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PROXIMAL CAVITIES IN INCISORS INVOLVING ANGLE 87

The Incisal Outline as it crosses the iiicisal edge of thick teeth
should have in its center a curve toward the axial caused by a slight
groove in the center of the dentine. This groove which ends at this
point in the cavity outline should originate at the external end of
the incisal line angle. If there is sufficient dentine, and there gen-
erally Avill be in the class of cases calling for this plan of restora-
tion, this groove is of best service if it be a flattened groove and
made Avith a small hoe or hatchet. (Fig. 45.)
' The Lingual Outline should be the same as for large Class Three
except in the incisal third when it should curve to the axial even
more rapidl}^ than the labial outline and for a longer distance, re-
sulting in cutting away more enamel from the lingual than is re-
moved by the labial outline. This is made necessary from the fact
that all stress is from the lingual.
With Lower Incisors the reverse is true and it is necessary to rp-
iiiove slightly more of the labial enamel in angle restoration, a fact
which materially mars these teeth from an esthetic point of view.
Fortunately we have comparatively few angles to restore on lower
incisors, but when they are presented the fact must be borne in
mind that they receive the major portion of stress from the ineiso-
labial direction.
Second Plan of Angle Restoration. (Class Four.)
The second plan of restoration is indicated in teeth that are of
medium thickness, particularly if they are of angular build or have
a direct contact on the incisal edge either in occlusion or articula-
tion, and consists in the additon to plan one of Avhat is termed the
incisal step. The cavity proper is prepared the same as has been
outlined in plan one up to the forming of the step.
The Incisal Edge is cut aAvay Avith a narrow-edged carborundum
stone, the cutting being extended toward the opposite angle a dis-
tance equal to the width of the cavity proper. The incisal outline
should avoid both the centers of primary calcification and the point
of coalescence, two weak places in enamel construction. The cut-
ting should be more at the expense of the lingual side of the tooth
by one-half to one millimeter.
The Depth of This Step, inciso-gingivally, Avill depend upon t)ie
thickness of the cutting edge, and the probable stress it will receive.
The thinner the edge and the greater the probal)le stress, the deep-
er must be the step. The majority of cases Avill show not to exceed
one millimeter of gold on the labial in the step portion.
Technic of Cutting. A small round bur is then used to cut a