True unilateral posterior crossbite can be efficiently treated by using asymmetric expansion appliances that essentially exert unilateral expansion forces thereby minimizing iatrogenic overexpansion of the normal pretreatment side.

To evaluate and compare the stresses and displacements generated by four different types of asymmetric maxillary expansion appliances in true unilateral crossbite using the finite element method.

A CBCT image of the skull was obtained from a 12-year-old female patient with a true unilateral posterior crossbite on the right side, for the FEM study. Asymmetrically split acrylic plate with jackscrew (ASAPJ), NORD crossbite expander, Asymmetric Maxillary Expansion appliance (AMEX), Asymmetrical Rapid Maxillary Expansion (ARME) appliances were simulated with a given force specific to the appliance. Von Mises stresses, displacements in the x, y, z-axis, and changes in the axial inclination were evaluated and compared on the selected skeletal and dental landmarks.

Overall ARME seemed to generate the highest asymmetric von Misses stress on skeletal landmarks followed by NORD; ASAPJ and lowest by the AMEX. ARME also produced the highest asymmetric expansion followed by AMEX; NORD and lowest with the ASAPJ. NORD produced the minimum extrusion and buccal tipping of the canine and 1st molar followed by ASAPJ; AMEX and maximum by the ARME.

Each of the four appliances expanded the maxillary arch more on the crossbite side as compared to the non-crossbite side, but the pattern of stress distribution, displacement and change in the axial inclination were unique for each appliance.