Sheller, BarbaraKim, Youkyung2026-04-202026-04-202026-04-202026Kim_washington_0250O_29304.pdfhttps://hdl.handle.net/1773/55480Thesis (Master's)--University of Washington, 2026Background: Maxillary hypoplasia, common in patients with cleft lip and palate, presents significant functional and esthetic challenges, including Class III malocclusion, negative overjet, and midface retrusion. While conventional Le Fort I osteotomy is effective for skeletally mature patients, growing patients are not eligible. Maxillary distraction osteogenesis using a rigid external distractor (MXDO-RED) is a surgical treatment for correcting severe maxillary hypoplasia and can be performed in growing individuals. Long-term data on stability following MXDO-RED, however, is limited by small sample sizes and short follow-up durations. Objective: This retrospective study evaluated the long-term skeletal stability of MXDO-RED in patients with severe maxillary deficiency associated with cleft lip and palate. Additionally, the study aimed to assess the association between maxillary stability following MXDO-RED and factors including age at distraction, magnitude of advancement, mandibular growth, and mandibular plane angle. Methods: A retrospective analysis was conducted on 60 subjects with severe cleft maxillary hypoplasia who underwent Le Fort I level MXDO-RED at a craniofacial center from 2008 to 2023. Records, including lateral cephalograms, extraoral and intraoral photos, and dental models, were analyzed at four time points: pre-operative (T0), immediate post-operative (T1), first follow-up (T2), and longest available follow-up (T3). Outcomes were categorized into short-term (total follow-up duration of 0.5 to 3 years post T1) and long-term (total follow-up duration of greater than 3 to 6.5 years post T1) post distraction follow-up groups. Generalized estimating equations (GEE) linear regression was used to evaluate longitudinal stability and the association between stability and secondary factors. Results: Significant improvements in maxillary retrusion, facial profile, upper lip position, overjet, and crossbite were observed following MXDO-RED. The mean age at the time of distraction was 14.9 + 1.7 years. The mean sagittal advancement at A-point was 12.7 + 5.6 mm. Significant sagittal relapse was observed in both the short-term group (−3.5 + 5.2 mm; 27.8% of advancement; p < .001) and the long-term group (−5.5 + 6.0 mm; 42.6%; p < .001). Longitudinal regression confirmed a significant posterior relapse of −0.9 mm per year over the follow-up period for both groups (95% CI: -1.6 to -0.2; p = .011). No significant vertical changes were observed (p = .850). The magnitude of initial advancement was the strongest factor associated with maxillary sagittal relapse. Each additional millimeter of sagittal advancement was associated with 0.42 mm of subsequent horizontal relapse (95% CI: -0.62 to -0.23; p < .001) and 0.88 mm of vertical relapse (95% CI: -1.03 to -0.74; p < .001). Mandibular body growth (Gonion–Menton) was significantly associated with both sagittal (p = .005) and vertical (p = .041) maxillary displacement after adjusting for follow-up duration. Age at distraction and mandibular plane angle were not significantly associated with relapse. Upper lip position demonstrated significant progressive retrusion over the follow-up period (p = .011). Of the 57 subjects for whom status of further orthognathic surgery could be determined, secondary orthognathic surgery was completed or planned for 50.9%, and 49.1% of subjects did not require further surgery. Conclusion: MXDO-RED achieves substantial correction of severe maxillary hypoplasia in growing patients with cleft lip and palate with significant improvements in facial profile and occlusion. Sagittal relapse approaching half of the initial advancement in the long term presents a clinical challenge. The strong association between magnitude of advancement and mandibular body growth and maxillary displacement underscores the multifactorial nature of post-distraction instability. The finding that half of subjects required secondary orthognathic surgery reinforces the importance of follow-up through skeletal maturity and preoperative counseling that MXDO-RED in growing patients may represent a single stage of a multi-stage treatment course.application/pdfen-USnoneCleftDistractionHypoplasiaMaxillaryOsteogenesisDentistrySurgeryDentistryThesis