Clinical Trial of Modified Endocrown and Personalized Post-core and Crown for Large-area Tooth Defects After Root Canal Treatment

Inclusion Criteria: * 1: The affected tooth was a premolar that had undergone complete root canal treatment for two weeks. Both imaging and clinical examinations indicated no abnormal periapical reactions. 2: The oral hygiene condition is good. There is no periodontitis or combined periodontal and endodontic lesions with a probing depth greater than 4mm. There are no severe oral bad habits (such as smoking more than 20 cigarettes per day, chewing betel nuts, etc.) 3: At least 50% of the crown structure should be retained, or at least two crown walls should be retained, and the tooth defect should not be located under the gums or can be aligned with the gums or located above the gums through crown lengthening surgery. 4: The affected tooth has sufficient root length to ensure a pedicle-crown ratio of at least 1:1 and a root tip closure of at least 3 mm. 5: The occlusal function is normal. 6: Treated premolars will not be used as abutments for FPD or RPD restoration. Exclusion Criteria: * 1: Root canal retreatment of the affected tooth. 2: Loosening \> I °, alveolar bone resorption exceeds 1/3 of the root length. 3: Loss of adjacent teeth and occlusal teeth. 4: The patient is in the preconception period and the pregnancy period. 5: Patients with night bruxism, deep overbite, tight occlusion or severe limited mouth opening, and temporomandibular joint diseases. 6: Patients who have a history of chemotherapy or radiotherapy in the head and neck region within 5 years, suffer from severe systemic and organic diseases, have physical disabilities or mental illnesses that affect oral hygiene care, or have received drug treatment that may affect or promote bone metabolism within the past 3 months. 7: The affected tooth has imaging manifestations of absorption inside and outside the root, or the anatomical morphology of the root and root canal is poor, such as short and small roots, curved root canals, small roots or residual roots that cannot meet the cord-to-root ratio standard for pile-core crown restoration. 8: The researchers consider other situations that are not suitable for participation.