Purpose
To assess the reliability and responsiveness of the duty factor variable for assessing pain originating from temporomandibular disorders.
Methods
The sample comprised 20 female volunteers, mean age 29 years 6 months (± 9.2), with a diagnosis of myogenic temporomandibular dysfunction according to the Research Diagnostic Criteria for Temporomandibular Disorders. Electromyographic (EMG) signals were collected at three times: during mandibular rest; in the presence of moderate to severe pain; and when pain was reduced to mild or absent after 45 minutes of transcutaneous electrical nerve stimulation (TENS). Electromyographic signals during mandibular rest were processed to obtain values for muscle activation time greater than 10% of maximum bite force. Reliability was tested with intraclass correlation for repeated data before analgesia. Standard error of measurement (SEM) and minimum detectable change (MDC) were also computed to determine reliability. Responsiveness of duty factor was analyzed between EMG recordings, before and after analgesia, by calculating effect size (ES) and standardized response mean (SRM).
Results
Duty factor presented intraclass correlation coefficient above 0.75 for all muscles. Standard error of measurement ranged from 4% to 8% and minimum detectable change from 5% to 12%. Regarding the responsiveness of duty factor to pain, effect size values fell between 0.2 and 0.5 and SRM values were greater than 0.8.
Conclusion
Duty factor showed excellent reliability. However, responsiveness to TMD-related pain was low as expressed by effect size and excellent as expressed by standardized response mean.
Electromyography; Temporomandibular joint dysfunction syndrome; Masticatory muscles; Pain; Transcutaneous electric nerve stimulation; Reproducibility of results
