Tinnitus as a comorbidity to temporomandibular disorders-A systematic review

The aim of this systematic review was to evaluate the prevalence of tinnitus in patients with temporomandibular disorders (TMD) and the possible effects of TMD treatment on tinnitus symptoms. A search of the PubMed, Web of Science and Cochrane databases from inception of each database up to January 2017 found 222 articles. After independent screening of abstracts by two of the authors, we assessed 46 articles in full text. The inclusion and exclusion criteria reduced these to 25 articles of which 22 studies reported prevalence based on 13 358 patients and 33 876 controls, and eight studies reported effect of TMD treatment on tinnitus based on 536 patients and 18 controls. The prevalence of tinnitus in patients with TMD varied from 3.7% to 70% (median 42.3%) whereas the prevalence in control groups without TMD varied between 1.7% and 26% (median 12%). The eight treatment studies indicated that treatment of TMD symptoms may have a beneficial effect on severity of tinnitus. However, only one treatment study included a control group, meaning that the overall level of evidence is low. The finding that tinnitus is more common in patients with TMD means that it can be regarded as a comorbidity to TMD. However, in view of the lack of evidence currently available, further well-designed and randomised studies with control groups are needed to investigate whether possible mechanisms common to tinnitus and TMD do exist and whether TMD treatment can be justified to try to alleviate tinnitus in patients with TMD and comorbidity of tinnitus.