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treated by constructing a veneer of porcelain for the labial surface. It
has been found that such operations check erosion and preserve the
vitality of the tooth for an indefinite period. A shoulder following
the curvature of the gingival line (Fig. 53) should be formed across
the labial surface, and enough of this surface should be involved to
permit the porcelain to be of a sufficient thickness to insure strength
and to prevent a change of color by the cement (Fig. 54). The entire
incisal edge should be involved to insure proper retentive resistance
and to prevent fracture of the porcelain. The incisal wall should form
an acute angle with the labial surface (Fig. 55).
After the incisal edge has been removed with flat-face stones, suf-
ficient enamel and dentin should be removed with stones from the labial
surface to insure proper thickness of porcelain. Then the shoulder
should be formed with flat-faced fissure burs at the gum margin. After
this has been done the approximal margins are to be made smooth with
sharp chisels and Arkansas stones.

Che Preparation of £at>ttic$ in Bicuspids and molars.

Experience has proved that porcelain is not the best filling material
for most cavities in bicuspids and molars. Their occlusal surfaces
present a series of inclined planes which when restored with a friable
material, lacking in edge strength, may cause imperfect fillings in a
short time, by the breaking of the margins of these fillings. There
are, however, many cavities in these teeth that should be filled with
porcelain for the cosmetic effect. The marks of occlusion should be
studied in the preparation of occlusal and approximo-occlusal cavities,
and their margins should be carried to points where they will have the
least masticatory stress, for thereby the life of the filling is increased.
If cavity margins are formed at points at which the stress is unduly
strong, these margins of porcelain will fracture and leave faulty fillings.
The function of a filling is : first, to check the existing decay and
to prevent if possible its recurrence ; second, to restore the original
form of the tooth in order that it shall maintain its proper relation
with the other teeth and to protect the gum in the inter-proximal space,
and third, to meet the cosmetic requirements. While porcelain is not
indicated in many forms of cavities in bicuspids and molars, there
are cases in which we should not lose sight of the cosmetics, and in
such cases porcelain should be given due consideration. Gold foil and
amalgam have preserved many teeth for a considerable length of time,
but when we note the number of failures that have been made with

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