Mechanical reactions of facial skeleton to maxillary expansion determined by laser holography.

The highly accurate laser holographic interferometry method was used to determine in what way low-magnitude forces during slow maxillary expansion are transmitted to the entire maxillary complex and its surrounding structures. The experiments were carried out on a macerated human skull which had a perfectly preserved, normally aligned maxillary dental arch and intact alveolar processes. The soft palatal and periodontal tissues were reconstructed with a semielastic material. The specimen was loaded gradually by widening of a split acrylic appliance with an expansion screw. Interferograms were taken simultaneously on the left and right sides of the maxillary complex, using the 10 mV He-Ne laser and the double-exposure method. Analysis of the fringe pattern on the recorded object surface was performed by graphically determining the deformation curves related to the bony surface in selected horizontal and vertical planes. Experimental results show that the application of laterally directed forces from the maxillary expansion appliance induced initial mechanical reactions of the entire maxilla, the circummaxillary sutures, and the surrounding bones. Each increase in dental arch width was obtained not only by the deformation of the alveolar process with dental tipping but also by the rotation of the entire maxilla within its sutures around horizontal and vertical axes. Moreover, displacement of the surrounding maxillary structures (pterygoid processes, zygomatic, lacrimal, and nasal bones) was detected in response to the rotational movement of the maxilla.