Jaw muscle size and bite force magnitude in relation to craniofacial morphology

In this thesis it is shown for the first time that jaw muscle size and craniofacial morphology are already significantly related during growth. This supports the assumption that the tensile forces of the muscles of mastication are a growth regulating factor in craniofacial morphogenesis. In the literature, the maximal bite force level, the size of the jaw muscles (expressed as the thickness, the cross-sectional area or the volume) and the EMG-level are often used as indications of the maximal possible muscle force. They are found to be significantly related to craniofacial morphology. These findings are confirmed by the results presented in this thesis. New is the conclusion that variation of the maximal possible bite force level mainly depends on the size of the masseter muscle. Another new finding is that the total amount of jaw muscle tissue, indicative for the maximal possible force that the jaw muscles can exert, is dependent on general, e.g., hormonal and metabolic, influences. However, the mechanical loading of the craniofacial complex is not only dependent on the size of the jaw muscles, but also on 1) their spatial orientation relative to the craniofacial skeleton, 2) their intrinsic properties, such as internal muscle architecture, fiber type composition and vascularisation, and 3) neuromuscular activation and feedback. In order to get a better understanding of masticatory muscle function and its interaction with craniofacial morphology, further investigations are needed in which as much different influences as possible are considered in one study.