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THE MINERAL CEMENTS. 255

Lightness of Color.—The means by which this property may be
secured have not as yet been well determined and should be the sub-
ject of extended experimentation. Some of the so-called white alloys
approximate stability in this respect, but the ratios of the modifying
metal have not been accurately determined.
Amalgam as a filling material is adapted to large cavities in the jjos-
terior teeth when the margins are too frail to permit gold to be con-
densed ; for positions where mechanical force cannot be exerted with
efficiency, notably the cavities of the third molar ; distal cavities of the
second molar when of large size ; and the lingual cavities of the lower
molars. When the teeth are of deficient resistance and when the con-
dition of the oral secretions favors the rapid progress of caries these
limitations may be extended to cavities where otherwise gold would
appear to be a more suitable material.
As a material for the filling of the deciduous teeth amalgam possesses
superiority over any other substance, for the reasons that it can be intro-
duced with less effort than tin and has greater durability than either
the mineral cements or gutta-percha preparations ; the exception to its
use here being when the conditions prevent retentive formation of the
cavity.
Concerning the /o/'?« of the cuvitij adapted to amalgam, it is necessary
that the retentive formation be equally exact as for gold, since many
of the formulas in use undergo slight movement for some time after
their introduction, during which there is liability of marginal displace-
ment which may lead to the defects treated of under the section con-
cerning " edge strength." Amalgam, while presenting in its appear-
ance an unfavorable comparison with gold, is capable of rendering
important service Avhen every consideration is given to the require-
ments governing its successful employment.
To attain the best results in the use of the amalgams requires
extreme exactness as to the ratios of the ingredients and great care in
all the procedures connected with the formation of the cavity, the form
of the filling, and the subsequent finishing process.
The disqualifications of amalgam are its unsatisfactory color and the
unknown character of the composition of the formulas as furnished by
the depots of supply.

THE MINERAL CEilENTS.
Oxychlorid of Zinc.—This material, because of its lacking the
quality of indestructibility, is contraindicated in all exposed situa-
tions. It possesses, however, a considerable degree of antiseptic power,
and for this reason renders valuable service in deep cavities not nearly
approaching the ]iulp, or even here \vhen the pul]) Avail of the cavity