Background: Mandibular hypoplasia may result from congenital deformities or trauma or infection during the early stage of facial skeleton development. Deficiencies in the growth of the mandible can not only cause various degrees of facial deformity but also affect breathing and occlusal function. Here, we report our experiences with mandibular distraction combined with orthognathic surgical techniques for the treatment of severe adult mandibular hypoplasia.
Methods: Cephalometric analysis was conducted in all patients for quantitative evaluation. A computer-assisted surgical simulation was prepared before distraction. According to the simulation data, an operative osteotomy guide plate was designed and three-dimensionally printed with photosensitive resin. With the help of the guide plate, the osteotomy line was precisely placed. An internal distractor was then placed through an extraoral incision created under general anesthesia. Distraction began after 7 days of latency at the rate of 1 mm/d. After a 6- to 8-month consolidation period, the distractor was removed. At the same time, genioplasty and/or subapical osteotomy was performed to correct the patient's crossbite and improve the facial contour for bilateral mandibular hypoplasia. For unilateral mandibular hypoplasia, a Le Fort I osteotomy was performed to correct the open bite on the affected side, whereas a mandibular outer cortex excision was performed on the unaffected side to improve lower facial symmetry.
Results: The mandible symmetry and chin protrusion were efficiently improved in all 36 patients (mean age, 20.3 y). No facial nerve palsy was reported, nor were there complaints about postoperative facial scarring. The postoperative infection rate was 2.8%. The distance of lengthening was 26.2 (2.8) mm. The increased ramus length on the affected side was 18.9 (9.3) mm. At the end of the consolidation period (T2), the affected mandibular ramus length increased by 46.3% (23.6%) in unilateral distraction osteogenesis; however, it decreased by 18.6% (12.4%) after device removal (T3). For bilateral distraction osteogenesis, condylion-gonion increased by 34.0% (50.0%) in T2 but had no significant change in T3.
Conclusion: Complicated mandibular hypoplasia can be well corrected with mandibular distraction combined with orthognathic surgery.