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Depending on clinical survey, unilateral and bilateral posterior crossbites can be approached using different appliance applications. Individual or groups of posteriors involved in a crossbite may be determined to be either dental or functional in origin and each may have a different anchorage requirement. The following appliance approaches are frequently requested for applications indicated.
Unilateral
For unilateral crossbite cases requiring bilateral expansion due to symmetrical constriction of the maxillary arch. Occlusal coverage serves to enhance the action of the appliance while opening the bite. A flat occlusal plane on the posterior section in crossbite eliminates interdigitation that may restrict movement. Lower cusp indents into the occlusal overlay on the opposing posterior segment maintains good function.
The Nord appliance is employed where a true unilateral crossbite requires movement in one posterior segment only. Increased anchorage is provided by an acrylic flange added to the occlusal coverage on the side opposite the crossbite. The flange extends to the lingual of the lower posteriors. The cut in the acrylic can be sectioned to include only that segment.
Bilateral
Two expansion screws are typically included in appliances for bilateral crossbite applications. Occlusal coverage with flat bite planes allows transverse development free of posterior occlusal interferences. As the case progresses, the screws may need to be reset for additional expansion. The labial bow can be adjusted away from the anteriors at each visit to avoid impingement.
Bilateral flanges extending to the lingual of the lower posterior segments will exert pressure to develop both arches. This appliance is preferred where patient cooperation with two removable appliances is doubtful and a lower fixed appliance is not feasible. A registration bite is recommended for any appliance having occlusal coverage to provide proper fit and function.