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Determinants of mandibular form during intra-oral food processing

Final Report Summary - MACACA (Determinants of mandibular form during intra-oral food processing)

A lot of attention has been paid to the morphological variations of the craniofacial skeleton and its adaptation to diet, but the study of the mandible and its relation to feeding behaviour lags behind. Whilst a combination of factors, not necessarily mutually exclusive, have been proposed as determinants of variation in mandible morphology (sexual dimorphism, facial orientation, dentition and phylogenetic constraints), most focus has been put on adaptation to mechanical loading during chewing. Chewing is a highly modulated behaviour during which the food particles are processed using the postcanine dentition till the size and texture of the bolus permit a safe swallow.

Previous studies on primates have shown that variations with regards to the material, structural, and physical properties of the processed food particles, coupled with the location of the bite force influence the activation patterns and the force modulation of the muscles of mastication. The electromyographic activity of the muscles of mastication and in particular the peak amplitude and timing affect the jaw kinematics and in particular the variance in the duration of gape cycles, gape-cycle phases and displacement of the lower jaw not only between chewing cycles but also within and between feeding sequences. But what is the effect of jaw kinematics and muscle activity on the skeletal morphology of the mandible?

This study uses an interdisciplinary approach to combine state of the art experimental, computer simulation and analytical techniques to investigate the function of the feeding apparatus during intra-oral food processing. Preliminary results show a high correlation between jaw kinematics, the activation patterns of the muscles of mastication, force modulation and the stress and strain magnitudes and orientations when consuming food particles of varying toughness. This correlation is affected by the bite location, chewing rates and different gapes.

The results of our study offer a better understanding of the functionality of the feeding apparatus during intra-oral food processing and shed light to important biological questions regarding the sensitivity of the feeding variables to the toughness of the food items consumed and the location of the bite, hitherto obscured. The incorporation of our unique experimental data into computer simulations ensured the most precise, complete and validated study on the mechanical determinants of the mandibular morphology in response to diet and will become a landmark reference for future feeding biomechanics studies.

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