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 permanent disk displacement in the temporomandibular joint (TMJ) is one causal factor in the development of mandibular midline asymmetry. Unilateral, nonreducing disk displacement was therefore created in growing rabbits. The right TMJ in seven experimental animals was surgically opened, and the disk was anteriorly displaced with the posterior disk attachment kept intact above the condyle. The right TMJ in seven sham animals was surgically opened and closed without any disk manipulation. Seven additional rabbits served as reference animals. For identification of mandibular growth, tantalum implants were inserted into the mandibular body, and lateral cephalograms were exposed at the beginning and at the end of the experimental period. After the animals had been sacrificed, the mandibles were dissected and measurements were performed on the mandibular specimens. Axial radiographs of the mandibles were then exposed and measurements of mandibular length and midline shift were performed in the radiographs. The mandible in the experimental animals was consistently shorter on the disk displacement side resulting in a midline shift to the ipsilateral side. No mandibular asymmetry was observed in the sham and reference groups. The hypothesis was verified; disk displacement in the TMJ with an onset during the growth period can cause mandibular length and midline asymmetry in growing rabbits.