Oralign

Hinge axis rotation

It looks like opening or closing a door, in which is the axis of rotation is mesial or distal not the long axis of tooth or the middle of it, so it is not a pure rotation. During staging of aligner treatment hinge rotation may be carried out simultaneously with expansion, stripping of contact points of the rotated tooth may be needed during treatment.

In Clear aligners therapy some tooth movements need adding attachment to tooth surface to act as a pressure area conveying the tooth to the planned position, as we all know tooth surface is smooth and force will be disipated on wide smooth surface that will lead to unplanned tooth movement.