Usually one or just a few species are recovered from
canals of teeth with persistent disease. These are
predominantly Gram-positive micro-organisms and
there is an equal distribution of facultative and obligate
anaerobes.
This microbial flora is distinctly different
from infections in untreated root canals, which typically
consists of a polymicrobial mix with approximately
equal proportions of Gram-positive and Gram-negative
species, dominated by obligate anaerobes.
There is some diversity of species isolated from root-filled
teeth with persistent periapical disease, but there
is a consensus amongst most studies that there is a high
prevalence of enterococci and streptococci.
Other species found in higher proportions in individual
studies are lactobacilli,
Actinomyces species and
peptostreptococci
and Pseudoramibacter alactolyticus,
Propionibacterium propionicum, Dialister pneumosintes,
and Filifactor alocis
and Candida albicans .
Some bacteriological findings from studies of root-filled
teeth with persistent disease are shown in Table 1.
There is a difference in the microbial flora between
poorly treated and well treated teeth when the canals
are sampled at re-treatment. In poorly root-filled teeth,
the flora is similar to the polymicrobial infection seen in
untreated root canals,
which is not surprising when
viewed in the context of the likely reasons for the
unsatisfactory treatment — inadequate aseptic methods
and poor coronal restoration — that together allow an
influx of carbohydrates and possibly new bacteria from
the oral cavity.
The prevalence of enterococci has been a conspicuous
finding in all studies that have investigated the flora in
root-filled teeth,
with one exception,
and implicates
Enterococcus faecalis as an opportunistic pathogen in
persistent apical periodontitis.