The control of condylar growth: an experimental evaluation of the role of the lateral pterygoid muscle.
The present study used 21 male albino rats to test the hypothesis that lateral pterygoid traction regulates the growth of the mandibular condyle. The condyles, the rami, and the top of each glenoid fossa were marked with metallic implants, and, following bilateral section of the condylar neck, one lateral pterygoid muscle was extirpated. On the basis of the literal details of Petrovic's cybernetic model, it was assumed that the continued forward growth of the midface and the backward translation of the glenoid fossa would combine to produce a progressive disturbance in the buccal occlusion that would, in turn, generate a reflex contraction of the remaining lateral pterygoid muscle. Initially, however, growth of the isolated condyles would have little impact on the spatial position of the rest of the mandible. As a result, the condyles on the side with the intact lateral pterygoid should grow for a time at a maximal, open-circuit rate, whereas the experimental condyle, deprived of all muscle traction, should show only a minimal "commanded" rate of growth. The serial change in the position of the condylar and ramal implants was assessed cephalometrically for 6 weeks, and between-sides differences were analyzed by randomized block analysis of variance. The presence or absence of the lateral pterygoid muscle had no significant effect on the anteroposterior position of the condylar implants and only a slight, transitory effect on their vertical position. The translation of the ramal implants, however, was greatly affected by the condylotomy. On both control and experimental sides, the mandible collapsed upward and backward until contact between the growing condyle and ramus had been achieved, whereupon a downward and forward pattern of translatory growth was re-established. Although it could not be shown that lateral pterygoid traction per se is a significant factor in the growth of isolated condyles, it was concluded that the condyle is vitally important to the translatory growth of the mandible as a whole. On the basis of these data and the current literature, a simple hypothesis was advanced for the control of condylar growth by the ongoing pattern of functional loading and for the role of this growth in the normal downward and forward displacement of the rest of the mandible.
D000818:Animals; D002508:Cephalometry; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000254:growth & development; D008335:Mandibular Condyle / Q000033:anatomy & histology / Q000254:growth & development* / Q000601:surgery; D008410:Masticatory Muscles / Q000502:physiology*; D019736:Prostheses and Implants; D011626:Pterygoid Muscles / Q000502:physiology* / Q000601:surgery; D051381:Rats; D011919:Rats, Inbred Strains; D012399:Rotation; D013314:Stress, Mechanical; D013704:Temporomandibular Joint / Q000033:anatomy & histology / Q000601:surgery