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CHAPTER XII.

THE OPERATION OF FILLING CAVITIES WITH METALLIC
FOILS AND THEIR SEVERAL MODIFICATIONS.

By Edwix T. Darby, D. D. S., M. D.

In the selection of a filling material the operator should consider the
character of the secretions of the oral cavity, the position of the tooth
to be filled, the extent of the diseased area, the physical structure of the
tooth, and the strength of the cavity walls. A filling material must
possess certain inherent qualifications, the most important of which are
adaptability, indestructibility, non-conductivity, hardness, absence of
shrinkage, harmony of color, and ease of manipulation. All of these
are not to be realized in any one material, and yet some of the more
important are to be found in a single metal or in a combination of
metals.
Lead possesses the quality of softness and is easy of adaptation but
is readily oxidized when exposed to the air or the secretions of the
mouth. Likewise tin possesses characteristics, such for instance as duc-
tility and softness, low conducting power, and the ease with which it
may be manipulated, which place it in the front rank as a preservative
of carious teeth, but it is inharmonious in color, and its very softness,
which is so desirable in manipulation, is an obstacle to its use upon
surfaces where there is much attrition. The zinc phosphates, which are
composed of zinc oxid and phosphoric acid in solution, form a com-
bination which at first attracted the favorable attention of the dental
surgeon as possible substitutes for metallic foil fillings. They possess,
owing to their plasticity, ease of manipulation, harmony of color, com-
parative non-conductivity, and absence of shrinkage, many desirable
qualities, but are lacking in one essential qualification, namely, inde-
structibility.
Gold.
Gold, which has been used for about a century, has fulfilled in a
more marked degree than any other material or combination of materials
the requirements sought for in a filling for carious teeth. It has one or
tvvo objectionable features, such as high conductivity of heat and inhar-
monious color.
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