Infected root canals can harbour between 10 to
more than 10 bacterial cells.
Manual instrumentation
with 6–10ml of saline per canal can reduce the number
of bacteria in infected root canals by 100 to 1000-fold.
However, root canal preparation with hand files
and saline irrigation is only moderately effective. Early
studies in which no antiseptic irrigants were used
reported that 20 to 30 per cent of the root canals
that were infected at the beginning of treatment
yielded negative cultures at the end of the first appoint-ment.
These studies are of limited value because
they were performed with bacteriological techniques
unsuited to the recovery of anaerobes.
Using advanced bacteriological techniques, it has
been shown that the number of bacteria can be
significantly reduced, but not to an extent that negative
cultures can be reliably obtained at the end of the first
appointment.
This underlies the importance of
supporting the mechanical cleaning of canals with
antimicrobial irrigation.
SEM studies of canals that have been manually
instrumented with saline irrigation show that loose
debris can be eliminated from the upper and middle
thirds of the root canal.
101
Filing with endodontic
instruments translocates and burnishes the superficial
components (organic and inorganic) of the circumpulpal
dentine and creates an amorphous smear layer on the
canal walls.
This layer is not affected by irrigation
with saline.