Abstract: Objective: This paper aims to report a case of integrated digital precision treatment of crown and root in low second molar with taurodontism and C-shaped root canal system. Diagnosis and treatment: After 3D reconstruction of root canal system and assessment of periapical lesions by dental Cone-beam Computed Tomography(CBCT), the definitive diagnosis was achieved. Obtaining the informed consent of the patient, micro-root canal retreatment and chairside computer aided design/computer aided manufacture(CAD/CAM) technique were performed. Results: After one-year follow-up, the patient had no symptoms. CBCT showed that the low second molar root obturation was filled in three dimensions, and the bone density in the apical area increased. Conclusions: Taurodontism of mandibular second molar with C-shaped root canal is rare and difficult to treat. In this case, the root canal system and periapical lesion were analyzed by preoperative CBCT 3D reconstruction. During the operation, dental microscope was used for step-by-step magnification and excellent lighting function to achieve accurate positioning of the root canal opening and visual operation. After retreatment, CAD/CAM technique realized the concept of crown and root integration, which combined the crown design with the characteristics of the root canal system, and finally achieved long-term stable clinical treatment effect.

Key words: c-shaped root canal system, taurodontism, periapical lesion, crown and root integration, computer aided design/computer aided manufacture (CAD/CAM) technique