“This study demonstrated that …‐TMJ injection of tramadol (500 &mgr;g/TMJ) was able to inhibit the … response induced by 1.5% formalin or 1.5% capsaicin , suggesting that tramadol has an antinociceptive effect, acting directly on the … nociceptive neurons activating the nitric oxide/cyclic guanosine monophosphate signaling pathway.”