Page 258 - My FlipBook

256 FILLING MATERIALS.

has been previously protected by a layer of frutta-percha or a disk of
asbestos paper. In such cases, particularly on occlusal aspects, the
cavity may bo nearly filled, leaving a remainder the thickness of enamel
to be completed Avith gold.
For the filling of root canals and pulj) chambers it otFers the best
solution of the problem of preventing septic changes in the devitalized
dentin. After many years, fillings of root canals and pulp chambers
of this material remain unchanged and are found clean and without
odor on removal—a result that is not presented by any other filling
material which may be introduced in these situations. Here it is im-
]>ortant that the material be not mixed very thin, especially on account
of the danger of forcing it through the apical foramen.
A further use of this substance is to infiueuce the shade of devital-
ized teeth by the color tone it imparts to the crown of the tooth on
account of its whiteness. This is enhanced by the fact that it comes
into exact contact and remains without change, a quality which cannot
be given to gutta-percha or other cements.
As a temporary filling to correct extreme sensitivity of dentin in
situations or under conditions which forbid ordinary therapeutic treat-
ment, oxychlorid of zinc lias considerable value. Here when the pulp
is not closely approached it may be retained for several months with
considerable advantage. To secure the best results the proportion of
zinc chlorid should be slightly greater than in the formulas used for
ordinary fillings.
Zinc Phosphate.—This material, because of its greater power to
withstand the influence of the oral secretions, has a wider use than the
previously described cement. It cannot, however, be depended upon
far permanent uses. While in some instances it may remain for several
years when the oral fluids are neutral and when every attention is given
toward the attainment of cleanliness, it is nevertheless a deceptive sub-
stance, since it is liable under temporary changes of the secretions to
undergo solution, more particularly in situations near the gum. When
placed in approximal cavities it is extremely liable to become fissured
at the cervical margin and then permit carious action insidiously to
take place.
Unlike oxychlorid of zinc, the phosphate has no antiseptic influence,
hence it does not inhibit decay of the dentin in its proximity. Its chief
use is as a temporary expedient for filling cavities on labial and buccal
surfaces, where, being under easy observation, it may be used with
benefit. On account of its chemical solution by the oral secretions,
however slow this may be, it requires frequent renewal.
Zinc phosphate is also of value for filling the principal portion of
large compound cavities where the teeth would be injured by the force