Persistence of a fistula after root canal treatment indicates that the root canal treatment was unsuccessful at reducing bacterial numbers to the point where the immune system can keep the infection under control.
Reasons for for root canal treatment failure include:
- Treating the incorrect tooth
- Missed root canal spaces that were not cleaned
- Leaking filling or crown
- Presence of an apical cyst
- Root cracks or fractures
When dealing with a previously root canal-treated tooth, a small 3D scan (CBCT) of the affected area and tooth is extremely useful. The CBCT provides information that would otherwise be obscured in a conventional 2D xray film. This will allow the dentist to provide more precise treatment.
In the case of the incorrect tooth being treated, missed root canal spaces or a leaking restoration, the root canal treatment should be performed on the correct tooth or repeated. Any defective restorations should be replaced to ensure a good seal from external oral bacteria.
Apical cysts may require root end surgery and retreatment of the root canal from the root end up (apicoectomy). The cystic material gathered from the root end should be biopsied to confirm the diagnosis.
If there are cracks or fractures in the root(s) then the prognosis is more dire as these cracks may be impossible to seal over. These fractures allow bacteria to recontaminate the root canal space and the root canal infection persists. Teeth with cracks in the root(s) may not heal and may require extraction to fully resolve the infection.
Identifying root fractures can be very difficult as usually the xrays/CBCT will appear normal. Surgical exploration under the gum to directly visualize the crack may be needed.
