Holographic and cephalometric study of the relationship between craniofacial morphology and the initial reactions to high-pull headgear traction

Eight macerated human child skulls with a dental age of approximately 9.5 years (mixed dentition) were consecutively subjected to an experimental standardized high-pull headgear traction system attached to the maxilla at the first permanent molar area via an immovable acrylic resin splint covering all teeth. This system produced tensile forces from 0.5 to 3.5 N (1 N = 0.10 kg) per side. Laser holography was used to measure displacements in a three-dimensional coordinate system. Displacements varied in direction, In addition, conventional cephalometric analysis of standardized lateral roentgen cephalograms was performed. Displacements and cephalometric data were then compared. Results indicate that the direction of initial displacements of bones of the facial skeleton bears a definite relationship to the morphology of the individual skull. In skulls with high divergency values (large angles, sella-nasion-occlusal plane, sella-nasion-mandibular plane), displacements are in a backward and posterior downward direction; in skulls with a small sella-nasion-occlusal plane angle, backward displacements occur in a direction almost parallel to the occlusal plane.