Operative dentistry aje qualtrough, jd satterthwaite la morrow, pa brunton

Apical preparation
The terminal extent of shaping should be at the junction between the
pulpal and periodontal tissues. This occurs at the apical foramen.
Usually, the apical foramen is the narrowest part of the root canal 
and this narrowing is termed the apical constriction (Fig. 3.7). It has
been shown by Kuttler
6
that this position is 0.5–1 mm from the radio-
graphic apex in the majority of cases. However, this is not always the
case, for example when the deposition of secondary cementum has
occurred. In addition, canal anatomy is variable and the constriction
may be at some distance from the foramen. It must also be remem-
bered that the primary root canal does not necessarily exit at the
radiographic apex.
Careful apical preparation is fundamental to the success of treat-
ment and several factors should be considered including the apical
extent of preparation, relative to the radiographic apex, and the three-
dimensional shape and size of the pulp chamber.
Most canals have some degree of curvature. An instrument placed
in a curved canal will tend to cut the outer dentine wall to produce 
a widened, apically directed funnel which is tear-shaped in cross-
section. The apical flare is called a zip and the section more coronal to
it is called the elbow (Fig. 3.8). To overcome these problems, it is
essential that shaping should reflect the canal size and curvature.
The degree to which the apical end of the canal should be prepared
is subject to discussion. There is an argument that any significant
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Chapter 3
Fig. 3.7
Apical anatomy for working length determination.
POOC03 02/18/2005 04:33PM Page 70

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Principles of endodontics


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widening is unnecessary if there has been adequate coronal flaring
and adequate irrigation. There is also the risk of zipping or stripping
the canal walls when larger size files are used, especially in curved
canals. A counter argument is that there needs to be a minimum
degree of preparation of the apical third so that infected dentine 
is removed. It is also easier to fill canals that have a larger apical
preparation.
The shape of the apical preparation has also been considered and
the terms ‘apical seat’ (or ‘apical box’) and ‘apical taper’ have been
described. The fundamental philosophy is that if the terminal end 
of the canal is wide, then creation of an apical seat reduces the risk of
overextension of the filling material. However, if the canal is fine and
curved in its apical extremity, then production of an apical seat runs
the risk of creation of apical stripping or zip formation.
Whichever method is adopted, it should be possible to place a
spreader (a tapered, blank, pointed instrument used to push gutta-
percha to one side when obturating) to within 2 mm of the radio-
graphic apex.
‘Stepping back’ by using sequentially increasing size files at 1-mm
increments short of the working length produces an apical taper. In
between each larger file, the master apical file (or a fine file) is inserted