Root canal retreatment is recommended when a tooth that has previously undergone root canal therapy does not heal properly or becomes reinfected months or even years later. This can occur due to complex canal anatomy, delayed placement of a restoration, new decay, or a fracture that allows bacteria to re-enter the tooth's structure. During the treatment, the existing crown or filling may be removed to access the root canals. The previous root canal filling materials are carefully taken out, and the canals are throughly cleaned, disinfected, and reshaped. The canals are then sealed again to promote healing and prevent further contamination.