Effect of hyperactivity of the lateral pterygoid muscle on the temporomandibular joint disk.
In this study, the effect of hyperactivity of the lateral pterygoid muscle (LPM) on the temporomandibular joint (TMJ) disk during prolonged clenching was examined with a mathematical model. Finite element models of the TMJ were constructed based on magnetic resonance images from two subjects with or without internal derangement of the TMJ. For each model, muscle forces were used as a loading condition for stress analysis for 10 min clenching. Furthermore, an intermittent increase of the LPM force with intervals of 1 min was applied. In the asymptomatic model, large stresses were found in the central and lateral part of the disk at the onset of clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. When the force of the LPM increased temporarily, the disk moved anteriorly and returned to its original position afterward. In the symptomatic model, large stresses were observed in both the posterior region of the disk and the retrodiscal tissue throughout clenching. Upon temporary increase of the LPM force, the disk was elongated anteriorly, which appeared to be irreversible. These results indicate that hyperactivity of the LPM may be involved in the progression of disk displacement.
Tanaka
Eiji
E
Department of Orthodontics and Craniofacial Developmental Biology, Hiroshima University Graduate School of Biomedical Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. etanaka@hiroshima-u.ac.jp
Hirose
Miho
M
Inubushi
Toshihiro
T
Koolstra
Jan Harm
JH
van Eijden
Theo M G J
TM
Suekawa
Yohei
Y
Fujita
Ryuji
R
Tanaka
Masao
M
Tanne
Kazuo
K
D000328:Adult; D001732:Bite Force; D002012:Bruxism / Q000503:physiopathology; D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D004204:Joint Dislocations / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D011626:Pterygoid Muscles / Q000503:physiopathology*; D013314:Stress, Mechanical; D019224:Temporomandibular Joint Disc / Q000293:injuries / Q000503:physiopathology*; D013705:Temporomandibular Joint Disorders / Q000209:etiology / Q000503:physiopathology*; D013997:Time Factors