Histo-chemical proof of the presence of protein matter in dental enamel.

There has been much speculation regarding the occurrence of protoplasmic matter in dental enamel but no demonstration of it, although recent histological work, by Bödecker particularly, has suggested the presence of organic structural elements. In a direct histo-chemical study, human teeth, after immersion for several days in 10 percent formalin solution, were sectioned transversely through the crowns. The sections were ground to the thickness of about 1 mm. or less; decalcified by Bödecker's process 1 in a mixture of methyl alcohol, nitric acid, and celloidin; freed from celloidin with a mixture of ethyl alcohol and ether, and kept in ethyl alcohol. Throughout this procedure the residual structure of the enamel retained the original outlines. A portion of the soft yellowish-white enamel residue, about a millimeter wide and several millimeters long was gently teased away, transferred carefully with a pipette to water, in which it was soaked for the removal of soluble extraneous matter; and then pipetted cautiously to a microscope slide, where the identity of the material was confirmed and absence of dentinal admixture established. At this stage the particle was slightly acid in reaction to litmus. The quantities of this material in dental enamel differ widely.

The fragment of soft enamel residue, which remained intact during these manipulations, was then treated on the slide with a few drops of Gies's reagent for Piotrowsky's (“biuret”) test. Gradually the particle under microscopic examination acquired a lavender tinge of uneven intensity, the coloration ultimately becoming evident to the naked eye. This result was obtained as well with fully as with incompletely decalcified specimens. The Molisch test for carbohydrate, and the ammoniacal silver test for aldehydes, applied to other pieces, were negative, indicating that the result with Gies's reagent was due neither to a reducing substance derived from the celloidin nor to retained formalin.