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

Fig. 3.8
Apical errors.
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to the full working length and irrigation is used to eliminate debris;
this is termed ‘recapitulation’. The step back process is continued
until this portion of the preparation reaches and blends with the 
coronal preparation.
Patency filing
Despite the careful and frequent use of irrigation, there is a risk that
the accumulation of canal debris may result in apical blockage. It has
been argued that this may be avoided by penetration of the apical con-
striction of the canal with a small file during the shaping procedure
7,8
.
This is thought both to direct the irrigating solution apically and 
also to dislodge the apical debris into the canal. Subsequent irrigation
results in its removal. A counter argument is that this only applies to
the main canal and there is a risk of inoculating infected canal contents
further apically.
Mid-third shaping
The ideal shape for obturation purposes is that of a continuously
tapering cone
9
. However, over-shaping brings with it the risk of
weakening the tooth structure or stripping the canal walls. On the
other hand, under-shaping may result in the accumulation of residual
infected dentine and debris.
Curved canals – the balanced force technique
There are a number of techniques for avoiding problems associated
with curved canals including step-back, pre-curving of files and 
anticurvature filing
10 
(the preferential filing of the outer curve of the
canal to reduce the chance of a strip perforation). The Balanced Force
Technique
11
is the use of instruments in a step-down manner to initi-
ate pre-enlargement procedures and to gain access to the apical third
efficiently. This is basically a reaming technique and adopts a 60–90°
clockwise action, for file insertion and dentine engagement, followed
by a 120–180° anticlockwise movement with apically directed pres-
sure for dentine removal. A final clockwise movement allows the 
file flutes to be filled with debris and removed from the canal. This
method is said to be efficient and less likely to cause stripping of the
canal walls due to the instrument being centrally located. There is also
thought to be less risk of apical extrusion of debris.
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Chapter 3
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Principles of endodontics