A cavity and an infected nerve can both cause tooth pain — but they need very different treatment. Here are five signs that tell us a root canal, not a filling, is the right call: pain that lingers after hot/cold, pain when biting down, a gum boil, a darkened tooth, and deep decay confirmed on X-ray.
Modern root canal treatment with rotary instruments is no more uncomfortable than getting a filling — the earlier you're seen, the simpler your treatment.