The illusive “Class 4” lasers

A comment on:  Ottaviani G, Gobbo M, Sturnega M, Martinelli V, Mano M, Zanconati F, Bussani R, Perinetti G, Long C S, Di Lenarda R, Giacca M, Biasotto M, Zacchigna S. Effect of Class IV Laser Therapy on Chemotherapy-Induced Oral Mucositis: A Clinical and Experimental Study.  Am J Pathol. 2013; 183 (6): 1747-1757.

By Jan Tunér

 

The international system of laser classification is concerned only with the risk for eye injury and, at higher powers, skin damage. It has nothing at all to do with suitability for laser treatment, nor does it mean a generational change nor ensure any improvement in efficacy. Many different parameters are considered in eye risk evaluation (laser wavelength, beam diameter, beam divergence, exposure time, pulsing vs. continuous emission, type of pulsing and more). Actually there are Class I (Class 1) lasers that are higher powered than many Class IV (Class 4) instruments! So, there is no sense in or reason for, other than deception, the term “Class IV laser therapy”.  [NB:  The terms 'Class 4' and 'Class IV' are, for practical purposes, interchangeable.]

For example, one manufacturer claims that their Class IV laser offer superb penetration through tissue (from 6-to-9 inches), and that the so-called “weak” class IIIB (3B) lasers (e.g. 500 mW, 808 nm laser) hardly penetrate the surface skin barrier at all.  However, in the chosen example below, the very opposite is the truth!  Due primarily to its absorption by water in the tissue, 970 or 980 nm penetrates much less than 808 nm, and this is not compensated by the higher power.  At around 808 nm we actually have the best penetration into tissue, and increasing power only increases the depth of penetration marginally. With the higher superficial absorbance of the 980 nm laser there will be considerable heating, and, while heat is fine for many conditions, the biostimulative effect does not depend on heat. There is one good side of giving more heat in the skin and that is that the patient “feels” the treatment better which might give a better placebo effect. There is more than one laser company using the same flawed argument to promote high-powered lasers.

It is also interesting to note the use of the term Class IV “technology”. There is no specific “technology” that enables a manufacturer to choose a laser diode that produces more than 500 mW, thus the term “Class IV technology” is simply used to infer a differential benefit that does not exist. Apart from power, the only differences between Class IIIB and IV lasers are the potential hazards and, usually, the price.

It is interesting to see that a recently published study by Ottaviano [1] is supposed to show that a “Class IV laser”, i.e. a 970 nm laser of 5 W can treat oral mucositis better than a class 3B laser. The authors claim to have been using a “standard 3B laser protocol” for comparison. In fact, they have not. The “standard” laser used is a laser pointer with a 635 nm diode of 2.5 mW, delivering 0.45 J per point and delivered from a distance of 1 - 3 cm, further reducing the power density. In spite of this, the authors refer to the review by Bjordal [2] where 10 - 60 mW and 3 J per point are recommended. This is clearly a study to distrust. This study seem to have the primary purpose to prove that this “new treatment” (Class IV laser therapy) is the only one that is really effective. However, many companies around the world produce therapeutic lasers in laser class IV (output power exceeding 500 mW) since more than 15 years ago, so that is nothing new.  Also, to make a laser that has a power of 600 mW (Class IV laser) is not more expensive than to make one that is 400 mW (Class IIIB laser) and not markedly more effective.

References:

1. Ottaviani G, Gobbo M, Sturnega M, Martinelli V, Mano M, Zanconati F, Bussani R, Perinetti G, Long C S, Di Lenarda R, Giacca M, Biasotto M, Zacchigna S. Effect of Class IV Laser Therapy on Chemotherapy-Induced Oral Mucositis: A Clinical and Experimental Study. Am J Pathol. 2013; 183 (6): 1747-1757.

2. Bjordal J M, Bensadoun R J, Lopes–Martins R A, Tunér J, Pinheiro A, Ljunggren A E. A systematic review of low level laser therapy (LLLT) in cancer therapy-induced oral mucosi­tis. Support Care Cancer. 2011; 19 (8): 1069-1077.