Increased risk of tinnitus in patients with temporomandibular disorder:
a retrospective population-based cohort study
Chun-Feng Lee • Ming-Chia Lin • Hui-Tzu Lin •Cheng-Li Lin • Tang-Chuan Wang • Chia-Hung Kao
C.-F. Lee
Department of Oral and Maxillofacial Surgery, Buddhist Tzu Chi General Hospital, Taichung Branch, Taichung, Taiwan C.-F. Lee
Department of Dental Laboratory Technology, Shu-Zen Junior College of Medicine and Management, Kaoshiung, Taiwan M.-C. Lin
Department of Nuclear Medicine, E-DA Hospital, Kaohsiung, Taiwan
H.-T. Lin
Department of Nursing, Changhua Christian Hospital, Changhua, Taiwan
C.-L. Lin
Management Office for Health Data, China Medical University Hospital, Taichung, Taiwan
T.-C. Wang
Otolaryngology-Head and Neck Surgery, China Medical University Hospital, Taichung, Taiwan
C.-H. Kao
Department of Nuclear Medicine and PET Center, China Medical University Hospital, Taichung, Taiwan
C.-H. Kao (&)
Graduate Institute of Clinical Medical Science and School of Medicine, College of Medicine, China Medical University, No. 2, Yuh-Der Road, Taichung 404, Taiwan
Abstract
This study determined whether there is an increased risk of tinnitus in patients with temporomandibular joint
(TMJ). We used information from health insurance claims obtained from Taiwan National Health Insurance (TNHI).
Patients aged 20 years and older who were newly diagnosed with TMJ disorder served as the study cohort. The
demographic factors and comorbidities that may be associated with tinnitus were also identified, including age,
sex, and comorbidities of hearing loss, noise effects on the inner ear, and degenerative and vascular ear
disorders. A higher proportion of TMJ disorder patients suffered from hearing loss (5.30 vs. 2.11 %), and
degenerative and vascular ear disorders (0.20 vs. 0.08 %) compared with the control patients. The crude hazard
ratio(HR) of tinnitus in the TMJ disorder cohort was 2.73-fold higher than that in the control patients, with an
adjusted HR of 2.62 (95 % CI = 2.29–3.00). The comorbidity-specific TMJ disorder cohort to the control patients’
adjusted HR of tinnitus was higher for patients without comorbidity(adjusted HR = 2.75, 95 % CI = 2.39–3.17).
We also observed a 3.22-fold significantly higher relative risk of developing tinnitus within the 3-year follow-up
period(95 % CI = 2.67–3.89). Patients with TMJ disorder might be at increased risk of tinnitus.
Keywords Comorbidity _ Temporomandibular disorder _Insurance _ Tinnitus _ Retrospective cohort study
Introduction
Temporomandibular disorder (TMD) is a common term used for problems concerning the temporomandibular
joint(TMJ) and masticatory muscles, and associated structures in the oral and maxillofacial region [1–3]. The
condition refers to injury of the jaw, temporomandibular joint, myofascial system of the head and neck, or
muscles of the head and neck that can cause TMD. These disorders are characterized by (1) facial pain in the TMJ
region or the mastication muscles; (2) limitation or deviation in the mandibular range of motion; and (3) TMJ
sounds during jaw movement and function. The etiology of the most common TMD remains unclear. The most
possible causes are associated with occlusal dysfunction and psychological distress [4, 5]. Intracapsular
inflammation (arthritis) or injury, and muscle pain or spasm may be caused by malocclusion, parafunctional
habits, stress, anxiety, or articular disc interference.
Several studies have observed the prevalence of ear or hearing symptoms associated with TMD [6, 7]. Costen [8]
first described this relation between the temporomandibular joint and otologic symptoms. Recent studies have
shown the association between TMD and tinnitus [9–11], a common problem in the ear, nose, and throat. Tinnitus
is a frequent otologic disorder characterized by perceived sound in the absence of an external sound source [12,
13]. Subjective tinnitus is a primary type in various forms of tinnitus, and its etiology remains unclear. Different
types of tinnitus are associated with specific etiological models[14], and its possible mechanism can arise from
hearing loss, noise trauma, presbyacusis, or ototoxic drug use. These lesions can cause abnormal neuronal
activity in central auditory pathways that can be eventually perceived as tinnitus [12, 13, 15].
Recent studies have observed that TMD is associated with tinnitus [9–11, 16]. However, although the relationship
between TMD and tinnitus is well documented, the mechanism is not understood. No large population-based
studies have outlined the relationship between TMD and tinnitus in Taiwan. Therefore, we investigated whether
TMD increases the risk of tinnitus. The original database was derived from the National Health Insurance (NHI)
system in Taiwan. The results presented in this paper were
based on a retrospective cohort study to assess the possibility
of a lower risk of tinnitus by clinical management of
temporomandibular disorders.
Methods
Data source
The Taiwan NHI program, established in 1995, is a mandatory health insurance program that offers
comprehensive medical care coverage, including outpatient, inpatient, emergency, and traditional Chinese medicine, to all residents of Taiwan, with a coverage rate of more than 99 %[17]. The National Health Insurance
Research Database(NHIRD) comprises comprehensive information of clinical visits for each insurant, such as
demographic data, date of visit, diagnostic codes according to the International Classification of Disease, 9th
Revision, Clinical Modification(ICD-9-CM), and prescriptions. The NHIRD is managed by the National Health
Research Institute (NHRI) and confidentiality is maintained according to the directives of the Bureau of the NHI.
To protect patient privacy, all personal identification numbers are encrypted before the databases are released to
the public. We used the Longitudinal Health Insurance Database 2000 (LHID 2000) as the data source for our
study. This data set released by the NHRI comprises one million randomly sampled beneficiaries enrolled in the
NHI program, consisting of all records collected on patients from 1996 to 2011.
Ethics statement
The NHRID encrypts the patients’ personal information for privacy protection and provides researchers with
anonymous identification numbers associated with the relevant claim information, which includes the patient’s
sex, date of birth, registry of medical services, and medication prescriptions. Patient consent is not required for
accessing the NHIRD. This study was approved by the Institutional Review Board of China Medical University
(CMU-REC-101-012). Our IRB specifically waived the requirement for consent.
We conducted a retrospective cohort study of patients aged 20 years of age and older who were newly
diagnosed with TMJ disorders (ICD-9 code 524.6) between January 1, 2000 and December 31, 2010 as the TMJ
disorder cohort. The index date for the patients was the date of the first medical visit for TMJ disorders. We
excluded patients who were diagnosed with tinnitus (ICD-9 code: 388.3) before the index date. For each patient
with TMJ disorder included in the final cohort, 4 age- (every 5 years), sex-, and index year-matched control
patients who were not diagnosed with TMJ disorder or tinnitus were randomly selected from the LHID 2000.
Outcome and relevant variables
All TMJ disorders and control patients were observed until diagnosed with tinnitus, withdrawal from the NHI
system, or December 31, 2011. Demographic factors and comorbidities that may be associated with tinnitus
were also identified, including age, sex, hearing loss (ICD-9 code:389), noise effects in the inner ear (ICD-9 code:
3881), and degenerative and vascular ear disorders (ICD-9 code 3880).
Statistical analysis
The independent t test, Fisher-exact test, and Chi-square test were used to examine the differences in the
demographic characteristics and comorbidities between TMJ disorders and the control patients. The incidence of
newly diagnosed tinnitus in TMJ disorders and the control patients, stratified by sex, age (B49 years, 50–64 years, and 65? years), and comorbidity (with any one comorbidity and without any one comorbidity) was calculated.
The univariable and multivariable Cox proportional-hazards regression model was used to identify variables that
predicted tinnitus in TMJ disorders and the control patients. The multivariable model simultaneously controlled
variables such as age, sex, and common comorbidities, including hearing loss and degenerative and vascular ear
disorders. For estimating the cumulative incidence of tinnitus risks in TMJ disorders and the control patients, we
performed survival analysis using the Kaplan–Meier method, with significance based on the log-rank test. All
statistical analyses were conducted using SAS software version 9.2 (SAS Institute, Inc., Cary, NC, USA). A p\0.05
was considered statistically significant.
Results
The sample comprised 7585 TMJ disorder patients and 30,340 control patients without TMJ disorders, among
whom 65.6 % were women. Approximately 65.4 % of the participants were B49 years of age (Table 1). A higher
proportion of TMJ disorder patients suffered from hearing loss (5.30 vs. 2.11 %) and degenerative and vascular
ear disorders (0.20 vs. 0.08 %) than did the control patients.The mean follow-up period was 5.80 years (SD, 3.18
years) for TMJ disorder patients and 5.79 years (SD, 3.18 years) for control patients (data not shown). In total,
362 tinnitus patients were observed among the TMJ disorder cohort, with an incidence of 8.23 per 1,000
person-years and 530 among the control patients, with an incidence of 3.02 per 1,000 person-person-years (Table 2). The crude
HR of 2.62 (95 % CI = 2.29–3.00). Figure 1 shows that the overall cumulative incidence of tinnitus was 2 % higher
in patients with the TMJ disorder than in patients without the TMJ disorder (p\0.001) at the end of the 12-year
followup.Tinnitus incidence was higher in women than in men in both cohorts. The adjusted HR of tinnitus in the
sex-specific TMJ disorder cohort to the control patients was significant for both women (adjusted HR = 2.66, 95 %
CI = 2.27–3.12) and men (adjusted HR = 2.53, 95 % CI = 1.98–3.24). The tinnitus incidence increased with age in
both cohorts, and the age-specific TMJ disorder cohort to the relative risk of the controls decreased as age
increased(adjusted HR = 2.87, 95 % CI = 2.35–3.49 for those B49 years; adjusted HR = 2.48, 95 % CI = 1.96–
3.14 for those 50–64 years; adjusted HR = 2.36 (95 % CI = 1.76–3.17) for elderly patients. The adjusted HR of
tinnitus of the comorbidity-specific TMJ disorder cohort to the control patients was higher for patients without
comorbidity(adjusted HR = 2.75, 95 % CI = 2.39–3.17). The multivariable Cox proportional-hazards regression
model further evaluated the role of age, sex, and comorbidity in the association with developing tinnitus for the
TMJ disorder cohort, compared with the control patients (Table 3). The adjusted hazard had a 3 % increment as
the function of age(adjusted HR = 1.03, 95 % CI = 1.03–1.04). The female gender (adjusted HR = 1.33, 95 % CI
= 1.15–1.54), and hearing loss (adjusted HR = 2.02, 95 % CI = 1.57–2.60) were also significantly associated with
tinnitus. The incidence density rates of tinnitus decreased with the follow-up periods among the TMJ disorder
cohort (Table 4). We observed a 3.22-fold significantly higher relative risk of developing tinnitus within the 3-year
follow-up period(95 % CI = 2.67–3.89).
Discussion
The main findings of our study suggesting that TMD increases the risk of tinnitus are consistent with current
studies [8, 10, 11]. This suggests that the pathological change of TMJ plays a crucial role in the development of
tinnitus. Higher age, and hearing loss, and male gender are confirmed as risk factors for developing tinnitus [18].
However, our finding indicated that female patients with TMD have a higher risk incidence than do male patients
with TMD. Studies have shown that an altered trigeminal nerve input caused by TMJ dysfunction may cause
activity changes in the dorsal cochlear nucleus that might affect the central auditory pathway, resulting in
perceived tinnitus [19, 20]. The etiology of TMD and tinnitus are multifactorial, and mutually associated with the
neuroanatomical relationship. Wright indicated that TMD therapy improved tinnitus symptoms [9]. This study
indicated that hearing loss was also significantly associated with tinnitus, which is recognized as clinically
relevant. The other possible mechanism associated with TMD and tinnitus is that they also share the same
psychological etiology (anxiety, stress, and depression) and further confirmation is required. This study provides
a largepopulation evidence base to depict the relationship between TMD and tinnitus (Table 4).
The strength of our study includes its use of populationbased data that are highly representative of the general
population. However, certain limitations of our findings should be considered. First, the NHIRD does not contain
systemic diseases, which may be risk factors for TMD or tinnitus. Second, the evidence derived from a
retrospective cohort study is generally lower in statistical quality than that from randomized trials because of
potential biases related to adjusting for confounding variables. Despite our meticulous study design and control
measures for confounding factors, bias resulting from unknown confounders may have affected our results.
Third, all data in the NHIRD are anonymous. Thus, relevant clinical variables, such as blood pressure, imaging
results, pathology findings, and serum laboratory data were unavailable regarding our study patient cases.
However, the data regarding TMD or tinnitus diagnoses were nonetheless reliable.
Conclusion
This population-based retrospective cohort study determined that patients with TMD have an increased risk of
tinnitus. This implies that TMD management can improve tinnitus symptoms by eliminating pathological causes
or modulating CNS sensation. The underlying mechanism of TMD remains unclear, and maintaining effective
functioning of TMJ may eliminate tinnitus risk factors. This study might also provide therapeutic hints for
clinicians. Additional large-scale studies are necessary to confirm these findings.
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