Effects of Chronic and Experimental Acute Masseter Pain on Precision Biting Behavior in Humans

Abstract

Chronic pain in the orofacial region is common worldwide. Pain seems to affect the jaw motor control. Hence, temporomandibular disorders (TMD) are often accompanied by pain upon chewing, restricted mouth opening and impaired maximal bite forces. However, little is known on the effects of pain, in particular the effects of chronic jaw muscle pain on precision biting. The aim of the study was to investigate the effect of chronic and acute jaw muscle pain on oral motor control during precision biting in humans. Eighteen patients with chronic masseter muscle pain and 18 healthy participants completed the experiment. All participants were examined according to the Diagnostic Criteria for TMD. Experimental acute pain was induced by bilateral, simultaneous sterile hypertonic saline infusions into the healthy masseter muscles. A standardized hold and split biting task was used to assess the precision biting. The data was analyzed with non-parametric statistical tests. The results showed no significant differences in the hold forces, split forces, durations of split or peak split rates within or between the pain and pain-free conditions. The mean split rate increased significantly compared to baseline values both in the chronic patients and the pain-free condition. However, this increase was not evident in the experimental acute pain condition. Further, there were no significant differences in the mean split rates between the conditions. The data suggest that jaw muscle pain does not seem to alter precision biting in humans, however, the possibility that a nociceptive modulation of spindle afferent activity might have occurred but compensated for cannot be ruled out.

Salivary Alpha-Amylase in Experimentally-Induced Muscle Pain

“…The main finding of this study was that experimentally-induced pain, i.e., acute pain, did not affect the levels of sAA, which seems to be in contrast to previous studies [ 20 , 21 , 22 , 23 ]. However, in contrast to the previous studies [ 5 , 8 , 20 , 21 , 22 , 23 ], this study used a short lasting, high intensity pain model [ 35 , 36 , 37 , 38 ]. This could have resulted in a pain state that was too short-lasting to activate the ANS, resulting in a secretion of sAA.…”

“…To our knowledge, this study is the first to observe changes in sAA during controlled, acute pain in an experimental setting. To compensate for the shorter pain duration compared to earlier studies, a higher dose of saline was used, compared to previous protocols [ 36 , 37 , 38 ], to induce a high intense but slightly prolonged pain sensation. Based on the study results, one may speculate that pain duration may have a stronger effect on the ANS and sAA secretion than we originally assumed, and that pain intensity has less significance.…”

“…Hypertonic saline injections have been used extensively to induce muscle pain, since the quality of the pain mimics acute clinical muscle pain [ 36 , 37 ]. The participants in the study reported moderate pain intensity, with a peak after 30 s that spreads to adjacent regions and pain referral to other structures similar to several previous studies [ 36 , 37 , 38 ]. Hence, the quality of pain induced can be regarded as clinically relevant.…”

“…It was ensured via the anamnesis and the oral examination that the participants were healthy, and they were matched for age and gender to eliminate the influence of these factors on enzyme activity or reported stress levels. The pain model applied are well-known, and numerous studies have shown good reliability [ 36 , 37 , 38 ]. The experiment and sample collection followed the exact same protocol for all participates, and to avoid variation in sAA secretion, experiments were mainly conducted during the early afternoon.…”

“…When analyzing the results, it could also be observed that more than half of the participants still reported mild pain 15 min after the injection. This time interval was set based on earlier experiments showing that the pain experiences usually decreases 15 min after injection of the hypertonic saline into the masseter muscle [ 36 , 37 ]. It may be suggested to wait longer than 20–30 min for the pain to completely disappear until saliva is collected.…”