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112 DENTAL JIISrOLOGY AND OPERATIVE DENTISTRY

the plane shown in No. 3 ; tlien the cavo-surfUce angle may or may not
be bevelled as the position demands.
In some positions, as on the axial surfaces, it is not possible to ex-
tend the plane of the entire ejiamel wall as described all that can be
;
done is to shave the cut surface, leaving the wall in the direction of the
enamel rods, and then the margin is strengthened by bevelling the cavo-
FiG. 94.

Occlusal tisMircj in a sniierior bicuspid, showing direction of rods. (About H) y.)

surface angle, so that the rods forming the margin are supported by at
least a few rods which are covered by filling material.
In cuttins; out the fissures on the occlusal surfaces of molars and
bicuspids, the rods are inclined centrally from the axial plane, as seen
in Fig. 94. In opening a fissure the lines of cleavage will not be in
the axial plane, but sloping inward toward the body of the cusp, in the