The initial reaction of a macerated human skull caused by orthodontic cervical traction determined by laser metrology.

Tensile forces were applied to the maxilla of a macerated human skull in a backward direction 10 degrees below the occlusal plane. The skull was fixed to a heavy metal support at the occipital and parietal bones. These forces were applied near the first permanent molars via a rigid stainless steel bar, which was fitted to a cast-metal splint attached to the palatal surface and buccal region of the maxillary arch. Forces were increased step by step from 2.0 N (1N = 100 grams) to 7.25 N per side. Using a holographic configuration with two 5 mW HeNe lasers, double-exposure holograms were made from the frontal and from the left lateral sides. Fringe shifts in different points of the hologram were measured and the x, y, and z components of the displacement were calculated for eight points located on various bones of the skull. Viewed from the frontal, force application to the maxilla resulted in a downward and backward rotation. The zygomatic bone was also rotated downward and backward with a small rotation in a transverse direction. Other craniofacial structures were also affected. With a force of 7.25 N per side, a deformation of the temporal bones and zygomatic arches occurred.