Hard and Soft Tissue Growth Comparison Following Mandibular Distraction Osteogenesis

Objectives:  Patients with hemifacial microsomia (HFM) have been treated with distraction osteogenesis (DO) in an effort to achieve a more symmetrical facial balance. Recent studies show that hard tissue (HT) gains are aided by a concurrent soft tissue (ST) expansion following DO. Despite the proven favorable short-term prognosis of this treatment modality, there are few studies following the long-term HT and ST changes. The purpose of this investigation was to perform a comparative analysis of HT and ST growth in the post-distraction craniofacial skeleton of HFM patients over an 8 year period.

Methods: Three patients with HFM treated with DO were recalled seven times (T1-T7) over eight years at different time intervals. HT changes in ramus height (HT-RH) and transverse occlusal plane angle (HT-OP) were recorded using posterioranterior cephalograms. This data was then compared to ST measurements involving the linear distance of contralateral lip commissures to orbital plane (ST-OP) and transverse labial plane angle (ST-LP), respectively, using frontal photographs. Ratios of linear measurements were calculated to avoid magnification error. Statistical analysis (a=0.05) was performed for descriptive purposes.

Results: A minimal correlation existed between HT and ST growth in consecutive time intervals (r=-0.2-+0.1). However, there was a clinical disparity between long-term changes in HT and ST. In comparison to T1, HT measurements at T7 exhibited worsening of asymmetry (T7-T1 HT-RH=-0.02, HT-OP=-1.20°). On the other hand, the corresponding ST measurements showed a clinical improvement at T7 (T7-T1 ST-OP=0.01, ST-LP=2.18°).

Conclusion: The congenital unpredictability of growth accounts for the skeletal imbalance persisting 8 years with gradual worsening one year following DO. However, greater ST improvement compensates for this HT problem to conceal the underlying asymmetry. This study provides a better understanding of the long-term mechanics of HT and ST growth permitting improved treatment planning with better functional and esthetic results.