Comparison of the Stability After Mandibular Setback With Minimal Orthodontics of Class III Patients With Different Facial Types

Abstract

Most studies on the surgery-first approach focused on skeletal relapse compared with conventional surgery. The objective of this study was to compare the stability of skeletal Class III patients with 2 different vertical facial types after mandibular setback surgery (MS) with minimal orthodontic preparation (MO). In this retrospective study, the patients were recruited from a population that had undergone MS. Consecutive patients were selected based on the following inclusion criteria: skeletal Class III malocclusion with mandibular prognathism, MO without extraction for less than 6months, and sagittal split ramus osteotomy. The vertical facial types of the patients were classified based on the Frankfort mandibular-plane angle (FMA). Lateral cephalograms were taken at the presurgical stage, at 1month after surgery (T1), and at the debonding stage (T2). To evaluate surgical changes (T1 - presurgical stage) and relapse (T2 - T1), the linear, angular, and dental measurements were analyzed using a paired t test and an independent t test. The 26 patients were divided into 2 groups: normal-angle group (n= 14; mean FMA, 23.58°) and high-angle (HA) group (n= 12; mean FMA, 30.26°). From T1 to T2, the normal-angle and HA groups showed significant forward and counterclockwise rotation of the mandible (distance between pogonion and perpendicular line to Frankfort horizontal plane from sella, 1.71mm and 1.51mm, respectively; distance between menton and perpendicular line to Frankfort horizontal plane from sella, 1.91mm and 1.60mm, respectively; angle between articulare-menton line and Frankfort horizontal plane, -0.55° and -0.89°, respectively). The HA group showed a significant upward movement of the mandible (distancefrom Frankfort horizontal plane to pogonion, -1.13mm; distance from Frankfort horizontal plane to menton, -0.78mm). However, there was no significant difference in the skeletal-dental changes between the 2 groups from T1 to T2. The vertical facial types of Class III patients with similar prognathic mandible and dental patterns may not cause any differences in the relapse pattern after MS-MO.