A cavity and an infected nerve can both cause tooth pain — but they need very different treatment. A filling repairs surface-level decay, while a root canal removes infection that has reached the pulp deep inside the tooth. Getting this distinction wrong (or ignoring it) usually means more pain and a more expensive fix later. Here are the five signs that tell us — and should tell you — that a root canal, not a filling, is the right call.
1. Pain that lingers after the trigger is gone
Sensitivity to hot or cold that fades within a few seconds is often just enamel wear or a small cavity. But if the ache lingers for a minute or more after you've stopped eating or drinking, it usually means the nerve inside the tooth is inflamed or infected — a strong sign root canal treatment is needed.
2. Pain when you bite down
Sharp pain specifically when chewing or biting often points to inflammation at the root tip, where the tooth meets the bone. A simple filling doesn't reach this deep, so this symptom is one of our clearest indicators for RCT.
3. Swelling or a "pimple" on the gum
A small bump on the gum near a tooth — sometimes called a gum boil or fistula — is often a sign of a draining infection at the root. This should never be ignored, even if it isn't painful, since it means active infection is present.
4. A tooth that has darkened
When the nerve inside a tooth dies, the tooth often changes colour — greying or darkening compared to the teeth around it. This discolouration from the inside can't be fixed with whitening; it needs root canal treatment to address the cause.
5. Deep decay confirmed on an X-ray
Sometimes there's little pain at all, but an X-ray shows decay has progressed close to or into the pulp chamber. In these cases, we often recommend RCT proactively — treating it while it's manageable is far better than waiting for a painful flare-up.
What happens if you wait?
- The infection can spread to the surrounding bone, causing an abscess
- Pain typically worsens and becomes harder to manage with medication alone
- The tooth becomes more likely to require extraction instead of being saved
- Infection can, in rare cases, spread beyond the tooth and become a medical emergency
The good news
Modern root canal treatment, done with rotary instruments and proper anesthesia, is no more uncomfortable than getting a filling. If you're experiencing any of the signs above, the earlier you're seen, the simpler and more comfortable your treatment will be. Read more about our root canal treatment or get in touch and we'll help you figure out what your tooth actually needs.