Root Canal Re-Treatment: When a Previous Root Filling Fails
For anyone told a root-filled tooth is infected again or not healing: why root fillings fail, even after careful treatment, how the cause is found, what re-treatment involves, how it compares with first-time treatment, and alternatives such as root-end surgery (apicectomy) or extraction. A failed root filling has more than one route, and the cause guides the choice.
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Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
Dr Ibraheem Ijaz, the practice's principal dentist, reviewed this page. He is a General Dental Practitioner registered with the General Dental Council, number 301711, and his qualifications are BDS, BSc (Hons), MSc (Leeds), PG Dip Implant Dentistry and PG Cert Restorative and Aesthetic Dentistry.
What is root canal re-treatment?
Root canal re-treatment removes an old root filling, cleans and disinfects the canals again, then re-seals them to clear infection that has persisted or returned.
Root canal re-treatment is also called endodontic retreatment, secondary root canal treatment or a redo root canal.
Why do root fillings fail?
Failed root fillings are usually caused by bacteria surviving inside the tooth or getting back in; even a carefully treated tooth can fail (Siqueira, 2001).
Leeds Teaching Hospitals NHS Trust lists four reasons a root filling can fail:
- Persistent infection: bacteria remain inside the root and the tissue at its tip stays inflamed (persistent apical periodontitis).
- Re-infection: bacteria get back in through a leaky filling or crown (coronal leakage), or new decay.
- Cracks or fractures in the tooth or root.
- A cyst around the root end.
An untreated canal is one way infection persists: in a retrospective US study of 3D (CBCT) scans of root-filled back teeth (Karabucak and colleagues, 2016), about 23% had one (about 40% of upper molars), and those teeth were 4.38 times more likely to have a lesion at the root tip. Leeds Teaching Hospitals NHS Trust lists failing to find a canal among the recognised risks of root canal treatment.
How is the cause of a failed root filling found?
In general, the cause is worked out from your history, an examination and X-rays, and sometimes only once the tooth has been opened.
Some failed root fillings cause no symptoms and show only on an X-ray (British Endodontic Society). X-rays help show how far the old root filling reaches, gaps, an untreated canal, an instrument fragment or perforation, and whether the restoration above seals. For a tooth to count as restorable, the same guidance looks for at least 2 mm of dentine above the gum all the way round and more than 30% of the original natural crown.
In general, the British Endodontic Society asks dentists to grade how difficult a re-treatment will be and to refer the case on when it is beyond their competence.
Is re-treatment possible for every failed root filling?
Not always: it depends on how much tooth is left, why the first treatment failed and whether the canals can be reached and cleaned again.
Leeds Teaching Hospitals NHS Trust says broken instruments, perforations or blocked canals, recognised risks of root canal treatment, can make further treatment much harder, and extraction may be advised if a certain standard cannot be reached.
The British Endodontic Society says that where re-treatment has a poor outlook, apical surgery may be more appropriate: for example when the first treatment was done to a high standard, or a blocked canal, an unreachable perforation or a large immovable post raises the risk of complications or root fracture.
Among the alternatives to re-treatment, Leeds Teaching Hospitals NHS Trust also lists waiting for clearer symptoms, or no treatment, which risks problems including infection, bone loss and early tooth loss.
What does root canal re-treatment involve?
In general, re-treatment shares the aims of first-time treatment, with extra steps to re-enter the tooth and clear the canals (British Endodontic Society).
- Isolation: a rubber dam keeps saliva away from the tooth.
- Access: the filling or crown over the root filling is removed, or worked through.
- Clearing obstructions: posts, separated instrument fragments or hard pastes are removed where possible, for which British Endodontic Society guidance recommends an operating microscope.
- Removing the old root filling: the rubber-like gutta-percha is softened with ultrasonic tips or solvents, then removed with files.
- Cleaning to full length: the canals are shaped and disinfected along their whole length, which British Endodontic Society guidance says improves the outlook.
- Re-sealing and restoring: the canals are filled again. Cracks are more common in re-treated teeth, and a restoration covering the cusps, which seals well and resists fracture, matters for the long-term outlook.
Questions about this treatment? Book online or call the practice.
How does the outlook of re-treatment compare with first-time treatment?
Evidence is mixed: one large UK study found similar results, while British Endodontic Society guidance says re-treatment generally has a reduced prognosis.
In a UK prospective study of treatment by endodontic postgraduate students at the UCL Eastman Dental Institute (Ng and colleagues, 2011), about 83% of roots healed completely after first-time treatment and 80% after re-treatment, at 2 to 4 years. About 95% of teeth survived, meaning they were still in place, at 4 years in both groups, though re-treated teeth that already had a perforation in the root were more likely to be lost.
A review of 17 mostly retrospective studies with at least six months' follow-up (Ng and colleagues, 2008) estimated re-treatment success at about 77%, with a lesion at the root tip beforehand, how far the root filling reached and the restoration above all affecting the result. A Leeds Teaching Hospitals NHS Trust patient leaflet gives 40% to 80%, depending on the original problem. In general, if re-treatment fails, apical surgery or extraction may have to be considered (British Endodontic Society).
These re-treatment figures come from published research and a hospital leaflet. In the studies, success means healing seen on X-rays and examination; survival means only that the tooth is still in the mouth.
What is the surgical alternative to re-treatment?
The surgical alternative is an apicectomy, or root-end surgery, which reaches the root tip through the gum and bone instead of through the tooth.
In an apicectomy, the lesion and the end of the root are removed through an opening in the bone, and the root end is commonly sealed (Cochrane, 2016); our page on apicectomy covers the operation.
Evidence comparing surgery with re-treatment is limited. A 2016 Cochrane review found no clear evidence that either heals better at one, four or ten years, from small trials rated very low quality, and in one trial of 87 people more reported pain in the first week after surgery (low-quality evidence). If pain after either treatment worries you, show it to a dentist.
What happens if the tooth cannot be saved?
A tooth that cannot be saved is taken out, and the gap can be left or filled with a bridge, denture or dental implant.
The British Endodontic Society says extraction may be necessary after extensive loss of tooth tissue, with gum disease, a lengthways split that cannot be restored or extensive root resorption. Our comparison of saving a tooth compared with removing it covers that decision in more depth.
Are re-treatment, apicectomy and extraction carried out at Deepcar Dental Care?
Root canal re-treatment, apicectomy and tooth extraction are all carried out at Deepcar Dental Care.
How much does root canal re-treatment cost at Deepcar Dental Care?
On the practice's current fee list, "Re-Root Canal Treatment" is shown as "Price on request". You can see each listed fee on our current fees.
When should you speak to your dentist about a root-filled tooth?
A root-filled tooth that hurts, swells or develops a spot on the gum needs a dentist's check, and NHS guidance sets out how urgently.
NHS guidance says to see a dentist if you have toothache that lasts more than 2 days, that does not go away when you take painkillers, that comes with a high temperature, pain when you bite, red gums or a bad taste in your mouth, or with a swollen cheek or jaw. If you do not have a dentist or cannot get an emergency appointment, call 111 or visit 111 online.
Go to A&E if you have toothache and the area around your eye or your neck is swollen, or swelling in your mouth or neck is making it difficult to breathe, swallow or speak. Do not drive to A&E: ask someone to drive you, or call 999 and ask for an ambulance.
If you think you have a dental abscess, ask for an urgent dentist appointment or get help from NHS 111. Call 999 or go to A&E if you are finding it hard to breathe, speak or swallow, have a swollen or painful eye or suddenly start having problems with your eyesight, have a lot of swelling in your mouth, or are finding it hard to open your mouth. Do not drive to A&E.
Where can you read more about saving a root-filled tooth?
Root canal re-treatment is one form of endodontic treatment, which aims to save a tooth by clearing infection from inside it. Both are part of repairing and rebuilding damaged teeth, which focuses on keeping natural teeth rather than replacing them with implants.
Frequently asked questions
Can a root canal fail years after treatment?
It can, though it was uncommon in one long-term study. Following 265 roots filled by dental students (Molven and colleagues, 2002), new lesions showed on X-rays at 20 to 27 years in 1.5% of roots with no lesion at 10 to 17 years, and more late changes were healing than failure.
Can a root-filled tooth be re-treated through its crown?
Sometimes. British Endodontic Society guidance says a recently placed crown or onlay, or one with sound edges, may stay in place while the canals are reached through it, though porcelain can crack or chip, so you should be warned first. Removing a crown risks fracturing the tooth, and a temporary one should be placed afterwards.
How long does a re-treated tooth take to heal?
Healing is judged on X-rays and examination over months or years. British Endodontic Society guidance advises reviewing a re-treated tooth at least one year afterwards and, if healing is incomplete, yearly for up to four years; large lesions can take longer. Leeds Teaching Hospitals NHS Trust gives six months to four years or longer.
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You can contact Deepcar Dental Care online or by phone, and the practice is open 8am to 8pm, Monday to Sunday. The practice is at 334 Manchester Road, Deepcar, Sheffield, S36 2RH, with free parking directly outside, and you can read patient reviews first.
334 Manchester Road
Deepcar, Sheffield S36 2RH
0114 288 2121
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Open 8am to 8pm, seven days
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