Page 336 - My FlipBook

334 PLASTIC FILLING MATERIALS.
should 1)0 given ani])lc time to harden before plaein^i^ tlic gutta-percha.
Indeed, it is a fundamental feature of good gutta-percha
work that while one cannot operate too rapidly when
the plastic is at its proper temperature, the preparatory
and completing processes should be given as much time,
care, and close scrutiny as more elaborate and often less
enduring gold operations. There is furthermore room
for the exercise of the artistic faculty in having at hand chloro-percha,
or cellulose varnish of varied colors, with which, by means of a small
brush, a gutta-percha filling as B, Fig. 301, and one in the like cavity
C, may be given an inconspicuous shade, and the painting be renewed
from time to time, if that be necessary by reason of wear. Fig. 314 is
a sectional view of fillings like 7?, C, Fig. 301."
Finishing- Gutta-percha Fillings.—If a gutta-percha filling has
been packed with the proper amount of care and skill, it should require
but little trimming. It should be undisturbed until cold. Its harden-
ing may be hastened and intensified by holding ice-water in contact
with it for a few moments.
The portions overlying the margins are to be trimmed wdth extremely
sharp lancets or by warm blades. Every cut should remove a little of
the surplus material, never a mass of it, and should be made toward the
cavity margins, never away from them. The filling should have been
made so that no fulness is present to require reducing.
It is a general practice to give a smooth face to a gutta-percha filling
by wiping it with a tape slightly moistened, not wet, with chloroform.
The surface produced by this means, although smooth, does not retain its
integrity so well as when the surface is formed by cutting.
The use of gutta-percha as a canal filling is discussed in Chap. XVII.

Basic Zinc Cements.
Zinc Oxychlorid.—The basic zinc cements employed in dentistry are
the oxychlorid and the phosphate ; the oxysulfate should also be included.
The oxychlorid is formed by the combination of calcined and pul-
verized zinc oxid w^th a solution of zinc chlorid :

ZnO + ZnCL + H^O = 2ZnClHO.

This compound was introduced as a dental filling material about 1850,
its hardness, whiteness, and apparent insolubility recommending it for
that purpose. It required no lengthy period of time to demonstrate
that as a filling material per se it was unfit for use. It disintegrated
rapidly and was not free from shrinkage.
Properties.—Freshly mixed, this material is irritating to vital
tissues with which it is brought in contact ; applied close to or upon an
exposed pulp it may be productive of a transient or a persistent irritation,