Emergency dental conditions
Pericoronitis: the infected gum flap over a wisdom tooth
Sore, swollen gum at the very back of the lower jaw, a bad taste and a mouth that will not open properly. This is the most common wisdom tooth emergency, and it is very treatable.
Clinically reviewed by Dr Ibraheem Ijaz, Principal Dentist · GDC 301711 · Last reviewed April 2026
Why the gum over a wisdom tooth gets infected
Wisdom teeth come through between about 17 and 25, and lower ones often arrive at an angle or only part of the way. While a tooth is half-erupted, a flap of gum (the operculum) lies over the back part of the crown like a loose lid. Under that lid is a warm, damp pocket that a toothbrush cannot reach. Food and plaque collect there, bacteria multiply, and the flap becomes inflamed. That is pericoronitis: peri around, corona crown.
Two things make it flare. The first is anything that lowers your resistance for a few days: a cold, exams, poor sleep, a run of late nights. The second is the upper wisdom tooth. Once the lower gum is swollen, the upper tooth on the same side bites straight down onto it every time you close your mouth, bruising the flap and keeping the infection going. This is why pericoronitis so often gets worse at night and why the upper tooth is sometimes part of the treatment.
It nearly always affects lower wisdom teeth, it tends to recur in the same spot until the tooth either comes fully through or is removed, and it is the single most common reason people in their late teens and twenties ring us as an emergency.
The symptoms most people notice first
- Pain and swelling of the gum behind the last molar, often first noticed when brushing or biting on the area.
- A foul taste or smell from pus seeping out from under the flap.
- Difficulty opening the mouth fully (trismus). The chewing muscles nearby stiffen in response to the inflammation. If you cannot fit two fingers between your front teeth, this is well established.
- Pain on swallowing, referred to the ear, or a sore throat on one side.
- A tender lump under the angle of the jaw where the lymph node has enlarged.
- In a heavier episode, swelling of the cheek, a raised temperature and feeling generally rough.
Pain at the back of the jaw has other causes, including a cracked molar, an abscess on the second molar and jaw joint problems. Our page on jaw pain covers how to tell them apart.
Checking the flap and the tooth above it
The £30 emergency examination includes an X-ray of the wisdom tooth, which shows us how it is lying, how much of it is through, and whether it will ever come through fully. We then:
- Measure how far you can open, so we know how much room we have to work and whether the infection is spreading into the muscles.
- Lift the flap gently and look for pus, debris and ulceration underneath.
- Check whether the upper wisdom tooth is biting on the flap. A clear tooth-shaped indentation in the swollen gum answers that.
- Feel the lymph nodes under the jaw and check your temperature if you feel unwell.
- Check the second molar in front, which sometimes has decay on its back surface where the wisdom tooth presses on it.
Settling the infection and stopping it coming back
The treatment on the day is mostly cleaning. We numb the area if needed, then irrigate under the flap with warm saline or chlorhexidine to flush out the trapped food and pus. This alone usually brings marked relief within a day. A soothing antiseptic dressing can be placed under the flap; this is described on our page on irrigation and antibiotic dressing. If the upper wisdom tooth is biting the flap we can smooth its sharp cusps, and where it serves no purpose, remove it, which is a straightforward extraction because upper wisdom teeth are usually easy to take out.
Antibiotics are not a first-line treatment. UK guidance from SDCEP is that they are only appropriate when the infection is spreading (cheek swelling, restricted opening, fever) or you are medically vulnerable. Prescribing them for a localised flare-up does nothing that a good clean does not, and breeds resistance for the day you really need them.
The acute episode usually settles within a few days of cleaning. The honest longer-term picture is this: if the tooth is going to come fully through, pericoronitis stops on its own once it does. If the X-ray shows it never will, expect repeated episodes until the lower tooth is removed. Fees for the day's treatment are quoted in writing at the examination before we begin.
| Treatment | What it involves | Fee |
|---|---|---|
| Emergency examination | 15 minutes, includes the wisdom tooth X-ray | £30 |
| Irrigation and dressing under the flap | Flushing out debris and pus, antiseptic dressing if needed | Quoted at the examination |
| Removing an upper wisdom tooth biting on the flap | Usually a simple extraction | £120–£260 |
| Removing the lower wisdom tooth once settled | Surgical extraction | £350–£450 |
| Conscious sedation for the extraction | Optional, per session | £200 |
Cleaning the area at home
Home care between now and your appointment, and after it, makes a real difference:
- 01Rinse with warm salt water (a teaspoon in a glass) every couple of hours, tilting your head so it pools over the sore side.
- 02Chlorhexidine mouthwash from the pharmacy, used as directed on the bottle, for no more than a week or two; it stains teeth with longer use.
- 03The most useful tool is a curved-tip syringe of the kind sold for wisdom teeth. Warm salt water squirted gently under the flap reaches the pocket a brush cannot. Do not push hard.
- 04Keep brushing the tooth and the flap, gently, with a small-headed brush. Avoiding the area because it hurts lets more plaque collect.
- 05Paracetamol and ibuprofen as directed on the packet. Ibuprofen is particularly helpful because it reduces the swelling.
- 06Soft food, plenty of fluids, and chew on the other side so the upper tooth is not pounding the flap.
Removing the wisdom tooth
Once the acute infection has settled, we talk about whether the tooth should go. The case for removal is strong when there have been two or more episodes, when the X-ray shows the tooth lying sideways against the second molar, or when the second molar is starting to decay. Removal is not done during an acute flare; the tissues are inflamed, anaesthetic works less well and limited opening makes the surgery harder.
Wisdom tooth extraction here is £350–£450 depending on how the tooth is positioned, and is carried out by Dr Ibraheem Ijaz, who holds a postgraduate diploma in implant dentistry and does the surgical extractions in the practice. If the thought of it worries you, conscious sedation is available at £200 per session. There is more detail on our extractions and wisdom teeth page. 0% finance over 6 to 18 months is available through Tabeo, subject to status.
When it is more than a dental problem
Infection from a lower wisdom tooth can spread into the spaces around the throat. Go to A&E, or ring 999, if you cannot open your mouth more than a finger's width, cannot swallow your own saliva, have swelling in the neck or the floor of the mouth, find breathing harder, or have a high fever with a rapidly growing swelling. The nearest A&E with a maxillofacial team is the Northern General Hospital, Herries Road, Sheffield, around 20 minutes from Deepcar. Outside our hours, NHS 111 can also direct you.
Questions, answered
Common questions
What is pericoronitis?
It is inflammation and infection of the flap of gum that lies over a partly erupted tooth, almost always a lower wisdom tooth. Food and bacteria trapped under the flap cause pain, swelling, a bad taste and sometimes difficulty opening the mouth.
Does pericoronitis go away on its own?
A mild episode can settle with careful cleaning and salt-water rinses within a few days. It tends to come back until the tooth either comes fully through or is removed.
Do I need antibiotics for pericoronitis?
Usually not. Cleaning under the flap is the treatment. Antibiotics are added only if the infection is spreading into the cheek or neck, you have a fever, or your mouth opening is badly restricted.
Why can I not open my mouth properly?
The chewing muscles next to the infected tooth go into protective spasm. It eases as the infection settles. Opening of less than two fingers' width, or getting worse, needs seeing urgently.
Will the wisdom tooth have to come out?
Not always. If the tooth is going to erupt fully, the problem resolves by itself. If the X-ray shows it will stay impacted, or you have had repeated episodes, removal is usually recommended once the infection has settled.
How much does treatment cost?
The emergency examination with an X-ray is £30. Cleaning and dressing on the day is quoted before we start. Wisdom tooth extraction is £350–£450, with sedation available at £200 per session.
Can pericoronitis be dangerous?
Rarely, but infection can spread towards the throat. Trouble swallowing, neck swelling, a very restricted mouth opening or difficulty breathing mean A&E, not a dental appointment.
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