A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part I: Development of the measuring system

Abstract

S ince the middle of the nineteenth century, there have been numerous studies analyzing mandibular movement. Many of these studies were successful when targets were attached in the incisal area where direct measurement was feasible.‘-’ However, the motion of the condyles was not successfully studied because it had to be measured indirectly from the outside of the face owing to the difficulty of placing targets inside the condyles.“’ Because the data obtained from these studies could not be accurately analyzed to determine the true movement of the condyles, the exact movement of the condyles is still not known. If the assumption is made that a human mandible is indeformable, mandibular movement may be treated as the movement of a “rigid body.” In order to describe the three-dimensional movement of a rigid body, it is necessary to measure the two-dimensional movement of three points fixed on the rigid body. These points should not be on a straight line. Then all six independent unknowns can be used to calculate the exact movement of a predetermined point fixed on the mandible. In this regard movement of a rigid body has six degrees of freedom. This measurement, however, requires only complicated calculations. If movement of the mandible can be measured with six degrees of freedom, if a vast amount of measured data can be recorded and stored, and if the great amount of calculations required can be accomplished, then movement of any point on the mandible, such as a condylar point, can be described as accurately as if it were measured directly inside the condyle. Studies of mandibular movement by means of elec-