(L.L.L.T.)
Q: What is LLLT, LPLT, therapeutic laser, soft laser, MID laser?
A: Regarding the therapy, we have chosen to use the term LLLT (Low Level Laser Therapy). 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 LLLT until agreement is reached on something else.
Q: Is laser therapy scientifically well documented?
A: Basically yes. There are more than 100 double-blind positive studies confirming the clinical effect of LLLT. More than 2500 research reports are published. Looking at the limited LLLT dental literature alone (370 studies), more than 90% of these studies do verify the clinical value of laser therapy.
Q: Where do I find such documentation?
A: The book "Laser Therapy - clinical practice and scientific background" is the best reference guide for literature documentation.
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 negative 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.
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: Can therapeutic lasers damage the eye?
A: Yes and no! Read the following:
The following factors are of importance regarding the eye risk of different lasers:
The divergence of the light beam. A parallel light beam with a small diameter is by far the most dangerous type of beam. It can enter the pupil, in its entirety, and be focused by the eye's lens to a spot with a diameter of hundredths of a millimetre. The entire light output is concentrated on this small area. With a 10 mW beam, the power density can be up to 12,000 W/cm2
The output power (strength) of the laser. It is fairly obvious that a powerful laser (many watts) is more hazardous to stare into than a weak laser.
The wavelength of the light. Within the visible wavelength range, we respond to strong light with a quick blinking reflex. This reduces the exposure time and thereby the light energy which enters the eye. Light sources which emit invisible radiation, whether an infra-red laser or an infra-red diode, always entail a higher risk than the equivalent source of visible light. Radiation at wavelengths over 1400 nm is absorbed by the eye's lens and is thus rendered safe, provided the power of the beam is not too high. Radiation at wavelengths over 3,000 nm is absorbed by the cornea and is less dangerous.
The distribution of the light source. If the light source is concentrated, which is often the case in the context of lasers, an image of the source is projected on the retina as a point, provided it lies within our accommodation range, i.e. the area in which we can see clearly. A widely spread light source is projected onto the retina in a correspondingly wide image, in which the light is spread over a larger area, i.e. with a lower power density as a consequence. For example: a clear light bulb (which is apprehended as a more concentrated light source) penetrates the eye more than a so-called "pearl" light bulb. A laser system with several light sources placed separately, such as a multiprobe (the probe is the part of the laser you hold and apply to the area to be treated: a single probe means there is only one laser diode in the probe, as opposed to a multiprobe, which has several laser diodes) with several laser diodes, can, seen as a whole, be very powerful but at the same time constitute a smaller hazard to the eye than if the entire power output was from one laser diode, because the diodes' separate placement means that they are reproduced in different places on the retina.
We have often heard this kind of remark: "If it's a class 3B laser then it's fine, otherwise it has no effect....". This is of course entirely incorrect and has lead to a situation where manufacturers have produced lasers to meet the 3B classification, so that they will sell in greater volumes. Let us look at a couple of examples:
* A GaAlAs laser with a wavelength of 830 nm, an output of 1 mW and a well collimated beam (1 mrad divergence) is classified as laser class 3B as it is judged to be hazardous to the eye. The reason for this is partly the collimated beam, and partly the wavelength, which is just outside the visible range and hence provokes no blink reflex in strong light.
* A HeNe laser with a wavelength of 633 nm, an output of 10 mW and divergent beams (1 rad divergence, which coresponds to a cone of light with a top angle of about 57°) is classified as laser class 3A because, owing to its divergence, it cannot damage the eye.
With the recent advent of "high power low power lasers", i.e. GaAlAs lasers in the range 100-500 mW there is another story. These lasers are indeed dangerous for the eye and should only be used by qualified persons and with proper protective measures taken.
Q: How do I know which laser I should buy?
A: The laser market is very complicated and full of pitfalls. How do you know which instruments are good? What is expensive? Will it be expensive in the long run to buy something cheap? It is easy to make hasty decisions when faced with a skilful salesman - who is likely to know much more about the field than the customer. Before you know it, you've signed on the dotted line.
Here are a number of questions which you should ask both the salesman and yourself. You would be well advised to read these carefully in case you regret not doing so later on!
1 "Laser instruments" have been sold which do not even contain a laser, but LEDs or even ordinary light bulbs. These instruments have been sold for between US $3,000 - $10,000. How can you acquire proof that the instrument really does contain a laser?
2 In a number of products, laser diodes have been combined with LEDs. This is often kept secret and the salesman has only talked about a laser. Are all light sources in the apparatus (except guide lights and warning lights) really lasers?
3 For oral work and wound healing HeNe and GaAlAs are the most common types, with GaAlAs as the most versatile one. Sterilizeable probes are normally only available for GaAlAs lasers. For injuries to joints, vertebrae, the back, and muscles, that is, for the treatment of more deep-lying problems, the GaAs laser is the best documented. For veterinary work, a laser is needed which is designed so that the laser light can pass through the coat, and penetrate to the desired depth. For superficial tendon and muscle attachments, the required depth can be reached with the GaAlAs laser. Many companies have only one type of laser, such as a GaAlAs, and the salesman will naturally tell you that it is the best model for everything, and that it is irrelevant which type of laser is used. However, research tells quite a different story. GaAs further requires lower dosage than GaAlAs, so nominal power is not everything.
4 Size, colour, shape, appearance and price vary a great deal from manufacturer to manufacturer. Because a piece of equipment is large, it does not necessarily follow that its medical efficacy is high, or vice versa. The most important factor is the dosage which enters the tissue. Make sure the laser you buy is designed so that all the light actually enters the tissue. Ask the salesman: how is the dosage measured? What kind of dosage is too high, and what is too low?
5 Many companies which import lasers have deficient knowledge in terms of medicine, laser physics, and technology. In fact, there are many examples of companies which have gone bankrupt. If a piece of equipment is faulty, it may have to be sent to the country of manufacture for repair. How long would you be without your equipment in such a case, and what would it cost to repair? Can the importer document his expertise? Who can you speak to who has used the apparatus in question for a long period of time? Is there a well-known professional who uses this make? What does it cost to change a laser diode or laser tube, for example, after the guarantee has expired? Can you get written confirmation of this? Try to get a list of references who you can call and ask.
6 The difference between a colourful brochure and reality is often considerable. There are examples of brochures which describe output ten times that which the equipment actually provides. How can you find out the real performance of the equipment (e.g. its output)? Are there measurement results from an independent authority? Is it possible to borrow an apparatus in order to measure its performance? Is there an intensity meter on the apparatus which can measure what is emitted and show it in figures? It is not enough simply to have a light indicator.
7 Some dealers know that their products are sub-standard. This can often be seen by the fact that they are anxious to get the customer to sign a contract. If a product is good, the dealer will have no doubts about selling it on sale-or-return basis, with written confirmation of this. What happens if the medical effects are not as promised? Is it possible to get a written guarantee of sale-or-return?
8 In most countries, therapy lasers must be approved. The approval certificate shows the laser type and the class to which the instrument belongs, e.g. laser class 3B. There is also a certificate number. A laser which is not approved is either not a laser, or is being sold illegally.
9 Many companies organize courses and "training" events of markedly varying quality. A serious importer or manufacturer takes pains to ensure that his equipment is used in a qualified way, and makes sure that the customer receives some training in its use. What are the instructor's background and qualifications? Has he or she published anything? Is there a course description? What does the training material cost? Is a training course included in the cost of the equipment? Is the training material included? Is it possible to buy the training material only?
10 Development is going on at a fast pace. Suddenly, you have out-of-date laser equipment and a new and perhaps more efficient type of laser comes onto the market. What happens if your laser becomes outmoded? Do you have to buy a new laser, or can your equipment be updated with future components lasers?
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 frequency (pulsing) should be used for the various therapies?
A: First we must differentiate between “chopping” and “superpulsing”. Some lasers, like the GaAs laser, are always pulsed. The pulses are very short but the peak power in the pulse is very high, several watts, but the pulse duration is typically only 200 nanoseconds. Other lasers like the HeNe and the GaAlAs are always continuous, but can be “pulsed” by mechanical or electrical devices. This means that the beam is turned off and on but the output of each pulse is still the same.
When pulsing one generally loses power. With most GaAs lasers the power decreases with lowered frequencies (unless there is a pulse train arrangement) and with “chopped” lasers we typically loose 50% (50% duty cycle).
There is sound evidence from cell studies that the pulsing makes a difference. But
the evidence from clinical studies is almost absent. Since GaAs is always pulsed, we have to choose a frequency and then to use the anecdotal evidence there is. But the loss of power on lowered frequencies must be observed! For other lasers the choice of frequency is pure guesswork.
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. HeNe lasers cost somewhere between US $3,000 and $7,000, depending on their power output and the quality of their fibres. InGaAlP lasers of the same power costs usually about half as much and can be had with considerably higher output.
* 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.
Prices are usually between US $3,000 and $6,000 for output power between 4 and 20 mW. 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.. As it is very easy to run electrically, small rechargeable lasers have been put on the market which are not much larger than an electrical toothbrush. (They can run on normal or rechargeable batteries.). 20-30 mW laser diodes are now relatively cheap and the GaAlAs laser gives "a lot of milliwatts for the money". Recently, GaAlAs lasers have appeared on the market with an impressive output of over 500 mW. In Europe, GaAlAs laser with powers above 500 mW can only be used by doctors and dentists, being Class 4 lasers.
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. The price tag for a GaAlAs laser of around 30 mW can be between US $2,000 and $4,000, excluding value added tax. Price differences depend on factors such as output, ergonomics, and standard of hygiene, to name but a few. GaAlAs lasers of 300-500 mW are in the range $4.000-$6.000 .
Q: Can carbon dioxide lasers be used for LLLT?
A: Yes.Therapeutic laser treatment with carbon dioxide lasers has become more and more popular. 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. There are small, portable CO2 lasers on the market today producing up to 15 watts, which is more than enough power output! Prices in the range of $ 10,000 - $25,000.
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. That means that, for instance, the healing of a wound will take longer time than normally. Very high doses on healthy tissues will not damage them.
Q: Are there any contraindication?
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 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.
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.
