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86 OPERATIVE DENTISTRY

gingival, particularly at the gingival angles, in some cases to the ex-
tent that the gingival Avail is made convex to the incisal.
The Gingival Point Angles should be deep and well defined at
the expense of both gingival and axial walls. This is particularly
true of the gingivo-lingual angles, to protect agahist the torsion
strain.
To Assist the Incisal Angle. To resist the tipping strain both the
labial and lingual Avails should be slightly grooved along the axio-
labial and axio-lingual line angles much in the same Avay as Avith
large Class Three cavities.
The Labial Outline should so proceed that the completed filling
Avill be of about equal Avidth for its entire length except that as it
approaches the incisal edge it should be slightly curved to the axial.

Fig. 45.—Shows incisal outline in Class Four, plan one, fillings with direct occlusion.
A Rule for Labial Outlines. All cavity outlines in incisal angle
restorations should curA'e to the axial as they approach the incisal
edge. The nearer this outline approaches the central axial line of
the tooth the greater should be the curve. When the central axial
line is reached by a cavitj' outline, the same should then be extended
to involve the opposite angle. There are exceptions to the aboA^e
rule but maximum resistance to stress is only thereby obtained.
The Necessity for Curving to the Axial. When approaching the
incisal edge curve to the axial that the last rods at the cavo-surface
angle may be adequately supported. A large per cent of fillings
AA'here this precaution has been neglected fail, shoAving a primary
fault due to the breaking aAvay of the enamel at this point.