Simplified stress analysis on the temporomandibular joint in Class III patients with and without mandibular asymmetry using a rigid body spring model.
OBJECTIVE
Aim of this study was to investigate the differences in stress on the temporomandibular joint (TMJ) between Class III patients with and without mandibular asymmetry using a rigid body spring model (RBSM).


METHODS
Menton (Me), the centre point of occlusal force on the line that connected the bilateral buccal cusps of the second molars and the most lateral, superior and medial points of the condyle were plotted on frontal cephalograms, and stress on the condyles was calculated with the 2-dimensional RBSM program of fortran.


METHODS
Eighty Japanese patients with diagnosed mandibular prognathism were divided into two groups, a symmetry group and asymmetry group on the basis of the Mx-Md midline position.


METHODS
The degree (force partition) of the resultant force, the direction (angulation) and displacement (X, Y) of each condyle were calculated. The horizontal displacement vector (u), the vertical displacement vector (v) and rotation angle (theta) of the mandibular body at Menton were also calculated.


RESULTS
There were significant differences between the deviated and non-deviated sides of both groups regarding resultant force (symmetry group: p = 0.0372, asymmetry group: p = 0.0054), X (symmetry group: p < 0.0001, asymmetry group: p = 0.0001) and Y (symmetry group: p = 0.0354, asymmetry group: p = 0.0043). For angulation, there was a significant difference between the deviated and non-deviated sides in the asymmetry group (p = 0.0095).


CONCLUSIONS
The results of this study suggest that difference in stress angulation on the condyles could be associated with asymmetry in mandibular prognathism.
Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kanazawa University, Kanazawa, Japan. kueki@med.kanazawa-u.ac.jp
K
K
Ueki
N
N
Takeuchi
K
K
Nakagawa
E
E
Yamamoto
D000293:Adolescent; D000328:Adult; D001732:Bite Force; D002508:Cephalometry; D003799:Dental Stress Analysis / Q000379:methods*; D005146:Facial Asymmetry / Q000150:complications*; D005260:Female; D006801:Humans; D008297:Male; D008312:Malocclusion, Angle Class II / Q000150:complications*; D008334:Mandible / Q000002:abnormalities; D008335:Mandibular Condyle / Q000503:physiopathology; D008954:Models, Biological; D003765:Models, Dental; D011378:Prognathism / Q000150:complications; D013314:Stress, Mechanical; D013704:Temporomandibular Joint / Q000503:physiopathology*; D013705:Temporomandibular Joint Disorders / Q000209:etiology*; D055815:Young Adult