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FILLING TEETH 139
cervical margin or gum-line. Owing to its inherent
defects of shrinkage and curled up margins it is not
as good a material as gold, where the conditions are
favourable for gold, but just in proportion to the
presence of unfavourable conditions, so its superiority
over the more precious metal is manifest.
Strictly speaking, a cavity that is properly prepared
for gold is the best cavity for amalgam, but what is es-
sential for gold is by no means essential for amalgam.
The very plasticity of the material enables amalgam
to be readily pressed into any deep depression or
undercut that may exist after a mere removal of the
decay is effected ; and any cavity that is larger in
its interior than at its orifice, can be well filled with
amalgam without the extensive mathematical cutting
that is needed with gold. It must, therefore, be
allowed that amalgam is superior to gold for filling
many teeth at the back of the mouth—or in cases
where the filling is not exposed to view— for all
patients who are sensitive or nervous, or who can-
not endure prolonged operations. The question of
hard and soft teeth need hardly be considered,
for Avhat is known as a soft tooth is generally one
that is softened by decay, and the cutting back to
sound, hard tooth structure, and the consequent
production of a hard tooth becomes usually merely
a question of cavity preparation, and it is on the