Large cavities, fractured teeth or broken fillings may cause your teeth to become overly sensitive and sometimes quite painful. When this occurs, bacteria have reached the pulp of the tooth and an infection starts. A root canal is a procedure where the nerve of the tooth (pulp) is removed and replaced with a root canal filling. Root canal therapy eliminates the infection by removing the infected pulp tissue, disinfecting and refilling the interior of the tooth. This can prevent widespread infection and permanent damage. Root canals can often be accomplished in one visit.