Mandibular length and midline asymmetry after experimentally induced temporomandibular joint disk displacement in rabbits

The purpose of the present investigation was to test the hypothesis that pe rmanent disk displacement in the temporomandibular joint (TMJ) is one causa l factor in the development of mandibular midline asymmetry. Unilateral, no nreducing disk displacement was therefore created in growing rabbits, The r ight TMJ in seven experimental animals was surgically opened, and the disk was anteriorly displaced with the posterior disk attachment kept intact abo ve the condyle, The right TMJ in seven sham animals was surgically opened a nd closed without any disk manipulation. Seven additional rabbits served as reference animals, For identification of mandibular growth, tantalum impla nts were inserted into the mandibular body, and lateral cephalograms were e xposed at the beginning and at the end of the experimental period. After th e animals had been sacrificed, the mandibles were dissected and measurement s were performed on the mandibular specimens. Axial radiographs of the mand ibles were then exposed and measurements of mandibular length and midline s hift were performed in the radiographs, The mandible in the experimental an imals was consistently shorter on the disk displacement side resulting in a midline shift to the ipsilateral side, No mandibular asymmetry was observe d in the sham and reference groups. The hypothesis was verified; disk displ acement in the TMJ with an onset during the growth period can cause mandibu lar length and midline asymmetry in growing rabbits.