Effects of transmandibular symphyseal distraction on teeth, bone, and temporomandibular joint

The aim of this clinical study was to investigate the clinical effects and long-term results of the transmandibular symphyseal distraction technique for the correction of mandibular transverse deficiencies. This was achieved by assessing the dental, skeletal, and temporomandibular joint changes in the sagittal, vertical, and axial planes using cephalograms, dental casts, and computed tomography (CT).

Seven patients with mandibular transverse deficiencies (3 females and 4 males), aged 14.3 to 22.5 years (mean 16.2), were treated with a bone-borne transmandibular distractor. Lateral and posteroanterior cephalometric films, CT scans of both temporomandibular joints, and dental casts were obtained preoperatively, at the end of the distraction period, and at the end of 3 years (clinical follow-up period). The clinical findings were assessed according to the morphologic and functional success criteria established by the Steering Group of European Collaboration on Cranial Facial Anomalies for patients with developmental dentofacial anomalies undergoing craniofacial distraction osteogenesis. The statistical analysis of cephalometric films and dental cast measurements was done using the paired t test. The mean postoperative examination period was 40 months (range 36 to 48).

The desired amount of distraction was achieved in all patients (mean 6.48 mm). The intraoperative and postoperative complications encountered included damage to the central incisors during vertical osteotomy (1 patient), wound dehiscence after a latent period (3 patients), mild temporomandibular joint pain during the distraction period (3 patients), and chronic gingivitis around the activation rods (7 patients). The success criteria for craniofacial distraction osteogenesis were fulfilled at the end of the 3-year follow-up period. Model analysis showed that the maximal amount of expansion was achieved at the premolar region (first premolar 5.79 mm, second premolar 5.07 mm). Frontal (posteroanterior) cephalograms taken at the end of the distraction period revealed significant increases in the bicondylar (0.35 mm), bigonion (3.43 mm), biantegonion (2.29 mm), and intermolar (4.0 mm) widths, and the ramal angle had decreased significantly (-1.64 degrees). The increase in the transverse measurements was greater at the dentoalveolar level than at the base of the mandible. Lateral cephalograms showed that transmandibular symphyseal distraction produced significant increases in the incisor mandibular plane angle (2.79 degrees) and mandibular body length (1.72 mm). The effect of the procedure on the condyle was 2.5 degrees to 3 degrees of distolateral rotation as calculated using the CT scans. Dental crowding was resolved rapidly by the movement of the teeth into the distraction regenerate.

The clinical and radiologic results of the present study have shown that a transmandibular distractor is a clinically effective bone-borne distractor for the correction of mandibular transverse deficiencies and anterior crowding. The follow-up cephalograms and CT scans showed the transverse skeletal stability of the distraction procedure and no permanent temporomandibular dysfunction. However, additional multicenter studies with more patients are necessary to precisely evaluate the long-term postdistraction changes on the skeleton, teeth, and temporomandibular joint.