STUDY OF HOLOGRAPHIC-INTERFEROMETRY ON THE INITIAL REACTION OF MAXILLOFACIAL COMPLEX DURING PROTRACTION

Most extraoral appliances used for protracting small or retropositione d maxilla do not allow for variations in the point of force applicatio n or in its direction. This variation may be necessary to control vert ical, anteroposterior, as well as transverse effects. The purpose of t his study was to investigate the initial reaction of the maxillofacial complex according to force magnitude, force direction, and point of f orce application. For this purpose, an antenna-type modified protracti on headgear was tested with double exposure holographic interferometry on a dry human skull with well-aligned upper teeth. Fringe patterns o f each protraction condition were compared and analyzed. In most cases , upward rotation of the anterior portion of the maxilla changed to tr anslation, or to downward rotation, as force direction was Changed fro m parallel to the occlusal plane to 20 degrees downward to the occlusa l plane. Furthermore, a 500 gm force applied 15 mm above and directed 20 degrees below the occlusal plane produced a translation of the maxi llary complex, indicated by a typical circular fringe pattern on the h olographic plate, which represents the center of resistance of the max illa. In most cases, with all force variables tested, a protraction of the maxilla with palatal expansion was more effective in producing tr anslation of the maxilla than was protraction without palatal expansio n. By varying force magnitude, force direction and point of force appl ication with maxillary protraction, the amount of maxillary rotation a nd translation might be controlled.