Page 39 - My FlipBook

ENAMEL MARGINS.
25
and at a right angle to the outer surface of the tooth, in all cavities
save those in masticating surfaces. These latter will be discussed
separately.
In Fig. 45 we see a section through a central incisor and con-
toured gold corner. The margin at the labial surface a is a sharp
as is also the on the In we of
right angle, margin palatal side. filling
course lap our gold well over the margin, and then trim away, seeking
a sharp edge line. Any method of polishing which scrapes across the
margin will deceive as to the true edge. That is to say, it is an
error to use stones, polishing wheels, or in disks or
sand-paper strips,
the same around the tooth from one
revolving approximal surface to
the other. This method may be employed at the outset to remove
the excess of gold ; but when it becomes necessary to polish away the
last remaining overlap, in order to reveal the true margin and leave
a beautiful fine line, the must be done the of
polishing along length
the margin, from the incisive edge toward the gum. If it is an approx-
imal cavity I prefer fine sand-paper disks, pliable enough to bend read-

FIG. 45. FIG. 46. FIG. 47.

ily, though stiff enough to cut well. Revolving the disk rapidly as
described, the edge of the disk is made to approach the edge of the
gold ; if the latter is overlapping the margin, the disk attacks it in-
and removes sufficient to the and
stantly perfect edge, leaving gold
tooth-surface exactly flush. The same result may occasionally be ex-
pected from the use of a fine polishing-stone (Arkansas or Colorado
stone, not corundum), but it must be fine enough not to cut enamel,
and must cut gold very slowly. Margins of fillings along the palatal
angle may best be polished with fine disks, but where the border
reaches the concaved surface small stones revolving from incisive edge
toward the gum best attain the finest finish. A stone turning in this
direction will not catch in the dam.
If approximal margins be beveled outwardly (Fig. 46), as some
that we no have a defined
contend is requisite, it is plain longer really
an obtuse a
margin at a or at b, but simply angle along receding slope.
it would be bad
If this were really an obtuse angle, enough, but it is
almost certain that the operator will produce a rounding bevel, so that
*here is really no distinct margin at all. Now if gold be lapped over
this, how shall it be polished so as to obtain a strong edge to thefil'rng