Evaluation of skeletal and surgical factors related to relapse of mandibular setback surgery using the bioabsorbable plate

Background: This study was to evaluate the stability of the bioabsorbable plate used in the orthognathic surgery for patients with prognathic mandibles and to evaluate the relapse tendency after surgery and the factors affecting the relapse. Materials and methods: The sample consisted of 30 subjects (14 males and 16 females) who underwent bilateral sagittal split ramus osteotomy (BSSRO) for mandibular setback using the poly-L/DL-lactide plate system (Biosorb FX (R), Linvatec Biornaterials Ltd., Tampere, Finland). The lateral cephalometric radiographs of each subject were taken pre-operatively within I month (TO), post-operatively within I month (T 1), and post-operatively between 4 and 10 months (T2) and skeletal changes were analyzed with V-Ceph (CyberMed (R), Seoul, Korea) software. The changes between T1 and T2 were evaluated with a paired t-test to estimate the stability of the surgery. The post-operative changes of mandibular body length and ramus height were used for a K-means clustering analysis to separate subjects into either the less changed (1,C), or the more changed (MC) group. The two groups were compared with TO and the surgical changes (T1 - T0) using the t-test. Results: Significant relapse after surgery was shown in vertical measurements but not in the horizontal plane measurements. The MC group showed significantly more vertical operative changes than the LC group independent of horizontal measurements. Conclusions: Usage of a bioabsorbable plate in mandibular setback surgery could provide stable fixation in the horizontal dimension, but also may allow an increase of vertical relapse due to the increase in vertical dimension post-operatively. Cc) 2008 European Association for Cranio-Maxillofacial Surgery