Three-dimensional loading and growth of the zygomatic arch

Despite a number of previous biomechanical studies on the zygomatic arch, u nanswered questions remain about its three-dimensional loading and growth. Using young miniature swine, we have for the first time recorded strains fr om both the medial and lateral aspects of the squamosal bone during mastica tion and masseter muscle stimulation. Strains from the! zygomatic bone flan ge and zygomatic arch growth data were also obtained from the same animals. A second study on a younger group of animals examined the growth of the zy gomatic flange following partial removal of the masseter. Strain data indicated that the squamosal bone is bent out-of-plane and that this pattern of loading is quite different from that of the adjacent zygom atic bone, which experiences much lower strains with little evidence of out -of-plane bending. Surprisingly, strains were higher in the zygomatic flang e during contralateral chews contralateral masseter stimulations than durin g ipsilateral chews/stimulations. These strains proved to arise from moveme nt of the condyle, explaining why partial removal of the masseter had littl e effect on the growth of the flange. Other growth results indicated an app roximately threefold greater rate of subperiosteal deposition on the latera l surface of the squamosal bone than on the zygomatic bone. This difference in growth rate is attributed to the presence of sutures that contribute to the lateral displacement of the zygomatic bone but not the squamosal bone. This explanation does not exclude the possibility that the rapid appositio n on the lateral squamosal surface is regulated by the high surface strains that result from out-of-plane bending.