Short answer
A tooth may need root canal treatment when pain lingers after hot or cold, when biting hurts in one specific tooth, when the gum near it swells or forms a small pimple, or when the tooth darkens. Only an examination and X-ray can confirm it, because a nerve can also die quietly with no pain at all.
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What a root canal actually treats
Inside every tooth is a soft core of nerve and blood vessels called the pulp. Deep decay, a crack, repeated dental work or a knock can let bacteria reach it. Once the pulp is infected or dying, it does not recover on its own, and the infection works its way toward the tip of the root and into the bone around it.
Root canal treatment removes that infected tissue, cleans and shapes the canals inside the root, and seals them. The tooth stays in your mouth and keeps doing its job, which is the whole point: the alternative is usually removing it.
Signs worth taking seriously
Pain that lingers for more than a few seconds after something hot or cold is one of the clearest signals. Normal sensitivity fades quickly; pulp inflammation keeps aching.
Pain on biting in one specific tooth, a dull throb that wakes you at night, swelling in the gum or face, a small pimple-like bump on the gum that comes and goes, or a tooth that has visibly darkened compared with its neighbours all point toward a nerve problem.
Just as important: a tooth can be badly infected and feel like nothing at all. Nerves that have already died stop sending pain signals, which is why routine X-rays sometimes find a problem before the patient does.
What the appointment involves
The dentist examines the tooth, tests how it responds to temperature and pressure, and takes an X-ray to see the root and the bone around it. That is what separates a nerve problem from a cracked filling, gum infection or sinus pain, which can feel similar.
If treatment is needed, the area is numbed first. Most people describe the appointment itself as similar to having a filling, just longer. The tooth is usually restored afterwards with a filling or crown, because a treated tooth is more brittle than an untouched one.
Why waiting costs more than it saves
Infection does not stay still. What starts as a treatable nerve problem can become an abscess, spread into the bone, and leave removal as the only realistic option. Losing the tooth then brings its own costs, because the gap usually needs replacing with a bridge or an implant.
If you have any of the signs above, book an examination rather than waiting to see whether the pain passes. Pain that comes and goes is still a signal.
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