Periosteal migration in the growing mandible: an animal model.

Migration of mandibular periosteum and attached musculature was tracked along the inferior border of the ramus in growing and nongrowing guinea pigs (Cavia porcellus) over a 6-week period. Particulate metallic growth-tracing implants were placed through the bony mandible and adjacent musculature at two anteroposterior locations and two bony reference markers were placed anteriorly. Quantification from weekly radiographs of growing animals showed marked posterior migration of the periosteum, whereas in nongrowing animals there was negligible periosteum movement. Significantly greater migration occurred in posterior (6.37 +/- 0.76 mm) implants relative to the anterior implants (3.45 +/- 0.86 mm, p < 0.001). The neutral zone, where little periosteal migration occurs, was calculated to be approximately at the anteroposterior center of the molar tooth row. Analysis of the orientation of the medial pterygoid muscle relative to the mandible showed that muscle fibers on average become more horizontal. Thus, the study found differential anteroposterior migration of the mandibular periosteum in growing animals and correlative changes in orientation of the medial pterygoid muscle.