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FAQ Index - Quick jump

Courtesy to the Swedish Laser-Medical Society - 2003©

Q.What is lllt, LPLT, low level laser therapy, low power laser, biosstimulation?
Q: Is laser therapy scientifically well documented?
Q: Where do I find such documentation?
Q: But I have heard that there are dozens of studies failing to find any effect of LLLT?
Q: Which lasers can be used in medicine?
Q: Can therapeutic lasers damage the eye?
Q: How come some LLLT equipment has power in watts and some only in milliwatts?
Q: Which type of laser is best suited to which job?
Q: Can carbon dioxide lasers be used for LLLT?
Q: How deep into the tissue can a laser penetrate?
Q: Can LLLT cause cancer?
Q: What happens if I use a too high dose?
Q: Are there any counter indications?
Q: Does LLLT cause a heating of the tissue?
Q: Does it have to be a laser? Why not use monochromatic non coherent light?
Q: Does the coherence of the laser light disappear when entering the tissue?

Q: What is LLLT, LPLT, therapeutic laser, soft laser, MID laser?
Regarding the therapy, we have chosen to use the term laser therapy instead of LLLT (Low Level Laser Therapy). The term low level has become somewhat untrue, due to the new lasers in laser therapy with output powers up to 3,5 W. This is the dominant term in use today, but there is still a lack of consensus. In the literature LPLT (Low Power Laser Therapy) is also frequently used.

Regarding the laser instrument, we have chosen to use the term "therapeutic laser" rather than "low level laser" or "low power laser", since high-level lasers are also used for laser therapy.

The term "soft laser" was originally used to differentiate therapeutic lasers from "hard lasers", i.e. surgical lasers. Several different designations then emerged, such as "MID laser" and "medical laser".

"Biostimulating laser" is another term, with the disadvantage that one can also give inhibiting doses. The term "bioregulating laser" has thus been proposed. An unsuitable name is "low-energy laser". The energy transferred to tissue is the product of laser output power and treatment time, which is why a "low-energy laser", over a long period of time, can actually emit a large amount of energy. Other suggested names are "low-reactive-level laser", "low-intensity-level laser", "photobiostimulation laser" and "photobiomodulation laser". Thus, it is obvious that the question of nomenclature is far from solved.

This is because there is a lack of full agreement internationally, and the names proposed thus far have been rather unwieldy. Feel free to forget them, but remember laser therapy, or LLLT until agreement is reached on something else.

Q: Is laser therapy scientifically well documented?

A: Basicly yes. There are more than 100 double-blind positive studies confirming the clinical effect of LLLT. More than 300 research reports are published. Looking at the limited LLLT dental literature alone (325 studies), more than 90% of these studies do verify the clinical value of laser therapy.

Q: Where do I find such documentation?

A: The new book from Tunér/Hode “Laser Therapy - Clinical Practice and Scientific Background" is a reference guide as well as a wealth of laser therapy knowledge. The book contains 600 pages, hard cover, multicoloured and loaded with new information about the clinical and scientific aspects of laser therapy. Among other things there are about 1400 references.

Q: But I have heard that there are dozens of studies failing to find any effect of LLLT?

A: That is true. But you cannot just take a any laser and irradiate for any length of time and using any technique. A closer look at the majority of the negtive studies will reveal serious flaw. Look for link under Laser literature and read some examples. But LLLT will naturally not work on anything. Competent research certainly has failed to demonstrate effect in several indications. However, as with any treatment, it is a matter of dosage, diagnosis, treatment technique and individual reaction. Se link critic on critic.

Q: Which lasers can be used in medicine?

A: Examples of lasers which can be used in medicine:
Laser name Wavelength Pulsed Use in medicine or cont.

Crystalline laser medium:

Ruby 694 nm p holograms, tattoo coagulation
Nd:YAG 1 064 nm p coagulation
Ho:YAG 2 130 nm p surgery, root canal
Er:YAG 2 940 nm p surgery, dental drill
KTP/532 532 nm p/c dermatology
Alexandrite 720-800 nm p bone cutting

Semiconductor lasers:

GaAs 904 nm p biostimulation
GaAlAs 780-820-870 nm c biostimulation, surgery
InGaAlP 630-685 nm c biostimulation

Liquid laser:

Dye laser (tuneable) p kidney stones
Rhodamine: 560-650 nm c/p PDT, dermatology,

Gas lasers:

HeNe 633, 3 390 nm c biostimulation
Argon 350-514 nm c dermatology, eye
CO2 10 600 nm c/p dermatology, surgery
Excimer 193, 248, 308 nm p eye, vascular surgery
Copper vapour 578 nm c/p dermatology

There are many other types, but those mentioned above are the most common.

Q: How come some LLLT equipment has power in watts and some only in milliWatts?

A: This applies to GaAs lasers. When a GaAs laser works in a pulsed fashion, the laser light power varies between the peak pulse output power and zero. Then usually the laser's average power output is of importance, especially in terms of dosage calculation. The peak pulse power value is of some relevance for the maximum penetration depth of the light. Some manufacturers specify only the peak pulse output in their technical specifications. "70 millwatt peak pulse output" naturally seems more impressive than 35 milliwatts average output! Rule of thumb is: Take the "watt peak pulse" figure, divide by 2, and you have the average output in mW. This rule of thumb is not valid for GaAs-lasers as these lasers are super pulsed (extremely low duty cycle).

Q: Which type of laser is best suited to which job?

A: There are three main types of laser on the market: HeNe (now being gradually replaced by the InGaAlP laser), GaAs and GaAlAs. They can be installed in separate instruments or combined in the same instrument.

* The HeNe laser or InGaAlP laser has been used a great deal in dentistry in particular, as it was the first laser available. The HeNe laser has been used for wound healing for more than 30 years. One advantage is the documented beneficial effect on mucous membrane and skin (the types of problem it is best suited to), and the absence of risk of injury to the eyes. A Japanese researcher has even treated calves with keratoconjunctivitis with excellent results, that is, irradiation of the eye through the eye lid. Because HeNe light is visible, the eye's blink reflex protects it.

Normal HeNe output for dental use is 3-10 mW, although apparatus with up to 60 mW is available. An optimal dosage when using a HeNe laser for wound healing is 1-4 J/cm2 around the edge of the wound, and approximately 0.5 J/cm2 in the open wound. HeNe lasers are used to treat skin wounds, wounds to mucous membrane, herpes simplex, herpes zoster (shingles), gingivitis, pains in skin and mucous membrane, conjunctivitis, etc.

It should be noted that HeNe fibres cannot be sterilized in an autoclave. The alternative is to use alcohol to clean the tip, or to cover it with cling-film or a thermometer sleeve.

* The GaAs laser is excellent for the treatment of pain and inflammations (even deep-lying ones), and is less suited to the treatment of wounds and mucous membrane. Very low dosages should be administered to mucous membrane! Most GaAs equipment is intended for extraoral use, but there are special lasers adapted for oral use.

A GaAs laser needs an integral output meter that shows that there is a beam and its strength in milliwatts - this is necessary because the light this type of laser emits is invisible. Protective glasses for the patient may be appropriate in view of the invisible nature of the light.

In older systems the power output of conventional apparatus follows pulsation. This means that a GaAs laser with an average output of 10 mW when pulsing at 10,000 Hz, only produces 1 mW when pulsed at 1,000 Hz, and at 100 Hz only 0.1 mW. If you therefore want to administer treatment at low frequencies around e.g. 20 Hz (for the treatment of pain), the output power is, clinically speaking, unusable. However, there are GaAs lasers with "Power Pulse", which means that the power output is held constant at all pulse frequencies. This would be of interest to a physiotherapist, for example, when one considers that the GaAs laser has the deepest penetration of the common therapeutic lasers. Large doses can be administered to deep-lying tissue over a short period of time. A GaAs multiprobe can also shorten treatment times for conditions involving larger areas (neck/shoulders).

The GaAs laser is, like GaAlAs and InGaAlP lasers, a semiconductor laser. A purely practical advantage of this type of laser is that the laser diode is located in the hand-held probe. This means that there is no sensitive fibre-optic light conductor which runs from the laser apparatus to the probe, but just a normal, cheap, robust electric cable. Optimum treatment dosages with GaAs lasers are lower than with HeNe lasers.

The GaAs laser is most effective in the treatment of pain, inflammations and functional disorders in muscles, tendons and joints (e.g. epicondylitis, tendonitis and myofacial pain, gonarthrosis, etc.), and for deep-lying disorders in general. As mentioned above, GaAs is not thought to be as effective on wounds and other superficial problems as the HeNe laser (InGaAlP laser) and GaAlAs laser. GaAs can, nevertheless, be used successfully on wounds in combination with HeNe or InGaAlP, but the dosages should be very low - under 0.1 J/cm2.

* The GaAlAs laser has become increasingly popular. GaAlAs lasers have appeared on the market with an impressive output of over 2 W.
There are several types of GaAlAs-lasers. The most well-documented type emits a continuous, invisible or barely visible light with the wavelength 820 nm. This laser assume an intermediate position as compared to the two other laser types, often proving effective on such skin conditions as leg ulcers but also, at least to some extent, on the problems of muscles, tendons and joints.
Many GaAlAs lasers have well-designed, exchangeable, sterilizeable intraoral probes. Output meters are essential because the light from this type of laser is largely invisible.

Q: Can carbon dioxide lasers be used for LLLT?

A: Yes.Therapeutic laser treatment with carbon dioxide lasers has become more and more popular, sometimes called EDL-laser (emitted defocused laser). This does not require instruments expressly designed for that purpose. Practically any carbon dioxide laser can be used as long as the beam can be spread out over an appropriate area, and as long as the power can be regulated to avoid burning. This can always be achieved with an additional lens of germanium or zinc selenide, if it cannot be done with the standard accessories accompanying the apparatus. T

It is interesting to note that the CO2 wavelength cannot penetrate tissue but for a fraction of a mm (unless focused to burn). Still, it does have biostimulative properties. So the effect most likely depends on tranmsittor substances from superficial blood vessels. Conventional LLLT wavelengths combine this effect with "direct hits" in the deeper lying affected tissue.

Q: How deep into the tissue can a laser penetrate?

A: The depth of penetration of laser light depends on the light's wavelength, on whether the laser is super-pulsed, and on the power output, but also on the technical design of the apparatus and the treatment technique used. A laser designed for the treatment of humans is rarely suitable for treating animals with fur. There are, in fact, lasers specially made for this purpose. The special design feature here is that the laser diode(s) obtrude from the treatment probe rather like the teeth on a comb. By delving between the animal's hair, the laser diode's glass surface comes in contact with the skin and all the light from the laser is "forced" into the tissue.

A factor of importance here is the compressive removal of blood in the target tissue. When you press lightly with a laser probe against skin, the blood flows to the sides, so that the tissue right in front of the probe (and some distance into the tissue) is fairly empty of blood. As the haemoglobin in the blood is responsible for most of the absorption, this mechanical removal of blood greatly increases the depth of penetration of the laser light.

It is of no importance whether the light from a laser probe, held in contact with skin is a parallel beam or not..

There is no exact limit with respect to the penetration of the light. The light gets weaker and weaker the further from the surface it penetrates. There is, however, a limit at which the light intensity is so low that no biological effect of the light can be registered. This limit, where the effect ceases, is called the greatest active depth. In addition to the factors mentioned above, this depth is also contingent on tissue type, pigmentation, and dirt on the skin. It is worth noting that laser light can even penetrate bone (as well as it can penetrate muscle tissue). Fat tissue is more transparent than muscle tissue.

For example: a HeNe laser with a power output of 3.5 mW has a greatest active depth of 6-8 mm depending on the type of tissue involved. A HeNe laser with an output of 7 mW has a greatest active depth of 8-10 mm. A GaAlAs probe of some strength has a penetration of 35 mm with a 55 mm lateral spread. A GaAs laser has a greatest active depth of between 20 and 30 mm (sometimes down to 40-50 mm), depending on its peak pulse output (around a thousand times greater than its average power output). If you are working in direct contact with the skin, and press the probe against the skin, then the greatest active depth will be achieved.

Q: Can LLLT cause cancer?

A: The answer is no. No mutational effects have been observed resulting from light with wavelengths in the red or infra-red range and of doses used within LLLT.

But what happens if I treat someone who has cancer and is unaware of it? Can the cancer's growth be stimulated? The effects of LLLT on cancer cells in vitro have been studied, and it was observed that they can be stimulated by laser light. However, with respect to a cancer in vivo, the situation is rather different. Experiments on rats have shown that small tumours treated with LLLT can recede and completely disappear, although laser treatment had no effect on tumours over a certain size. It is probably the local immune system which is stimulated more than the tumour.

The situation is the same for bacteria and virus in culture. These are stimulated by laser light in certain doses, while a bacterial or viral infection is cured much quicker after the treatment with LLLT

Q: What happens if I use a too high dose?

A: You will have a biosuppressive effect. At least if you try to heal of a wound or treat for hairloss, then it will take longer time than normally. Very high doses on healthy tissues will not damage them.

Q: Are there any counter indications?

A: You should not treat cancer, for legal reasons. Pregnant women is not a counter indication, if used with common sense. Pace makers are electronical, do not respond to light. Epilepsy may be a counter indication.The most valid counter indication is lack of medical training

Q: Does LLLT cause a heating of the tissue?

A: Due to increased circulation there is usually an increase of 0.5-1 centigrades locally. The biological effects have nothing to do with heat. GaAlAs lasers in the 300-500 mW, or higher range will cause a noticable heat sensation, particularly in hairy areas and on sensitive tissues such as lips.

Q: Does it have to be a laser? Why not use monochromatic non coherent light?

A: Monochromatic non coherent light, such as light from LED's can be useful for superficial tissues such as wounds. In comparative studies, however, lasers have shown to be more effective than monochromatic non coherent light sources. Non coherent light will not be as effective in deeper areas. Also for more info, see the internet discussion on LaserWorld

Q: Does the coherence of the laser light disappear when entering the tissue?

A: No. The length of coherence, though, is shortened. Through interference between laser rays in the tissue, very small "islands" of more intense light, called speckles occur. These speckles will be created as deep as the light reaches in the tissue and within a speckle volume, the light is partially polarized. It is easy to show that speckles are formed rather deep down in tissue and the existence of real speckles prove that the light is coherent.


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