Long-term (6.5 years) follow-up of mandibular midline distraction.

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To assess the long-term stability and biomechanical effects of mandibular midline distraction (MMD), a prospective observational study was conducted with a retrospective cohort. Included were 17 MMD patients, of whom 9 completed the long-term follow-up with a mean of 6.5 years. In all patients, a bone-borne distractor was used. Dental casts and postero-anterior (PA) cephalograms were taken at fixed time points: pre-operative (T1), directly post-distraction (T2), 1-year post-operative (T3) and long-term follow-up (T4). Inter canine (ICD), inter first premolar (IPMD), inter first molar (IMD) distances and arch length (AL) were measured on dental casts. From the PA cephalograms intercondyle distance (ID) and the ramal angle (RA) were obtained. A significant and sustained widening was observed in most measurements. The greatest overall transverse expansion (T1-T4) occurred in the IPMD (4.1±0.76mm, P<0.05), the ICD, IMD and AL increased, respectively: 2.0±0.72mm, 3.8±0.82mm and 3.5±0.82mm. The ID did not change significant (P>0.05) during all phases of the study. An increase of RA was observed initially; however, no difference was noted in the long-term. This study showed that MMD is a stable method to expand the mandible, with no skeletal effect on the temporomandibular joint.