Most people arrive at this question through pain, and pain is genuinely one of the signals. But it is not the most reliable one, and the tooth that hurts most is not always the tooth that needs treating.
Here is what actually points at a problem inside the tooth rather than on it.
The signals that matter most
- Cold or heat that lingers. This is the single most useful symptom you can report. A healthy nerve reacts to something cold and then settles within a second or two. A nerve that is inflamed beyond recovery keeps aching for thirty seconds, a minute, sometimes longer after the cold is gone. That lingering is the difference between a sensitive tooth and a dying one.
- Pain that wakes you at night, or that arrives unprovoked while you are sitting still. Pain with no trigger is a different category from pain when you bite something.
- Pain on biting, or on release. Tenderness when you let go after biting down often points at a crack, which is one of the ways a nerve gets into trouble in the first place.
- A tooth that has gone dark. A single tooth turning gray or brown compared with its neighbors usually means the nerve inside died some time ago, and it frequently does not hurt at all.
- A bump on the gum. A small pimple-like swelling near the root, which may come and go and may taste unpleasant when it drains, is a sinus tract. It is pus finding a way out. This is not a maybe.
- Swelling of the face or jaw. Different urgency entirely – see below.
The one that catches people out: it can stop hurting
A tooth that hurt badly for a week and then went quiet has not got better. Frequently what has happened is that the nerve finished dying. The pressure that was causing the pain is gone because the tissue generating it is gone, and the infection is now free to move out of the root end into the bone without a warning signal attached.
This is why we would rather see you during the bad week than three months later. Relief is not the same as resolution, and the quiet period is when a treatable tooth often becomes an extraction.
When it is an emergency instead
Most of this can wait for a normal appointment. One thing cannot.
If there is facial swelling that is spreading toward your eye or down under your jaw into your neck, difficulty swallowing or breathing, a changed voice, or fever alongside the swelling, that is a hospital emergency department rather than a dental chair. An infection that starts at a tooth can move into the tissues of the neck and become an airway problem. It is rare and it is genuinely dangerous. Our emergency page covers it.
Why a symptom list is not a diagnosis
Everything above is a reason to be examined, not a conclusion. Several things imitate a tooth needing root canal treatment, and getting it wrong means treating a tooth that did not need it while the real problem carries on.
- A cracked tooth can produce almost the same symptoms and sometimes needs a different answer.
- Referred pain. Upper and lower teeth on the same side share nerve pathways, and people routinely point at the wrong jaw. Sinus problems mimic upper back teeth convincingly.
- Grinding and clenching make teeth ache and feel bruised without anything being wrong inside them. Our article on jaw clenching goes into that.
- A high filling or crown can leave a tooth sore for weeks, and the fix is an adjustment rather than treatment.
- Exposed root surfaces are sensitive to cold and settle quickly, which is exactly the distinction the lingering test is for.
How we work out which it is
We test the nerve rather than guessing from the story. Cold testing on the suspect tooth and on its neighbors, tapping to check the ligament around the root, and digital X-rays to look for the dark area at the root tip that appears when infection has been there long enough to affect bone. Where a case needs more, 3D CBCT imaging shows things a standard X-ray cannot.
Comparing against the neighboring teeth is the part that matters. A tooth that responds differently from the ones either side of it is telling you something; a tooth that responds the same way as its neighbors probably is not the culprit, however much it hurts.
What happens if it is a root canal
We diagnose it here and refer the treatment itself to an endodontist who does them every day, then handle what comes afterward. The full reasoning is on our root canal page, including why a back tooth almost always needs a crown once the treatment is done.
One thing worth knowing now rather than later: root canal treatment and the crown that follows are a single sequence with a real combined cost, and it is better to hear that at the start. Our article on dental insurance explains why that particular pairing tends to exhaust an annual maximum on its own.
The question underneath the question
People asking whether they need a root canal are often really asking whether they are about to lose the tooth. Usually not. A root canal is the treatment that lets you keep a tooth that would otherwise have to come out, and keeping your own tooth is worth a good deal – as our article on implants argues at some length, even the best replacement is not the same as the tooth you were born with.
If something in your mouth is behaving the way this page describes, call 702-734-0776.