Intramuscular pH modulates glutamate-evoked masseter muscle pain magnitude in humans

Background This study was conducted to determine whether glutamate‐evoked jaw muscle pain is modulated by the acidity and temperature of the solution injected. Methods Thirty two participants participated and received injections of high‐temperature acidic (HT‐A) glutamate (pH 4.8, 48 °C), high‐temperature neutral (HT‐N) glutamate (pH 7.0, 48 °C) and neutral temperature neutral (NT‐N) glutamate (pH 7.0, 38 °C) solutions (0.5 mL) into the masseter muscle. Pain intensity was assessed with an electronic visual analogue scale (eVAS). Numerical rating scale (NRS) scores of unpleasantness and temperature perception, pain‐drawing areas, mechanical sensitivity and pressure pain thresholds (PPT) were also measured. Participants filled out the McGill Pain Questionnaire (MPQ). One or two way ANOVAs were used for data analyses. Results Injection of HT‐A glutamate solutions significantly increased the area under the VAS‐time curve compared with injection of HT‐N glutamate and NT‐N glutamate solution (p