THE TEETH. 613 



DENTINE, CEMENT, AND ENAMEL. BY C. F. W. BODECKER, D. D. S., M. D. S.* 



Methods. The best method for preparation of bone-tissue for microscopical 

 purposes is doubtless the treatment with chromic acid solution of the strength 

 of a half to one per cent. The same treatment has repeatedly been resorted 

 to by different investigators of tooth-substance. I have used this solution 

 extensively for this purpose, with precautions suggested by the experience on 

 bone. These are : to immerse only a few teeth in a large vessel with a con- 

 siderable amount of chromic acid solution ; to renew the same every third or 

 fourth day, and add, to enforce the action of the fluid, very small quantities 

 of dilute hydrochloric acid. By this treatment the teeth, after a few months, 

 become dark green from the reduction of the chromic acid to the sesquioxide 

 of chromium. This method is doubtless the best for softening teeth, although 

 the chromic acid softens the cement and dentine only to a certain depth, so 

 that a tooth kept in the chromic acid solution never is fit to be cut through in 

 its whole substance at one time. The sections so obtained are ready for 

 staining with carmine or hasmatoxyloii, and after they have been immersed 

 in and washed with distilled water, also for staining with chloride of gold. 



The greatest objection to the chromic acid treatment is that enamel 

 never can be obtained in connection with the dentine. If hydrochloric acid 

 has been used, in addition to the chromic acid solution, the enamel is almost 

 completely dissolved. If chromic acid alone has been used, the enamel 

 becomes so brittle that it crumbles into small particles under the knife. 



Lactic acid acts upon teeth, if diluted sufficiently, by dissolving the lime- 

 salts much faster than chromic acid. Specimens prepared in this way, how- 

 ever, in my experience, are not distinct enough for study with high powers. 



The only method which enabled me to obtain specimens of teeth provided 

 with all hard tissues is the following : A fresh tooth, or one kept a short time 

 in chromic acid solution, is sliced under water by a watch-spring saw, and 

 ground as thin as possible upon a corundum-wheel of a lathe, always being 

 kept under water. The lamella thus obtained should be placed in a large 

 quantity of chromic acid solution, of the strength of half of one per cent., for 

 one or two days, with the view of hardening the soft parts of the tooth and 

 dissolving the lime-salts. After this the specimen may be stained with car- 

 mine, heematoxylon, chloride of gold, etc., as above described, and mounted 

 in dilute glycerine. The saturated solution of picric acid in water may also be 

 used for the decalcification of a ground slice of a tooth. 



Dentine. We know that the basis-substance or matrix of the dentine is 

 analogous to that of bone, viz. : glue-yielding, and at the same time infiltrated 

 with lime-salts. We learned from the researches of E. Neumann that the 

 basis-substance is denser on the walls of the tubuli, and more resistant to the 

 action of strong acids, which cause the appearance of a sheath around each 

 tubule after the solution of the intermediate substance of the matrix between 

 the tubuli. 



With low powers we cannot see in the dentine anything but the tubuli, 

 which I propose to term hereafter dentinal canalicuU. These, as is well known, 

 run in curved sigmoidal lines from the boundary of the pulp-cavity to the 

 periphery of the dentine ; they are directed obliquely upward in the crown, 

 and assume a more horizontal direction in the region of the neck, while in the 



* Extracted from the author's essay, "The Distribution of Living Matter in Human Den- 

 tine, Cement, and Enamel." The Dental Cosmos, Philadelphia, 1878 and 1879. 





