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We identified masseter muscle fiber type property differences in subjects with dentofacial deformities.

Samples of masseter muscle were collected from 139 young adults during mandibular osteotomy procedures to assess mean fiber areas and percent tissue occupancies for the 4 fiber types that comprise the muscle. Subjects were classified into 1 of 6 malocclusion groups based on the presence of a skeletal Class II or III sagittal dimension malocclusion and either a skeletal open, deep, or normal bite vertical dimension malocclusion. In a subpopulation, relative quantities of the muscle growth factors IGF-I and GDF-8 gene expression were quantified by real-time polymerase chain reaction.

Fiber properties were not different in the sagittal malocclusion groups, but were very different in the vertical malocclusion groups (P ≤ .0004). There were significant mean fiber …