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be made along the labial and lingual walls at their union with the pulpal
wall, and a slight concavity should be made in the dentine of the incisal
wall. Grooves should be formed along the walls of the ridge of the inlay
which fits in the cavity. When the inlay is cemented into position, this
gives it something of a mortised form of retention (Fig. 22).
In case only a shallow cavity can be cut between the labial and
lingual walls, and more retentive resistance than this would yield is

Fig. 24 A. Fjg. 24 B. Fig. 24 C.

required, a hole, two mm. deep, running at right angles to the axis of the
tooth, may be drilled between the enamel plates and as far from the
incisal edge as the pulp will permit (Fig. 23). A threaded pin from
three to four mm. long No. 19 gauge platinum wire is then inserted
through and attached to the matrix. The pin becomes an integral part
of the inlay, and may give the necessary retentive resistance in many
cases. This method can not be used, however, unless sufficient space can
be secured for the insertion of the inlay. It is also contraindicated in
those teeth, whose enamel plates are thin ; for the resistance from the
enamel plates or the porcelain would not be sufficient to retain the inlav,
and the reflection from the platinum pin would affect the color of the
enamel and the porcelain. The author believes that this method of cavity
preparation is a poor one and questions the advisability of its use.

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