If the caries is not treated, it will develop to the deeper part step by step. The caries just discovered is shallow or medium caries, and there is no painful symptom, mainly causing the change of tooth color and texture, but the caries will develop further to form deep caries, and will invade the tooth pulp to form pulpitis, then the patient will have obvious pain, spontaneous pain, night pain, etc. If not treated at this time, the pulpitis will develop further to the periapical area and form periapical inflammation, causing severe biting and jumping pain. If the periapical infection remains untreated, it may form an apical fistula or directly form a jaw bone osteomyelitis, causing infection in the surrounding space, which may further lead to bacteraemia, sepsis and even life-threatening systemic multi-organ infections.