The control of bacteria within the root canal might
appear to be straightforward since such a large
proportion of the bacterial flora is sensitive to oxygen.
However, the penetration of oxygen into the canal
during treatment does not seem to have any significant
effect on the bacteria. The reason for this is that many
of the bacteria are protected in the irregularities and
branches of the root canal system and in dentinal
tubules. Only a few cells need to survive treatment so
that when the canal is closed, the anaerobic milieu will
be restored and the bacteria can re-multiply. The
microbial flora within the root canal must be actively
eliminated by a combination of physical debridement
and antimicrobial chemical treatment.
Although the most important aspect of root canal
instrumentation is undoubtedly the elimination of
bacteria and the removal of remnants of pulp tissue and
debris, the shaping of the root canal to accommodate
the root filling material is also of importance. A great
deal has been written about the preparation of the root
canal to achieve a tapering form
since this shape
facilitates cleaning of the apical third,
preserves the
apical foramen from over-instrumentation and facilitates
filling of the canal.
Preparation of the root canal consists of two main
phases: debridement by manual and mechanical
instrumentation, and chemical disinfection by irrigation
and subsequent antibacterial dressing. The relative
effectiveness of these measures has been studied in a
series of investigations with advanced bacteriological
techniques
and the cleansing effect of the
mechanical instrumentation has been studied by
histology
and by scanning electron microscope
(SEM) analysis of the appearance of the root canal wall
before and after instrumentation of the root
canal.