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Modeling the distance between the molar tooth rows in mammals

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Abstract:

The sum of all possible bite forces along a mammalian tooth row is related to the area under the curve when bite force is plotted from one end of the tooth row to the other. Integrating the equation of this plot and dividing by the length of the entire jaw, from joint to incisor, gives the average bite force along the entire jaw (as opposed to along the tooth row). Calculations indicate that for any jaw shape there is only one location for the tooth row relative to the midline of the skull, where the average bite force is maximized; the average force is lower when the tooth row is closer to, or farther from, the midline. In addition, for animals with long narrow jaws, the location where this maximum is realized is relatively closer to the midline than it is for animals with short wide jaws. In many mammals, the distance between the jaw joints (jaw width) often varies between 60 and 80% of the distance from the jaw joints to the incisor (jaw length) in narrow and wide jaws, respectively. Length is measured perpendicular to the resultant force of the jaw muscles. Accepting that average bite force will be maximized, the model predicts that in the longer, narrower jaws the distance between the two molar rows will be approximately half the width of the jaw (and will approach 60% in the shorter, wider jaws).

La somme de toutes les forces occlusales possibles le long d'une rangée de dents chez un mammifère est en relation avec la surface sous la courbe qui décrit l'évolution de la force occlusale d'un bout à l'autre de la rangée. L'intégration de l'équation de cette courbe et sa division par la longueur totale de la mâchoire depuis l'articulation à l'incisive donne la force occlusale moyenne le long de la mâchoire entière (et non seulement le long de la rangée de dents). Pour toute forme de mâchoire, on peut calculer qu'il n'existe qu'une seule position pour la rangée de dents relative à l'axe médian du crâne qui maximise la force occlusale moyenne; cette force moyenne diminue lorsque la rangée de dents se rapproche ou s'éloigne de l'axe médian. De plus, chez les animaux à mâchoires longues et étroites, la position où la force est maximale est relativement plus près de l'axe médian que chez les animaux à mâchoires courtes et larges. Chez plusieurs mammifères, la distance entre les articulations de la mâchoire (largeur de la mâchoire) varie souvent, des mâchoires étroites aux mâchoires larges, de 60 à 80 % de la distance de l'articulation à l'incisive (longueur de la mâchoire), lorsque la longueur est mesurée perpendiculairement à la force résultant de l'action des muscles de la mâchoire. Si la force moyenne doit être maximisée, le modèle prédit que, dans les mâchoires plus longues et plus étroites, la distance entre les deux rangées de molaires sera en moyenne à peu près la moitié de la largeur de la mâchoire; elle s'approchera de 60 % dans le cas de mâchoires plus courtes et plus larges.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2002

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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