Root canals need to be treated when the infection has reached them.
Normally it accompanies with tooth sensitivity to hot ( when the bacteria reach the canals, they expand upon heat getting to them, e.g. drinking hot tea or coffee…, hence causing the sensation of tooth ache. Sometimes tooth dies, meaning there is no pain anymore because the nerve inside the canals is completely gone but then the jaw or cheek swells up due to bacteria getting access to them via the canals. In this case tooth needs to be treated as well. During root canal treatment, the inflamed or infected pulp is removed and the inside of the tooth is carefully cleaned and disinfected, then filled and sealed. Afterwards, the tooth is restored with a crown or filling for protection.