Efficacy of Low-Level Laser Therapy in Subjective Tinnitus Patients with Temporomandibular Disorders

Abstract

Objective and background: Tinnitus is an apparent sound, perceived in the ear with no stimulus. It has been described as a sound originating from the brain. It affects 17% of the general population. Etiological factors for tinnitus include temporomandibular joint disorders (TMJ, TMD) and Costen's syndrome. The aim of treatment is to eliminate the tinnitus or at least decrease its apparent volume. Materials and methods: In total, 46 patients referred to our department with bilateral subjective tinnitus with TMDs were selected for this study. Low-level laser therapy (LLLT) with an neodymium-doped yttrium aluminum garnet (Nd:YAG) (1064 nm) laser, LLLT with a diode laser (810 nm), and placebo treatment were applied to the patients. There were 15 patients each in the Nd:YAG and placebo groups and 16 patients in the 810 nm diode laser group. LLLT was applied for 10 days, once per day. A visual analog scale (VAS) was used, with values between 0 and 10. VAS scores were recorded before treatment, on the last day of treatment, and 1 month after treatment. The VAS scores were the same on the last day of treatment and 1 month after treatment. The VAS scores before treatment and at 1 month after treatment were compared in a statistical analysis. Results: There were statistically significant differences in the Nd:YAG laser (p = 0.001) and 810 nm diode laser groups (p = 0.005), but no difference in the placebo group (p = 0.065). Conclusions: Both the Nd:YAG and 810 nm diode lasers were effective for the treatment of subjective tinnitus related to TMDs.

Introduction

Otologic, neurologic, and traumatic factors, as well as side effects of drugs, immaturation, depression, and temporomandibular disorders (TMDs) play important roles on etiology of tinnitus. Aural symptoms such as tinnitus are generally interested in TMDs.¹ The primary symptoms of TMDs are jaw/face pain, pain on jaw movements and impaired jaw mobility, temporomandibular joint (TMJ) sounds (click, crepitation), auricular pain, head and neck pain, tinnitus, and vertigo.² Several theories have been proposed to explain the relationship between TMDs and tinnitus. One of them is that the hyperactivity on myofascial muscles is transferred to tensor tympani and tensor veli palatini muscles. The second is that TMDs contain all disorders of mandible, facial muscles, and TMJ. The etiology of TMDs is multifactorial, including factors related to patient's health status, psychological, psychosocial, and gender factors, as well as local factors such as overload due to bruxism.³

Tinnitus is a kind of hearing in the ear, which is not associated with external stimulus, and occurs involuntarily.⁴ Tinnitus is divided into two groups: objective and subjective tinnitus.⁵ Objective tinnitus is real sound that is heard by other people, but subjective tinnitus cannot be heard by another person.⁶ TMDs and Costen's Syndrome are dental causes for tinnitus.⁷

Tinnitus treatment aims to eliminate tinnitus completely or decrease its severity. However, it is not possible to eliminate tinnitus completely in most of the patients. Management of tinnitus includes masking, medications, educational behaviors, and rarely surgical treatment. Other complementary therapies include herbal therapies, electromagnetic therapies, hypnotherapy, and low-level laser therapies (LLLT).⁸ Clinical effect of LLLT is defined as photobiomodulation. LLLT increases the cell proliferation, collagen synthesis, fibroblast activity, growth factor release, and bleeding circulation, and accelerates the metabolism.⁹ Recovery of peripheral nerve damage is accelerated by local bleeding circulation in the ear. According to some opinions, recovery of cochlear dysfunction is based on this mechanism.^10,11 Neodymium-doped yttrium aluminum garnet (Nd:YAG) and diode lasers are often used for photobiomodulation.¹²

The aim of this study was to evaluate the effectiveness of LLLT in subjective tinnitus with TMDs.

Materials and Methods

This study was designed as a prospective, randomized, placebo-controlled, and single-blinded trial. The study sample consisted of 46 patients ranging in age from 13 to 65 years, presenting with simultaneous subjective tinnitus and TMDs. Initially, all patients were evaluated by an otolaryngologist and underwent thorough otologic examination and audiologic evaluation. Tinnitus severity, type of tinnitus, and frequency of tinnitus were noted. Patients who diagnosed with subjective tinnitus at the Otolaryngology Clinic were referred to Department of Prosthodontics, Faculty of Dentistry, Gaziantep University for detailed evaluation of TMDs. Each patient was examined and diagnosed according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). The patients were classified into three main groups according to the RDC/TMD as follows: group I (muscle disorders), group II (disk displacement), and group III (arthralgia, osteoarthritis, and osteoarthrosis). The same clinician performed the clinical examinations to standardize the study. All participants had experienced tinnitus for at least 6 months. Patients with hearing loss, Meniere's disease, chronic otitis media, otitis media with effusion, vestibular schwannoma, cardiac disease, degenerative changes in TMJ, pregnancy, and orofacial pain for more than 6 months were excluded from the study. A form consisting of RDC/TMD, tinnitus evaluation criteria, and a tinnitus questionnaire were filled out for all patients. Systemic diseases, mandibular movements, oral parafunctional habits, myofascial pain, occlusions, and status of teeth, buccal areas, the tongue and TMJ were noted. All patients provided written informed consent and Gaziantep University Ethics Committee approved the study.

Patients were randomly assigned to the following groups: Nd:YAG laser (Nd:YAG), 810 nm diode laser, and placebo. The 46 patients were assigned randomly to the following therapy groups: Nd:YAG laser (Nd:YAG; n = 15), 810 nm diode laser (n = 16), and placebo (n = 15).

In the literature, scales based from 0 to 10 had been used for the severity of tinnitus, hypoacusis sensation, hyperacusis, and dizziness/vertigo.¹³ Considering the literature before treatment, all patients were required to complete a questionnaire that was used to determine the effectiveness of LLLT with a visual analog scale (VAS). The VAS questionnaire had symptom rating scales that required the patient to assign a score of 1–10 based on the severity of the tinnitus. At the end of treatment, each patient was required to answer the VAS questionnaire again (minimum tinnitus score = 0, maximum = 10). The same questionnaires were used again 1 month after treatment.

In this study, the laser wavelength and settings were adjusted as described by Demirkol et al.⁹ An Nd:YAG laser (1064 nm, Fidelis Plus III; Fotona, Ljubljana, Slovenia) and an 810 nm diode laser (XD-2 diode laser; Fotona) were used with a single-probe laser handpiece parallel to the external auditory canal. The energy density was set at 8 J/cm², with 0.25 W output power. The probe diameters of Nd:YAG and 810 nm diode laser were 0.9 and 0.6 cm, and the focal spot areas were 0.625 and 0.282 cm², respectively. LLLT was applied precisely and continuously into the external auditory meatus for 20 sec for Nd:YAG laser and 9 sec for 810 nm diode laser. The patients were exposed to the laser while seated in a dental chair with their necks supported, five times per week, for a total of 10 sessions. The dosage was calculated as power (W)/beam area (cm²) × time (s) = J/cm².

The laser parameters for the Nd:YAG laser irradiation were as follows: 0.25 W output power, 1000 μsec pulse duration (VLP mode), 10 Hz frequency, 25 mJ pulse energy, 25 W peak power, and 8 J/cm² energy density.

For the placebo group, the laser device was used and the handpiece was anteromedially applied to the external auditory meatus with no irradiation. At 1 month after the last laser irradiation, the patients were contacted and tinnitus VAS scores were recorded. The same protocol was followed for all groups.

Statistical analysis

The data were analyzed using SPSS software (version 22.0 for Windows). The level of significance was set at 5% (p < 0.05). Data for the pretreatment tinnitus values in the groups were analyzed with the Kruskal–Wallis and multiple comparisons tests. The tinnitus VAS scores at baseline and 1 month after treatment were analyzed using the Wilcoxon test in each group. Median (25–75%) values for numeric variables and numbers and percentages (%) for categorical variables are reported.

Results

In this prospective study, 46 patients with simultaneous subjective tinnitus (23 females and 23 males; aged 13–65 years) and TMDs were included. No statistical analysis of patient age or sex was conducted between the groups (Table 1).

Table 1.

Demographic Characteristics of the Patients

Characteristics	Male no. (%)	Female no. (%)	Age (mean ± SD)
Nd:YAG (n = 15)	7 (46.7)	8 (53.3)	36.6 ± 14.7
Diode (n = 16)	10 (62.5)	6 (37.5)	40.1 ± 14.6
Placebo (n = 15)	6 (40)	9 (60)	37.7 ± 13.8
Total (n = 46)	23 (50)	23 (50)

Nd:YAG, neodymium-doped yttrium aluminum garnet; SD, standard deviation.

Statistical analyses were performed only on the VAS scores before treatment and 1 month after the last laser irradiation. The mean VAS score differences, significance levels, and median values are shown in Table 2. There were statistically significant differences between the values at baseline and 1 month after treatment in the Nd:YAG laser (p = 0.001) and diode laser (p = 0.005) groups, but no such difference in the placebo group (p = 0.065; Wilcoxon test; Table 2).

Table 2.

Comparison of Subjective Tinnitus Scores on a Visual Analog Scale at Baseline and 1 Month After Treatment

	VAS score (range 0–10)
Groups	Baseline median (25–75%)	1 month median (25–75%)	p^*
Nd:YAG	5 (3–5.5)	0 (0–2)	0.001^*
Diode	8 (4.25–9.50)	5.5 (1.5–8)	0.005^*
Placebo	6 (4–8)	5 (4–7)	0.065
p (Intergroups)	0.032^*	0.001^*

Statistically significant p < 0.05.

The percentage improvement in tinnitus severity scores, according to the VAS and based on the median values, was 100% (group Nd:YAG), 30% (group diode), and 0% (placebo). Values indicating the percentage improvement between the groups are shown in Table 3.

Table 3.

Percentage Improvement in Tinnitus Visual Analog Scale Scores Between Baseline and 1 Month After Treatment

	Groups
Percentage improvement (%)	Nd:YAG	Diode	Placebo	p
Median (25–75%)	100 (60–100)^†,‡	30 (0–65.63)	0 (0–22.2)	0.001^*

Significant at p < 0.01, Kruskal–Wallis.

†

Significant versus Placebo at 0.05 level, Dunn's test.

‡

Significant versus Diode at 0.05 level, Dunn's test.

Discussion

This study was designed to investigate the clinical effects of LLLT applied directly to the meatus acusticus externus on subjective tinnitus patients with TMDs. The results of this placebo-controlled study demonstrate that Nd:YAG laser or 810 nm diode laser treatment was effective for subjective tinnitus with TMDs versus placebo treatment. VAS scores were used as subjective criteria for the evaluation of tinnitus severity before and after treatment.^4,14 VAS scores have been used in other studies to measure tinnitus severity. Significant reductions in tinnitus VAS scores were observed in both LLLT groups at 1 month after treatment. The tinnitus VAS scores on the last day of treatment and 1 month after treatment were the same; thus, only the tinnitus VAS scores recorded before and 1 month after treatment were compared statistically.

This study included patients with simultaneous tinnitus and TMDs. Many theories have been proposed regarding the etiological relationship between otologic symptoms and TMDs.⁷ Earache, hearing loss, and tinnitus symptoms associated with TMDs were first reported by Costen in 1934.¹⁵ Another study showed that subjects with tinnitus had a significantly higher frequency of TMDs and a higher mean number of painful masticatory muscles.¹⁶ However, the relationship between tinnitus and TMDs has been variable and inconsistent. Numerous attempts have been made to explain the connection according to anatomical, functional, embryologic, or neurological theories, but there is no consensus.¹⁷ The most accepted theory is that a mandibular deep bite leads to pressure on the Eustachian tube, which causes tonic contractions in the tensor tympani and stapedius muscles, and results in difficulty hearing low tones.¹⁸ Another theory is that TMDs are related to middle ear diseases, which are mainly caused by Eustachian tube dysfunction.¹⁹ Considering this relationship between subjective tinnitus and TMDs, etiologic treatment is important.^9,20

Many clinical studies have investigated the effects of LLLT on tinnitus. Our results are consistent with the literature regarding the efficacy of LLLT for tinnitus treatment. It has been reported that LLLT is an effective treatment for tinnitus, or at least that it can reduce the severity.^21

–25 Although the precise mechanism of action of LLLT remains unclear, its clinical effect is referred to as “photobiomodulation.”¹¹ The major mechanism of photobiomodulation is based on metabolic activation through stimulation of the cellular respiratory chain in mitochondria. This increases vascularization and enhances the oxygen supply in hypoxic cells.²⁶ At the cellular level, protons are released into the cytoplasm with low-level laser application. This reduces the permeability of the duct to Na⁺ and K⁺ ions, decreasing the action potential frequency.⁴ LLLT also accelerates the functional and morphological recovery of severely injured nerve tissues, including damaged cells in the auditory system, and it provides therapeutic effects in patients with inner ear disorders.²⁷ LLLT has been used for hyperacusis, sound distortion, chronic hearing disorders, sudden hearing loss, Ménière's disease, and tinnitus treatment in otology.²³ In this study, both the etiologic factor and the tinnitus were targeted by the photobiomodulation effect of LLLT, and successful results were obtained.

In the literature, over the last 30 years, there has been growing interest in the clinical application of LLLT. However, there is still no standard protocol for LLLT in terms of low-intensity laser type, dose, duration, wavelength, session, frequency, or evaluation period.⁹ In these studies, the LLLT procedures applied were typically similar, He-Ne and/or Ga-Al-As lasers with wavelengths between 630 and 900 nm and a maximum output power between 10 and 50 mW.²⁸ LLLT was first used to treat inner ear diseases in 1988, by Dr. Uwe Witt of Hamburg, Germany.²¹ In 1997, LLLT was used for tinnitus treatment with an output power of 40 mW and a wavelength of 830 nm for 9 min per week for 10 or more weeks. Using a 5-point scale, decreases in tinnitus volume were reported by 55% of patients.²⁹ In a recent clinical trial, 65 patients were treated for 20 min once a day for a total of 3 months with a laser set to an output power of 5 mW and a wavelength of 650 nm; this LLLT was found to be useful in the treatment of chronic tinnitus.³⁰

In the literature, diode lasers have been used for photobiomodulation in LLLT; however, few studies have used Nd:YAG lasers. The most important reason for this is that Nd:YAG lasers are quite costly.³¹ In some studies, an Nd:YAG laser was used to provide a photobiomodulation effect, and positive results were reported.^9,12 Both of the low-level laser treatments in this study were effective versus the placebo for tinnitus. Better results were obtained in the Nd:YAG laser group, likely because of the high penetration depth of the Nd:YAG laser in tissues.⁹ However, details regarding the exact mechanism need to be worked out and long-term effects should be followed.

Conclusions and Summary

The particular types of LLLT used in this study (1064 and 810 nm, with settings of 8 J/cm² and 250 mW output power) were effective for subjective tinnitus patients with TMDs according to this placebo-controlled randomized clinical trial. LLLT with the Nd:YAG laser was more effective than that with the 810 nm diode laser. There was no statistically significant difference in the placebo group. No negative side effect was reported under the conditions of this study.

Footnotes

Acknowledgments

Gaziantep University Scientific Research Projects Governing Unit supported this study (Project No.: DHF.12.03).

Ethical Approval

Ethics committee approval was received for this study from the ethics committee of Gaziantep University (20.12.2011/251). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration, and its later amendments or comparable ethical standards.

Author Disclosure Statement

No competing financial interests exist.

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