The mandible's ongoing development presents a contraindication for combined orthodontic–orthognathic treatment. The aim of this study was to evaluate the mandibular stability before and after preoperative orthodontic treatment in late adolescent patients with skeletal Class III malocclusion and to investigate the most appropriate time to start preoperative orthodontic treatment.

The study population consisted of 58 adolescents, aged between 15 and 21 years, with skeletal Class III malocclusion; the adolescents underwent CT scans at the beginning (T1) and the end (T2) of preoperative orthodontic treatment. The CT data were analyzed using ITK-SNAP and 3D Slicer software, and the effects of age and gender on mandibular development were investigated.

In these 58 patients, there were no significant local bone alterations in the condyle and anterior chin point between T1 and T2 and no significant changes in the mandibular branch height, mandibular body length, condylar distance, and mandibular angle distance (p>0.05). The mandibular growth at the angel of mandible was statistically significant (p<0.05), but it was not clinically significant because the mean value of the growth was small (right: 0.416±0.986 mm, left: 0.328±0.886 mm). No effect of age and gender on mandibular development was observed.

The mandibular morphology was stable during preoperative orthodontic treatment in patients at the late adolescent stage. This study provides evidence for the possibility of early implementation of preoperative orthodontics.