Distraction Osteogenesis (DO) uses controlled fracture (osteotomy) and tensional force to induce bone growth. However, the enormously complex strains experienced by the mandible during mastication interfere with the distractor's control of the mechanical environment. Objective: This acute study is designed to characterize the chewing patterns, strain orientations, and strain magnitudes of the condyles after unilateral osteotomy and installation of a distractor appliance. Methods: Under anesthesia, rosette strain gages were bonded directly to the condylar necks of 12, young farm pigs, Sus scrofa. A right side mandibular osteotomy was stabilized with a (Synthes™) distractor appliance. Electrical activity was recorded from bilateral masseter and temporalis muscles. After administering analgesics, the pigs awoke and were fed. Condylar strain and muscle activity were recorded. Strain data were compared to data from intact control pigs. Chewing pattern was compared to a pre-surgical feeding session on the same pig. Results: Chewing pattern alternated between left and right before surgery but was predominantly left after the osteotomy (44% vs. 75%, p=0.015). Condylar compressive strain was increased on the left side (-456 µstrains vs. -223 µstrains, p=0.001), but decreased (-130 µstrains, p=0.05) and reoriented about 60° more posteriorly on the right side (p=0.01). Conclusions: Two factors may explain these results, increased compliance of the osteotomy and partial reflection of the right masseter during surgery. Loss of the right side masseter causes the chewing pattern to shift left. The intact but more horizontally positioned right temporalis would tend to tilt the proximal fragment of the mandible backward, re-orienting condylar strain. Elevated left condylar strain is likely due to increased activity of the left masseter compensating for the injured right-side muscles. This research was supported by PHS grants ROI DE14336, P60 DE 13061 and R25 GMO624628.

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