Root Canal Treatment: What Success Depends On and What to Expect

When is root canal treatment needed?

Root canal treatment, or endodontic therapy, is needed when the pulp, the tissue with nerves and blood vessels inside the tooth, is inflamed beyond recovery or has become infected. The usual causes are deep decay, a blow to the tooth, a crack or repeated restorations on the same tooth. The procedure removes the pulp, cleans and disinfects the canals, seals them and then restores the tooth. The goal is to keep your natural tooth instead of extracting it.

What the studies say about success

The numbers vary from study to study because they do not all measure the same thing. Two terms are worth separating:

• Success, or healing: the tooth has no symptoms and the X-ray shows no lesion at the root tip, or the one that was there has repaired.
• Survival: the tooth is still in the mouth and working, even if the X-ray shows a lesion that is still being monitored.

Patient information from Leeds Teaching Hospitals in the UK puts success at about 96% when there is no inflammation at the root tip before treatment, and about 85% when inflammation is already present (Understanding your Endodontic Root Canal Treatment, Leeds Teaching Hospitals NHS Trust).

In everyday general practice the numbers can look different. A study by the PEARL network in the United States followed 1,312 teeth treated by general dentists for an average of 3.9 years. Over that time 3.3% of the teeth had been extracted, and when every failure criterion was counted together (extraction, retreatment, pain when the tooth was tapped, or a lesion on the X-ray) the rate was 19.1% (Outcomes of endodontic therapy in general practice, JADA 2012). In other words, the vast majority of teeth were still in place, although some needed monitoring or further treatment.

These are averages across groups of patients. The outlook for any one tooth depends on its starting condition and on how it is treated and restored.

Factors that affect the outcome

A systematic review of 63 studies identified four conditions that significantly improve the outcome (Outcome of primary root canal treatment, Int Endod J 2008):

1. No visible lesion at the root tip before treatment.
2. A root filling with no voids.
3. A root filling that ends within 2 mm of the root tip on the X-ray.
4. A satisfactory restoration on the crown of the tooth.

In the PEARL study, a pre-existing lesion at the root tip and teeth with multiple canals were also linked to more failures.

The final restoration is part of the treatment

Finishing the canals is not the last step. The tooth then needs a definitive restoration that seals the canal openings: a filling, an inlay or onlay, or a crown, depending on how much tooth is left. The Leeds guidance warns that not having it done promptly significantly increases the risk of the treatment failing or the tooth fracturing, because success depends on that final seal.

How long healing takes

Discomfort usually settles within a few days, but the bone around the root takes longer. Leeds notes that healing can take from six months to four years or more, and that it is monitored with periodic X-rays. That is why your dentist may ask you to come back even when you feel fine.

If the treatment does not work

Leeds lists the causes of failure as persistent infection, reinfection through a leaking filling, crown or new decay, cracks or fractures, and a cyst at the root tip. When infection persists or returns, there are options:

• Retreatment: redoing the root canal. Leeds puts its success at 40% to 80%, depending on what caused the original failure.
• Apical surgery (apicoectomy): the root tip is removed and sealed from that end.

In a minority of cases the tooth cannot be saved and has to be extracted. At that point, options to replace it, such as a dental implant, are considered.

Frequently asked questions

Does it hurt? It is done under local anesthesia, so you should not feel pain during the procedure. Leeds notes that the tooth may feel sore for 3 to 4 days, sometimes longer, and that 1% to 5% of people have a flare-up with more pain or swelling a few days later. If that happens, contact your dentist.

How many appointments does it take? It depends on the tooth and on whether there is infection. Some teeth are finished in one visit; others take two or more.

Will I always get a crown afterward? Not always. It depends on how much of the tooth remains and which tooth it is. In the PEARL study, the type of restoration was not associated with more failures; what matters is that it seals well and protects the tooth.

Next steps

On our endodontics page you can see how this treatment is approached at Gloss Dent.

You can read more in the sources consulted: Understanding your Endodontic Root Canal Treatment, Leeds Teaching Hospitals NHS Trust, Outcomes of endodontic therapy in general practice, JADA 2012 and Outcome of primary root canal treatment, Int Endod J 2008.

If you have pain that will not go away, swelling or discomfort in a tooth that already had a root canal, you can schedule an individualized assessment. During the assessment we can review your case and walk you through the options and their outlook.