Root Canal Retreatment

Most teeth that have had root canal treatment stay free of problems for many years. Sometimes, though, months or years later, a treated tooth starts to hurt when you bite, or the gum swells or discharges; or a routine X-ray shows an area of inflammation at the root tip that has not healed, or has even grown. This shows that bacteria have remained inside the canals or have found their way back in.

Root canal retreatment means removing the old root filling, then cleaning and filling the canals again. We explain what the nerve is, the symptoms and the steps of the procedure on the root canal treatment page; here we focus on why treatment fails and what happens next.

Why does root canal treatment fail?

• A missed canal. The number and shape of the canals vary from person to person. Some, such as the fine second canal in upper molars, are easily overlooked, and the tissue and bacteria left inside keep the inflammation going.
• Incomplete cleaning or filling. If the canal was not cleaned all the way to the root tip, or the filling is short or has gaps in it, there is room left for bacteria.
• Leakage from above. A temporary filling left in for too long, a crown with an open edge or new decay starting underneath lets bacteria from saliva back into the canal. Even a well-done root canal can become reinfected this way.
• Difficult anatomy. Canals that are very curved, calcified or have side branches, or a fragment of an instrument that broke off and was left in the canal.
• Inflammation outside the canal. Occasionally bacteria take hold outside the root tip, in the bone, or a cyst develops there. However well the inside of the canal is cleaned, it may not heal, and surgery is needed.
• A cracked root. A vertical crack running along the root cannot be fixed with root canal treatment; in that case retreatment is pointless.

Retreatment, surgery or extraction?

The decision depends on how much sound tooth remains, what is on it (a filling, a crown, or a post placed in the canal) and where the problem is coming from. An X-ray is often enough; if a missed canal or a cracked root is suspected, a 3D scan (CBCT) shows far more. Imaging is covered in more detail on the oral diagnosis and dental imaging page.

Retreatment deals with a problem inside the canal at its source. An apicoectomy, by contrast, clears the problem at the root tip from the outside but does not reach inside the canal. That is why the usual order is retreatment first, then surgery if needed.

How is retreatment done?

The steps are similar to the first treatment, but each one takes more time. It is done under local anaesthetic, and you usually feel no pain during the procedure. If the tooth has a crown, we either work through the crown or remove it; a crown that has been removed cannot always be reused, and a new one may be needed. If there is a post in the canal, it is taken out carefully, without weakening the root. The old filling material is cleared with solvents and files, and we search for missed canals; working under magnification makes a big difference at this stage. Once the canals have been disinfected, an antibacterial medicine is often left inside them for a week or two, and the filling is done at a second visit. After that, closing the tooth with a tightly sealed restoration, usually a crown on back teeth, is part of the treatment.

What is a realistic expectation?

Studies show that the inflammation at the root tip heals in most retreated teeth. The success rate is somewhat lower than for a first treatment, however, and varies widely with the state of the tooth. Where a missed canal is found and cleaned, the outcome is generally good; if there is a perforation in the root, a broken instrument that cannot be removed or a very large lesion, the outlook is more guarded.

Healing takes time. Pain and swelling usually ease within days, but the bone takes months to repair itself. We usually take the first follow-up X-ray after 6–12 months and check whether the area of inflammation is getting smaller. If it is, we keep waiting; with large lesions it is normal for complete healing to take several years. If the area is growing or the symptoms have come back, surgery or extraction is discussed. In the meantime, if you develop swelling that spreads across the face, a fever or difficulty swallowing, see a dentist without delay (the nearest one if you are not in İzmir) or seek emergency care.

If there are no symptoms, does it still need retreatment?

Not always. If a small shadow at the root tip on an X-ray has not changed for years and causes no symptoms, monitoring it can be a reasonable choice. But if a new crown or bridge is going to be made on that tooth, we recommend putting the root canal right first; retreating it later would mean damaging the new crown. We make this decision together, with the risks laid out. The cost depends on the number of canals, whether a crown or post has to be removed and the restoration needed afterwards; at our clinic in İzmir you receive a written, itemised quote after the examination.