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TOILET OF THE CAVITY 45

Finishing Enamel Walls.
Definition. The last cutting done in the preparation of a cavity
is the finishing of enamel Avails. This should always be done with
the rubber dam in place or at least sufficient means taken to pre-
vent the margins from again becoming moist.
No Moisture should be Permitted to come in contact with any
portion of the cavity surface, after final instrumentation, and if
by accident any portion should become wet that portion should be
thoroughly dried and freshened by cutting away the surface, and
the filling immediately placed.
The Cavo-surface Angle of the cavity in every part of the cavity
outline should receive special attention at this step in cavity prep-
aration.
The Plane of the Enamel a\ all should be so laid with reference
to the cleavage of the enamel that these will be cut more from the
outer than the inner ends of the rods, resulting in the last rod at
the cavo-surface angle being a full length rod, supported by short-
ened rods. The shortened enamel rods are covered with the fill-
ing material when the completed filling is in position.
This is accomplished by a slight planing motion parallel to the
external enamel line, using a keen-edged chisel or enamel hatchet.
The gingival margin trimmers are especially adapted for this pur-
pose when finishing the margins in the gingival third.
The Marginal Bevel should be laid in a plane at an angle of from
six to ten centrigrade degrees from the plane of the enamel cleav-
age.
The Depth of the Marginal Bevel should generally not include
more than one-fourth of the enamel wall, but Avhen making a fill-
ing of inferior edge strength, as amalgam, porcelain, cement, etc.,
it becomes necessary to bury the bevel angle more deeply.
Locations subject to great stress also require the placing of the
bevel angle more deeply, even carrying it beyond the enamel and
laying it in the dentine.

Toilet of the Cavity.
Definition. The toilet of the cavity is the final step in the prep-
aration of the cavity and consists of freeing the cavity of all loose
particles of tooth substance which are not firmly attached to the
cavity walls.
This is best accomplished by a blast of air from the chip blower,
followed by a thorough sweeping and brushing of all surfaces with