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PROXIMAL CAVITIES IN BICUSPIDS AND MOLARS 63

pulpal line angle. A failure to observe this rule endangers the
pulp through a liability of crossing its recessional tracts.
Convenience Form. In the making of a cohesive gold filling a
convenience point for the retention of the first piece of gold is
desirable. This is best accomplished by employing a small in-
verted cone bur, say number thirty-three and one-half.
The flat face is placed on the gingival wall and first sunk to one-
third its depth then drawn for a short distance occlusally along
the axial line angle, taking dentine slightly at the expense of both
axial and external walls.

A B
Fig. 20.—Fillings shown in Fig. 25 contacted, illustrating the marble contact.

With the making of a plastic filling there is no need of cutting
for convenience form in this cavity.
Inlays. When using an inlay proper convenience form is ob-
tained by thorough separation and causing the external walls of
both step and cavity proper to meet the gingival and pulpal wall
at slightly obtuse angles. This Avill give draw to the occlusal.
Finish of Enamel Walls. The enamel walls are planed to full
cleavage and the margins arc slightly beveled. All but the gingival
margins may be done with the chisel. Special instruments are re-
quired to bevel the gingival cavo-surface angle, known as gingival
marginal trimmers. These are made rights and lefts for mesial
cavities, and rights and lefts for distal cavities and should be on