What is pericoronitis, and why does the gum over a wisdom tooth become inflamed?

Pericoronitis is inflammation of the soft tissue surrounding the crown of a partly erupted tooth. The piece of gum left over the tooth is called the operculum, or simply the gum flap. The narrow space between the flap and the tooth is open to the bacteria in the mouth; food debris gets in easily, but a toothbrush cannot reach it. In a study cited by StatPearls, 95% of pericoronitis cases were associated with lower wisdom teeth. It is also most common between the ages of 20 and 29, when wisdom teeth come through.

Not every case of pericoronitis follows the same course, and what decides this is the position of the tooth. When the tooth finishes coming through and meets the tooth opposite it in the bite, the flap usually recedes by itself; the literature calls this transient pericoronitis. If the tooth cannot come through fully because it is tilted or there is no room in the jaw, the flap stays and the inflammation comes back from time to time. That is why the first thing your dentist will look at is whether the tooth can come through; the treatment plan takes shape around that answer.

The second factor that makes things worse is the opposing tooth. When you close your mouth, the swollen flap gets caught under the upper wisdom tooth, is crushed with every bite, and swells further the more it is crushed. If this vicious circle continues, the dentist also assesses the upper tooth; StatPearls notes that extracting the opposing tooth that is crushing the flap may be considered. If you have noticed the pain getting clearly worse when you bite, mention it at your appointment.

Pericoronitis takes two forms. Acute pericoronitis comes on quickly: severe pain around the back teeth, red and swollen gum, a discharge of pus, pain on swallowing, limited mouth opening, and sometimes a high temperature and swollen lymph nodes in the neck. Chronic pericoronitis is quieter; as Cleveland Clinic describes it, it shows itself as a mild ache that comes and goes around the back teeth, bad breath and a bad taste. Episodes that flare up from time to time are also counted as part of the chronic picture.

The dangerous side of pericoronitis is that the infection can spread into the deep spaces behind the lower jaw. StatPearls writes that difficulty swallowing, being unable to open the mouth and swelling that extends outside the mouth can indicate that the infection has spread into the neighbouring deep spaces, and that if help comes too late, the airway can be put at risk. The NHS also says that, with a dental abscess, anyone who is having difficulty breathing, speaking or swallowing, whose eye is swelling, who has a lot of swelling inside the mouth or who is struggling to open their mouth should go to A&E without waiting. If you have any of these symptoms, do not wait for a dental appointment; go to A&E or call 112.

Not every pain around a wisdom tooth is pericoronitis. A 2021 study by Schmidt and colleagues, which compiles recommendations on managing pericoronitis and systematically reviews antibiotic prescribing for it, states that decay, inflammation of the pulp, an abscess at the root tip, food getting trapped between the teeth and jaw joint problems should also be considered when making the diagnosis, and that finding one of these does not rule out pericoronitis. The same review recommends taking an X-ray in severe, persistent or recurring cases, and when there is no response to treatment.

When it comes to antibiotics, there is a marked gap between practice and recommendation. In the surveys brought together by the same review, around 74% of dentists reported prescribing antibiotics for pericoronitis. Yet Scotland's dental prescribing guidance (SDCEP) says that local treatment is enough in most cases, and that antibiotics should be considered only if there is systemic involvement, meaning you are generally unwell, or if swelling persists despite local treatment. Not being prescribed antibiotics does not mean your treatment is incomplete; the real treatment is cleaning under the flap.

Pericoronitis raises two separate questions: how to settle an episode, and whether the tooth should stay in the mouth. The answer to the first is the same for almost everyone: local cleaning. On the second, NICE, the body that appraises health technologies in England, acknowledges in its 2000 guidance on wisdom teeth that it is not clear how much the number and severity of episodes should weigh in the decision, and gives this criterion: unless it was particularly severe, a first episode is not in itself a reason for extraction, while second and later episodes are an appropriate reason. The lists below summarise this criterion and the other reasons in the guidance; the decision is made by the dentist who examines you.

Pericoronitis is a single-tooth problem; see your own dentist for diagnosis and treatment. The sequence below is based on the SDCEP guidance and StatPearls, and shows what to expect from the first appointment through to the long-term decision.

1. 1

   Examination and ruling out other causes

   The dentist looks at the flap, the opposing tooth, how wide you can open your mouth and the lymph nodes in your neck, and asks whether you have had a high temperature. To tell whether the pain is coming from decay or from an abscess at the root tip, they will ask for an X-ray, particularly in severe or recurring cases.

2. 2

   Rinsing and cleaning under the flap

   This is the local treatment SDCEP recommends: the area under the flap is rinsed, and the plaque and debris that have built up are cleaned out with instruments. StatPearls lists sterile solutions such as saline or chlorhexidine for rinsing, and includes local anaesthetic among the options for pain control. In most episodes, relief starts with this step.

3. 3

   Pain control

   StatPearls states that anti-inflammatory painkillers taken by mouth are the first choice for pain. Your dentist, who knows the other medicines you take, will tell you which one suits you.

4. 4

   Antibiotics, only if needed

   According to SDCEP, if you are generally unwell or swelling persists despite local treatment, a short, three-day course of metronidazole may be prescribed; the alternative is amoxicillin. Do not drink alcohol while taking metronidazole or for at least 48 hours after stopping it. SDCEP advises against prescribing metronidazole to people taking warfarin, so if you take warfarin, be sure to say so.

5. 5

   Assessing the opposing tooth

   If the upper wisdom tooth bites on the flap, the dentist may suggest adjusting or extracting that tooth. Otherwise, even if the flap heals, it is crushed again with every bite.

6. 6

   A long-term decision once the episode has passed

   Once the swelling has gone down, the position of the tooth, the number of episodes and the state of the neighbouring tooth are assessed together. The options are monitoring, removing the flap, extraction, or a coronectomy, which aims to protect the nerve.

Below are the options you will discuss with your dentist once the episode has settled. Which one suits you depends on the position of the tooth, how close the root is to the nerve and your history of episodes. Asking these questions at your appointment will make things easier: Can this tooth come through fully? Does the upper wisdom tooth bite on the flap? How close is the root to the nerve in the lower jaw? Is there decay or bone loss on the neighbouring molar?

A mild case of pericoronitis can settle within a few days; the following are problems seen with episodes that are put off or only patched up with medicines.

The sequence below describes what happens after the area under the flap has been cleaned at the dentist. According to Cleveland Clinic, mild cases clear up in a few days and severe cases can last a few weeks; with treatment, most cases improve within a week or two.

1. The first day after cleaning

   The pain eases as the pressure and build-up reduce. Cleveland Clinic recommends rinsing with warm salt water three or four times a day; your dentist may also recommend a chlorhexidine mouthwash.

2. Within a few days

   The swelling and the bad taste go down, and you can open your mouth wider. Keep gently cleaning the back of your mouth with a soft brush; do not poke under the flap with a toothpick.

3. Within a week or two

   Most episodes settle within this time. If you have been prescribed antibiotics, finish the course as your dentist has told you.

4. Once the episode has passed

   Book a follow-up appointment for the long-term decision. The position of the tooth and your history of episodes are assessed at this appointment; if you have had two episodes, it is time to discuss extraction.

Pericoronitis is a single-tooth problem, and your own dentist plans its treatment; we do not give a figure here. These are the main factors that determine how many steps treatment takes and how much it involves:

The position of the tooth

With an upright tooth that is still coming through, local cleaning and monitoring may be enough; with a tilted or impacted tooth, extraction and more extensive surgery may be needed.

The need for imaging

A panoramic X-ray is usually enough. If the root appears to be close to the nerve, the dentist may ask for a CBCT scan.

The long-term solution chosen

Removing the flap, a simple extraction, a surgical extraction that involves removing bone, and a coronectomy are different procedures, and they take different amounts of time.

Treating the upper tooth too

If the upper wisdom tooth that bites on the flap also needs a procedure, the plan covers two teeth.

The severity of the episode

With a spreading infection, the episode has to be brought under control first, with hospital treatment if needed; the long-term procedure is planned after that.