Emergency dental conditions
Fractured cusp: when a corner of a back tooth breaks off
A corner of a molar has sheared away, often beside an old filling, leaving a sharp edge and a hole. Here is why it happens, how we repair it and what it costs.
Clinically reviewed by Dr Ibraheem Ijaz, Principal Dentist · GDC 301711 · Last reviewed April 2026
What a cusp is and why it shears away
Cusps are the raised points on the biting surface of a back tooth. A molar has four or five of them, a premolar two. They interlock with the cusps on the opposite jaw so that food is crushed between them. In a healthy tooth each cusp is backed by a thick wall of dentine and is very hard to break.
The problem comes when a filling has been placed in the middle of the tooth. To remove decay, the dentist hollows out the centre, and the cusps that are left standing are now thin shells around a filling that does not hold them up. Amalgam in particular is simply packed in; it does not bond to the tooth. Each bite bends the thin cusp a tiny amount, a crack starts at the base of it, and one day, often over something quite soft, the corner snaps off. This is why a fractured cusp is nearly always next to a large, old filling and nearly always on a lower molar or an upper premolar, which take the most sideways load.
Root-treated teeth that were never crowned break the same way for the same reason. So do teeth in people who grind at night, where the cusps have been worn flat and thin before they ever had a filling.
How to tell a broken cusp from a deeper crack
The most surprising thing about a fractured cusp is that it often hurts less after it breaks than before. For weeks you may have had a twinge on biting or a jolt when you released the bite. That was the cusp flexing on its crack. Once the piece comes away there is nothing left to flex, and the sharp biting pain disappears. What you are left with is:
- A rough or razor-sharp edge that catches your tongue or cheek.
- A hole or ledge you can feel with your tongue, sometimes with the old filling now loose or gone.
- Sensitivity to cold and sweet things, because dentine is now exposed to the mouth.
- Food packing into the gap and a sore gum next to it after a day or two.
- Possibly the piece itself, which you may have found in your mouth.
What you should not have is throbbing, pain that wakes you or pain lingering for minutes after a hot drink. Those suggest the nerve is inflamed, which means either the break exposed the nerve or the crack has continued past the cusp into the body of the tooth. That is a different problem, described in our guide to a cracked tooth. If you are not sure which you have, the symptom page on a broken tooth helps you decide how urgent it is.
What we check at your emergency visit
The emergency examination is £30, takes about 15 minutes and includes the X-rays we need. For a fractured cusp we are answering four questions:
Where does the fracture end?
Is the nerve exposed or close?
Is the nerve healthy?
Are the other cusps about to go?
Bring the broken piece if you have it. We rarely bond it back on a molar, but seeing its shape tells us exactly how much tooth is missing.
Repair options and what each one costs
If the nerve is healthy and the break is clean, a bonded filling can usually be placed at the emergency visit itself, so you leave with the tooth rebuilt. Where a crown is the right answer, we smooth the edges, place a temporary filling or temporary crown on the day, and book the crown preparation. Prices are written down and agreed before anything starts, and 0% finance over 6 to 18 months is available through Tabeo, subject to status.
On prognosis: a fractured cusp repaired with a well-made crown is one of the more predictable things we do, and the tooth can last for decades. A cusp rebuilt with a filling alone is a compromise; it is quick and inexpensive but the remaining cusps carry the same risk the broken one did, so we will tell you if we think a crown is the sounder long-term choice.
| Situation | Repair | Fee (from) |
|---|---|---|
| Small cusp lost, plenty of tooth left, nerve healthy | Smooth the edge and rebuild with a bonded white filling | £150–£220 |
| Large cusp lost or two cusps affected | Onlay or all-ceramic crown to cover and protect what is left | £750–£1,000 |
| Break exposes the nerve, or nerve already inflamed | Root canal treatment, then a crown | Emergency stage from £200; root canal from £450 |
| Fracture runs well below the gum, too little tooth to hold a crown | Extraction, then discuss an implant, bridge or denture | £120–£260 |
Looking after the tooth until your appointment
- Cover the sharp edge with a piece of sugar-free chewing gum or orthodontic wax so it stops cutting your tongue. A pharmacy temporary filling kit also works for a day or two.
- Keep the hole clean. Rinse with warm salt water after eating so food does not pack in and inflame the gum.
- Chew on the other side and avoid anything very hot, cold or sweet.
- If the tooth is sensitive, a smear of sensitive-teeth toothpaste rubbed onto the exposed dentine and left there helps.
- Do not use superglue or household products in your mouth.
More self-care for broken teeth, lost fillings and sharp edges is in our page on temporary fixes before your appointment. Ring 0114 288 2121 and we will find you a slot; most people with a broken cusp are seen the same day, and you do not need to be registered with us.
Leaving a broken cusp unrepaired
Because the biting pain often vanishes when the cusp goes, it is tempting to leave it. Three things then happen, slowly. Exposed dentine is soft and decays several times faster than enamel, so a cavity forms in the fracture surface. The remaining cusps, now taking all the load, crack in turn. And the gum grows into the gap, so that when you do come in, the tooth margin is under the gum and harder to restore. A cusp that could have been rebuilt with a £150 filling this month can need a crown, then a root canal, within a year or two.
Questions, answered
Common questions
What is a fractured cusp?
A cusp is one of the raised points on a back tooth. A fractured cusp is when one of those corners cracks and breaks off, nearly always beside a large old filling that left the cusp thin and unsupported.
Why did my tooth break when I was eating something soft?
The cusp had usually been cracking for weeks or months under normal chewing. The soft food was just the bite that finished it. Twinges on biting beforehand are the typical warning sign.
Why does the tooth hurt less now the piece has come off?
The pain came from the cusp flexing on its crack. With the loose piece gone there is nothing to flex. The tooth still needs repairing, because exposed dentine decays quickly and the other cusps are under the same strain.
Can a fractured cusp be fixed the same day?
Often, yes. If the nerve is healthy and enough tooth remains, we can rebuild it with a bonded filling at the emergency visit. If a crown is needed, we protect the tooth with a temporary on the day and book the crown.
How much does a fractured cusp cost to repair?
The examination with X-rays is £30. A white filling is £150–£220 and an all-ceramic crown £750–£1,000. If the nerve is involved, root canal treatment starts from £450. Every price is agreed in writing first.
Should I keep the broken piece?
Yes, bring it with you. We seldom bond a molar fragment back, but it shows us exactly how much tooth has gone and where the fracture ends.
Will a fractured cusp need a root canal?
Usually not. Most fractured cusps break above the nerve. A root canal is only needed if the fracture has exposed the nerve or the tooth was already inflamed, which shows as lingering pain to heat or throbbing at night.
In pain? Don’t wait
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