Introduction: Occlusal splint therapy is a well-known method for the treatment of TMD. Muscle stretching and pain relief are effects of occlusal appliance. The aim of this study was to evaluate the plasma level of CGRP in patients with myofascial pain (RDC/TMD Ia) and myofascial pain with limited opening (RDC/TMD Ib) before and after muscle stretching with occlusal splint therapy.

Material and methods: A randomised trial was performed including 35 subjects (males = 10, females = 25) in the experimental group and 30 subjects (males = 9, females = 21) in the control group. Blood samples were taken from the external jugular vein before and after 30 days of occlusal splint therapy. Plasma levels of CGRP were measured with a Radio Immunoassay Kit (Phoenix Pharmaceuticals Inc.) and Cobra Series Auto-Gamma Counting System.

Results: The results of the study demonstrated that CGRP concentrations were significantly higher after occlusal splint than before splint therapy: CGRP2 = 17.02 pg/mL (SD = 5.85), CGRP1 = 13.78 pg/mL (SD = 5.12), in the experimental group (p < 0.05). In the control group, there were no statistically significant changes in CGRP levels: CGRP1 = 14.5 pg/mL (SD = 4.87) to CGRP2 = 13.5 pg/mL (SD = 4.63). In the experimental group, there was a statistically significant reduction in pain intensity, VAS1 = 5 (SD = 2.5) to VAS2 = 1 (SD = 1.04) after splint therapy (p < 0.05). In the control group, there were no statistically significant changes in pain intensity: VAS1 = 5 (SD = 2.3) to VAS2 = 4 (SD = 2.6), (p < 0.05).

Conclusions: CGRP plays an important role in muscle blood flow, which is altered by changes in muscle length. Further investigation is needed to clarify the mechanism of muscle blood flow and the muscle healing process in patients with TMD.