Facial pain can arise from a whole host of structures: Sensitive nerve endings in the facial and neck muscles, the temporomandibular joint, the middle ear, the teeth and the mucosal linings in the sinuses can transmit pain signals to a small area in the brain stem. In the brain stem the pain centres for the individual anatomical structures are in close proximity to each other and can therefore affect and activate each other too. Pain that we feel in the temporomandibular joint can then actually be projected by another structure, such as the masticatory muscles or the middle ear. Conversely, TMJ pain can be projected into the muscles and ear region. The patient then experiences this as earache or pain of the chewing muscles.
Or it could also be that the pain does not actually originate in a specific structure, but rather that the nerve that acts as a pathway sending pain signals to the brain is inflamed. This is then called "neuritis" or "neuralgia" (trigeminal neuralgia).