A root canal is a dental procedure that relieves pain caused by an infected or inflamed tooth. During root canal treatment, the inflamed pulp is removed. The inner surfaces of the tooth are then cleaned and disinfected, and a filling is placed to seal the space. Root canal treatment is necessary when oral bacteria invade the pulp inside the tooth. This usually happens when a cavity goes untreated for a long time. This can also happen if your tooth is cracked or damaged from trauma.