Biomechanics of the mammalian masticatory apparatus: Moment arms estimation based on 3d landmarks

CASSINI, GUILLERMO HERNÁN; TOLEDO, NESTOR; BARGO, MARÍA SUSANA; VIZCAÍNO, SERGIO FABIÁN

Punta del Este -Uruguay

Congreso; 9th International Congress of Vertebrate Morphology; 2010

Universidad de La República - International Society of Vetebrate Morphologyst

The application of biomechanics to the study of fossil mammals is a good approach to test functional hypothesis. Jaws act as a lever system, with the pivot at the craneomandibular joint, with masticatory muscles providing the input force, whereas the output force is produced by the teeth on food. The moment arms of the lines of action of the muscles can be estimated to analyze relationships between bite force and velocity.  A morphogeometric approach was applied to estimate muscles moment arms in a static bite model. 3D landmarks and semi landmarks of occluded skulls and mandibles of carnivorous, omnivorous and herbivorous living mammals were collected on temporal and masseteric muscles scars, as well as on bite points along incisors and check teeth, using a G2 Microscribe. Two methods are proposed and compared. First, the distance between the centroid of the 3D surface area of each muscle and the pivot was used as estimator of average moment arm for that muscle, instead than the line linking the centroids of the origin and insertion scars. The second consist on a 3D geometric model to calculate averages of the moment arms at the most anterior, middle and posterior origin and insertion of the muscles. Average moment arms obtained with both methods are close similar, herbivores showing higher values of masseteric and lower of temporal moment arms than carnivores. Although further discrimination within herbivores remains to be clarified, the approach proposed here seems to be useful to compare masticatory performance between fossil taxa.