There are different kind of injections that are given into the Temporomandibular joint (TMJ) to relieve the symptoms of osteoarthritis of the jaw.. You did not what kind of injection will be given to your TMJ. But lately the most common injection( fluid in your term) that has been given into the TMJ is Hyaluronic acid derivatives that acts as a intra articular( inside joint) lubricative so that your joint moves more freely and it prevents the friction between the surface of the bones inside your TMJ. That will naturally reduce your symptom of pain and headache. Generally this kind of lubrication is repeated every six months.