Discoloration usually occurs after root canal treatment of a tooth. The discoloration may be caused by pulpal tissue and residual medication used during root canal treatment, as follows. 1. Pulp tissue: Iron generated from the decomposition of hemoglobin in the residual pulp tissue may generate iron sulfide into the dentin tubules, causing discoloration of the tooth. 2. Root canal medication: Root canal rinsing agents, root canal sealers, and root canal sealers used during root canal treatment will form crystals in the pulp cavity, attach to the walls of the pulp chamber or enter the dentin tubules, causing tooth discoloration. In addition, after root canal treatment the tooth loses its nutrient supply from the pulp and loses its luster, which can also lead to tooth discoloration. There may be other reasons for tooth discoloration after root canal treatment. If tooth discoloration is severe or accompanied by other symptoms, it is recommended to go to the hospital in time.