Apical Periodontitis: Signs That Infection Has Reached the Jawbone

Most people assume that an infected tooth hurts. Often it does — but a substantial proportion of infections at the root tip produce no symptoms at all and are discovered as a dark shadow on a routine radiograph, sometimes years after the process began.

Apical periodontitis is inflammation of the bone and tissues immediately around the tip of a tooth root, caused by bacteria that have colonised the pulp space inside the tooth. It is one of the most common findings in dentistry, and understanding it explains why dentists take radiographs on teeth that feel perfectly fine.

This article covers how it develops, what it looks like, when it becomes an emergency, and what can be done about it.

Inside every tooth is a pulp chamber containing nerve tissue and blood vessels, running down through canals to an opening at the tip of each root. If bacteria reach that space — usually through deep decay, a crack, a leaking restoration or trauma — the pulp becomes inflamed and eventually dies.

Once the pulp is necrotic, it cannot mount an immune response, because its blood supply has gone. Bacteria multiply within the canal system and their products pass out through the opening at the root tip into the surrounding bone. The body responds there, and that inflammatory response is apical periodontitis.

The bone at the root tip is resorbed as part of that response, which is why the lesion appears as a dark area on a radiograph — bone has been lost.

The usual sequence:

1. Bacterial entry. Tooth decay progressing through enamel and dentine is the most common route. A cracked tooth, a failing filling, repeated dental treatment on the same tooth, or a knock that damages the blood supply can all do it too.

2. Pulpitis. The pulp becomes inflamed. This is the stage that often produces the classic symptoms — lingering pain to hot or cold, pain that wakes you at night, discomfort that is hard to localise. Reversible pulpitis may settle if the cause is removed; irreversible pulpitis will not.

3. Pulp necrosis. The pulp dies. Interestingly, symptoms frequently reduce at this point, which is why some patients believe the problem has resolved. It has not.

4. Spread beyond the root. Bacterial products exit the root tip and the bone responds. Acute apical periodontitis produces pain on biting and tenderness; chronic apical periodontitis often produces nothing.

5. Abscess or granuloma. The lesion may organise into a chronic granuloma or cyst, or become an acute dental abscess with pus, swelling and significant pain.

Symptoms that may be present:

• Pain on biting or when the tooth is tapped

• A feeling that the tooth is raised or does not meet the others properly

• Deep, throbbing ache, sometimes worse when lying down

• Tenderness over the gum above or below the tooth

• A small pimple-like swelling on the gum that discharges and refills — this is a sinus tract draining the infection

• A persistent bad taste

• The tooth darkening in colour, particularly a front tooth after trauma

• Swelling of the face or jaw

• Tender, swollen glands under the jaw

Signs there may be none of. Chronic apical periodontitis very often produces no symptoms whatsoever. The tooth may have stopped hurting long ago. This is why radiographs at routine check-ups matter — they detect the condition before it becomes acute.

Signs requiring urgent care. Facial swelling, particularly if it is spreading or involves the eye or the floor of the mouth; difficulty swallowing or breathing; difficulty opening the mouth; fever with a dental infection; a rapidly worsening condition. Spreading dental infection can become serious, and swelling that affects breathing or swallowing needs emergency medical attention rather than a dental appointment.

The root canal system is a protected environment once the pulp dies. There is no blood supply, so immune cells and antibiotics circulating in the bloodstream cannot reach the bacteria inside. This is the central fact that explains everything else: antibiotics alone do not resolve apical periodontitis, because they cannot reach the source.

Meanwhile, in the bone at the root tip, the body mounts a defence. Immune cells accumulate, inflammatory mediators are released, and osteoclasts resorb bone — partly as a consequence of inflammation and partly creating space for the defensive response. The lesion is essentially a standoff at the boundary between the infected canal and the body's tissues.

Chronic lesions may develop into a periapical granuloma (inflammatory tissue) or a radicular cyst (an epithelium-lined cavity). Both appear as dark areas on a radiograph and both persist until the source of bacteria in the canal is removed.

Acute exacerbation — an abscess — occurs when the balance shifts, often when bacterial load increases or immune resistance is temporarily reduced. This is why a tooth that has been quiet for years can suddenly flare up.

Root canal treatment. The primary treatment where the tooth is restorable. The canal system is accessed, cleaned mechanically and chemically to remove the bacterial reservoir, shaped, and sealed with an inert filling material. Once the source is removed, the bone at the root tip typically heals over months, and healing is confirmed radiographically at follow-up. Our root canal treatment page explains the procedure in more detail.

Re-treatment. Where a previously root-treated tooth develops or retains a lesion, the existing filling can be removed and the canals re-cleaned.

Apical surgery. Where conventional treatment is not possible or has not resolved the lesion, the root tip can be surgically accessed, removed and sealed from the end.

Extraction. Where the tooth is not restorable — extensive decay below the gum, a vertical root fracture, or inadequate remaining structure. Replacement options such as a dental implant or a bridge would then be discussed, and ridge preservation may be considered at the time of removal.

Antibiotics. Prescribed as an adjunct where there is spreading infection, systemic involvement or facial swelling — not as a treatment in themselves. They may temporarily settle symptoms while leaving the underlying infection untouched, and inappropriate prescribing contributes to antimicrobial resistance.

Drainage. An acute abscess may be drained to relieve pressure, which usually provides rapid relief, but definitive treatment of the tooth still follows.

Arrange an assessment if:

• A tooth hurts when you bite on it

• You have a persistent toothache

• There is a recurring pimple on the gum

• A tooth has changed colour

• You have a persistent bad taste from one area

• A tooth has previously had root canal treatment and has become tender

• You have not had radiographs taken for some years

Seek urgent care the same day for facial swelling, fever alongside dental pain, difficulty swallowing, or rapidly worsening symptoms. Our emergency dentist page explains how to be seen quickly.

The condition begins with bacteria reaching the pulp, so prevention is largely about preventing and detecting decay and cracks early.

• Brush twice daily with fluoride toothpaste and clean between the teeth daily

• Reduce the frequency of sugar intake, not just the amount

• Attend routine check-ups with radiographs at the interval advised

• Have hygiene appointments as recommended

• Deal with small cavities promptly — a white filling placed early prevents the situation that leads to root canal treatment

• Wear a night guard if you grind, since cracks are a common route of bacterial entry

• Do not ignore a tooth that has stopped hurting after a period of pain

• Apical periodontitis is inflammation in the bone at the root tip caused by bacteria inside the tooth

• Chronic lesions frequently produce no symptoms and are found on radiographs

• Pain stopping does not mean the problem has resolved — it often means the pulp has died

• Antibiotics cannot reach bacteria inside a dead root canal system

• Root canal treatment or extraction removes the source; bone then heals over months

• Facial swelling, fever or difficulty swallowing require urgent care

• Regular radiographs are how symptomless lesions are detected

The NHS page on dental abscess covers symptoms and when to seek urgent help.

The most useful thing to know about apical periodontitis is that it is often silent. A tooth that hurt badly and then settled has not necessarily recovered — quite often the pulp has simply died, and the process has moved into the bone where there are fewer nerve endings to report it.

If you have had persistent toothache that resolved on its own, or you have not had radiographs for several years, that is worth an appointment even if nothing currently hurts.

To have a tooth assessed, arrange an appointment at 22 Wimpole St, London W1G 8GQ, or call 020 7183 0692.

Dental symptoms and treatment options should always be assessed individually during a clinical examination.

This article is for general educational information only and is not professional dental advice, diagnosis, or a treatment recommendation. Information here is general and cannot replace an in-person assessment by a qualified, GDC-registered dental professional. Symptoms, suitability, fees, timelines, and outcomes vary according to individual clinical circumstances. If you have pain, swelling, or other concerning symptoms, seek prompt professional dental care. Always request a written treatment plan and cost estimate before proceeding with treatment.

Written Date: 3 August 2026 Next Review Date: 3 August 2027