Page 201 - My FlipBook

PORCELAIN INLAYS 185

The retention of the inlay by means of the
cement will greatly depend on the form and depth
of the cavity. Cement adheres to dentine better
than to porcelain, and it is therefore of more import-
ance to groove or undercut the inlay, than to groove
or undercut the cavity, although a double under-
cutting both of inlay and cavity is often desirable.
The simplest means of enabling the cement to grip
the inlay sufficiently to hold it in place, is to merely
remove the glaze from the interior surfaces of the
porcelain. This is effected by covering the exterior
surface and margins with wax, and then applying
hydrofluoric acid until the glaze is removed from
the whole of the exposed porcelain. It was pointed
out by Dr. George Evans {Dental Cosmos, January
1902) that this can be more easily and quite as
effectually obtained by means of a diamond drill in
the dental engine. If a watchmaker's eyeglass is
used the drill can be easily and accurately applied
until the glaze is completely rubbed off, and the
surface etched all over close to, but not quite up
to, the margins. The writer makes frequent use of
this method, and finds it a thoroughly practical
proceeding.
Dr. Jenkins cuts a groove all around the inlay
with a diamond disc in such a manner that a
distinct and fast -holding stud is formed. Mr.