Tooth discoloration is caused by exogenous or endogenous staining; pulp necrosis can cause endogenous staining, but not all tooth discoloration is caused by pulp necrosis. Pulp necrosis is mainly caused by dental caries, pulpitis or dental trauma, which will lead to necrosis of the nerve infection and inflammation; necrosis of the nerve will decompose and produce melanin and other inflammatory substances, which will cause staining of the teeth, and ultimately, the teeth will appear dark and black and tooth discoloration, which is endogenous tooth discoloration. Tetracycline or dental fluorosis can also cause endogenous staining of the teeth, resulting in yellowing and chalky lesions. Tartar or tobacco stains, and certain foods can cause exogenous tooth coloration. Tooth discoloration is recommended to seek medical attention for a clear diagnosis and treatment, and is not necessarily a symptom of necrosis of the pulp.