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FILLING TEETH 155

electrical action that is caused by the presence in
the mouth of two dissimilar metals. The genera-
tion of a painful electric current may take place
when two dissimilar metals are in fairly close, but
not absolute, contact ; but the presence of moisture
between the metals is required to bring it about.
A gold clasp which impinges on an amalgam tilling
in a live tooth may cause pain, and two fillings,
one of gold and the other of amalgam, in opposing
teeth, may do so whenever the teeth are brought
into contact, as the following case will show : the
writer made a large contour amalgam tilling in a
pulpless upper molar ; the opposing lower molar
having a fairly large gold filling in its occlusal
surface. The amalgam filling was trimmed free of
the bite, but as soon as, and each time, the patient
closed his mouth, he received a shock of pain in his
lower molar. To at once remedy this, a small hole
was drilled in the centre of the gold filling, and
filled up with amalgam before the patient left the
chair. He could then immediately close his mouth
with perfect comfort. In the same way, if a gold
clasp causes pain in a tooth filled with amalgam, a
hole may be drilled in the amalgam and filled up
with gold. These cases are comparatively rare, but
the same experience may happen to any one whose
teeth are sensitive, and whose gold fillings should