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HISTORY OF DENTAL SURGERY 195

"What basis there may be in conditions surrounding the teetli for the selection
and adaptation of tilling materials must be left to future developments to
discover.
"With our present knowledge, the only basis for the selection and adapta-
tion of filling materials to classes of cases is the individual operator's judg-
ment as to which he can so manipulate as to make tlie most perfect filling,
considering the circumstances, his own skill, and the durability of materials.
"There is no basis for the supposition that calcic inflammation of the peri-
dental membranes or jjhagedenic pericementitis (so called pyorrhea) attacks
persons who have dense teeth in preference to those whose teeth are less dense.
"There is no basis for the treatment of pregnant women medicinally with
the view of furnishing lime salts to prevent the softening of their teeth, or
with the view of producing better calcified teeth in their ofEspring."
The second pajier discussed "the force exerted in the closure of the jaws,"
and that required for the crushing of various kinds of meat and other articles
of food, and gave a history and description of the instruments used for
measuring these forces. Dr. Black says: "It seems curious that men should
have filled teeth all tliese years without liaving entered into a closer study of
this subject than that afforded by clinical observation. In May, 1893, I
presented a paper to the Illinois State Dental Society on the anchorage of
pro.ximate fillings in bicuspids and molars, in which the stress exerted in the
occlusion of the teeth was treated as an unknown quantity. Attention was
somewiuit strongly called to the fact that it was unknown, and to its important
relation to the anchorage of fillings. Within the next two months two
members of the Illinois State Dental Society devised and constructed instru-
ments for measuring the stress exerted by the jaws, both of which were pre-
sented at the World's Columbian Dental Congress which met in Chicago. One
of them was the late Dr. Patrick of Belleville, 111., and is illustrated on page
fifty-three of the published proceedings. The other was by Dr. George J.
Dennis, of Chicago, who presented to the congress a paper on the subject."
The instrument for this purpose is called a gnathodynamometer and Dr.
Black made several of them, seeking to overcome the varioixs difficulties of con-
struction, which proved to be very great, and finally got one that proved
fairly satisfactory and strong enough so that only a very few individuals were
found able to close the jaws together, thus registering the full capacity of the
instrument. Dr. Black does not believe the instrument will give a perfectly ac-
curate test of the force of the jaws, but thinks there is a probable uncertainty
of at least ten per cent., the actual force that may sometimes be used upon food