Hemi-Mandibular Elongation: Is the Corrected Occlusion Maintained Long-Term? Does the Mandible Continue to Grow?

Publication date: Available online 24 August 2016
Source:Journal of Oral and Maxillofacial Surgery
Author(s): Jeffrey C. Posnick, Jorge Perez, Anish Chavda
PurposeThe purpose of this study was to assess for the maintenance of a corrected occlusion and ongoing mandibular growth in a group of patients less than 26 years of age with hemi-mandibular elongation (HME) who underwent bimaxillary orthognathic reconstruction.Materials and MethodsThe authors conducted a retrospective cohort study of HME subjects operated on by a single surgeon at one institution between 1999 and 2013. At a minimum, all subjects underwent LeFort I and bilateral sagittal ramus osteotomies. Study exclusions included subjects ≥ 26 years of age; those with clefting, craniofacial disorders, or tumors; and/or those with a history of previous TMJ or orthognathic surgery. Study variables included: age; sex; side of condylar hyperactivity; premolar extractions; extent of mandibular deformity and malocclusion; planned surgical change; and longitudinal follow-up. The outcome variables studied were the achievement and maintenance of a corrected occlusion and the occurrence of continued mandibular growth after surgery. We compared the occlusion at intervals including: prior to surgery (T1); 5 weeks post-op (T2); and either at 6 – 24 months after surgery (T3); or at >2 years after surgery (T4). Anterior occlusion assessment included evaluation of: overjet; overbite; and dental midline position. Posterior occlusion assessment included: Angle classification; first molar vertical position; and first molar transverse position. If the corrected anterior occlusion remained stable and no posterior open bite occurred, then no clinically significant condylar hyperactivity and/or ongoing mandibular growth was judged to have occurred.ResultsSeventy-six consecutive subjects met the inclusion criteria. Age at operation averaged 18 years (range 14.5 to 25) and the study included 44 females (58%). T3 subjects (10/76, 13%) had documentation of occlusion at a mean of 19 months after surgery. T4 subjects (66/76, 87%) had documentation of occlusion at a mean of 5 years and 8 months after surgery. Only 1 of the 76 study subjects (1%) was judged to have clinically significant ongoing mandibular growth after reconstruction. For all other subjects, a corrected anterior occlusion was maintained long-term and none developed a posterior open bite. In 7 of the 76 subjects (9%) there was a recurrent posterior crossbite by 1 year after completion of orthodontics but without need for re-treatment. An association was confirmed between mandibular setback and long-term posterior malocclusion even with simultaneous maxillary advancement (p=0.05).ConclusionsIn HME, a favorable occlusion can be reliably achieved and maintained long-term in most cases using standard bimaxillary orthognathic technique. The need for mandibular setback, even in the presence of simultaneous maxillary advancement, proved to be a factor in the recurrence of long-term posterior malocclusion, although the risk remains low. The results clarify that in patients with HME, using techniques and timing for surgery described, there is no need for an ablative open joint procedure to arrest condylar growth.



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