Strain pattern in the upper facial skeleton: Preliminary model development

Abstract

In the human upper facial skeleton, the patterns of strain caused by physiological loading are not known. It is generally accepted that these patterns can be predicted based on the morphology of the bone, but this is not necessarily the case. The elucidation of these patterns of strain has a significant impact on the plating techniques of facial fractures, the development of bone substitutes and tissue-engineered bone, and the understanding of facial development. The goal of this study was to initiate the development of a model that could be used to measure strain magnitude and direction in the upper facial skeleton from physiological loading of facial musculature. A strain gauge was bonded to the lateral orbital rim of a cadaveric skull that had been dissected, leaving only muscular origins and insertions intact. Braided nylon straps were sutured to the origins and insertions of the masseter and levator labii superioris, and these were pulled individually using a hydraulic testing machine. When the masseter origin was pulled, the recorded strain increased with increasing force and the angle of the strain corresponded directly to the angle of pull. When the levator labii superioris origin was pulled, the angle of strain was directed anteriorly and inferiorly, but did not correspond with the axis of the muscle or the axis of the lateral orbital rim where the strain gauge was located. It was concluded that this model is reliable and reproducible for investigating strain magnitude and direction in the human upper facial skeleton.