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220 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
cutting away some portion of the marginal ridge and so sloping
the surface toward the embrasure that, when the food is crushed
upon it, it will tend to slide into and through the embrasure.
A change in the form of the proximal surface may often
be made that will improve the cleaning of the parts, especially
in broad proximal cavities in the molars and bicuspids. The
distal surface of the first molar, particularly when the disto-
lingual cusp is large and protrudes to the distal so that the
lingual embrasure is much narrowed, will not have its disto-
lingual angle well cleaned by the excursions of food, and on this
account decay is especially liable to occur along the gingival por-
tion of the lingual margin after the filling is made, if the original
form is preserved or reproduced. In this case it is much better
to carry the cutting somewhat beyond the disto-lingual angle of
the tooth, and, in finishing the filling, reduce the distal protru-
sion of this cusp and widen the embrasure. If, at the same time,
the distal marginal ridge is left low, or the occlusal surface
sloped a little toward the embrasure, so as to direct the crush
of food into it, the cleaning of the lingual margin of the filling
will be so improved as to prevent this tendency to recurrence
of decay at this point.
In the bicuspids there are great differences among differ-
ent individuals in the mesio-distal breadth of the lingual cusps
as compared with the buccal. "When the lingual cusps are broad
in this direction, the lingual embrasures are very narrow, so
that the cleaning of the lingual marginal lines of fillings will
be very imperfect; these embrasures should be broadened by
narrowing the lingual cusps wherever practicable, or by separat-
ing the teeth sufficiently to build out a prominent contact point,
and the occlusal surface so finished as to direct the excursions
of food into and through these embrasures so that they will be
continually cleaned by the act of mastication. In making these
form changes, every care must be had to slightly increase the
mesio-distal breadth of the tooth at the contact point. The
observant operator will find many places other than those cited
in which to apply the principles which the particular cases given
illustrate. Whenever cases of great intensity of susceptibility
to decay demand treatment, every means at our command of
increasing or facilitating the natural cleaning of the marginal
lines of our fillings should be studied for the individual case.
LODGMENTS OF FOOD IN THE INTERPROXIMAL SPACE.
The effect of lodgments of food in the interproximal space
has been pointed out in connection with the two groups of illus-