CXCL8 and Myalgia: Interleukin 6 (IL-6) and interleukin 8 (IL-8) levels increased in response to tooth clenching in both groups, while interleukin 7 (IL-7), interleukin 13 (IL-13) and tumor necrosis factor (TNF) rose only in patients with TMD-related myalgia.