Assessment of proprioceptive allodynia after tooth-clenching exercises

To (A) evaluate test-retest reliability of vibrotactile sensitivity in the masseter muscle and (B) test if (1) the vibration threshold is decreased after experimental tooth clenching, (2) intense vibrations exacerbate pain after tooth clenching, (3) pain and fatigue are increased after tooth clenching, and (4) pressure pain thresholds are decreased after tooth clenching.

In part A, 25 healthy female volunteers (mean age: 42 ± 12 years) participated, and 16 healthy females (mean age 32 ± 10 years) participated in three 60-minute sessions, each with 24- and 48-hour follow-ups in part B. Participants were randomly assigned tooth-clenching exercises with clenching levels of 10%, 20%, or 40% of maximal voluntary clenching. A Vibrameter applied to the right masseter muscle measured perceived intensity of vibration and perceived discomfort, which were assessed on 0-50-100 numeric rating scales. An electronic algometer measured pressure pain threshold (PPT). Two 0- to 100-mm visual analog scales measured pain intensity (VASpain) and fatigue (VASfatigue). Measurements were made on the right masseter muscle. Interclass correlation coefficient (ICC) was used to calculate test-retest reliability of VT measurements. Outcome variables were tested with two-way ANOVAs for repeated measures and Dunnett's post-hoc test.

Moderate long-term (ICC 0.59) and good short-term (ICC 0.92) reliability was found for VT on the masseter muscle. Clenching level had no main effect on perceived intensity of vibration; time effects (P < .05) were only observed at 40 minutes (Dunnett's test: P < .01). Clenching level and time had no effect on perceived discomfort. Only time effects were significant for PPT (P < .01), with reductions at 50 and 60 minutes compared to baseline (Dunnett's test: P < .05). Clenching level and time had main effects for VASpain and VASfatigue (P < .001).

Experimental tooth clenching appears to evoke moderate levels of pain and fatigue and short-lasting hyperalgesia to mechanical stimulation, but not proprioceptive allodynia. The absence of proprioceptive allodynia does not necessarily exclude delayed onset muscle soreness (DOMS) but warrants further studies on the clinical manifestations of DOMS in jaw muscles.