Wisdom teeth

Wisdom teeth are the third molars, the last four teeth at the back of the mouth, and they arrive late — usually in the late teens or early twenties, sometimes much later, and in some people never, because around a quarter of people are missing one or more of them altogether.

They are also the subject of the largest change in dental practice that most people have not heard about. For decades, impacted wisdom teeth were removed as a matter of routine on the assumption that they would cause trouble eventually. UK guidance ended that: removing a wisdom tooth that is impacted but not causing any problem should not be done. A healthy impacted wisdom tooth is left where it is, watched, and cleaned like any other tooth.

That is worth knowing because the older assumption is still widespread, including in a great deal of writing on the subject.

Impaction, and what it does and does not cause

A tooth is impacted when it cannot come through into a normal position — because there is no room, or because it is angled sideways, backwards or forwards against the tooth in front. It may be fully buried in bone, or partly through the gum with a flap of gum over part of it.

Partial eruption is the situation that causes most genuine trouble, because the gap under that flap of gum cannot be cleaned and collects plaque and food. That leads to the two real problems: pericoronitis, an infection of the gum around the tooth, and decay — in the wisdom tooth, and more importantly in the back of the second molar next to it, which is a sound and useful tooth.

One thing impaction does not reliably cause is crowding of the front teeth. The belief that wisdom teeth push the lower front teeth out of line is long-standing and is not supported: lower incisors tend to crowd in the twenties whether or not third molars are present, and crowding is not accepted as a reason to remove them.

When removal is justified

UK guidance limits surgery to cases where there is actual evidence of a problem. The recognised reasons are:

• decay in the tooth that cannot be restored
• infection or inflammation of the pulp that cannot be treated
• cellulitis, an abscess or osteomyelitis
• resorption of the tooth itself or of the tooth next to it
• a fractured tooth
• disease of the follicle around the tooth, including a cyst or tumour
• a tooth obstructing jaw surgery or reconstruction, or lying within the field of a planned tumour operation

On pericoronitis specifically: a first episode, unless it is unusually severe, is not in itself a reason to remove the tooth — it is treated and the tooth is kept. A second or subsequent episode is accepted as a reason for removal, because a pattern has then established itself.

Severe decay in the second molar behind the wisdom tooth, caused by the wisdom tooth making that surface impossible to clean, is also a real reason to act, since the second molar is the tooth worth protecting.

Pericoronitis, and what to do about an episode

It presents as a swollen, tender gum over or beside a partly erupted wisdom tooth, often with a bad taste, difficulty opening the mouth fully, and sometimes swollen glands and feeling unwell. Biting on the swollen gum with the opposite teeth makes it worse, which is why it tends to escalate over a day or two.

An episode is managed by cleaning the area as thoroughly as can be tolerated, rinsing frequently with warm salt water, and paracetamol or ibuprofen taken by the label. A dentist can clean under the gum flap properly, which is the thing that actually settles it. Antibiotics are for cases where the infection is spreading or the person is unwell rather than for every episode.

Facial swelling that is spreading, or any difficulty swallowing, breathing or opening the mouth, needs urgent attention the same day — hospital if it is progressing.

Assessment

An X-ray shows the position and angle of the tooth, how its roots are shaped, and — critically — how close those roots lie to the nerve that runs through the lower jaw. Where they are very close, a three-dimensional scan may be taken, because that proximity is what determines the main risk of the operation and sometimes changes the plan entirely.

The operation, and its risks

Most lower wisdom teeth are removed under local anaesthetic, in a practice or a hospital clinic depending on how difficult the tooth is. Sedation is available for anxious patients or more complex cases, and general anaesthetic is used where several difficult teeth are being removed or where sedation is unsuitable. Access often requires an incision in the gum, sometimes removing a little bone and dividing the tooth into pieces, and a stitch or two afterwards.

What to expect afterwards: swelling peaking at around two to three days, soreness for several days, difficulty opening the mouth for a while, and some bleeding on the first day.

The risks are worth knowing before consenting, because they are not trivial and are frequently glossed over:

• Nerve injury. The nerve supplying the lower lip and chin runs close to the roots of lower wisdom teeth, and the nerve supplying the tongue runs close to the inner side. Bruising either causes numbness, tingling or altered sensation in the lip, chin or tongue. It is usually temporary, resolving over weeks or months, but it is occasionally permanent. This is the single most important risk to discuss, and the closer the roots are to the nerve, the more it matters.
• Dry socket, where the healing clot is lost and the socket becomes severely painful several days later. Smoking is the main avoidable cause.
• Infection, bleeding, and more rarely damage to the adjacent tooth or a fracture of the jaw.

Coronectomy is worth asking about where the roots are intimately close to the nerve. The crown of the tooth is removed and the roots are deliberately left in place, which avoids disturbing the nerve. It is not suitable for every case — not where the tooth is infected or mobile — and the retained roots occasionally need removing later, but it substantially reduces the risk of nerve damage in the cases where that risk is highest.

Afterwards

Nothing to rinse with for the first day, so the clot is left undisturbed. After that, warm salt water rinses several times a day, particularly after eating. Soft food, nothing very hot, and no smoking — smoking is the clearest cause of a painful healing failure. No strenuous exercise for a day or two. Pain relief taken regularly for the first couple of days works better than waiting for the pain. Bleeding that restarts is dealt with by biting firmly on a clean rolled handkerchief or gauze pad for twenty minutes without checking it every two.

Reasons to go back: pain that is worsening rather than settling after about three days, bleeding that will not stop with pressure, spreading swelling, or fever.

Upper wisdom teeth

These are a different proposition. There is no nerve in the same position, the bone is softer, and removal is usually quicker and the recovery milder. An upper wisdom tooth with nothing opposing it sometimes over-erupts and bites into the opposite gum, which is one of the more common genuine reasons to remove one.

See also tooth decay and cavities, gum disease and dental check-ups.