Methods: In 8 healthy asymptomatic subjects (age: 25-36; 3 females, 5 males) jaw movement was tracked with an optoelectronic jaw tracking system (JAWS3D) that recorded the movement of the mandible in 6 degrees-of-freedom during 2 trials (each trial was 20 s duration) of free chewing (gum). Tasks were performed in two sessions: control (no infusion), and pain (continuous infusion into right masseter of 4.5% hypertonic solution) to achieve 40–60 mm pain intensity on a 100-mm visual analogue scale (VAS). Mean velocity and amplitude were compared with paired t-tests (significance: p<0.05).
Result: Closing velocity was significantly (p<0.05) faster during hypertonic saline infusion (42.4 ±12.4 mm/s) than control (34.6±11.6 mm/s). There was no significant difference in chewing amplitude between hypertonic saline infusion (14.3±3.1 mm) and control (13.5±2.7 mm), or in opening velocity between hypertonic saline infusion (38.9±11.4 mm) and control (33.1±9.8 mm).
Conclusion: These data suggest that under experimentally induced masseter muscle pain, subjects can move their jaw faster than in the absence of pain. These findings are not consistent with the proposals of the Pain Adaptation Model. Supported by NHMRC of Australia (512309) and Australian Dental Research Foundation, Inc., and the Australian Dental Association, NSW branch.