How Cold Lasers Work…

“Cold Lasers” seem to be the latest Buzz Word in Laser Dentistry. Cold Lasers are also known as “Soft Lasers” or, more scientifically, Biostimulatory Lasers.  As already mentioned in previous posts, these lasers do not cut or vaporise any tissue.  Although often very powerful, these lasers are defocused enough so that the tissue interaction is that of biostimulation and not thermal.

As we have seen earlier, cold lasers can be used for a variety of applications not only in dentistry, but also in medicine.  Their typical application field is that of tissue healing (Well, lately the application of hair re-growth has also been added and actually FDA approved, but there is little if any scientific substantiation to this at this point).

In order for laser light to be absorbed, there must be receptors.  Such receptors are well known in plants, but there are human light receptors other than those in the eyes and the skin.  In fact, to date more than three hundred photochemically reactive proteins, capable of harvesting low light energy, have been identified in both prokaryotic and eukaryotic organisms.  In humans, the most commonly known photochemically active receptor proteins are the rod and cone pigments in the eye.  However, other human photoreceptors have been discovered in recent times.  In fact today, we know that the majority of our cells have photoreactive molecules in them and we call those CHROMOPHORES.

It has been observed that if laser light is administered in the right dose, certain cell functions are being stimulated, and this is particularly evident if the cell in question has an impaired function.  It is known that laser light will cause certain chromophores in our cells to allow the build-up of radical oxygen species (singlet oxygen, instead of O2), which in turn influences the the formation of ATP (Adenosine Tri-Phosphate), which is the cells basic energy and fuel molecule.  Now, if the production of ATP reaches a certain level within cells, this will lead to a host of secondary effects, which have been studied and measured in several contexts:

  • increased cell metabolism and collagen synthesis in fibroblasts
  • increased DNA and RNA formation in the cell nucleus
  • increased cell division cycles
  • increased cell differentiation cycles of primitive cells (stem-type cells)

All of the above cellular effects will translate into faster healing by virtue of an increased population of cells which are involved in the inflammatory and healing cascades of the body.  Bone and soft tissue tend to heal faster and better after surgery, nerve cells can regenerate themselves at higher rates and pain is often reduced due to a laser-induced block of the pain receptor cells.

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A 100 Watt Laser – And My Doctor Says It Won’t Hurt?!?!

It is an unfortunate business practice, but the sale of medical lasers is largely being promoted by their hardware profile: “X” number of watts, “Y” number of pulses at “Z” nanometers etc.  What is unfortunate about this is that it does not really paint a good picture on what the clinical qualities of a laser really are, because this type of advertising does not really address what kind of “tissue interaction” it produces.  This however is ultimately the most important quality of any laser.  I’ll explain…

First and foremost, the power of the laser (usually displayed in Watts) is the true output power in terms of light energy emitted.  This is in direct contrast to a light bulb for instance.  A 60-Watt light bulb will draw 60 Watts of power out of the socket, but only deliver a fraction thereof as light energy, because most of the power drawn gets converted to heat energy.  In a laser the power rating is NOT what it draws out of the electric socket, but rather the light energy it produces.

Another concept that needs to be addressed is that this power claim describing a laser, can often be misleading.  More often than not, a “high-powered” healthcare laser in the 20 – 100 Watt range achieves this kind or output power mostly in a “pulsed” mode.  This means that the laser will be “on” and “off” several hundred or even several thousand times a second and every time it is “on” it emits 100 Watts.  Since this is a pulse train of laser light, it is important to note that the AVERAGE power may only be in the milliwatt range, so there is effectively only less than 1 Watt being absorbed by the tissues.

The last and most important concept which needs to be addressed is that of the power density at the output tip (aka “fluence”).  A 50-Watt laser with an output diameter of 1 cm will have an entirely different effect on tissues than a 6-Watt laser with an output diameter of only a few hundred microns.  The former will have a biostimulatory effect, whereas the latter will be able to cut tissue.

So, as we can see, the advertising profiles of lasers do not really always reflect the clinical relevance.  It is my opinion that this needs to change eventually, so that the tissue interaction is placed into the foreground and not the hardware profile.

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