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126 METHODS OF FILLING TEETH.

; but where both are absent, as in the
which remains standing figure,
the retaining arrangement is sufficiently unique to excuse a special
I should make a in
description. gingival groove ending deep dips at
each end, similar to the palato- and labio-gingival extensions alluded
to in other cases. From these I should extend toward the
grooves
crown, as shown at a, a. It is the formation of these which is unique.
I take a rose bur first, and make the groove as as determined
deep ;
then I follow with a wheel bur larger than the diameter of the rose
FIG. 135. FIG. 136.

bur. This wheel, passing from end to end of each groove, forms a
lateral undercut in each, which must be made deepest toward the
To better illustrate the idea I introduce is a
pulp. Fig. 136, which
section the center of a in such a The
through filling placed cavity.
approximal surface is shown at b, whilst a, a indicates that part of the
which
filling occupied the grooves. In addition to these retainers, if
considered necessary, an extension may be made across the crown and
into the opposite sulcus, as already described in discussing bicuspids.

CHAPTER VI.

SPECIAL PRINCIPLES INVOLVED IN THE PREPARATION OF CAVITIES AND
THE INSERTION OF FILLINGS CAVITIES IN THE MASTICATING SURFACES
INCISORS TREATMENT OF IMPERFECTIONS OF FRACTURES OF ABRA-
SIONS OF MALFORMATIONS CUSPIDS BICUSPIDS MOLARS OXYPHOS-
PHATES IN COMBINATION WITH GOLD UNITING TEETH BY BAR AND
FILLING.
I NOW come to the consideration of cavities in the incisive edges of
incisors and and the surfaces of
cuspids, masticating bicuspids and
molars.
Strictly speaking, a cavity in the incisive edge of an incisor is a
less so in the inferior than in the In
rarity, superior teeth. making
this statement I do not include abraded teeth, but refer to such only