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USE OF AMALGAM. 325

no carving of contour, and no smoothing, the amalgam being ready for
polishing strips. The occlusal surface is smoothed and polished with
moosehide points and pumice, using a stiif brush to polish the sulci.
Finishing-.—The process of finishing hard amalgam fillings is simi-
lar to that of finishing gold. For example: a compound cavity occu-
pying the approximal and occlusal faces of a molar. A fine saw is
placed in a frame as in Fig. 294, but set to draw-cut with its teeth
Fig. 294.

The Kaeber saw frame.
pointing toward the frame. The blade is passed above the cervical
margin of the filling, engaging any projecting amalgam, which is then
sawn oif. It is just as essential with an amalgam as with a gold filling
that the cervical edge should be exactly flush.
The lateral margins of the filling are next carved smooth ; strips of
emery cloth are passed into the interdental space and the filling smoothed
and rounded, completing this portion of the operation with emery strips
of the finest grit.
Linen tapes or metal polishing strips are next charged with pumice
and passed over the surfaces until they are smooth and the margins are
perfect. The occlusal portion is polished by means of rubber or moose-
hide points and pumice.
Should it be a plain approximal filling, not a " contour," the saw is
used to cut away surplus amalgam, and the polishing accomplished by
means of disks and powders.
Fillings upon the buccal surfaces of teeth are smoothed by means
of disks and polished with rubber cups or disks and pumice.

Gutta-percha.
Origin.—The gutta-percha of commerce is the coagulated juice of
the Isunaudra gutta, a tree of the order of ISapotacece. The juice is
found in all trees of this order, but some specimens are of much higher
value than others. That from Borneo is regarded by manufacturers as
being inferior ; it is the variety from which the name is derived—Malay,
gatah or gittaJi, gum, and pertja, a tree. The gutta Tuban from Singa-
pore is regarded as a superior variety.