Chewing in patients with a history of trigeminal neuropathic pain

Objectives: The Pain Adaptation Model (PAM) proposes that pain results in a reduction in amplitude and velocity of movement to protect the motor system from further damage. We have recently proposed, in the Integrated Pain Adaptation Model (IPAM), that psychological factors may play a role in this pain-motor relation. There is little information regarding the effects of trigeminal neuropathic pain (TNP) on the jaw motor system. The present study aims to determine (a) whether TNP patients who are not in pain exhibit kinematic parameters of jaw movement identical to controls, and (b) whether there is evidence for correlations between psychological variables obtained from the TNP patients and kinematic variables of their jaw movement.

Methods: Fourteen subjects with chronic TNP (mean duration: 9.7 years) and 14 age- and gender-matched asymptomatic subjects were recruited. An optoelectronic jaw tracking system (JAWS3D) recorded the movement of mandible in 6 degrees-of-freedom during free chewing. Subjects completed the Pain Catastrophising Scale at the recording session.

Results: TNP subjects did not report any pain either before, during, or after the experimental session. The velocity (TNP: 24.2±12.3 mm/s; control: 27.4±6.2 mm/s) and amplitude (TNP: 10.7±5.3 mm; control: 11.2±2.4 mm) of jaw movement during free chewing were not significantly (p>0.05) different between TNP and control groups. However, TNP subjects exhibited significantly greater variability in velocity (Levene's test for equality of variances, p = 0.009) and amplitude (Levene's test for equality of variances, p = 0.002) between individuals compared to controls. There was a significant negative correlation between pain catastrophizing scores and velocity (r=-0.56, p=0.004) and amplitude (r=-0.70, p=0.005) of movement among the TNP group.

Conclusions: The data suggest that, consistent with the IPAM, psychological factors may influence the association between pain and motor function.

Supported by NHMRC of Australia (512309) & Australian Dental Research Foundation, Inc