Low level laser therapy of tinnitus - a case for the dentist?

Jan Tunér DDS, Swedish Laser-Medical Society (www.laser.nu)
Jan.tuner@swipnet.se

ABSTRACT
Tinnitus is a debilitating condition with an increasing incidence, especially among the young generation, due to intensive sound levels at concerts and in headsets. It is, however, not solely a problem of the modern world. The condition is described in papyrus documents dating back 600 BC. Some famous historic persons have suffered from tinnitus, such as Martin Luther, Jean-Jaques Rousseau and Ludwig van Beethoven. It is estimated that roughly one person in ten is affected by tinnitus of some degree. The origin of tinnitus is controversial. It is claimed that tinnitus is located in the inner ear but also that it actually is situated in the brain cortex, as evidenced by PET-scanning. It is reasonable to beleive that the condition can have several origins and that one of these then is of interest to the dentist. Low level lasers have been claimed to have a therapeutic effect on tinnitus and vertigo. In these cases the irradiation has been directed towards the cochlea. Low level laser therapy (LLLT) is also reported to be useful in the treatment of temporo-mandibular disorders (TMD). Furthermore, some patients are cured from their tinnitus when a proper TMD therapy has been performed. It now also appears that low level lasers can be used to advantage in the treatment of TMD-related tinnitus, and without actually irradiating the inner ear.

LOW LEVEL LASERS
Since the beginning of the 80's low level lasers have become increasingly popular as an additional treatment possibility in many professions, such as chiropractors, naprapaths and physiotherapists but not so much in traditional medicine and dentistry. In spite of more that 100 positive double blind studies there remains a sceptical attitude. In dentistry alone, more than 90% of the published studies show positive results. It is true that several studies have failed to show any result, but it is not uncommon for such studies to contain serious flaw [1]. And it is not to be expected that any dosage or any wavelength of low level laser will produce a biological response.
Low level lasers are generally in the visible - near visible range of the spectrum. The most common types are HeNe (633 nm), InGaAlP (630-685 nm), GaAlAs (780-870 nm) and GaAs (904 nm). Power output in the beginning ranged from 1-10 mW. With the advent of less expensive diodes the power has increased considerably and GaAlAs lasers are now available with power of even 1 000 mW (1 Watt). Increased dosage and power density have proven to be important and the clinical results have consequently been improved. Suitable dosage varies depending on the condition and the depth of the target tissue, but generally 4-20 J/cm2 are applied. Red laser light is optimal for superficial conditions such as mucosa and skin whereas infrared is better for pain and deeper lying conditions because of its superior penetration.
Biological responses of cells to laser irradiation are suggested [2] to occur due to physical and/or chemical changes in photoacceptor molecules, components of the respiratory chain like cytochrome c oxidase and NADH-dehydrogenase. Hypotheses about primary mechanisms at the interface of laser irradiation and tissue are redox properties alterations, NO release, superoxide anion reactions, singlet oxygen production and local transient heating of chromophores. Further, secondary processes are triggered where the mechanisms are performed "in the dark". Thus, distant effects can be obtained far from the irradiated area. The redox-regulation mechanism may explain the positive effect of tissues characterized by acidosis and hypoxia.

LOW LEVEL LASER OF TINNITUS - THE LITERATURE
Low level laser therapy (LLLT) has been suggested as a possible therapy for tinnitus. Several studies have used Ginkgo biloba infusions in combination with LLLT, the former being a widespread but not well documented therapy for tinnitus. The number of studies are few and they will be briefly described in the following.

Witt [3] is one of the pioneers in this field, but to the knowledge of the author his results have not been published in any peer-review journal. Witt combines infusion of Gingko biloba (Egb 761, 17.5 mg dry extract per 5 ml amouple)) and laser. This may be a favourable combination but an evaluation of the contribution of the laser is not possible. More than 500 patients have been treated since 1989 and Witt claims that more than 60% of the patients have reached a considerable or total relief . The laser used is a combination of HeNe 12 mW/GaAs 5 x 10 mW. Treatment technique not stated.

Swoboda [4] did not find any significant effect of Gingo/laser. However, the ginkgo infusion used was at a homeopathic level (D3 = 1:1000 dilution), acc. to Witt.

Partheniadis-Stumpf [5] also failed to find any effect from the combined ginkgo (6 ml Tebonin) infusion and laser. However, the laser was applied at a distance of one cm above the mastoid. The non-contact mode reduces penetration considerably and the mastoid is not ideal for reaching the inner ear.

Plath [6] treated 40 tinnitus patients with 50 mg Ginkgo biloba. 20 patients received sham laser irradiation, 20 real laser. A HeNe 12 mW/GaAs 5 x 15 mW GaAs laser was used, irradiation procedure approximately the same as for Partheniadis-Stumpf. In this study, 50% of the patients reported a reduction of the tinnitus of more than 10 dB, compared with 5% in the control group, in both self-assessment and audiometric findings.

A similar study has been performed by von Wedel [7]. 155 patients were treated with Ginkgo infusion (5 ml Syxyl D3) and laser. The outcome was negative. No information about the type of laser, treatment technique or dosage is given, making an evaluation impossible.

Shiomi [8] has investigated the effect of infrared laser applied directly into the meatus acusticus, 21 J, once a week for 10 weeks. The result of this non-controlled study is as follows: 26% of the patients reported improved duration, 58% reduced loudness and 55% reported a general reduction in annoyance.

The same author [9] has also examined the effect of light on the cochlea, using guinea pigs. Direct laser irradiation was administred to the cochlea through the round window and the amplitude of CAP was reduced to 53-83% immediately after the onset of irradiation. The amplitude then returned to the original level. The results of this investigation suggest that LLLT might lessen tinnitus by suppressing the abnormal excitation of the 8th nerve or the organ of Corti.

More or less the same parameters were used in a controled study by Mirtz [10] but in this case there was no significant effect.

Wilden [11] [12] has applied a different method where the dose has been increased considerably. A set consisting of one HeNe laser and three powerful GaAlAs lasers is used, covering a large area over and around the ear, in the non-contact mode. Doses between 3.000 and 5.000 J are given each session. Laser is applied as a monotherapy. More than 800 patients have been treated with this concept and positive effects are reported, even for vertigo. Recent injuries in "the disco generation" are more easily treated than long-term chronic conditions. In a separate study [13] Wilden reports improvment of the hearing capacity of these patients, as evaluated by audiometry.

Beyer [14] has performed a very exact ex-vivo laser penetration study. Based on these findings it was possible to calculate the energy needed to obtain a dose of 4 J/cm2 in the cochlea itself. 30 patient were treated five times within 2 weeks. One group was irradiated with 635 nm diode laser, the other with 830 nm diode laser. By self-assessment around 40% of the patients reported a slight to significant attenuation of the tinnitus loudness of the irradiated ear. This study has been followed by a double blind study.

Prochazka [15] has evaluated the effect of combined Egb 761 Ginkgo infusion and laser in a double blind study. 37 patients were divided into three groups. One group had Egb 761 only, one Egb761 and placebo laser, one Egb761 and real laser, 830 nm. The results in the three groups were as follows: no effect 29/26/19, less than 50% relief 44/48/29, more than 50% relief 18/26/36, no more tinnitus 9/0/26. Irradiation was performed over the mastoid and over the meatus acusticus, twice a week, 8-10 sessions, total 175 J.

Rogowski [16] divided a group of 32 tinnitus patients into one group receiving LLLT and one receiving a placebo procedure. Dose, wavelength and treatment technique not stated in the available English abstract. The effect was evaluated through VAS. Within the patient group transiently evoked otoacoustic emissions (TEOAE) were measured before, during and after therapy. No significant difference between laser and placebo was found in annoyance or loudness of the tinnitus and in changes of TEOAE amplitude. These results indicate that there is no relationship between the effect of low-power laser and changes in cochlear micromechanics.

A few other indications in otorhinolaryngology have been treated with low level lasers, even with intravenous irradiation. [17-20]

It is obvious that the available literature on laser therapy of tinnitus is scarse and ambiguous. Some studies have used a combination of Ginkgo and laser, others laser as monotherapy. Differences in wavelengths, pulsing, dosage and treatment technique makes a firm evaluation impossible. However, the positive results reported in some studies do merit attention and further research. Recent clinical experience also suggests that the doses necessary for successful outcome of the therapy have to be increased considerably. Tinnitus is a grave condition, sometimes leading to suicide. It is also an increasing problem and the existing treatment modalities offered to tinnitus patients are not very effective. Young persons suffering from acoustic chocks (concerts, discos) can be more successfully treated with laser therapy. Understandably enough, a long standing condition in elderly persons is a severe condition taking 10-20 sessions to influence.

LASER THERAPY OF TMD
The following is an account of some studies published in the field of low level laser therapy for TMD.
Hansson [21] studied the effects of GaAs laser on arthritis of the temporo-mandibular joint. The author stresses that lasers are not an alternative to conventional treatment, but that it seems possible to reduce healing periods and more quickly reduce inflammation.

Bezuur and Hansson [22] treated a group of 27 patients suffering from long-term problems related to TMD with a GaAs laser. The treatment was administered over the joint on five consecutive days. 80% of the 15 patients with arthrogenous pain experienced total pain relief. The maximum jaw-opening ability increased during the treatment period, and continued to increase during the year that the group was monitored. The group suffering from myogenic problems also improved, both in terms of pain and jaw-opening ability. The effect here was, however, much lower. As the muscles were not treated, it is assumed that this group also had undiagnosed arthritis. The reduction of joint sounds may possibly have been due to an increase of metabolism in articular cell structures, e.g. an activation of the synovial membrane, producing more synovial fluid.

Eckerdal [23] reports on the clinical experience of a 5-year non-controlled study of perioral neurapathias. The treated diagnoses were trigeminal neuralgia, atypical facial pain, paresthesias, and TMD pain. Of these diagnoses, the TMD pain group was the most successful one. At the end of treatment, 73% of the patients (N = 40) had a good response, at six months still 73%, and at one year 70%. 10 J/cm2 was applied to the joint over 4-8 sessions.

In a study comprising 75 cases, Bradley [24] found LLLT effective as a monotherapy when treating acute joint pain (less than eight weeks duration). In more chronic cases, without bone changes on X-ray, LLLT was used as an adjunct to splints and the like. In osteoarthritic cases, LLLT can be almost as useful as intra-articular steroids.

Bradley [25] used GaAs laser acupuncture when treating a small group of patients suffering from TMJ pain dysfunction syndrome who had not responded to treatment with a bite splint or psychotropic medicine. Needle acupuncture was used in a comparative group. Both types of acupuncture can be studied with thermography. Biostimulation was observed to yield vascular effects which locally resemble the vascular effects achieved with needle acupuncture, although it takes more time for laser stimulation to take effect. Both forms of acupuncture were more effective on known acupuncture points than on randomly chosen points. St 6 was used throughout as a "known acupuncture point".

Kim [26] divided a group of 36 patients with maxillary joint problems into three therapy groups. The patients were treated with bite splints, GaAlAs laser treatment, or laser acupuncture. The treatment results were compared after two and four weeks with a check on status before treatment. The following conclusions were drawn: The patients' subjective discomfort was reduced in both the bite splint and laser treatment groups. The improvement in the laser group was much greater than in the bite splint group. Clinically observable symptoms showed a significant reduction in all groups, but the group treated with laser light responded faster to treatment than the other groups. EMG activity gradually decreased in all the groups - and without any great difference between groups. Laser treatment had more beneficial effects than bite splints, while laser acupuncture produced the poorest results.

Lopez [27] treated a group of 168 patients with problems related to TMD with a combination of bite splints and HeNe laser. An obvious improvement could be observed in 52 of the patients after a single treatment. After ten treatments, 90% of the patients had improved. No further improvement was brought about in the other 10% by administering further treatments. The laser treatment was given directly over the maxillary joint - 6 mW for five minutes (1.8 J). The extent of healing was inspected using a tomographic X-ray before treatment and after six months. At that point, healing had advanced to a stage usually seen after 12 to 18 months when only a bite splint is used. In a group of 88 patients with pains in the jaw muscles, pain was alleviated for up to six hours, but without lasting results. The author concluded that HeNe lasers are effective as a complementary method to bite splints when treating arthrosis and arthritis, but that this wavelength is not optimal for myogenic pain.

Hatano [28] used a GaAlAs laser to study the effect on palpation pain in 15 patients with TMD. A 30 mW laser was used for 3 minutes (5.4 J) in the area of one temporo-mandibular joint. The other side served as control. Palpation score was estimated directly after irradiation and at 20, 40, and 60 minutes after irradiation. There was a significant decrease in palpation pain with better values at 20, 40, and 60 minutes than directly after irradiation.

Bertolucci [29] compared two groups of patients (16+16) receiving physical therapy for mandibular dysfunction. One group received sham irradiation, the other GaAs during three weeks. The results were as follows (treatment group/placebo group): change in pain 40.25/1.56; change in vertical opening 1.35/-0.05; change in left and right deviation 3.78/0.62.

Interleukin-1b in the synovial fluid is associated with TMD pain [30]. In a study by Shimizu [31], GaAlAs laser light influenced the production of this substance.

Ivanov [32] treated 109 patients with temporomandibular joint arthritis and arthrosis with an HeNe laser (12 mJ/cm2, 3-7 treatments). 89% of the patients reported clinical improvement.

In a double blind study by Sattayut [33], the higher doses (20 J per point, 300 mW) were clearly more effective than 4 J and 60 mW . In this study GaAlAs was used as monotherapy. Following a period of 2-4 weeks after therapy (3 sessions in one week) there was an average of 52% reduction of pain as assessed by SSI pain questionaire.

CMD, TMD, LLLT AND TINNITUS
It has been know for decades that patients with temporo-mandibular joint dysfunction (TMD) and crano-mandibular disorders (CMD) also may have tinnitus problems, and that there is a connection between the two.

In a book by Myrhaug [34], the author underlines the fact that there are two muscles in the inner ear which are innervated by two facial nerves. M. tensor tympani is innervated by n. trigeminus and m. stapedius is innervated by n. facialis. Intensive action in the masticatory muscles could therefore influence these two small muscles as well and thereby cause the tinnitus sensation.

Bjorne [35] compared a group of 31 patients suffering from Ménière's disease with a control group, matched for sex and age. The patients in the Ménière group had statistically significant more signs of crano-mandibular disorders, such as tenderness to palpation upon the masticatory muscles, of the temporo-mandibular joint, upper part of the trapezius in the area of the atlas, the axis and the third cervical vertebra.

In a second study by Bjorne [36] 24 of the 31 patients from the previous study were compared with 24 control subjects regarding the frequency of signs and symptoms of cervical spine disorders. Symptoms of cervical spine disorders as head and neck/shoulder pain, and signs as limitations in side-bending and rotation movements were more frequent in the patient group as well as tenderness to palpation of the neck muscles. 39% of the Ménière patients could influence their tinnitus, both sound level and pitch, by protrusion or lateral movement of the mandible or by clenching their teeth. 75% of the patients could trigger their attacks of vertigo by extension, flexion or side-rotation of the head and neck.

A correlation between tinnitus and tension of the lateral pterygoid muscle has also been found [37]. Further correlation between signs and symptoms of TMD and tinnitus is indicated in studies by Rubenstein [38] and Ciancaglini [39].

Wong [40] reports that the styloid process and its attachments are often the center of TMD problems and that no less than 11 symptoms have been observed in connection with soft tissue lesions in this region, one of them being tinnitus. The muscular symptoms are suitable for low level laser therapy acc. to the authors.

DISCUSSION
There is reason to beleive that a subgroup of the tinnitus (and vertigo) patients actually have a primary crano-temporo-mandibular dysfunction problem and that the tinnitus sensation is a secondary phenomenon. A greater awareness of this possibility and a closer cooperation between otorhinologists and dentists would probably reduce the problems of the patients in this subgroup. The size of this group is unknown, since the CMD relation is seldom diagnosed, nor treated. The correlation between Mènière's disease and CMD seems to be more frequent than the correlation between an isolated tinnitus problem and CMD.
Some of these patients in the mentioned subgroup can change the intensity or pitch of their tinnitus by clenching or opening their mouth wide, and in some cases even by changing the position of their head. Irradiating a muscle involved in the creation of the tinnitus phenomenon can alter the carachter of the tinnitus. This offers a possibility of an initial diagnosis of the type of tinnitus. It is not unusal for the tinnitus sensation to disappear temporarily after laser irradiation. Repeated irradiation can keep the patient free of tinnitus and also make the patient more aware of the hypertension in the muscles.
CMD/TMD is a very common condition and the suggested treatment modalities are multifold. Occulsal splints and elimination of occlusal interferences are standard procedures but the scientific documentation of these, and other treatment modalities are still poor, although the clinical experience seems to verify their effectiveness.
The concept of treating tinnitus and vertigo patients through occlusal stablisation is not new but so far not very much explored. Adding low level laser irradiation to this therapy is even less explored and there is very little research. The objective of this article is not to give precise recommendations about treatment procedures but rather to put the light on the possibility for the dentist to improve the quality of life of many vertigo and tinnitus patients and that the dentist could play an important role in this treatment. Further research is warranted.

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