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FILLING MATERIALS. 97
with artificial crowns, as well as in building up badly decayed
teeth with metal.
Filling Materials.

The fining materials at present in use for permanent opera-
tions are, gold, which holds the first place, and amalgam, which
holds a second place, in value. Added to these many would
reckon tin as holding a place equal or nearly equal to amalgam,
but the. general judgment of the dental profession would seem
to consign tin to a very obscure position as a filling material, as
nowadays very few persons make much use of it.
The filling materials for temporary operations are the cements,
especially the oxy-phosphate of zinc cements, and gutta-percha.
The qualities most desired in a filling material for permanent
operations are indestructibility in the fluids of the mouth,
adaptability to the walls of cavities, freedom from shrinkage or
expansion after having been made into fillings, and resistance to
attrition and the force of mastication.
The qualities of secondary importance are color, or appear-
ance, non-conductivity of the thermal impressions, and conveni-
ence of manipulation.
Of these first qualities gold seems to possess in much the
greatest degree those most essential. It is perfecdy indestructi-
ble in the fluids of the mouth;
it is very perfecdy adaptable to
the walls of cavities; it is free from objectionable shrinkage or
expansion
; its resistance to attrition is good and it resists the
force of mastication better than amalgam.
It conducts
Of these second qualities gold is not so good.
thermal impressions strongly, its yellow color is objectionable,
and it is not very convenient of manipulation.
Indeed, it may be
said of this last quality, that its successful manipulation requires
much study and careful experience, and yet, when this study is
given it and the required experience has been obtained, it may
be worked into fillings more perfectly than any other material.
Amalgam, as alloys for which are at present produced by
the best makers, is possessed of the first (jualities in a high
degree, yet inferior to gold in all. It is not completely inde-
structible in the fluids of the mouth, but oxidizes or sulphurets
slightly, just sufficient to change
its color from a silvery white-
ness to brown or black.
Its adaptability to the walls of cavities
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