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THE PORCELAIN INLAY 203
change of form and tendency to destroy fine lines, as a result
of the heat applied. Neither should the gold be heated to
too high a temperature before casting, this also resulting in
increased tendency to shrinkage on cooling. If these brief
details are followed, much better results will be obtained in
the fitting of inlays than otherwise.
TECHNICAL EXERCISES
1. Prepare eight cavities of various types in extracted
teeth for metal inlay work.
2. Make wax models, invest, cast inlays in acolite or an
alloy of silver and copper, set and polish.
THE PORCELAIN INLAY
Cavity Preparation.—Cavity preparation for the porcelain
inlay requires certain modifications of the types shown and
described in the section on the gold inlay. The principal
features of the cavities designed for the reception of this
material are as follows, viz.
Adequate access is a necessity, either by cutting or separa-
tion, or both, to allow for withdrawal of the matrix. The
outline form should not follow a developmental groove, or
cross a ridge at its highest point. Owing to friability of the
material, margins should be extended to points least sus-
ceptible to crushing stress. The outline form should never
be circular, else difficulty may be experienced in seating the
inlay into its proper position, after fusing (Fig. 256). Ade-
quate resistance form is a necessity, and maximum retention
form is required in all directions, except one, until the inlay
is completed, when retention should then be added in the re-
maining direction, by cutting the cavity walls. All line and
point angles should be rounded, until the matrix is completed.
THE PORCELAIN INLAY 203
change of form and tendency to destroy fine lines, as a result
of the heat applied. Neither should the gold be heated to
too high a temperature before casting, this also resulting in
increased tendency to shrinkage on cooling. If these brief
details are followed, much better results will be obtained in
the fitting of inlays than otherwise.
TECHNICAL EXERCISES
1. Prepare eight cavities of various types in extracted
teeth for metal inlay work.
2. Make wax models, invest, cast inlays in acolite or an
alloy of silver and copper, set and polish.
THE PORCELAIN INLAY
Cavity Preparation.—Cavity preparation for the porcelain
inlay requires certain modifications of the types shown and
described in the section on the gold inlay. The principal
features of the cavities designed for the reception of this
material are as follows, viz.
Adequate access is a necessity, either by cutting or separa-
tion, or both, to allow for withdrawal of the matrix. The
outline form should not follow a developmental groove, or
cross a ridge at its highest point. Owing to friability of the
material, margins should be extended to points least sus-
ceptible to crushing stress. The outline form should never
be circular, else difficulty may be experienced in seating the
inlay into its proper position, after fusing (Fig. 256). Ade-
quate resistance form is a necessity, and maximum retention
form is required in all directions, except one, until the inlay
is completed, when retention should then be added in the re-
maining direction, by cutting the cavity walls. All line and
point angles should be rounded, until the matrix is completed.
