[A holographic study to demonstrate the initial displacements of a macerated human skull under the influence of the orthodontic force from headgear with traction in different directions].

The phenomena of maxillary displacement and the subsequent growth modifications which result from the application of orthopedic headgear traction are very complex and not yet completely understood. The aim of this study was to investigate with the help of holographic interferometry the influence of the headgear's differing traction directions on the initial bone displacement in the maxillary complex. 560 g high, straight, and low pull headgear traction exerted above, through, and below the center of resistance of the upper first permanent molars was simulated on a macerated human skull and skeletal changes were recorded by laser holography as they occurred. On the basis of the frontal and lateral holograms thus obtained, the initial displacement of the maxilla, zygoma, and zygomatic arch in both horizontal and vertical planes was evaluated. Substantial displacements in various parts of the studied structures, displacements such as bending, relative deformation, rotation, and translation, were detected, and, further, the direction of this complex displacement often deviated from the direction of the influencing force. The results obtained by this study indicate that the initial 3-dimensional skeletal displacements brought about by the headgear are very complex. The clinical implication is that they do not always correspond with the direction intended by the force applied.