In a study that examined the influence of infection at
the time of root filling on the outcome of treatment,
68 per cent of teeth that were infected at root filling
healed after the treatment. Similar results have also
been reported in other studies.
Whilst infection at
the time of root canal filling will adversely affect the
outcome of treatment, the mere presence of an
endodontic pathogen is not in itself sufficient for
disease persistence. Several parameters must be met for
micro-organisms to maintain apical periodontitis
following endodontic treatment.
Persistent endodontic treatment disease involves
multiple microbial and location factors. Micro-organisms must possess an ability to survive the
antimicrobial treatment and require ‘persistence’
characteristics such as a capacity for starvation survival
and an ability to utilize serum-like periapical transu-date as a nutritional source.
The location of microbes
within the root canal system is crucial for access to
nutrients. They must be situated near the apical (or an
accessory) foramen and have an open communication
for the free exchange of fluid, molecules and for
organisms to inflame the periapical tissue (Fig 5).
Together, these microbial characteristics and
opportunities of location determine whether micro-organisms that
survive treatment are able to maintain
apical periodontitis following such treatment.