It’s a ringing sound, a buzzing, a hiss…. It can be soft or loud, intermittent or present all the time, affecting one ear or both. In whatever way it affects you, it’s damned annoying, unpleasant, distracting. Indeed, it is considered the worst problem affecting human beings after pain and dizziness. What it is is tinnitus, a sound in your ears that seems to come out of nowhere that you hear and sometimes other people can hear as well. And it’s mysterious.
For generations, hearing specialists have speculated about what causes the sound. They know that tinnitus increases with age (up to a point, after which it peters out) and it can occur in association with various diseases or with the use of certain drugs. Researchers have come up with theories, but as yet no hard and fast evidence has established what actually generates the sounds. One theory says that tinnitus is caused by abnormal firing (hyperactivity) of the auditory sensory cells in the inner ear. Another says that disease or damage to these cells causes a “phantom” sound to be transmitted to the brain. Still a third neuromuscular theory suggests that abnormal stimulation of the muscles that control the ear drum and bones of the middle ear is at fault. Sadly, there are as yet no truly effective treatments for tinnitus. What has emerged over the years, however, from what many patients have told The TMJ Association and from clinical studies, is that the risk for tinnitus is higher among TMJ patients than people without TMJ.
Now comes a study to suggest that not all TMJ patients have the same degree of risk. The study makes use of the fact that TMJ diagnosis has grown more refined over the years, using criteria that enable classifying patients into three major subgroups. The groups are based on whether symptoms primarily involve pain in the chewing muscles associated with the TM joint (called MPD for myofascial pain diagnosis); whether symptoms chiefly relate to displacement of the disc that separates the head of the mandible from the skull (called DD for disc displacement)), or whether the joint itself is affected by degenerative arthritic changes (called DJD for degenerative joint disease). These are not mutually exclusive groups, since patients can have symptoms spanning all three categories.
The study conducted by Susee Ravuri of the University of Washington Dental School was based on a large number of volunteers seen at three sites (the Universities of Washington, Minnesota and Buffalo). Of the initial 705 subjects seen, 614 met the diagnostic criteria for TMJ and were classified according to the three TMJ subtypes. They were also assessed for the presence of tinnitus and answered other health and behavior questions. The remaining 91 subjects served as controls. Tinnitus was reported by 41 percent of the TMJ population compared to only 5.5 percent in the controls. However, when analyzed by subtype, the rate of tinnitus in the MPD group was 48 percent, compared to 15.6 percent in the non-MPD group (who had been diagnosed as either DD, DJD or both). Patients diagnosed with MPD only had the still higher tinnitus rate of 64.3 percent.
The study also considered whether other factors might contribute to the risk of tinnitus, such as pain when mild pressure was applied to various sites in and around the TM joint, the presence of oral habits like tooth clenching or grinding, headaches in the temporal region, and psychological symptoms such as anxiety and depression. Here the factor that stood out in relation to tinnitus was headaches in the temporal region. Thirty-seven percent of patients with a diagnosis of MPD only (no DD and no DJD) had tinnitus, but that percentage increased to 52 percent if they also had temporal headaches. MPD patients overall experienced a higher number of painful pressure sites compared with the other subgroups, and if they also reported tinnitus, they scored higher on scales of anxiety, pain intensity, and interference of pain with daily activity. Interestingly, oral habits such as clenching or grinding or other abnormal jaw movements were not found to be associated with tinnitus.
A follow-up study
The original subjects were followed for a period of 7.8 years and then follow-up studies were conducted on 388 subjects. Of this smaller-sized and older-aged group, 279 subjects were diagnosed with TMJ and classified by subtype, but the rate of tinnitus had dropped to 28 percent compared with the 41 percent in the baseline study (consistent with studies that show declines in tinnitus with age). In the follow-up group, the highest tinnitus rate (30 percent) was found in the MPD subgroup.
The availability of diagnostic criteria to classify TMJ patients into three distinct but not mutually exclusive subgroups has enabled an analysis indicating different risks for tinnitus per subgroup. The risk for tinnitus is greatest in patients who present with MPD (pain in the masticatory or chewing muscles associated with the TM joint). If these patients also report headaches in the temporal region, their risk for tinnitus is at least three times higher for tinnitus than MPD patients without headaches. These findings lend some support to the neuromuscular theory as a basis for tinnitus, the idea that excessive tension or other dysfunctional stimulation of the masticatory muscles affects nearby ear muscles leading to the generation of tinnitus sounds.