Page 145 - My FlipBook

TREA TMEXT OF FRA CTURES. 1 3 1

by the same dentist proved that he knew how to pack gold. The
reason of his failure to do so here was seen as soon as the borders of
were examined
the cavity closely. All around the semicircle the
could be seen
gold showing through the thin, transparent enamel,
whilst the enamel itself showed minute cracks, such as would
appear
in a bit of china or glass first heated and then dropped into cold
water. The probability is, that whilst packing his gold the dentist
noted that his borders were breaking down, and deciding that it was
the fault of the tooth-structure, he felt obliged to use either a lighter
mallet-stroke, or else to depend entirely upon hand-pressure. The
truth is, the whole fault lay in the preparation of the cavity, and in
showing this I will indicate to the student a cause which is productive
of a large proportion of failures along the margins of fillings. What
this dentist had neglected to observe, if expressed as an axiom,
would read, "As far as possible, avoid placing gold in contact with
the dentinal surface of enamel." In the preparation of all cavities,
it should be the constant care that in some dentine be
undercutting, left
in contact -with the enamel. In the case under consideration the
dentist had made a deep groove all around his semicircle, and had
removed the dentine from beneath the enamel. Thus as soon
entirely
as he packed gold into the grooves, especially where he attempted to
use the mallet, his acted as a wedge to lift the enamel, and,
gold
being extremely brittle, it will never endure this. Yet I have myself
' '
recommended a But observe that I the finest of
groove. say only
burs should be used," and as to the
groove itself, my description is,
With a rose bur cut a tiny groove around the semicircle, making it
' '
deeper laterally at a, a in Fig. 141, and deepest at the mesial and
distal corners b, b." By "laterally" in the above sentence I mean
and do not use the word to describe
simply at the sides of the cavity,
the formation of the as to depth. I would not make this
groove except
but rather inward toward the
groove horizontally, obliquely, dipping
dentine. At the corners b, b this dip should be more pronounced, as
can reach stronger dentine, and must
here we are in safer territory,
depend most for the retention of the filling.
In one more important essential had the dentist erred. He con-
toured the edge of his filling, restoring the incisive edge to its original
or made it more use of his corundum. When it is
shape, square by
morsel of food into the oral
remembered that almost every passed
cavity is first cut off with the incisors, it is plain that much strain must
come upon this weak spot. Where the filling is left square at the
incisive edge, it becomes a lever which tends to dislodge the gold.
such a wise to round erf the
Therefore in finishing filling it is always
edge thoroughly, even though it be necessary to dress down the full
width of the tooth along the labial eclee.