Page 97 - My FlipBook

FILLING TEETH —
8i
avoided, a step extension, which, owing to the
presence of two approximo-occhisal fillings in the
same tooth, necessarily forms a trench-like cutting
right across the occlusal surface, may, by thus
weakening the cusps, cause a very extensive break
to occur. For this reason some operators deprecate
the step, and, while following out Dr. Black's direc-
tions at other parts of the cavity, prefer to slightly
undercut the occlusal part, but avoid altogether
the step extension.
In practice, however, it will be found that acci-
dents of this kind rarely occur with any kind of
— providing it is carefully carried out
preparation
and that if an accident occurs it is generally due to
the filling of a frail tooth. Accidents of this kind
may often be prevented by shortening and rounding
the cusps of the filled tooth, and also the cusps of
the opposing tooth or teeth. This is a proceeding
that should always be considered, and practised,
whenever the circumstances of the case present
the possibility of an accident occurring.
A careful preparation of the margin is impera-
tive. All little cracks, chalky patches, or defects
must be cut out ; and it is advisable to carefully
examine the enamel in the neighbourhood of the
margin with a magnifying glass. Many fillings fail
because of some small defect in the enamel, close to,
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