Long-face subjects have smaller maximum molar bite forces than do normal individuals. This has been attributed both to differences in moment arms and size of the jaw muscles.
In this study, a comparison was made between the mid-belly cross-sectional areas of the jaw muscles of 13 long-face and 35 normal adults by means of serial MRI scans. The subjects were selected on the basis of anterior lower face height as a percentage of anterior total face height. These and other cephalometric variables were measured from lateral radiographs.
In the long-face group, the cross-sectional areas of the masseter, medial pterygoid, and anterior temporal muscles were, respectively, 30%, 22%, and 15% smaller than in the control group. By a discriminant analysis and a multivariate analysis of variance, these differences were found to be significant (p < 0.001).
The findings of this study hint that differences in the sizes of the jaw muscles of long-face and normal subjects might explain, in part, the observed differences in maximum molar bite force.
Get full access to this article
View all access options for this article.
References
1.
Björk A. (1969). Prediction of mandibular growth rotation. Am J Orthod55:585-599.
2.
Bolt KJ, Orchardson R. (1986). Relationship between mouth-opening force and facial skeleton dimensions in human females. Arch Oral Biol31:789-793.
3.
Boyd SB, Gonyea WJ, Finn RA, Woodard CE, Bell WH ( 1984). Histochemical study of the masseter muscle in patients with vertical maxillary excess. J Oral Maxillofac Surg42:75-83.
4.
Burke RE (1981). Motor units: anatomy, physiology and functional organization. In: Handbook of physiology, section 1: the nervous system. Vol. 2, Motor systems. Washington (DC): American Physiological Society, chapter 10.
5.
Burke RE, Levine DN, Tsairis P., Zajac FE (1973). Physiological types and histochemical profiles in motor units of the cat gastrocnemius. JPhysiol (Lond)34:723-748.
6.
Close RI (1972). Dynamic properties of mammalian skeletal muscles . Physiol Rev52:129-197.
7.
Fields HW, Proffit WR, Nixon WL, Phillips C., Stanek E. (1984). Facial pattern differences in long-faced children and adults. Am J Orthod85:217-223.
8.
Finn RA ( 1978). Relationship of vertical maxillary dysplasias, bite force, and integrated EMG. In: Abstracts of conference on craniofacial research. Ann Arbor (MI): University of Michigan Center for Human Growth and Development
9.
Finn RA, Throckmorton GS, Gonyea WJ (1980). Neuromuscular aspects of vertical maxillary dysplasias . In: Surgical correction of dentofacial deformities. Philadelphia (PA): W.B. Saunders Co., 1712-1730.
10.
Gazit E., Bornstein N., Lieberman M., Serfaty V., Gross M., Korczyn AD (1987). The stomatognathic system in myotonic dystrophy . Eur J Orthod9 :160-164.
11.
Gionhaku N., Lowe AA( 1989). Relationship between jaw muscle volume and craniofacial form. J Dent Res68:805-809.
12.
Hannam AG, Wood WW ( 1989). Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton and jaw biomechanics. Am J Phys Anthropol80:429-445.
13.
Ingervall B. (1976). Facial morphology and activity of temporal and lip muscles during swallowing and chewing. Angle Orthod46:372-380.
14.
Ingervall B., Bitsanis E. (1987). A pilot study of the effect of masticatory muscle training on facial growth in long-face children. Eur J Orthod9:15-23.
15.
Ingervall B., Thilander B. (1974). Relation between facial morphology and activity of the masticatory muscles. J Oral Rehabil1:131-147.
16.
Koolstra JH, Van Eijden Tgmj, Weijs WA (1988a). Three-dimensional performance of the human masticatory system: the influence of the orientation and physiological cross-section of the masticatory muscles. In: International series on biomechanics 7-A. Amsterdam (The Netherlands) : Free University Press, 101-106.
17.
Koolstra JH, Van EijdenTgmj,Weijs WA, Naeije M. (1988b). A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces. J Biomechan21:563-576.
18.
Kreiborg S., Leth Jensen B., Møller E., Björk A. (1978). Craniofacial growth in a case of congenital muscular dystrophy: a roentgencephalometric and electromyographic investigation. Am J Orthod74:207-215.
19.
Leonard L. (1984). Histochemical characteristics of the masseter and medial pterygoid muscles and craniofacial form (M.Sc. Thesis). Chapel Hill (NC): University of North Carolina, Department of Orthodontics.
20.
Møller E. (1966). The chewing apparatus. Acta Physiol Scand69 (280 Suppl): 1-229.
21.
Nanda SK (1988). Patterns of facial growth in the face. Am J Orthod Dentofac Orthop93:103-116.
22.
Nanda SK (1990). Growth patterns in subjects with long and short faces. Am J Orthod Dentofac Orthop98:247-258.
23.
Norusis MJ (1985). Balancing on beams, multivariate analysis of variance . In: SPSSx, advanced statistics guide. Chicago (IL): McGraw-Hill Book Co., chapter 6.
24.
Proffit W., Fields HW, Nixon WL (1983). Occlusal forces in normal- and long-face adults . J Dent Res62:566-571.
25.
Ringqvist M. (1973a). Isometric bite force and its relation to dimensions of the facial skeleton. Acta Odontol Scand31:35-42.
26.
Ringqvist M. (1973b). Fiber sizes of human masseter muscles in relation to bite force. J Neurol Sci19:297.
27.
Ringqvist M. (1974). Fiber types in human masticatory muscles, relation to function. Scand J Dent Res82:333-355.
28.
Sasaki K., Hannam AG, Wood WW ( 1989). Relationships between the size, position, and angulation of human jaw muscles and unilateral first molar bite force. J Dent Res68:499-503.
29.
Sassouni V. (1969). A classification of skeletal facial types. Am J Orthod55:109-123.
30.
Sassouni V., Nanda S. (1964). Analysis of dentofacial vertical proportions. Am J Orthod50:801-823.
31.
Schantz P., Randall-Fox E., Hutchinson W., Tyden A., Astrand PO (1983). Muscle fibre type distribution, muscle cross-sectional area and maximal voluntary strength in humans. Acta Physiol Scand117:219-226.
32.
Schendel SA, Eisenveld J., Bell WH ( 1976). The long face syndrome: vertical maxillary excess. Am J Orthod70:398-408.
33.
Schudy FF (1964). Vertical growth versus anteroposterior growth as related to function and treatment. Angle Orthod34:75-93.
34.
Shaughnessy T., Fields HW, Westbury J. (1989). Association between craniofacial morphology and fiber-type distributions in human masseter and medial pterygoid muscles. Int J Adult Orthod and Orthog Surg4:145-155.
35.
Subtelny JD, Sakuda M. (1964). Open bite diagnosis and treatment. Am J Orthod50:337-358.
36.
Throckmorton GS (1985). Quantitative calculations of temporomandibular joint reaction forces-II. The importance of the direction of the jaw muscle forces. J Biomechan18:453-461.
37.
Throckmorton GS, Finn RA, Bell WH ( 1980). Biomechanics of differences in lower facial height. Am J Orthod77:410-420.
38.
Throckmorton GS, Throckmorton LS (1985). Quantitative calculations of temporomandibular joint reaction forces-I. The importance of the magnitude of the jaw muscle forces. J Biomechan18:445-452.
39.
Van Eijden Tmgj (1989). Jaw muscle activity in relation to the direction and point of application of bite force. J Dent Res69:901-905.
40.
Van Eijden Tmgj (1991). Three-dimensional analysis of bite-force magnitude and moment. Arch Oral Biol36:535-539.
41.
Van Spronsen PH, Weijs WA, Prahl-Andersen B., Valk J., Van Ginkel F. (1989). Comparison of jaw muscle bite-force cross-sections obtained by means of magnetic resonance imaging and high resolution CT-scanning . J Dent Res68:1765-1770.
42.
Van Spronsen PH, Weijs WA, Prahl-Andersen B., Valk J., Van Ginkel F. (1991). Relationships between jaw muscle cross-sections and craniofacial morphology in normal adults, studied with magnetic resonance imaging. Eur J Orthod13:351-361.
43.
Warner M. (1984). Relationships between dentoskeletal morphology and myofiber characteristics of the human masseter muscle (PhD Dissertation) . Dallas (TX): University of Texas Health Center, Department of Cell Biology.
44.
Weijs WA, Hillen B. (1984a). Relationship between the physiological cross-section of the human jaw muscles and their cross-sectional area in computer tomograms . Acta Anat118:129-138.
45.
Weijs WA, Hillen B. (1984b). Relationship between masticatory muscle cross-section and skull shape. J Dent Res63:1154-1157.
46.
Weijs WA, Hillen B. (1985). Physiological cross-section of the human jaw muscles . Acta Anat121:31-35.
47.
Weijs WA, Hillen B. (1986). Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape. Am J Phys Anthrop70:423-431.
