Why a Root-Filled Tooth Usually Needs a Crown

Evidence suggests changes to the dentine after root canal treatment play a smaller part in fractures than the tooth structure lost before and during treatment.

A 1992 study compared 23 root-filled teeth, treated about 10 years earlier, with the matching healthy tooth on the other side of the mouth. It found no significant difference in strength, toughness or the load needed to break them.

A 1989 laboratory study of 42 extracted premolars found root canal treatment reduced stiffness by about 5%, while a cavity through the biting surface and both sides reduced it by 63% on average.

Moisture loss is part of the picture, but not the main part. A 2025 British Dental Journal review says small changes in dentine moisture after treatment do not, on their own, make dentine significantly more brittle. A 2022 International Endodontic Journal review notes that dentine changes after root canal treatment may make the tooth behave in a more brittle way and raise the risk of root fracture, although how large these changes are has not been clearly shown, and it suggests loss of sound tooth is the most critical factor.

Back teeth missing a side wall usually need cusp coverage, such as a crown or onlay, while front teeth often do not.

A dental crown is a cap that completely covers the tooth, NHS guidance explains, so it covers every remaining wall and cusp. The BES guide sets out when a root-filled tooth needs cuspal coverage, a restoration covering the biting points, or cusps:

• Each case is considered individually.
• A back tooth opened only through its biting surface, with all walls thick enough and no cracks, is not likely to need cuspal coverage.
• In most cases, a back tooth missing one side wall needs cuspal coverage.
• Where two or more walls are missing, cuspal coverage should be used, and cases that justify leaving it out are rare.
• Restorations should be designed to keep as much sound tooth as possible.

Front teeth are different. The 2025 British Dental Journal review says a simple access hole through the back of a front tooth can be sealed with a tooth-coloured composite filling, restoring strength similar to an intact tooth. Where a large filling or cavity on the side of the tooth was already there, or the access hole has been widened near the gum, the review says thought needs to be given to how the final restoration is held in place and made strong enough to resist biting forces.

Where both sides of a front tooth are involved, especially with large fillings, it says this tends to indicate that a full crown should at least be considered.

The practice's fee list, shown on 17 October 2026, lists Root Canal from £450, and the restorative cost page covers the crown. The fee list says all its prices are "from" prices, based on individual clinical needs.

The cost page explains what it costs to restore a tooth, including a crown after root canal treatment, and what changes a fee. Our finance page covers spreading the cost of treatment.

NHS guidance says to see a dentist if a tooth breaks or a filling or crown comes out. It also says the area around a root-filled tooth may feel swollen and sore, but should get better in a couple of weeks.

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
• with a high temperature, pain when you bite, red gums, or a bad taste in your mouth
• and your cheek or jaw is swollen

To see a dentist in an emergency or out of hours, call your dentist, whose answerphone may say what to do if they are closed. 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.