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30 THE TIGHTENING OF LOOSE TEETH

the patient's mouth, and the porcelain surface on the
lingual side is decidedly more agreeable to the tongue
than metal.
As abutments there may serve crowns, caps, collars,
and inlays. In preparing teeth to act as supports
of bridges also, the principle should be observed of
preserving the vitality of the pulp, and taking care
of the enamel. Only in case the crown of the tooth
is weak, decayed, or too short, should a shell crown
be adapted.
Shell crowns on bicuspids ought to be adapted with
a porcelain or silicate facing on the facial side, for
obtaining a more natural appearance. By means of
a round burr a window is cut out of the crown, the
edges bevelled with a carborundum wheel, and an im-
pression taken as for a porcelain filling. In the case
of a very flat face, silicate cement is to be preferred.
In arched molars where there is much undercut a
strong gold collar should be made, that may be bur-
nished beyond the margin into the fissures of the
grinding surfaces, at places where the articulation
may permit it, and filled with solder. The collar is
put round the plaster tooth, cut at the four corners,
l)ent over, burnished, and soldered. Only on the buccal
face does the collar extend to the gingival margin.
Shorter molars where there is not much undercut
should be fitted with a collar extending beyond the
margins, and burnished into the fissures to prevent
its sinking.
If the grinding surface be defective, a hole is drilled