Changes in condylar postition and occlusion associated with maxillary expansion for correction of functional unilateral posterior crossbite.

The purpose of this study was to confirm that correction of functional posterior crossbite through maxillary expansion is associated with a change in condylar position and occlusal relationships, and to determine whether maxillary expansion is associated with autonomous increase in mandibular arch width. Pretreatment and posttreatment study models of 61 patients ages 4.1 to 12.0 years (mean 8.5 years, SD 1.5) were available after maxillary expansion with a Quad Helix or a Haas expander for correction of a functional posterior crossbite. Pretreatment and posttreatment tomograms were available for 22 of the patients. Tomographic evaluation revealed that the condyles moved posteriorly and superiorly on the noncrossbite side from before to after treatment (p < 0.05). No differences were observed on the crossbite side. Superior joint space was greatest on the noncrossbite side before treatment, whereas, conversely, it was greatest on the crossbite side after treatment (p < 0.05). Relative condylar position was more anterior on the noncrossbite side before treatment (p < 0.05), but similar on both sides after treatment. Molar and canine relationships were more Class II on the crossbite side before treatment (p < 0.01 and < 0.05, respectively) and similar on both sides after treatment. A significant reduction in midline deviation was seen from before to after treatment (p < 0.001). A small, but significant autonomous increase in mandibular intermolar width (p < 0.001) occurred concomitant with the maxillary expansion.