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STRENGTH OF THE BITE. 117

to be considered with great care by every operator, both in
general and in relation to each individual operation. The
strength required in fillings is very much greater than was for-
merly supposed. It has been but a few years since we began
to know definitely of the strength of the bite or of the strength
actually required of fillings. I believe the first paper that
brought this prominently before the profession was one which I
presented to the Illinois State Dental Society in May, 1893.
Following that, two instruments were presented for measuring
the strength of the bite at the meeting of the World's Dental
Congress in Chicago, later in the year of 1893, and very con-
siderable interest was at once manifested in this subject, which
has led rapidly to considerable changes in the preparation of
cavities and to a radically new study of the strength of filling
materials. These instruments were presented, one by the late
R. Patrick, of Belleville, Illinois, and one by Dr. George
J. J.
Dennis, of Chicago. The instrument we are now using is a
modification of the instrument presented by Doctor Dennis. It
was immediately found that the actual strength of the human
bite was very much greater than had been supposed, and that
the strength of fillings had been insufficient, and this was the
cause of the rapid failure of many fillings, particularly proxi-
mate fillings. In order that the instrument should well repre-
sent the strength of the bite, the surface upon which the biting
is done should be spread over the crowns of at least two molar
teeth, but as it is the force of the bite is generally expended
upon a single cusp of an upper tooth and a single cusp of a
lower tooth, which does not give sufficient space to properly
present the full power with which the jaws may be closed upon
food. The strength of the teeth is found to be ample; one can
not break a tooth with the power of the muscles of the jaw,
unless the biting is done on steel or some other very hard sub-
stance. In biting upon steel, or other substance equally hard,
the area of tooth substance presented to the steel will be very
small indeed, and by hard biting the enamel may be fractured.
But when the substance bitten upon is soft, as a piece of hard
rubber, the tooth will sink into it a little and spread the area of
stress more upon the surface of the tooth. On hard rubber or
the softer metals I have never known a person to check the
enamel of a tooth in biting with all the power of the muscles.