An evaluation of mandibular asymmetry in adults with unilateral posterior crossbite.

A retrospective study was conducted to determine whether mandibular symmetry in adults with untreated unilateral posterior crossbite was different from that found in adults with untreated Class I malocclusions. Thirty adults, 18 years or older, with a unilateral posterior crossbite were compared with 30 adults exhibiting Angle Class I malocclusions. Skeletal and dental symmetry were assessed with submentovertex (SMV) radiographs, whereas condylar position within the glenoid fossa was analyzed with horizontally corrected tomograms. Relative to a mandibular coordinate system, the mandibular first molar on the crossbite side was found to be more lateral and relatively distal in comparison to the contralateral side. Skeletally, the mandible showed no asymmetry. Relative to the cranial floor, the mandible was "rotated" so that the condyle on the crossbite side was positioned relatively posteriorly in comparison to the contralateral side. A relative posterior positioning of the glenoid fossa was inferred, since there was no demonstrable mandibular skeletal asymmetry or condylar displacement within the fossa as shown on corrected tomograms in the crossbite group as compared with the Class I group. The results question whether it is appropriate to correct unilateral posterior crossbites in adults by orthodontic tooth movement alone, given the skeletal remodeling in the temporomandibular joint, which may have already occurred.