Tooth nerve necrosis can be judged from oral examination, pulp vitality test, X-ray film, etc.: First, if there are deep cavities, hidden cracks, deep periodontal pockets around the tooth along with loose teeth, obvious knocking pain, red and swollen gum surface forming fistula, etc., and it does not respond to external hot and cold stimulation, it can be judged that the tooth nerve has necrosis; Second, the tooth color is dark yellow or gray-black, and it contrasts with the neighboring teeth above and below, left and right. Third, the X-ray film shows the widening of the periodontal membrane gap and the presence of low-density shadows at the root tip, which combined with the pulp vitality test indicates that the pulp has lost its activity.