Mandibular Distraction Osteogenesis: Bone Growth and Masticatory Loading

Objective: Mandibular distraction osteogenesis (DO) has become a common treatment for severe mandibular hypoplasia or retrognathia. In addition to the distraction force, mastication may substantially load the DO site and affect the healing process. The purpose of this study is to characterize bone formation and masticatory mechanics at the DO site and assess their relationship. Methods: Eighteen 3-6 month-old miniature pigs that received a right mandibular osteotomy were distracted for 5 days (1mm/day) and consolidated for 0, 1 or 2 weeks. Using chronically implanted ultrasound crystals and differential reluctance variable transducers, interfragmentary micromovement during soft-diet mastication was measured from lateral-superior and lateral-inferior locations during the entire course of DO. Osteogenesis, chondrogenesis and angiogenesis were evaluated using histological and immunohistochemical methods. Results: Mastication moved the distraction site cyclically. The average magnitude increased slightly during the distraction phase to a peak of 0.34±0.16mm and decreased to control levels after 1 week of consolidation. Bone volume, mineral advancement, cartilage matrix and endothelial cell density all increased significantly with consolidation time. The periosteum contributed significantly to osteogenesis measures, and areas with damaged periosteum lagged in their rate of repair. However, angiogenesis markers were not influenced by periosteal damage and appeared to be cortical bone-dependent. Masticatory micromovement generally had no effect, but excessive mobility (>0.3mm) tended to affect osteogenesis negatively. Conclusion: Provided fixation is adequate, soft-diet masticatory loading does not delay healing. However, preservation of the periosteum is important for the early osteogenic response at the mandibular DO site. Supported by PHS award DE 14336.