The most serious indications of tooth decay include the following: first, the patient feels pain inside the decayed tooth and has hot and cold pain, spontaneous pain, and lasts longer after entering food; second, the symptom of night pain appears, and the pain radiates to the ear-temporal area or the lateral side of the head with severe pain may appear; third, the color of the tooth with the decayed tooth has become black and dark, and the patient feels that the tooth dares not bite hard and cannot bear the huge chewing force. All these indicate that the tooth has been damaged to a certain extent and should be treated in time, otherwise the tooth may continue to be damaged or need to be extracted.