There are several reasons for tooth splitting after root canal treatment: I. Root canal treatment removes the original nerve, blood vessel and lymph of the tooth, and the tooth loses the nutrient supply, resulting in increased brittleness. Second, the cavity is too big, the residual tooth tissue is too little, and the resistance of the tooth is weak. In the process of root canal treatment, the pulp top and root canal preparation will remove a large amount of healthy tooth tissue, resulting in the weakening of tooth resistance. Fourth, the filling is too tight when the root canal is filled, resulting in excessive internal stress. Fifth, the occlusal high point exists when filling the occlusal surface, leading to stress concentration. Therefore, to avoid tooth fracture, patients are routinely advised to undergo crown restoration after root canal treatment.