If tooth decay is left untreated, it will keep spreading deeper and deeper. At that point, a root canal may be the only option to save your tooth.
When tooth decay makes it to the pulp, the part of the tooth with the nerves, there is usually a lot of pain. However, since this is happening on the inside of the tooth, you won’t necessarily see the damage. Instead, you will feel it as pain, and you may notice other signs like bleeding, tenderness, swelling, and bad breath.