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.
A Sectioning and Planing Machine for Plano-Parallel Tooth Sections
Recent investigations of the calcified dental tissues have necessitated improvements in methods for preparing ground sections. Even though special methods of decalcification are available (1, 2, 3, 4), microscopic studies of enamel, and of the dentino-enamel junction, have been made almost entirely by the use of ground sections. Not only is the enamel destroyed by decalcification methods, but certain changes in the dentin are also obscured. The differences between young and old (metamorphosed) dentin, which led Beust (5), Fish (6) and Bodecker and Applebaum (7) to the conclusion that dentin of old teeth contains areas of variable permeability, are evident only in ground sections. Figs. 1 and 2, ground and decalcified sections made from the same molar of an old individual, demonstrate the differences between the two types of sections. Fig. 1, a ground section, shows acute root caries and highly metamorphosed crown dentin (8). This dentinal change causes the tubules to appear black by transmitted light. The decalcified section (fig. 2) has lost its enamel and the dentin appears almost homogeneous and not metamorphosed; only the infected dentinal tubules of the cavity wall show as dark areas. Dental lymph was discovered by Bodecker (9) solely through the study of ground sections. In later corroboration by "vital" staining of teeth (10) ground sections played an important part. Fig. 3 shows the dentino-enamel junction in a ground section in which there appear to be two types of dentinal tubules. Originally the same, they now differ in that the metamorphosed tubules (MT) are impermeable while
Effects of Alizarine Red S Injections on the Teeth and Bones of Macacus rhesus Monkey.∗
Seventeen Macacus rhesus monkeys of mixed or adult dentition, ranging in age from 1½ to 7 years, 1 were given multiple intravenous, intraperitoneal or subcutaneousi injections of 5-10 cc. of 2% Alizarine Red S (Sodium Sulphalizarate) of color index 1034 (Coleman and Bell Company) at 5- to 30-day intervals. The time between the last injection and death ranged from 3 hours to 125 days. The dosage ranged from 40 to 60.5 mg. per kilo. For each injection a distinct red ring was observed in the dentin and the bone that were forming and calcifying at the time. 2 This effect was immediate, as indicated in the animals sacrificed within a few hours after the last injection. In 6 animals 4 months elapsed between the first injection and death. This long survival did not alter the staining reaction. Measurement of the distances between successive rings indicated the amount of apposition during the corresponding intervals. The rate of apposition of dentin based on 1164 measurements made chiefly in the ground sections of bicuspids and molars ranged from 1.6 to 5.6 μ per 24 hours. This range may be explained on the basis of a growth gradient with its maximum at the cusp and along the outer dentinal surface and its minimum apically and toward the pulp. Alizarine lines were also found in the cementum. Definite staining effects could be recognized macroscopically in the jaws and long bones. Subcutaneous administrations were found to be complicated by a sloughing of the tissues at the site of injection. Intravenous injections gave sharper effects than intraperitoneal injections of the same dose. However, thrombosis of the veins at or near the site of injections occurred frequently. The intraperitoneal injections were as effective as the intravenous ones when the dosage was increased to 10 cc.