Paper 1/2012

J Orofac Pain. 2010 Summer;24(3):293-7.

The anti-inflammatory effect of low-level laser therapy on experimentally induced inflammation of rabbit temporomandibular joint retrodiscal tissues.

Kucuk BB, Oral K, Selcuk NA, Toklu T, Civi OG.
Department of Prosthodontics, Faculty of Dentistry, Yeditepe University, Istanbul, Turkey.

AIMS: To investigate the effect of low-level laser therapy (LLLT) on experimentally induced inflammation in retrodiscal tissues of the rabbit temporomandibular joint (TMJ) using scintigraphic imaging.

METHODS: Eleven male New Zealand rabbits were included in this study. Six randomly selected rabbits were imaged to provide normal joint images (normal group) before the initiation of the experiment. A 5% formalin solution was locally injected into both right and left TMJs of all rabbits. Subsequently, Ga-Al-As laser (wavelength: 815 nm; energy density: 12 J/cm^2; output power: 250 mW) was applied for 48 seconds. The treatment was performed six times for 2 weeks to the left TMJ of all rabbits. The right TMJs of the rabbits were used as the control (nontreated) TMJ group, while left TMJs were used as the treated TMJ group. Static images of TMJ were taken at 24 hours, 7 days, and 14 days after the beginning of the treatment. The images of all TMJs were taken in the posteroanterior direction with the rabbit under sedation and its mouth open. The Mann-Whitney U test was used to compare group differences, and intragroup differences were determined by the Friedman test and Wilcoxon sign test.

RESULTS: Significant differences were found between normal and both the control and treated TMJ groups. A reduction of inflammation in both treated and control TMJ groups was obtained, but there was no statistically significant difference between the groups.

CONCLUSION: Under the conditions used in this study, quantitative scintigraphic measurements of TMJ inflammation of the treated TMJ group decreased but did not differ significantly from those of the control TMJ group.

Annal Comments:

 The paper by Kucuk in J Orofac Pain 2010 Summer;24(3):293-7 on the anti-inflammatory effect of low level laser therapy (LLLT) on TMJ inflammation would suggest that the use of this therapeutic modality has little or no effect. In fact, this is a misinterpretation of the paper.

To understand how LLLT works, it is essential to be able to evaluate the involved parameters. The physical parameters required are: wavelength (nanometer), output of the laser (milliwatt), size of the laser aperture (cm^2), applied energy (joule) and the dose (J/cm^2). The numbers of irradiated points, number of sessions, intervals between sessions, contact or no contact with tissue are other important parameters. An independent measurement of the actual output of the laser is also needed if the researcher wants to be in control. Without an account of all these parameters, a future control study may very well become a completely different study.

Too often the difference between the applied energy and the dose is confused. The energy is calculated by multiplying the output of the laser times the seconds of irradiation. Thus, 100 mW during 10 seconds becomes 1000 millijoule = 1 J. The dose (also called fluence or radiant exposure), on the other hand, is the energy divided by the size of the irradiated area – often the size of the laser aperture in contact. Too often only one of these parameters is accounted for in scientific papers and in unfortunate cases other authors confuse the dose and energy. For example, in the study by Brosseau the dose is 3 J/cm^2 for finger arthritis. This may appear to be a reasonable dose. But since the laser fiber used was very thin, this dose was reached in a few seconds and the applied energy was only 0.12 J per finger joint. Energy and dose are two independent parameters which both have to reach an effective level.

In the paper by Kucuk, a laser of 250 mW was used for 48 seconds. This produces an energy of 12 J. This parameter is not reported, only the dose of 12 J/cm^2. Since the laser aperture is reported to deliver a spot of approximately 10 mm, the dose and the energy in this case gets more or less the same numeric value. So far so good. The problem is the understanding of the therapeutic window for biostimulation. The authors cite other researchers and here the complications start. For instance, Hansson used 904 nm, 0.3 mW, 3 minutes. 0.3 x 180 = 0.054 J for clinical use. Mazetto used 780 nm, 70 mW, 10 s, 89.7 J/cm^2 = 0.7 J for clinical use. Venanzio used 780 nm, 30 mW, 10 s, 6.3 J/cm^2 at three TMJ points. 0.3 x 3 = 0.9 J. The energies in these studies have had to be recalculated since they are not reported. The three examples above are for arthritic pain. The myalgic studies discussed in the Kucuk paper have the same problem.

Now, looking at the energies used in the three studies above, these have been in the range 0.5 – 0.9 J per point. For an average human (keeping in mind that TMD appears to be more common in females) of 60 kg, this would mean approximately 0.01 J per kg. The mean weight of the rabbits was about 3 kg. The 12 joules applied brings 4 joules per kg. The Arndt-Schultz law stipulates that For every substance, small doses stimulate, moderate doses inhibit, large doses kill. The exact optimum for biostimulation of inflammation in the TMJ is not known, but the World Association for Laser Therapy recommends 1-2 points and a total energy of 4 J for clinical use. The TMJ is quite superficial whereas muscles require considerable higher energies due to the poor penetration into these well vasculated tissues. The power density (mW/cm^2) is also of importance and low power and longer time are reported to be more effective for tissue repair than high power and short time, even using the same total energy.

We suggest, therefore, that the lack of effect in the Kucuk paper is due to over dosage and subsequent inhibition.