Digital technique-assisted repair of the secondary mandibular angle deformity after mandibular osteotomy

Objective To repair the secondary mandibular angle caused by madibular osteotomy by using digital technology and to make quantitative comparative evaluation. Methods Thirty-nine patients with secondary mandibular angle with unsmooth mandibular margin or bilateral asymmetry after mandibular osteotomy in Southern Theater General Hospital from 1996 to 2017 were included. The three-dimensional model of skull was established by CT skull scan and Mimics 13.0 software. The computer aided design was used to carry out the secondary surgical repair according to the design line, and the mandibular angle was quantitatively measured and evaluated before and after the revision operation. The mandibular angles before, after design and after restoration were measured on the reconstructed images, and the bilateral symmetry and the consistency between the design result and the final result were compared by Paired-t sample test. P< 0.05 indicates statistical difference. Results All the 39 patients completed the operation successfully, and 1 case developed hematoma 15 days after operation, which was drained and bandaged by oral dressing. Two weeks after operation, the hematoma was resolved. No infection, nerve injury and accidental fracture of mental process were found in all patients. During the 6-month follow-up, the mandibular angle of 39 patients improved from 118.12°±18.08° on the left side and 114.60°±16.01° on the right side to 121.28°±6.96° on the left side and 121.32°±5.88° on the right side. There was significant difference between the left and right sides before operation (t=1.744, P=0.045), but there was no significant difference between the two sides about 6 months after operation(t=-0.074, P=0.529). The angle of mandibular angle after design was compared with the actual outcomes of patients 6 months after operation and there was no significant difference(t=-0.527, P=0.601). All the patients were satisfied with the improvement of the secondary mandibular angle and facial shape. Conclusions The application of digital technique to repair the secondary mandibular angle after mandibular osteotomy not only avoids the injury of inferior alveolar neurovascular bundle and mental nerve, but also effectively improves the facial shape of the patients. Key words: Mandibular angle osteotomy; Digital design; Restorative surgery; Quantitative judgement