Repairing a Broken Back Tooth: A Patient's Guide

When a back tooth breaks, patients usually want to know one thing: is it a filling or a crown? The answer is decided by an assessment that is largely invisible to the patient but entirely predictable once you understand what is being counted.

A molar is a hollow box. It has four walls — the cheek side, the tongue side, and the two sides facing the neighbouring teeth — plus a floor. Chewing force pushes outwards against those walls. How many of them remain intact, and how thick they are, determines whether the tooth can withstand that force with a simple filling or whether the cusps need to be covered.

That is the whole logic. Everything else follows from it.

They take the load. Molars generate and absorb the majority of chewing force. Force at the front is a fraction of what the back teeth handle.

They are frequently already filled. A large old filling — particularly a deep amalgam — has already removed internal structure, leaving walls that are thinner than they look and unsupported from within. Most broken back teeth in adults are teeth that were previously restored. Our article on whether a large filling can break your tooth covers the mechanism.

Grinding accelerates everything. Sustained lateral force fatigues cusps over years. Our article on whether grinding can crack teeth covers this.

A single unexpected bite. An olive stone, an unpopped kernel, a piece of bone. The tooth was usually already compromised; the stone was the last cycle rather than the whole cause.

Root-treated teeth are more brittle. A tooth without a vital pulp has lost its internal fluid and usually a good deal of structure through access and cleaning. Our article on when a tooth needs a crown even without a filling explains related reasoning.

Before any decision about the restoration, several things are established:

How much tooth remains, and where. The number and thickness of remaining walls, and whether the break extends beneath the gum. A fracture that runs below the gum margin is materially harder to restore, because a restoration needs a clean, dry margin on sound tooth structure.

Whether the pulp is involved. If the break has exposed the nerve, or if the tooth is symptomatic of irreversible pulpitis, root canal treatment is needed before or alongside the restoration. Sensitivity tests and radiographs inform this. Our article on a broken tooth with an exposed nerve covers the urgent situation.

Whether a crack extends into the root. This is the critical finding, because a vertical root fracture generally means the tooth cannot be saved. Transillumination, dye, magnification and radiographs are used, and sometimes the extent is only confirmed once the old filling is removed.

Whether the bite is contributing. If the broken tooth was taking a heavy or eccentric contact, restoring it without addressing that repeats the problem.

Composite filling. Appropriate where a small area has chipped, the remaining walls are substantial and the fracture is above the gum. Done in one visit, minimal removal of further tooth structure. Not appropriate for a large restoration in a heavily loaded molar, where the composite is being asked to substitute for missing structure rather than fill a cavity.

Onlay. A laboratory-made or digitally milled restoration that covers one or more cusps while preserving the walls that are still sound. This is frequently the right answer for a broken molar and is under-used. It gives cuspal protection — the biomechanical benefit of a crown — without reducing the entire tooth.

Crown. Full coverage, holding the remaining structure together like a band. Appropriate where multiple walls have gone, where the tooth is root-treated, or where the remaining structure is too thin to support anything less. It requires reduction of the whole tooth, which is the trade-off. Our article on whether a crown stops a tooth cracking sets out the reasoning and its limits.

Root canal treatment and then a cuspal-coverage restoration. Where the pulp is involved. The root treatment addresses the infection or inflammation; it does not restore strength, which is the job of the restoration that follows.

Extraction and replacement. Where the fracture extends too far below the gum, splits the tooth, or runs into the root. Attempting to restore a tooth in that condition often means a restoration that fails within a short period. Our article on choosing between a crown and extraction covers the decision, and missing tooth replacement options covers what follows.

The general principle is to use the least coverage that will reliably withstand the load — but not less than that, because an under-engineered restoration in a heavily loaded molar tends to fail and take more tooth with it.

• Rinse gently with warm salty water to clear debris

• Keep any fragment in milk or saline in case it is usable, though for a molar it usually is not

• Avoid chewing on that side

• Cover a sharp edge with sugar-free chewing gum or a pharmacy temporary dressing if the tongue is being cut — see our article on a broken tooth edge cutting the tongue

• Take over-the-counter pain relief as directed on the packet if needed

• Do not place aspirin against the gum, which causes a chemical burn

• Arrange assessment promptly

Seek urgent care the same day if there is facial swelling, difficulty swallowing, fever, uncontrolled bleeding or severe pain that is not settling. Our article on a broken tooth with swelling covers the warning signs.

A break that would have taken an onlay in week one can require a crown by month three, and root canal treatment by month six. The mechanisms are straightforward: the exposed dentine admits bacteria towards the pulp; the remaining unsupported cusp continues to flex and eventually fractures further, often beneath the gum; and food packing into the defect drives decay at the margin.

The tooth does not repair itself, and the damage does not stay the same size. Our article on the hidden cause of pain from a fractured tooth explains the bacterial route.

• Address grinding with a night guard where it is present

• Have large, old restorations reviewed before they fail — a planned onlay is a better outcome than an emergency repair

• Treat unexplained sharp pain on biting as a signal, not a nuisance; our article on cracked tooth syndrome covers the presentation

• Be cautious with foods that may contain something hard

• Keep routine examinations, where cracks and failing margins are picked up before they break

• The number and thickness of remaining walls determines whether a filling, onlay or crown is appropriate.

• Most broken back teeth in adults were previously restored; old fillings leave walls thin and unsupported.

• Onlays provide cuspal protection without reducing the whole tooth and are often the right middle option.

• A fracture extending below the gum or into the root changes the prognosis substantially.

• Root canal treatment addresses infection; it does not restore strength, so a coverage restoration follows.

• Damage progresses — delay commonly converts a smaller repair into a larger one.

Can a broken back tooth always be saved?

No. Most can, but a fracture that extends well below the gum margin, splits the tooth vertically, or runs into the root generally cannot be restored predictably. Assessment, including radiographs and sometimes removal of the existing filling, establishes which situation applies.

Does a broken back tooth always need a crown?

No. A small chip in a tooth with sound walls can often be restored with composite. A crown becomes appropriate when multiple walls have been lost, the remaining structure is thin, or the tooth is root-treated. An onlay covers the middle ground.

Is repairing a broken back tooth uncomfortable?

Treatment is carried out under local anaesthetic, so the procedure itself is not usually uncomfortable. Some tenderness afterwards is normal, particularly where the tooth was inflamed beforehand. Tell your dentist if you are anxious about treatment — the appointment can be paced accordingly.

How long does the repair take?

A composite repair is usually one appointment. An onlay or crown traditionally takes two visits with a temporary in between, though same-day digital workflows are available in some circumstances. Root canal treatment followed by a crown takes longer and involves more appointments.

What happens if I leave a broken back tooth untreated?

Typically the defect enlarges, bacteria reach the pulp, and the remaining unsupported cusp fractures further — frequently beneath the gum, where restoration is harder. What began as a straightforward repair often becomes root canal treatment, a crown, or extraction.

Can the piece that broke off be glued back on?

For a molar, rarely. Fragments from molars are usually small, contaminated and mechanically unsuitable for rebonding. Reattachment is more often considered for a clean fragment from a front tooth.

If you have broken a back tooth, prompt assessment usually means a smaller repair and more options.

You can contact our team at our Wimpole Street practice, or read about dental crowns and our emergency dental care.

This article provides general information about the repair of broken back teeth and does not constitute individual dental advice. The appropriate treatment for a broken tooth depends on the extent of the fracture, the condition of the pulp and the remaining tooth structure, all of which require clinical examination and radiographs. Wimpole Dental is regulated by the Care Quality Commission, and our clinicians are registered with the General Dental Council.

Next review due: 16 September 2027