[The experimental study of the effects of J-hook type headgear on the craniofacial complex. A study using strain gauge method].

In this study, the dry skull with Multibanded appliance was employed in several tractional directions and positions for the investigation of the effects of J-hook headgear on the craniofacial complex including the palate. The traction was carried out by the tractor constructed by J-hook headgear exerting the load of 3 kg on the dry skull applied with the strain gauges. The tractor was connected to the four positions: the gingival and the incisal hooks on the archwire between the central and the lateral incisors, and onto archwire mesial to the canine and the 1 st premolar brackets. The tractional directions were five, varied from -20 degrees - (+)60 degrees to the occlusal plane at the interval of 20 degrees. The distribution of two-dimensional strain in several tractions and the effects on the craniofacial complex were investigated. The results were as follows: 1. In the right side view, the maxillary complex was not rotated when the tractional directions were set about at +40 degrees in the incisal traction, and between +40 degrees and +60 degrees in the canine and the 1 st premolar tractions. In the maxillary complex, clockwise rotation was induced by downward traction less than these angles, and the counterclockwise rotation was induced by upward traction more than these angles. 2. In the horizontal view, the degree of the curvature of the zygomatic arch tend to increase by the horizontal traction in any positions. 3. The palatine region was suggested to enlarge in the lateral direction at -20 degrees traction in any tractional positions. The enlargement gradually lessened in upward traction by the incisal traction. The palatine region between the canines was suggested to compress at +40 degrees and +60 degrees traction in the gingival hooks, and at +60 degrees traction in incisal hooks. In the canine and the 1 st premolar tractions, palatine region was suggested to enlarge in the lateral direction in any tractional directions. 4. The palatine region was suggested to compress in the backward direction in any tractional direction. The trend was not found to be different among tractional points. The maximum compression was produced in -20 degrees traction, and then gradually decreased in upward traction.