When the distalmost molar on the lower arch erupts in lingual version, this special expansion screw can upright it very efficiently -- provided no more than approximately 3mm of movement is needed. It affords a precisely controlled tipping of the crown without bodily movement.

A key is provided with the appliance for weekly adjustments. If the molar is in a locked lingual cross bite, it is advisable to request that a posterior bite plane be added to the appliance to facilitate this movement. Note: This appliance also shows a micro-screw -- a very effective way of moving a single tooth labially in both arches.