Characteristics of Daytime Clenching in Individuals Affected With Myofascial Pain of the Masticatory Muscles and Pain-free Controls During Standardized Ability Tasks

Objectives: Daytime tooth clenching, i.e., awake bruxism, has been the subject of intense discussions within the dental community for its possible relation with temporomandibular pain. Quantitative and/or qualitative information about the characteristics of daytime clenching episodes are rather limited and it is not known whether they differ between TMD (temporomandibular disorders) and TMD–free individuals.
This study aimed to measure the frequency, amplitude and duration of daytime clenching episodes in individuals suffering from myalgia of the masticatory muscles and pain free controls.
Methods: Fifteen women suffering from myalgia of the masticatory muscle (MP group, mean±SD age=26.4±7.6 years) matched for age to a control group made of 18 TMD-free women (CTR group, mean±SD age=25.3±2.8 years) were submitted to three different ability tasks (filling out questionnaires for 40 minutes, reading a magazine for 20 minutes, and a playing a videogame session for 20 minutes). A portable device (Bruxoff®, Orthorizon, Torino, Italy) was used to acquire the electromyographic signals (activity periods–AP) of the right masseter greater than 10% (AP10), 20% (AP20), and 30% (AP30) of the maximum voluntary contraction.
Results: The number of AP10, AP20, and AP30 was significantly greater in MP than in CTR individuals (all p<0.05). The mean duration of AP10 was higher in MP group than CTR group only while filling out the questionnaires (p=0.0033). The mean cumulative durations of AP10, AP20, and AP30 were significantly higher in MP than CTR group (all p<0.05). CTR group had a higher count of AP10, and a higher duration of these episodes while playing the videogame than while reading a magazine. The ability task did not affect the muscle activity outcomes in the MP group.
Conclusions: Individuals affected with myofascial pain of the masticatory muscles present a greater frequency of both high and low-intense daytime clenching episodes than pain-free individuals during standardized ability tasks. The type of ability task affects the frequency and the duration of clenching episodes only in pain-free individuals.