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The labial and lingual walls of the cavities should slightly diverge from
the pulpal wall. This form of cavity preparation is particularly indicated
in the preparation of mesio-distal cavities in lower incisors. The step
should be changed so that the labial plate of the incisal edge is involved
instead of the lingual, thereby making the resistance from the lingual
surface.

Fig. 38. Fig. 39.

One of the most perplexing forms of cavities is
found in those cases where only a small portion of
Tracturcs of
the approximo-incisal angle has been lost by fracture
Incisors.
(Fig. 36). Such fractures can be successfuly treated
by forming the cavity on the lingual surface without further involving
the labial plate. Fig. 36 shows the labial outline, while Fig. 37 shows the
cavity formed in the lingual surface. Enough of the Imgual surface
should be included to form a step of sufficient area to retain the inlay se-
curely. The labial wall of the step should be flat, while the gingiva! wall
should form a concave surface. The axial wall of the step should run
almost parallel with the long axis of the tooth, and it should form an acute
angle with the labial wall.
In case of more extensive diagonal fractures of the incisal edge and
where the pulp remains vital (Fig. 38), it has been found advisable to

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