Page 74 - My FlipBook

70 OPERATIVE DENTISTRY
With Bicuspids this buccal or lingual outline is carried past the
crest of the cusp involved and partially down the opposite slope.
This procedure results in disarticulating the frail enamel wall and
so placing the metal that it Avill receive the force of mastication.
In Mesio-Disto-Occlusal Cavities in both bicuspids and molars,
which are vital, and when using cohesive gold as a filling, the occlusal
outline should include all of the middle third bucco-lingually. It
should be made sufficiently deep to remove all of the enamel in the
central fissure.
For cohesive gold the buccal and lingual Avails should be parallel
and Avithout retention as the retentive form should all be placed low
in the gingival angles of both mesial and distal cavities.
In the use of amalgam the outline should be farther extended buc-
co-lingually, to include about one-half of each of the buccal and lin-
gual thirds. Thus two-thirds of the occlusal surface bucco-lingually
Avill be filling. This occlusal portion should be Avithout retentive
form Avith the buccal and lingual Avails meeting the pulpal Avail at
angles slightly obtuse. This is the minimum amount of extension
for favorable A'ital cases.
In Cases of Extreme Frailty the entire occlusal surface of molars
and bicuspids sliould be replaced Avith filling of at least one milli-
meter in thickness. AVith upper molars and bicuspids, A\'hen non-
Adtal and very frail mcsio-occluso-distal cavities, the lingual cusps
should be removed for one or two millimeters and replaced Avitli
filling material.
Retention Form is Completed by squaring up the side Avails and
sub-pulpal Avail, making a box shape of the pulp chamber, Avith
fairly definite point angles.
Convenience Form. No convenience form is necessary in this
class of cavities, except for inlay fillings, Avhich AAdll be considered
later.
Neglected Access Form. In cases AA-here large proximal cavities
are of long standing and there has been much tipping to the prox-
imal of one or both teeth, preliminary separation for good access
is essential. Without this preliminary step complete contour res-
toration and proper contact is impossible. This is particularly true
Avhen the cavity is in the mesial of the first molar. Many times
the second bicuspid Avill seem to haA^e been engulfed Avithin the
molar cavity. In cases AA'here preliminary separation for obA^ious
reasons is impossible, the evil may be partly overcome by the free
cutting aAvay of both buccal and lingual Avails until the filling may