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HISTORY OF DENTAL SUEGERY 255
soon becomes yellow in the mouth and the fluids decompose it. At the present
day, the teeth and tusks of the hippopotamus are much used, both with and
without enamel ; these teeth come from Asia and Africa and are considered the
best of any similar material, though they vary much in size, color, form and en-
amel. When using them or working them, be careful not to expose them to
the sun, fire, or a current of air, as they are liable to crack. These teeth
sooner or later turn bluish or yellowish. Artificial bases of this material often
have human teeth inserted in them. The teeth of the whale are strong but
difl^er very much from the above in form and durability, and are not so much
used in dentistry. Human teeth merit the preference and they are generally
obtained from the mouths of persons who die in hospitals; they are capable
of resisting for a long time the destructive agents to which they are con-
stantly exposed ; we prefer the teeth of adults, and should reject all that are
not entirely sound; they should be thoroiighly cleaned and polished, and im-
mersed in alcohol, then buried in fine clean sand to exclude the air, heat and
cold. These teeth can be adjusted on a gold or platina, or mounted on an
ivory base by means of platina rivets. x\nimal substances of which artificial
teeth are made are liable to speedy softening and decomposition, and they tar-
nish and emit a disagreeable odor. We are therefore ol)liged to renew them
frequently. To obviate this inconvenience it has been proposed to manufac-
ture artificial teeth of earth capal)le of being hardened by heat, and enameled
like porcelain. These teeth are called incorruptible."
In 18-17 Desirabode says: "To manufacture a complete denture with the
teeth and their base, sculptured from a single piece, is decidedly the most dif-
ficult piece of dental mechanism that can be made from the tusk of the hip-
popotannis, for it not only possesses difiiculties inherent to the teeth and to
their basis, but still more, those which are the result of the union of the two
parts.
"Thus the central or groat incisors should be liroad and flat, particularly
those of the upper jaw, which are about a quarter larger than those of the
lower jaw; the lateral or smaller incisors should be one-third narrower: the
canines more or less rounded, elongated or pointed, according to the person,
should be nearly as wide as the lateral incisors. The small molars should be
one-fifth smaller than tlie canines, and the large ones should have a volume
equal to the small ones. In order to hollow the triturating face of the large
and small molars some dentists employ a sharp drill. We prefer the engraver,
which cats less circularly.
"Osseous teeth or plates can be colored by boiling in lye, then remove and