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Temporomandibular Joint Pain Analgesia by Linearly Polarized Near-Infrared Irradiation

Yokoyama, Kozo D.D.S., Ph.D.; Sugiyama, Kazuna D.D.S., Ph.D.

The Clinical Journal of Pain: March 2001 - Volume 17 - Issue 1 - p 47-51
Special Topic Series: Musculoskeletal Pain
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Objective: The objective of this study was to describe a pilot treatment of temporomandibular joint pain by linearly polarized near-infrared irradiation.

Design: A prospective clinical study.

Setting: University teaching hospital.

Patients: Patients comprised 20 women (mean age ±SD: 26.6 ± 15.2 years) with unilateral temporomandibular pain. The patients had already received other conservative treatments, but temporomandibular pain did not attenuate.

Intervention: Linearly polarized near-infrared irradiation with the Super Lizer was used.

Results: The painless interincisal distance of the mouth opening, which is one of the objective parameters of temporomandibular dysfunction, and the visual analogue scale of the affected temporomandibular joint before treatment were 33.4 ± 6.5 mm and 5.0 ± 2.7 points, respectively. Pilot linearly polarized near-infrared irradiation was applied weekly to the skin areas overlying four painful points. The present treatment alleviated temporomandibular pain after the patients had received only four weekly irradiation treatments, with final measured values of the visual analogue scale being 1.4 ± 1.6 points. The final painless mouth-opening distance increased by 7.6 ± 4.6 mm compared with the first measured distance without complications.

Conclusion: This pilot treatment using the Super Lizer provided relief from temporomandibular pain over a period of 4 weeks.

Department of Anesthesia, Kagoshima University Dental School Hospital, Sakuragaoka, Kagoshima, Japan

Received March 31, 2000; revised July 10, 2000; accepted August 15, 2000

Address correspondence and reprint requests to Dr. Kozo Yokoyama, Department of Anesthesia, Kagoshima University Dental School Hospital, Sakuragaoka 8-35-1, Kagoshima 890-8544, Japan; e-mail: yoko@dentc.hal.kagoshima-u.ac.jp

Symptoms of temporomandibular disorders (TMDs) include restricted jaw movement and pain in the temporomandibular joint (TMJ) area associated with opening of the mouth. Current management of TMDs includes physiotherapy, pharmacotherapy, occlusal therapy, injection therapy, surgery, and psychotherapy. The occlusal therapy has gained further support through studies in which occlusal adjustment aimed at elimination of deflective occlusal interferences resulted in relief of pain.1 The causes of TMDs are not clearly understood, however, and no specific effective short-term treatments have been established. In the previous pilot treatment, we reported that linearly polarized near-infrared irradiation treatment using the Super Lizer system (model HA-550; KSK Tokyo Iken, Tokyo, Japan) provided relief from the TMJ pain in patients affected with rheumatoid arthritis (RA).2,3 In the present pilot treatment, the non-RA-affected TMD patients received the same treatment and experienced alleviation of TMJ pain in the short-term treatment protocol.

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CASE REPORT

It is well known that there is a significantly higher female:male ratio in TMD patients.4 We observed 20 female patients (mean age ± SD: 26.6 ± 15.2 years) complaining of TMJ pain in the unilateral TMJ area associated with jaw movement to ensure an equal exposure time to irradiation. These patients had no systemic diseases and were taking no medications. Magnetic resonance imaging of the affected side of the TMJ revealed anterior displacement of the articular disk without reduction and no degenerative change in the mandibular condyle (Fig. 1). They had already received other conservative treatments that included pharmacotherapy or occlusal therapy, but the TMJ pain did not alleviate. In conformance with the ethical standards set out in the Declaration of Helsinki, this pilot treatment was performed only after patients had given informed consent with approval of the Institutional Review Board for Human Subjects.

FIG. 1

FIG. 1

The Super Lizer uses the latest developments in optical electronics technology such as a superiodine lamp to generate the light and an optical fiber as the light path to emit a near-infrared ray (Fig. 2). The Super Lizer is the first linearly polarized light therapeutic equipment ever made to have a wavelength range of 600 to 1,600 nm (Fig. 3).

FIG. 2

FIG. 2

FIG. 3

FIG. 3

The irradiation points used included four skin areas where the TMD patients complained of pain-generated tenderness or pain triggered with jaw movement as shown in Figure 4. The duration of irradiation to each point was 2 seconds on and 10 seconds off per cycle. Initially, with the patient's mouth closed, the four points were irradiated in 15 cycles. Next, with the patient opening the mouth maximally for 12 seconds, the four points were again irradiated. Then, with the patient's mouth closed for 12 seconds, the four points were irradiated again. A series of patterns of irradiation was performed in eight cycles as shown in Figure 5, with the intensity at each point being approximately 138 J/cm2 at a wave-length of 830 nm. The irradiation treatment regimen was performed once a week for 5 weeks.

FIG. 4

FIG. 4

FIG. 5

FIG. 5

Reduction in maximal mouth-opening capacity and pain in the TMJ area proved to be reliable indices of TMDs. The effectivness of treatment of TMDs was judged from the interincisal opening distance.5 The interincisal distance was measured at the maximal mouth opening in the absence and presence of pain before and after each treatment. Additionally, subjective TMJ pain scores (on a scale of 0-10 points) were analyzed on a visual analogue scale (VAS) to evaluate pain in maximal mouth opening before and after each irradiation treatment.

The data were represented as means ± SDs. Two-factor ANOVA with repeated measures on one factor followed by Bonferroni correction of the paired t test was performed to determine if there was a significant difference in maximal mouth-opening distances and TMJ pain scores between the first visit and subsequent visits. The paired t test was performed before and after treatment during each visit. Probability values less than 0.05 were considered to be significant.

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RESULTS

The painless maximal-mouth opening distance before treatment at the first visit was 33.4 ± 6.5 mm, and the painful maximal mouth-opening capacity was 37.6 ± 6.0 mm (see Fig. 6). These observed interincisal distances were shorter than those of healthy women.6-8 These distances were increased significantly by degrees before treatment. The average painless and painful maximal mouth-opening distances after the fifth treatment were 42.4 ± 5.7 mm (range, 33-53 mm) and 44.2 ± 4.2 mm (range, 39-53 mm), respectively. Compared with the first measured distance, the mouth-opening distances without pain increased by 7.6 ± 4.6 mm, and those with pain increased by 5.6 ± 4.3 mm as a result of our pilot treatment. These improvements in maximal mouth-opening distances were considered to be significant and clinically important.

FIG. 6

FIG. 6

Additionally, both painless and painful maximal mouth-opening distances measured immediately after each treatment were significantly longer than those measured before treatment. Although these improvements were not sustained until the next visit, the painless and painful mouth-opening distances measured at the fifth visit were maintained at the same lengths as the previous mouth-opening lengths measured after the fourth treatment.

All patients reported moderate pain (5.0 ± 2.7 points) associated with jaw movement in the unilateral mandibular condyle area when assessed using the VAS method at the first visit. Average pain scores for all patients at painful maximal mouth opening immediately after each treatment decreased relative to scores taken before treatment (Fig. 7).

FIG. 7

FIG. 7

Although this improvement was not sustained for a long period of time, pain scores before treatment decreased by degrees, with the fifth and final measured VAS values being 1.4 ± 1.6. The TMJ pain scores decreased significantly from the third visit onward. In addition, the pain scores measured at the fourth visit were maintained at the same pain scores as measured at the previous visit, which showed improvement during the previous treatment. From that stage onward, sustained relief has continued for 1 year without any treatment, and the VAS value at the 12-month follow-up examination was 0.5 ± 0.5. Our treatment had an analgesic effect on TMJ pain in the short term.

As regards the safety of this treatment, no complications occurred during the observed period.

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DISCUSSION

The current pilot treatment involved the first known application of linearly polarized near-infrared irradiation to TMD patients. An advantage of the present method is that the probe used focuses the light beam to a diameter of 10 mm, enabling it to irradiate a broader region of the joint than the probes of conventional low-power lasers, which focus on a diameter of approximately 1 mm. Therefore, the Super Lizer does not require accuracy in selecting an irradiation point. Additionally, no complications were observed in any of the patients irradiated. Because the Super Lizer emits a high-energy light beam, there is a greater risk of creating a tingling sensation or of burning the skin when irradiating continuously for more than 3 seconds at the maximum power output of 1,800 mW than there is with low-power lasers. Therefore, we performed intermittent irradiation as shown in Figure 5.

The average painless maximal mouth-opening distance before treatment was 33.4 ± 6.5 mm, which represents a shorter interincisal distance than that of healthy women.6-8 Cox and Walker8 reported that the mean value of maximal mouth opening of 700 healthy Nepalese adults with an age range of 18 to 68 years was 47.1 mm (range: 33.7-60.4 mm) and that 98% of the population surveyed fell within this range. In the present pilot study, the average painful maximal mouth-opening distance at the fifth visit was 43.2 ± 4.5 mm (range: 36-53 mm), and it was suggested that our pilot treatment using the Super Lizer resulted in a marked maximal mouth opening. In the previous pilot study, the same treatment in RA-affected TMD patients alleviated TMJ pain, with the fifth visit arrival values of VAS being 0.3 ± 0.5, but showed no remarkable improvements in painful maximal mouth-opening capacity.2,3 The difference in results between RA-affected and non-RA-affected TMDs may be caused by degenerative changes in the mandibular condyle. Conti9 demonstrated that irradiation using a gallium aluminum arsenide 830-nm laser applied to TMD patients did not lead to any marked improvements in TMJ pain. Thus, some differences are evident in the mechanism of TMJ pain relief between the Super Lizer and other low-power lasers.10,11

Although painless and painful maximal mouth-opening distances increased markedly immediately after each treatment, these effects were not sustained until the next visit (Fig. 6 and 7). The maximum power output of the Super Lizer is 1,800 mW at a wavelength of 830 nm and is approximately 20 times as high as that of gallium aluminum arsenide 830-nm diode lasers. This high-energy light beam is partially converted to thermal energy and thus produces a warm sensation. The thermal actions of the Super Lizer probably contribute to these temporary immediate improvements.

Our treatment using the Super Lizer alleviated TMJ pain successfully. In terms of the thermal action on analgesic relief of pain, Carpenter12 showed that thermal energy had an influence on neuronal membrane potential. Additionally, Bellometti and Galzigna13 showed that thermal mud pack therapy using simple methods involving the application of heat decreased prostaglandin (PGE2) and leukotriene (LTB4) serum levels in osteoarthrosis. These researchers concluded that this therapy induced pain relief by reducing inflammatory reaction. Hence, the heat action of the Super Lizer can be a potential etiologic mechanism for relief from TMJ pain in short-term treatment. The potential exists for experimental bias and a placebo effect, however, given that all patients were aware that they were receiving a new treatment for TMDs. Further studies involving a random double-blind trial are needed to clarify the precise mechanism of TMJ pain relief using the Super Lizer.

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CONCLUSIONS

Our pilot irradiation to four painful TMJ points using the Super Lizer provided relief from the TMJ pain in TMD patients over a period of 4 weeks without complications. Additionally, there was a marked improvement in maximal mouth opening length. The present findings suggest that both the light and thermal actions of the Super Lizer may contribute to relief from the TMJ pain in short-term treatment.

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REFERENCES

1. Eversole LR, Machado L. Temporomandibular joint internal derangements and associated neuromuscular disorders. J Am Dent Assoc 1985;110:69-79.
2. Yokoyama K, Oku T. Relief from the pain of the juvenile rheumatoid arthritis-affected temporomandibular joint by the irradiation of linear polarized near infrared ray. Pain Clin 1998;10:197-202.
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8. Cox SC, Walker DM. Establishing a normal range for mouth opening: its use in screening for oral submucous fibrosis. Br J Oral Maxillofac Surg 1997;35:40-2.
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12. Carpenter DO. Temperature effects on pacemaker generation, membrane potential, and critical firing threshold in Aplysia neurons. J Gen Physiol 1967;50:1469-84.
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Keywords:

Analgesia; Mouth opening; Near-infrared ray; Pain; Temporomandibular disorder

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