If the depth of tooth decay has reached the pulp cavity, that is, it is connected to the pulp and there is already a pulp perforation, it often causes local reversible pulpitis. Clinically, we can judge whether the tooth decay has injured the pulp according to the following symptoms and examination: 1.If the patient shows that the tooth is very painful when eating hot or cold food, and even when not eating food, the tooth produces severe pain, even night pain, this situation often indicates that the decay has injured the pulp; 2.Sometimes a larger decay can be seen, and the tooth nerve is completely exposed in the mouth, take a probe to probe slightly, the patient will feel special pain, and even the pulp will bleed. The patient will feel special pain and even the pulp will bleed, which definitely has injured the pulp at this time; 3, with the X-ray film for judgment, when the tooth decay has injured the nerve, it is obvious that the scope of tooth decay has spread to the pulp cavity. If it has developed into periapical inflammation, it will form an obvious shadow in the apical part of the tooth. Once the cavity is diagnosed to reach the pulp, root canal treatment must be performed. However, it is important to note that the patient should avoid biting on the affected tooth during the root canal treatment. This is because the affected tooth has a large crown defect and cannot withstand large occlusal forces, which may lead to tooth extraction if the bite splits. If the amount of tooth remaining after root canal treatment is small, it is recommended to make a crown to restore the missing tooth tissue so that the tooth will not be split and extracted due to excessive biting force.