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.
The effect of differing high-carbohydrate diets on dental caries in the albino rat
1. Fifty-six albino rats were distributed between four dietary groups in fourteen randomized blocks of four animals. Each block consisted of siblings and each member of the block received a different dietary treatment. 2. The diets permitted normal growth and the only variations were: group I contained 67% sucrose, group 2 an equivalent amount of uncooked maize starch and groups 3 and 467 % of finely ground Thin Wine and Morning Coffee biscuits respectively. 3. After 31 days on the diet, the animals were killed and assessed for dental caries. The rats of group I had significantly more caries than the other groups. The rats of group 2 had significantly less caries than the other groups. The biscuit diets produced significantly less caries than the sucrose diet, but significantly more caries than the starch diet.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.