Objectives: The aim of the study was to identify and correlate myofascial trigger points (MTPs) in the masticatory muscles, using thermography and algometry.
Methods: 26 female volunteers were recruited. The surface facial area over the masseter and anterior temporalis muscles was divided into 15 subareas on each side (n=780). This investigation consisted of three steps. The first step involved thermographic facial examination, using lateral views. The second step involved the pressure pain threshold (PPT), marking the MTP pattern areas for referred pain (n=131) and local pain (n=282) with a coloured pencil, and a photograph of the lateral face with the head in the same position as the infrared imaging. The last step was the fusion of these two images, using dedicated software (Reporter® 8.5-SP3 Professional Edition and QuickReport® 1.2, FLIR Systems, Wilsonville, OR); and the calculation of the temperature of each point.
Results: PPT levels measured at the points of referred pain in MTPs (1.28±0.45 kgf) were significantly lower than the points of local pain in MTPs (1.73±0.59 kgf; p<0.05). Infrared imaging indicated differences between referred and local pain in MTPs of 0.5 °C (p<0.05). Analysis of the correlation between the PPT and infrared imaging was done using the Spearman non-parametric method, in which the correlations were positive and moderate (0.4≤r<0.7). The sensitivity and specificity in MTPs were 62.5% and 71.3%, respectively, for referred pain, and 43.6% and 60.6%, respectively, for local pain.
Conclusion: Infrared imaging measurements can provide a useful, non-invasive and non-ionizing examination for diagnosis of MTPs in masticatory muscles.