Evaluation of skeletal relapse after mandibular setback surgery with nm Low Z plasty technique in skeletal Class III patients

Bilateral sagittal split osteotomy (BSSO) was considered an effective mandibular setback surgery to improve prognathic profile in patients with skeletal Class III malocclusion characterized by mandibular prognathism, maxillary deficiency, or some combination of these two features. Novel Modification of Low Z Plasty (NM Low Z) is a BSSO technique introduced in our center since 2016. Purpose: To evaluate skeletal changes after mandibular setback surgery with NM-Low Z. Methods: Three lateral cephalograms were obtained from 38 skeletal Class III malocclusion patients. Films were traced and digitized with Dolphin Imaging software at different stages: presurgical (T0), immediate postsurgical (T1), and six months to one-year postsurgical (T2). Mean skeletal changes were defined in distance between B-point to SN7 perpendicular line in immediate postsurgical change (T1-T0) and postsurgical stability (T2-T1). A reliability test was analyzed with six randomly selected films retraced at two week intervals. Paired t-tests were computed. Results: Mean mandibular setback at B point was 9.78 mm, and mean skeletal relapse at B point was 2.61 mm, representing an 26.69% skeletal relapse rate. Statistical analysis showed significant differences between postsurgical stabilities (p>0.05). Vertical measurement showed significantly decreased in B-SN7 immediately after surgery and in the postsurgical period. Conclusions: Mandible was significant relapsed in forward and upward direction after mandibular setback surgery using NM-low Z plasty tecnique. Lower incisors was retroclined after surgery to compensate the autorotational counterclockwise of mandible. Patient selection, overcorrection and orthodontic mechanics to deal with relapse must all be considered. Clinical significance: With rotational relapse (forward upward movement of the mandible) immediately after surgery, might benefit from decreased facial height in skeletal Class III malocclusion patients and hyperdivergent patterns. However, hypodivergent and normodivergent patients must be treated cautiously. Vertical control of overbite and anterior facial height were considered in the finishing-stage for normal overbite.