An index for analysing the stability of lateral excursions.

Five lateral excursions on both left and right sides of 20 healthy subjects were recorded by Gnatho-hexagraph, which was an opto-electronic system with six degrees of freedom. The incisor point, the working condylar point (WCP) and the balancing condylar point (BCP) were analysed. When the incisor point moved 1, 2, 3, 4, 5 mm on its path, the incisor point and corresponding condylar points were analysed. The linear distances from the intercuspal position (ICP) to each analysed point at each analysed position were calculated as Linear distance. The distance between five lateral excursions in x, y, z, space coordinates at each analysed position of three analysed points were calculated as Dx, y, z, s. To evaluate the stability of lateral excursions, the Index S was defined as the equation (S=D/Linear distance * 100) and calculated. From the result of Index S, the WCP showed significantly less stability than the other two analysed points (P < 0.05). The incisor point showed best stability, especially in upper-lower direction. The BCP also showed good stability. Index S revealed the characteristic movement in x, y, z, space coordinates at each analysed point and it showed clearly the stability of lateral excursions.