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The search for the optimal parameters

By Jan Tunér

The mainstream opinion about dosage in laser phototherapy is as follows: low energies and long time is best for reduction of inflammation and for cellular proliferation. High energies are better for acute pain since these levels cause a temporary inhibition of neural transmission. But what happens if these rules are broken and the outcome of a study still is positive? Search me! But read this abstract first:

Peimani A, Sardary F. Effect of low-level laser on healing of temporomandibular joint osteoarthritis in rats. J Dent (Tehran). 2014;11(3):319-327.

Thirty-two male Wistar rats (250-200 g) were housed in standard plastic cages. After injection of Complete Freund’s adjuvant into the TMJ, rats were randomly divided into two groups of 16 (case and control) and anesthetized; then osteoarthritis was induced via intraarticular injection of 50 µl of Complete Freund’s adjuvant; into the bilateral TMJs. In the case group, LLLT was done transcutaneously for 10 minutes daily, starting the day after the confirmation of osteoarthritis. Exposure was performed for 10 minutes at the right side of the TMJ with 880 nm low-level laser with 100 mW power and a probe diameter of 0.8 mm. Control rats were not treated with laser. RESULTS: After three days of treatment the grade of cartilage defects, number of inflammatory cells, angiogenesis, number of cell layers and arthritis in rats in the case group were not significantly different compared with controls (P>0.05). After seven days, the grade of cartilage defects, number of inflammatory cells, number of cell layers, and arthritis in the case group improved compared to controls (P<0.05); angiogenesis in both groups was similar. CONCLUSION: Treatment of TMD with LLLT after 7 days of irradiation with a wavelength of 880 nm was associated with a greater improvement compared to the control group.

So, let us look closer at the chosen parameters:

  • Irradiated area: The temporomandibular joint of a rat
  • Weight of the rats: 200-250 g
  • 880 nm reported, but a photo shows red light. Aiming beam light?
  • 100 mW, 10 min = = 60 J daily, right side only
  • 3-7 days of irradiation, 180 - 420 J cumulated energy
  • Weight of the smallest rat: 200 g
  • Now, if this is to be translated into a clinical situation, what would it mean?

  • A person of 60 kg = 300 times heavier, equals 18 000 J per day
  • Maximum accumulated energy (7 days) = 126 000 J
  • The parameters in a clinical situation, at the present stage of knowledge, would be very different, to say the least. Yet, the researchers do report some significant positive results of the irradiation. An older study on the TMJs of rats reported inhibitory results of much lower energies. Interestingly enough, these latter researchers used the contralateral TMJ as control, and found positive changes on the control side. This means that after passing through the head of the rat, intensities started to land within the therapeutic window. Now, in the present study, the energies were much higher and the actually irradiated side showed some positive changes.

    Have the researchers found out something new or is this just a serendipity result? Search me!

    Thinking outside the box (also thinking out of the box or thinking beyond the box) is a metaphor that means to think differently, unconventionally, or from a new perspective. This phrase often refers to novel or creative thinking. [Wikipedia]

    Certainly, thinking outside the box is fine and even necessary in science, but there is a lot of void outside of the box. Using exceptional parameters in LPT studies requires that there has been some thinking before putting them outside of the box.

    The wound healing study by Leclère has the following parameters:

    In the laser group, 980 nm InGasAs diode laser (power 15 W, spot size 8 mm, time 3 seconds, fluence 90 J/cm2) was applied weekly for 9 weeks to the ulcers in a homogenous standardized manner, resulting in a local temperature of 45-50 °C, which was controlled with a thermal infrared camera.

    The authors do not further comment on the fact that this is a 15 W laser used for 3 seconds per wound. Anyone familiar with LPT basics should realize that this procedure is bound for failure. Too high fluence, too short time, too much heat, less tested wavelength. And it was not an InGasAs laser, but a GaAlAs laser. So who did the thinking? The manufacturer or the researchers? Or nobody? Search me!

    Reference:

    Leclère FM, Puechguiral IR, Rotteleur G, Thomas P, Mordon S. A prospective randomized study of 980 nm diode laser-assisted venous ulcer healing on 34 patients. Wound Repair Regen 2008;18:580-585.