To date, no method is available to quantify jerk at a local point of the human joint along a direction that depends on the 3D curvature of the articular surface. This paper proposes a new measurement technique of normalized jerk-cost(NJC)of a target point movement along a direction that is normal to the 3D curvature of the condyle of human temporomadibular joint (TMJ). This study aimed to investigate the reliability and effectiveness of NJC measurements at 9 condylar points. Five control subjects and 3 subjects with condylar asymmetry participated in this study. Each participant performed unilateral gum-chewing. In all control subjects, an artificial occlusal interference(OI)was inserted to the lower molar. The NJCs and intra-articular space of the TMJ on the working side were calculated with and without OI. In 3 control subjects and 3 test subjects, the experiment was repeated after an average interval of 2 months to evaluate reproducibility of the measurements. By means of dynamic stereometry, the NJCs of the 9 condylar point movements towards a direction normal to the condylar surface and intra-articular space were calculated and compared between control group with and without OI, between control group without OI and test group, and between group data measured in two separate sessions. Significantly greater NJC and joint space were observed after insertion of OI(P< 0.05). The NJC in test subjects was greater than that in the control group without OI(P< 0.05). In addition, these parameters measured at different sessions did not differ significantly. These findings suggest that measurement of the NJC and intraarticular space are effective and reliable to evaluate the instability of condylar movements due to OI or joint deformation.