Mandibular Jerk Profiles of Dysfunctional and Control Subjects Chewing Gum

Objectives: An internal derangement (ID) of the TMJ may affect the process of mastication. This research tested the null hypothesis: No difference in the Jerk function during mastication between ID patients and control subjects.
Methods: Incisor-point motions were recorded from patients (56 F & 56 M) with documented ID of at least one TMJ while chewing gum on the left or right side (n = 112). An age (p > 0.37) and gender matched control group (21 F & 21 M) was likewise recorded. From each patient and subject recording cycles 2 through 11 were averaged to produce 40 point movement profiles (20 opening points and 20 closing points). The 112 ID subjects’ data were divided into 2 groups; a.) 56 subjects with average cycle times not significantly different from the control group (p > 0.90) and b.) 56 subjects with significantly longer average cycle times (p < 0.000). A mean Cumulative Absolute Jerk function (CAJF - the third derivative of motion |d³x/dt³|) was calculated for each of the 3 groups. The mean CAJF values were compared statistically using a two-tailed Student’s t test (alpha = 0.05) after testing the data for normalcy with Jarque-Bera.
Results: The CAJF for the ID group with comparable cycle times was significantly larger (454 + 98) compared to the Control Group (355 + 55; p < 0.000). However, the CAJF in the ID group with longer cycle times was significantly smaller (223 + 55) compared to the Control Group (p < 0.000).
Conclusions: The ID group with comparable cycle times produced a CAJF significantly higher than the controls (less smooth), while the lengthened cycle time group produced a significantly lower Cumulative Absolute Jerk. The null hypothesis was rejected.