Page 390 - My FlipBook

388 RESTORATION OF TEETH BY CEMENTED INLAYS.

Those not aifeoted are simple labial cavities, corners of centrals and
laterals, cusps of canines, bicuspids, and molars.
Those most affected are tips of centrals and of lateral incisors, and
approximal and halfmoou-sliaped cavities running through the palatal
enamel. The broader the adjacent teeth the greater will be the shutting
out of light and the consequent darkening of color. Tips of central and
lateral incisors running entirely across the tooth are so subject to the
shadow variations from cross light, side light, top light, and bottom
light, that the restoration of more than a third is not advisable. When
half of a tooth has been carefully matched and cemented into place, the
tip may look very well in good daylight, but at night it may turn
dark ; also in an artificial light shining from above the tooth and
cement line show very dark while the porcelain seems snow-white. In
all such cases, whenever possible, a portion of the tooth should be
allowed to run down to the cutting edge.
And now let ns consider how we may partly conquer these shadow
variations. Halfmoon-shaped cavities, as in Figs. 368 and 309, may be
filled on the palatal wall with gold, an absolute match thus being made
possible. A porcelain tip may be built up as two corners, to avoid the
side lights ; but generally all attempts to antagonize shadow variations
will result in an effort to lighten the fillings, so that the shadows
will be overcome. This lightening is now quite possible, for experi-
ments indicate that an addition of from one-tenth to one-fifth of oxid
of tin to the ordinary white enamel gives a white so dense as to be
practically the reverse of shadow. If, therefore, we have a filling half-
moon-shaped or approximal, we should first match the porcelain tooth
as though it were a simple labial cavity ; then by adding to this paste
one-fourth to one-third of the dense white powder mentioned above
we shall find that, if the colors have been properly mixed, the filling
when cemented into place will darken to the original color of the tooth.
And now having described the process of using high-fusing porce-
lain for inlays, the next consideration will be the modifications necessary
when the low-fusing porcelain is melted in a gold matrix. The best
of the low-fusing bodies are said to keep their color and texture in the
mouth indefinitely, to be strong enough for all necessary wear, and to
retain their color in fusing,—which would indicate that the low-fusing
materials have greatly improved during the last eight or ten years.
Porcelains capable of being melted in a gold matrix are of two classes:
those that are sufficiently low fusing to be melted in a bare matrix, and
those that melt so near the fusing-point of gold as to render necessary
the investment of the gold matrix in order to prevent its being war])ed
by the fire. In porcelains of the first class the method of procedure is
very similar to that in which the high-fusing porcelains are fused in a