The most common causes of crown discoloration are probably related to tooth necrosis and residual necrotic pulp tissue in the pulp horns after root canal treatment. Haemosiderin pigment from lysed red blood cells diffuse into the dentinal tubules and result in a dark staining of the dentine. Caries and restorations may also cause characteristic discolorations. Other reasons for discoloration include silver or paraformaldehyde-containing filling materials and sealers. Some medicaments taken during tooth development (eg tetracyclines) and other developmental disturbances may also cause discoloration. External stains from drinks (such as tea and coffee) and food may also cause superficial staining of the tooth tissues.