Labial movement of a lingually erupted tooth is usually accomplished in two steps. Initial wire engagement leads to uncontrolled tipping of the crown labially, resulting in further lingual movement of the root apex. Subsequently, the root apex is moved labially with the application of the labial root torque. Such tipping of the root apex could be avoided by the use of µ spring. It is designed in a way that allows generation of a counter moment large enough to allow labial translation of the tooth, while a labial force is applied to the crown. Simultaneous intrusion and labial translation of the tooth could also be accomplished, with appropriate pre-activation bends, before insertion of the spring.
Keywords: biomechanics, labial translation, intrusion, Australian archwire, vertical slot
