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

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*It may be appropriate to carry out access cavity preparation 
before isolation.
Negotiation of the coronal two-thirds
Coronal shaping is usefully preceded by negotiation of the canal with
small flexible hand files. The aims are to:
• Reveal information about the cross-sectional diameter of a canal
and the presence of any constrictions/pulp stones, etc.
• Confirm the presence of straight line access.
• Provide information about the anatomy of the root canal 
system.
Coronal two-thirds shaping
Coronal flaring (Fig. 3.5) may be accomplished in either a step-back 
or a crown-down approach. The step-back technique is the sequential
use of instruments starting with the smaller sizes and progressing
towards the larger. A crown-down approach is the serial use of 
instruments, starting with the larger and progressing to the smaller.
Usually, nickel titanium rotary instruments are used in a crown-down
technique, whereas ISO hand files and Gates Glidden drills are best
used in a step-back technique for the following reasons:
• Smaller instruments can be placed at a deeper level and cut on the
up stroke (thus facilitating the removal of debris).
• The coronal two-thirds can be moved and relocated from the
region of the furcation and towards the greatest bulk of dentine.
Working length determination
The working length establishes the apical extent of canal shaping and
the end of the root canal filling and should be determined accurately
before preparation of the apical third of the canal. When the coronal
two-thirds has been pre-enlarged, there is excellent access for negotia-
tion and preparation of the apical one-third.
A file of no smaller than a size 20 should be used as a diagnostic
instrument as it may be difficult to distinguish the position of the tip
of smaller size files by radiographic means. The file (pre-curved if 
necessary) is placed in the canal until it has reached this estimated
length and a radiograph taken or an apex locator used. A locating stop
on the handle of the file should be carefully positioned against a
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reproducible reference point on the tooth to define the coronal aspect
of the diagnostic length.
Following working length determination, apical preparation con-
tinues by the successive use of progressively larger instruments at the
full working length. Copious irrigation and frequent recapitulation
with a fine file will prevent build-up of canal debris.