The reason why the tooth has turned black may be due to the fact that the nerve has become necrotic and the crown of the dead pulp tooth will gradually turn black after a long time. It is treated by firstly doing root canal treatment to completely remove the infected and inactive nerve, followed by disinfection and molding of the root canal system, and then filling the root canal tightly with dental cement to eliminate reinfection. Metal porcelain crowns and all-porcelain crowns are recommended to restore the defect and improve the color of the tooth. If the defect in the crown itself is large, it is recommended to use fiber pile resin core restoration followed by encapsulation of porcelain and all-porcelain crowns for restoration. Another reason for the darkening of teeth is due to pigmentation on the tooth surface, it occurs mostly in people who have the habit of smoking, drinking tea and coffee, and the symptoms are most obvious in the lower front teeth. The treatment for this condition is ultrasonic cleaning and tooth polishing, using ultrasonic high-frequency vibration to remove the pigment on the teeth, and then polishing the teeth to achieve a high degree of polish, to avoid the re-deposition of pigment.