This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by van Spronsen, P.H. Articles by Prahl-Andersen, B. Search for Related Content PubMed PubMed Citation Articles by van Spronsen, P.H. Articles by Prahl-Andersen, B. Social Bookmarking                         What's this?

Jaw Muscle Orientation and Moment Arms of Long-face and Normal Adults

Department of Orthodontics, Academic Center for Dentistry Amsterdam (ACTA)

W.A. Weijs

Department of Functional Anatomy, ACTA, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands

EC van Ginkel

Department of Orthodontics, Academic Center for Dentistry Amsterdam (ACTA)

B. Prahl-Andersen

Department of Orthodontics, Academic Center for Dentistry Amsterdam (ACTA)

Long-face subjects have strongly reduced bite forces relative to normal subjects. This difference cannot be fully explained by the reduced cross-sectional area of the jaw muscles. In this study, we investigated whether the orientation and moment arms of the jaw muscles of normal and long-face subjects are different, and if so, to what extent these differences contribute to the observed differences in maximum molar bite-force levels. Three MRI scan series with different orientations were made of the jaw muscles of 30 normal and 13 long-face subjects. These served as the basis for computer reconstructions of the external shape of the muscles. The spatial orientation of the jaw muscles was defined by the regression line through the centroids of the muscular cross-sections. The moment arms of the jaw muscles and the bite point of the first mandibular molar were measured with respect to the center of the ipsilateral condyle. The muscular variables-including angles, moment arms, and mechanical advantage-were analyzed with a discriminant analysis and a multivariate analysis of variance (MANOVA). Differences in the spatial orientation of the temporalis muscle and the anterior digastric muscle contributed most to the distinction of the normal and long-face group. With MANOVA, it was shown that the normal and long-face group did not significantly differ with respect to the jaw muscle moment arms and mechanical advantage data. Only small differences were found between the sagittal muscle angles of the masseter and anterior digastric muscles in the two groups. In both the normal and long-face group, the orientation and moment arm data of the right and left muscles differed significantly. It was concluded that the variation of the spatial orientation of the jaw muscles is small and does not significantly contribute to the explanation of the different molar bite-force levels of long-face and normal subjects. Therefore, it is tempting to assume that the jaw muscles of normal and long-face subjects are different with respect to the maximum force they can exert per unit of cross-sectional area.

Key Words: jaw muscle orientation • vertical craniofacial morphology • MRI

Journal of Dental Research, Vol. 75, No. 6, 1372-1380 (1996)
DOI: 10.1177/00220345960750060801


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				L. J. Pereira, M. B. D. Gaviao, L. R. Bonjardim, P. M. Castelo, and A. van der Bilt Muscle thickness, bite force, and craniofacial dimensions in adolescents with signs and symptoms of temporomandibular dysfunction Eur J Orthod, February 1, 2007; 29(1): 72 - 78. [Abstract] [Full Text] [PDF]

				R. Gonzalez, I. Montoya, and J. Carcel Review: the Use of Electromyography on Food Texture Assessment Food Science and Technology International, December 1, 2001; 7(6): 461 - 471. [Abstract] [PDF]

				M.C. Raadsheer, T.M.G.J. van Eijden, F.C. van Ginkel, and B. Prahl-Andersen Contribution of Jaw Muscle Size and Craniofacial Morphology to Human Bite Force Magnitude Journal of Dental Research, January 1, 1999; 78(1): 31 - 42. [Abstract] [PDF]