Study on the Axis of small Opening and Closing Movement of the Mandible in and around Intercuspal Position (2nd. Report)

Abstract

To investigate the mounting method of the cast to the articulator using inter occlusal record with a certain thickness for the aim to realize the intercuspal position, we studied the axis of habitual small opening and closing motion of the mandible, using 5 dentulous subjects who are normal in stomatognathic system.We sought for position and displacement distance of “N” axis which is smallest moveing point when mandible takes habitual opening and closing motions, “H” axis which is the smallest moving point when mandible takes terminal hinge motion and “C” axis which is average condyle point.Further more we analyzed mathematically anteropostero gap in anterior region based on positional difference between the axis used mounting and “N” axis. The results were as follows:1.“N” axis existed 4.5 mm anterioly, 50.5 mm posterioly, 2.5 mm-5.2 mm inferioly from “C” axis. The position of “N” axis had a variety among subjects.2. Displacement area of “N” axis in habitual small opening and closing motion of the mandible is the smallest of the other and is 1/1.4-1/27.0 compared with “C” axis and 1/1.3-1/48.6 compared with “H” axis.3. Not exceeding 0.2mm displacement of “N” axis is so small that “N” axis is valuable as mounting axis of the cast to the articulator and also “N” axis is valuable compared with “H” axis.4. Antero-postero gap in anterior region based on positional difference between the axis used mounting and “N” axis tend to be greater when “N” axis appear postero-inferior position and supro-anterior position from the articulator axis by mathematical analysis.5. Mathematical analysis shows farly large error when mounting without true mandibular opening and closing axis, therefore using “N” axis lead desirable result.