Bone strain patterns of the zygomatic complex in response to simulated orthopedic forces

Craniofacial bone strain upon orthopedic loading has rarely been characterized, despite its fundamental importance in our understanding of the anabolic and catabolic effects of orthopedic forces. The present study tested the hypothesis that zygomatic bone strain is modulated upon loading by headgear, a device widely used in craniofacial orthopedics. Ramp forces from 0 to 50 Newtons were applied via headgear attached to the permanent maxillary first molars in four juvenile and five adult human skulls. The average peak bone strain of the juvenile temporal articular eminence was significantly higher than the adult articular eminence (p < 0.05). Contrasting bone strain patterns were identified in the zygomatic arch: tensile in its lateral surface but compressive in its medial surface. The peak bone strain of the temporal articular eminence and the zygomatic arch both depend upon loading direction. Thus, headgear-generated orthopedic forces evoke bending of the zygomatic arch and stresses of the temporal articular eminence in vitro, suggesting the need to verify whether bone strain induces in vivo bone modeling and remodeling.