Changes in Pressure-Pain Thresholds of the Jaw Muscles During a Natural Stressful Condition in a Group of Symptom-Free Subjects

Aims: To investigate the effects of a natural emotional stressor on pressure-pain thresholds (PPTs) of the masticatory muscles of symptom-free subjects. Methods: Sixteen healthy dental students were selected before they undertook an academic examination. Sixteen gender-matched students who were not exposed to an examination served as controls. The 2 groups of students were monitored in parallel on 5 separate days over a 1-month period: 2 days before the examination (T1), on the day of the examination (T2), 2 days after (T3), 1 month after (T4), and again after another 2 days (T5). On the day of the examination (T2), the control students were only required to complete a brief, non-demanding questionnaire. On each day, the following parameters were assessed: PPTs of the masseter, the anterior temporalis, and the Achilles tendon; state anxiety; and present stress (measured on a visual analog scale [VAS]). Furthermore, in the students undergoing the examination, venous blood samples for assessment of ß-endorphin levels were obtained at T2 and T5. Results: In the stressed students, the PPTs of the masticatory muscles and the Achilles tendon were significantly lower (analysis of variance [ANOVA], P = 0.02) on the day of the examination (T2) and on the days nearest the exam (T1, T3), and state anxiety and present stress were significantly higher (ANOVA, P = 0.003). No significant change was found in b-endorphin plasma levels (P > 0.05). In the control group, PPTs, state anxiety, and present stress did not change significantly (ANOVA, P > 0.05). Conclusion: The results support a relationship between psychologic stress and pressure-pain sensitivity of the masticatory muscles.