Page 179 - My FlipBook

LINGUAL CAVITIES. 165

As in the labial cavity, a slight shoulder must be formed toward the
incisive in order to avoid a bevel, and so assure a good border
portion,
to the gold. The same cavity in a cuspid is much simpler. After
forming the groove, deep extensions may be made at the gingival
angles, owing to the fact that there is a sufficient amount of tooth-
substance to make it safe to form There is another
strong anchorages.
difference between the labial and the palatal cavity, which must be
noted. Of two cavities having the same depth, the palatal will reach
nearer to the pulp than the labial. This is because the labial surface
is convex, whilst the palatal is concave. Consequently in palatal
cavities it is often wiser to adopt the oxyphosphate method of starting
the Where this is done, the gold is pressed into the mass
gold filling.
of toward the incisive edge. When set, the oxyphos-
oxyphosphate
phate is removed from the retaining grooves and the gold extended
into them, thus the without special dependence upon
securing filling
the adhesive property of the plastic, which is inserted as an insulator.
FIG. 190. FIG. 191. FIG. 192.

A lingual cavity in the bicuspids or molars is a rarity, and, when found,
usually extends along the gum-border. In nine cases out of ten an
ill-fitting clamp has caused the mischief. The lingual surfaces of
almost any of the lower teeth may almost be said to be exempt, save
where the clamp induces decay. This is perhaps because the tongue
and fluids of the mouth keep the parts washed and cleansed. Never-
theless, I have seen long, narrow cavities, partly under the gum, all
along the lingual surfaces of lower molars. Their preparation may
require that they be packed with cotton for a day, in order that the
gum may be forced away. This accomplished, a rose bur which will
cleanse the of will leave it retentive in If
cavity decay usually shape.
not, a slight extension at each end is all that is needed. Here is a
place where I might almost say gold should never be employed. To
insert a perfect gold filling in such a position, with all the obstacles
offered by situation, saliva, and presence of the tongue, would require
and even then would be accomplished at an
extraordinary ability,