No. 1

I

HAVE been asked to talk on the principles of cavity preparation as set forth by Dr. G. V. Black. The subject is so extensive that in a talk of an hour you can readily understand I can simply touch it in its most essential features. In such a talk, therefore, it becomes a matter more or less of my personal viewpoint, founded on some years of teaching, as to what is most important. If I were asked to select the three most essential principles upon which this comprehensive system is built, I should probably answer: First, upon a thorough study and comprehension of the inclination of enamel rods in the different areas of the various teeth; second, upon the extension of cavity margins to areas of immunity, or, as it is usually termed, extension for prevention of the recurrence of decay; and third, the establishing of definite angles at the junction of the surrounding walls with the floors of cavities.

VOL. LX.-1

INCLINATION OF ENAMEL RODS.

No scientific cavity preparation can be attained without a thorough knowledge of the structure of enamel and dentin, which of course carries us into the realms of histology. May I, therefore, for a brief space recall to your minds what we learned in our college days, and with the aid of these charts refresh them in what must of course be a very superficial way, with the structure of enamel and dentin, but more especially the former?

Enamel is composed of rods or fibers held together by an intervening cement substance. The enamel rods in turn are made up of globules or little balls held. together in rows or lines. These can best be likened, in a gross way, to the result one would obtain if he were to take small balls of putty or soft clay, and by stacking them one upon another apply just pressure enough to make them

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