The mechanical advantage of the masseter muscle in subjects with different vertical and sagittal facial morphology.
OBJECTIVE
To study the relationships between the mechanical advantage of masseter muscle (the ratio between the muscular and the bite force moment arms) and two parameters describing vertical and sagittal facial morphology.


METHODS
Retrospective analysis of pre-treatment lateral cephalometric radiographs.


METHODS
The Laboratory of Functional Anatomy of the Stomatognathic Apparatus at Milan University, Italy. Four hundred and sixty-eight orthodontic patients (209 males, 259 females) aged between 6 and 50 years.


METHODS
Mechanical advantage of masseter muscle, posterior-to-anterior facial height ratio, corrected ANB* angle were measured in all cephalograms.


RESULTS
Masseter muscle mechanical advantage was, on average, 79.5% (SD 6.1), ranging between 53 and 94%. No sex-related characteristics were found. A moderate effect of age was found (r = 0.19), with a certain increment in the mean mechanical advantage in adults. No relationship with the corrected ANB* angle was found (r = 0.099), while a significant effect of the posterior-to-anterior facial height ratio was detected (r = 0.542).


CONCLUSIONS
The lack of correlation between the mechanical advantage of masseter muscle and corrected ANB* angle might be explained by: (1) when the occlusal point moves depending upon Angle skeletal classification, the ramus width might also modify, and both arms change; (2) the present assessment analysed only the lateral two-dimensional projection of a three-dimensional structure: the retroposition of occlusal point involves also a modification of line slope, and a subsequent reduction of its projection and arm.
Ferrario
V F
VF
Functional Anatomy Research Center (FARC), Laboratorio di Anatomia Funzionale, Facoltà di Medicina e Chirurgia, Università degli Studi di Milano, Italy. farc@imiucca.csi.unimi.it
Sforza
C
C
Sartori
M
M
Ciusa
V
V
D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D001732:Bite Force; D002508:Cephalometry; D002648:Child; D005147:Facial Bones / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008310:Malocclusion / Q000473:pathology; D008406:Masseter Muscle / Q000502:physiology*; D008445:Maxillofacial Development; D008875:Middle Aged; D012189:Retrospective Studies; D014716:Vertical Dimension