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326 PLASTIC FILLING MATERIALS.

The mode of securing the juice is by tapping tlie cambium layer of
the tree and catching tlie juice as it exudes. From this stage to its
formation into sheets it undergoes several processes (see works on gutta-
percha) ; it is possible that in some of these operations it may have its
texture injured by overheating.
"The purified gutta-percha probably consists of a hydrocarbon (pure
gutta) having the formula CiuH,g ; albane, C,oH,gO ; fluavile, C^dHg^O,;
and a variable compound named guttune. Pure gutta possesses all the
good qualities of gutta-percha in a much enhanced degree, becoming
soft and plastic on heating and hard and tenacious on cooling without
being in the least brittle. The resins appear to be simply accessory
components which have a decidedly detrimental eifect when they ]ire-
ponderate. Water, wood, fibers, bark, sand, etc., occur as mechanical
impurities of gutta-percha." (Obach.)
History.—Gutta-percha was introduced into dental practice as a fill-
ing material about the year 1847. Soon after this a secret preparation
was introduced by a Dr. Hill, which received his name. Numerous
alleged analyses of Hill's stopping have been given, all of which are
untrustworthy. It was found to subserve so useful a ])urpose that it
received the tribute of wide imitation ; in fact, the white gutta-percha
preparations of the present day had their foundation in this imitation.
There is no entirely trustworthy evidence that the original was superior
to the best of contemporary preparations.
As at present employed as a filling material gutta-percha is in two
forms, the first the well-known pink gutta-percha base plate, which is
colored by the insoluble sulfid of mercury, the second the white prep-
arations, made firmer in texture by additions of the soluble zinc oxid.
The specimens of crude gum differ as to the amount of heat required
to soften them to an equal degree. Dr. Flagg ^ states that the speci-
mens requiring the greatest degrees of heat for softening, prior to the
addition of the zinc oxid, afford the best dental gutta-perchas. The
method of making the gutta-percha of dentistry is by softening a mass
of the brownish-yellow gum on a slab which has been heated over boil-
ing water, and driving zinc oxid into the softened mass by a process
of kneading, using a wedge-shaped steel instrument as the kneader. It
requires infinite patience and much time to distribute the powder evenly
throughout the mass. Overheating the material at any stage of its
manufacture or manipulation is ruinous to its texture.
Classes.—Gutta-perchas are divided into three classes according to
the temperature of softening : Low heat, softening below 200° F. 3Ie-
dium heat, becomes plastic at 200° to 210° F. Hif/h heat, 210° to 218° F.
The low-heat specimens contain 1 part by weight of gutta-percha to 4
^ Plastics and Plastic Filling.