Internal Derangement of the TMJ Alters Gum Chewing Amplitude and Velocity

Objectives: To test the null hypothesis that the mandibular movements during gum chewing do not differ significantly in the presence of a verified TMJ internal derangement.
Methods: 30 symptomatic subjects with confirmed internal derangement of at least one TMJ (15 f, 15 m, 38.9 + 15.8 years old) consented to chew gum on their left and right sides while their movements were tracked by a magnetic jaw tracker (n = 60). A gender and age matched group (p > 0.15) of 30 asymptomatic subjects with confirmed normal TMJ conditions (15f, 15m, 33.4 + 13.3 years old) volunteered to be likewise recorded (n = 60). Each chewing cycle was divided into 40 equal segments (20 opening and 20 closing) and the instantaneous velocity was calculated at each point. Cycles 2 to 16 were averaged from each subject’s left chewing sequence and likewise from the right chewing sequence. This created a complete set of 60 mean velocity profiles for the dysfunctional group and an equal number for the control group. Student’s two-tailed t-test for unequal variances was used to compare the internal derangement group’s movement amplitudes and mean opening and closing velocities to the control group after checking the datasets for normalcy using the Jarque-Bera test.
Results: The control group opened wider (p < 0.0005) and chewed faster (p < 0.0000) than the age and gender matched dysfunctional group. The cycle time of the dysfunctional group (0.934 sec.) was significantly longer than the control group (0.760 sec; p < 0.00001) and more variable (p < 0.0000).
Conclusions: The presence of TMJ internal derangement reduced both the amplitude and the velocity of chewing movements, but increased the variability of movements during gum chewing within this sample.