.* On the other hand, as in our 1946 machine, the unwavering edge of a narrow and thick saw blade enables very thin sections to be cut, but there is a regrettable loss of material and moreover only small blocks of tissue can be cut. In general, a thin free saw blade can be given a firmness comparable to that of a narrow thick blade by subjecting it to a tension as is done in the ordinary bow saw. Our first apparatus built on this principle was a miniature reciprocating saw. The length of the saw blade (a narrow strip of phosphobronze 2 mm. in width and 0.120 mm. thick) was 3 cm. and the stroke 2 cm. It was driven at the rate of 150 strokes per minute. Diamond powder applied to the edge of the saw blade acted as a cutting agent. Owing to the relatively short stroke and the slowness of action only small pieces of dental tissue could be sectioned by this machine, but not less than four 0.075 mm. sections per mm. could be obtained. The saw cuts were 0.175 mm. in width.
Reproducibility of dental caries in BALB/c mice induced by the bacterium Streptococcus mutans.
Dental caries induced by infection with Strep. mutans C67-1 (serotype c) or Strep. mutans 50B4 (serotype d/g) and feeding a 30 per cent sucrose-containing diet was found mainly in fissures; smooth surface caries was not detected. A decrease in the mean caries score was observed with time, coinciding with lower recoveries of Strep. mutans at the end of the experimental period. The decrease in caries formation may be attributed to changes in some of the cariogenic properties of the individual Strep. mutans strains during maintenance in the laboratory, as re-isolation of the strains from caries-active mice yielded similar and reproducible caries scores to those in early experiments. Hence Balb/c mice can be used as an experimental model in caries research, provided that great care is taken in selecting and storing the bacteria.
Recycling of silicon powder waste cut by a diamond-wire saw through laser-assisted vacuum smelting
Abstract This paper proposes laser granulating technology for recycling harmful silicon powder waste cut by a diamond-wire saw. The silicon block produced by laser was easily melted in a traditional vacuum smelting furnace to form a silicon ingot with a high yield and filling rate, which could reach up to 94.7% and 65.7%, respectively. The removal efficiency of the carbon contamination was 74.2% during laser melting process and reached 86% after 30 min of vacuum smelting. In addition, laser melting process promoted the removal of most metal impurities, such as Al, Na, Ca, Mg, and so on, in the silicon powder waste without introducing any other impurities. The residual impurities could be further removed by vacuum smelting. The experiment revealed that the out capacity of the silicon block melted by a single laser gun was 1.91 kg/h, the energy consumption of laser melting was 2.63 kWh/kg, and the yield of the silicon block exceeded 97% at a laser power of 2000 W, a laser scanning interval of 5 mm, and a scanning speed of 6 mm/s. Therefore, the proposed approach is one of the most simple and efficient silicon powder waste pretreatment methods.