Experimental determination of the center of resistance of the upper first molar in a macerated, dry human skull submitted to horizontal headgear traction.

Laser speckle interferometry, recently developed for noninvasive measurement of small displacements (microns), was used to study the movement of maxillary molars submitted to extraoral traction. Using an antenna-headgear at different horizontal levels, loadings of 700 gm were applied perpendicular to the long axes of these teeth. Bodily movement was observed when the traction line passed slightly occlusal to the trifurcation of the roots. Therefore, the center of resistance of the upper molar was experimentally localized at this level. Laser speckle interferometry proved to be a promising technique for dental research.