Holographic measurement of incisor extrusion.

A technique based on pulsed laser hologram interferometry was used to study the dynamics of incisor extrusion. Maxillary central incisors of four subjects were loaded with forces acting along the long axis of the tooth, and the resulting motions were measured noninvasively in three dimensions. The incisor translations and rotations were used to determine centers of rotation. The experimentally determined centers of rotation are shown to depend on tooth root geometry and are found to lie at a vertical level coincident with the centroid of the root.