Force delivery from a transpalatal arch for the correction of unilateral first molar cross-bite.

The forces and moments delivered by prefabricated transpalatal arches of the makes Unitek, GAC, and Ormco were studied in laboratory experiments. The Unitek and GAC arches were made of steel, and the Ormco arch of beta-titanium alloy (TMA). Three types of activation were investigated: for bilateral expansion in a statically indeterminate system and for unilateral expansion in a statically determinate system with and without torque activation. In addition to the arch design, composition, and mode of activation, the influence of arch size and degree of activation were studied. It was found that activation for unilateral expansion with the inclusion of torque in the statically determinate system produced forces and moments suitable for the correction of a unilateral cross-bite.