A Study on the Effect of the Sagittal Incisal Inclination upon the Fischer's Angle

Abstract

Fischer's angle is defined as the angle formed by the path of the advancing condyle during lateral movement and the path of the advancing condyle during protrusive movement, as viewed in the sagittal plane. Although the term Fischer's angle has such an clear definition, and this angle has long been believed to be an important characteristic of condylar path, several studies have thrown some doubts on its existence.
It may be pointed out that the controversy of existence of Fischer's angle is two-fold. One aspect of the controversy concerns the existence of Fischer's angle itself, and the other concerns the effect of central bearing plate configuration upon features of condylar path including Fischer's angle.
It was the purpose of this study to observe the effects of central bearing plate configuration upon condylar path. For this, Fischer's angle being one of the features of condylar path was investigated in the sagittal plane.
Five adults, who were diagnosed to have normal occlusion, were selected. Fischer's angle was recorded for each of them by means of modified pantograph with each of three different types of central bearing plates, namely Denar-type, Stuart-type, and flat-type, respectively. Denar-type central bearing plate had concave contour, where protrusive and lateral path had inclinations of 15°and 18°, respectively against occlusal plane. Angular difference of those path was 3°. Stuart-type central bearing plate had also concave contour, where both protrusive and lateral paths had inclinations of 16°against occlusal plane, and angular difference of those paths was 0°. Among three types of central bearing plates, Stuart-type had the feature being located more parallel to the sagittal condylar path. Flat-type central bearing plate had literally flat contour, where both protrusive and lateral paths had 0°inclinations against occlusal plane, and angular difference of those was 0°. Flat-type, however, was not located on the dentition as parallel as Stuart-type to the sagittal condylar path.
Observation revealed that Fischer's angle recorded with Denar-type central bearing plate was the largest, that with Stuart-type was the smallest, and that with flat-type was the medium.
The followings are the findings of this study.
1. There exists Fischer's angle.
2. Fischer's angle was affected as configuration of central bearing plate altered. This fact may connotate that Fischer's angle may be affected as anterior guidance alters.
3. Angular difference between protrusive and lateral paths of central bearing plate had effect upon Fischer's angle. For instance, the more the angular difference was, the more the Fischer's angle was.
4. Fischer's angle became smaller as central bearing plate was located to be more parallel to the sagittal condylar path.