What it is and how it forms
When the pulp dies — from deep decay, untreated pulpitis, trauma, or a crack — bacteria colonise the empty canal and exit through the tiny opening at the root tip. Your immune system meets them there, in bone. The battleground becomes a lesion: inflamed tissue replacing bone, visible on a radiograph as a dark round area at the root apex.
The important implication: a periapical lesion is not a disease of the tooth. It is a disease of the bone around the tooth, driven by a source inside the tooth. That is why cleaning the canal system resolves it, and why treating it with antibiotics alone does not.
The three forms you may hear named
| Type | Character | Symptoms |
|---|
| Acute abscess | Rapid, pus-forming | Severe pain, swelling, tooth tender to touch, possible fever |
| Chronic granuloma | Slow, walled-off inflammatory tissue | Often none — found incidentally on radiograph |
| Radicular cyst | Fluid-filled sac from long-standing lesion | Usually painless; can grow and displace structures |
Why so many are silent: once the pulp is dead, the tooth has no nerve left to report pain. The chronic form can sit quietly for years while slowly enlarging. This is why routine radiographs matter even when nothing hurts — a symptomless lesion is still destroying bone.
Signs that should prompt a visit
- A tooth that feels different when you bite — slightly raised, or tender to tapping.
- A small bump on the gum near the root, sometimes draining a bad-tasting fluid. This is a sinus tract, and it means the infection has found an exit.
- Facial or gum swelling.
- A tooth that has darkened relative to its neighbours — see tooth discoloration.
- A history of trauma to that tooth, even years ago.
- Pain that stopped on its own after a period of severe toothache.
When it becomes urgent: rapidly spreading swelling, difficulty swallowing or breathing, swelling that closes the eye, fever with malaise, or inability to open the mouth. Dental infections in the lower jaw can spread into fascial spaces of the neck, which is a medical emergency. Do not wait these out — go to an emergency department if you cannot reach a dentist.
Treatment
- Remove the source. Root canal treatment cleans and seals the canal system, eliminating the bacterial reservoir. This is the definitive treatment for most lesions.
- Drainage if there is an acute abscess with pus under pressure — this gives the fastest pain relief.
- Antibiotics as an adjunct when infection is spreading, not as the treatment itself.
- Apical surgery if a lesion persists after properly performed root canal treatment, or in cases of combined pathology.
- Extraction when the tooth is not restorable.
Healing is monitored radiographically. Bone fills back in slowly — expect 6 to 24 months for a lesion to resolve on film, with larger ones taking longer. A follow-up radiograph at six to twelve months is standard, and this is the step patients most often skip.
Good news that surprises people: bone regenerates here. Unlike the bone lost to
gum disease, periapical bone destruction typically fills back in completely once the source of infection is removed. The lesion size on the initial radiograph is not a verdict on the tooth.
Frequently asked questions
I have an abscess but no pain. Is it still a problem?
Yes. The chronic form is frequently painless precisely because the nerve inside the tooth is already dead and cannot signal. Meanwhile the lesion continues destroying bone and can enlarge into a cyst. Painlessness reflects a dead nerve, not a resolved infection, and treatment is still required.
Can antibiotics clear it up without a root canal?
No. The bacterial reservoir is inside a canal system with no blood supply, so antibiotics cannot reach it. They can reduce spreading infection and swelling temporarily, and that relief often convinces patients the problem is gone. Once the course finishes, bacteria repopulate from the untreated canal and the lesion returns.
Will the bone grow back?
In most cases yes, and completely. This is a meaningful difference from bone lost to gum disease, which does not regenerate. Once the source inside the tooth is eliminated, periapical bone typically fills in over 6 to 24 months depending on lesion size. Follow-up radiographs confirm it — which is why that appointment matters.
There is a small pimple on my gum that keeps draining. What is that?
That is a sinus tract — a channel the infection has created to release pressure. It explains why the tooth may not hurt much: the pus has an escape route, so pressure never builds. It is a sign of established chronic infection and needs the source treated. The tract itself usually closes on its own once the tooth is treated.
When is a dental abscess an emergency?
Seek immediate care for rapidly spreading swelling, difficulty swallowing or breathing, swelling that closes your eye, fever with feeling generally unwell, or inability to open your mouth. Lower molar infections can spread into neck spaces, which is life-threatening. If you cannot reach a dentist quickly, go to an emergency department rather than waiting.
My tooth was injured years ago and now shows a shadow on X-ray. Are they related?
Very likely. Trauma can kill a pulp without any visible fracture and without immediate symptoms, and the resulting lesion may take years to become radiographically obvious. A darkened tooth with a history of impact and a periapical shadow is a classic combination, and it is usually treated successfully with root canal treatment.