What is Low Level Laser Therapy/Phototherapy
What is the difference between a Low Level Laser and an SLD? 
What are the clinical effects of Laser Therapy?
What are the different therapeutic lasers?

What is a Low Level Laser? 

The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. A Low Level Laser, also known as a cold or soft laser, emits coherent and focused energy to stimulate healing and decrease pain.

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What is a Superluminous Diode (SLD)?
An SLD is a high-powered light emitting diode (LED) that delivers a non-coherent, broad beam of light. SLD’s are generally found in large clusters.
What is Phototherapy?
Phototherapy uses light energy from Low Level Lasers or SLD’s to elicit biological responses in the body. The effects of phototherapy on tissues are commonly referred to as biostimulation or biomodulation.
What is the Difference between a Low Level Laser and an SLD? 
There are a few differences between Lasers and Superluminous Diodes (SLDs); the coherence, spectral width and divergence of light waves.
Coherence
The coherence is the order or synchronicity of the light waves. Laser light is coherent, meaning the light waves are in phase. Superluminous Diodes are non-coherent, or out of phase. 
Spectral Width
The spectral width is the amount of the electromagnetic spectrum the light wave covers. A laser has a very narrow spectral width and is, in fact, monochromatic, meaning it has one wavelength. An SLD has a wide spectral width, meaning it has a band of wavelengths. For example, a laser may have a wavelength of 660nm, whereas an SLD will have a wavelength of 630-690nm.
Divergence
The divergence is the spread of the light waves. A laser is collimated meaning the light waves do not diverge at all. An SLD has light waves that diverge or spread over a larger area.
 

 

There has been some debate as to whether the light source makes a difference in the treatment outcomes (e.g. from a low level laser or a Superluminous Diode). Originally it was thought that only light from a true laser would produce clinical results because of the coherence of laser light, but more recently, it has been hypothesized that light loses its coherence in the first few layers of tissue, thus the source may not make a difference. However, other theories state that coherence is not lost in the first few levels of tissue, but shortened. This will result in small speckles of more intense light deep in the tissue, creating polarization. It is hypothesized that polarization is what will allow lasers to penetrate more deeply and have a greater effect on the mitochondria of the cell.
Though both theories are currently under debate and being studied extensively, clinical results are showing that effective treatment outcomes are being seen with both lasers and SLDs. The clinical outcomes of laser therapy depend mainly on wavelength and dose, not the source of light.

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 What are the Clinical Effects of Laser Therapy

  Low Level Laser Therapy (LLLT), also known as phototherapy or photobiomodulation, uses light energy in the form of photons to produce cellular responses in the cell. Light photons are absorbed by cytochromes and porphyrins in the mitochondria of the cell.  it has been proposed that three things occur:

·         Stimulation of ATP (adenosine triphosphate) synthesis by activation of the electron transport chain
 
·         Transient stimulation of reactive oxygen species (ROS), which increases the conversion of ADP to ATP
 
·         A temporary release of nitric oxide (NO) from its binding site on cytochrome-c oxidase, which results in an increase in cell respiration and transcription.
The above are though to activate numerous intracellular pathways; regulate nucleic acid synthesis, protein synthesis; modulate levels of cytokines, growth factors and inflammatory mediators; and stimulate proliferation and differentiation of different cell types. The result is the restoration of cell function, tissue repair, wound healing, pain relief, nerve repair and modulation of the inflammatory response.

 A fantastic article discussing the mechanisms of Low Level Light Therapy by Dr. Michael Hamblin can be found at http://www.photobiology.info/Hamblin.html.  

The clinical effects of laser therapy come not only from the direct irradiation of the tissue, but from the secondary and tertiary effects as well. Please see below for some of the secondary effects seen after laser/SLD irradiation:
Increased Lymphatic Flow
Reduced Edema (swelling)
Stimulation of β-endorphins
Reduced Pain
Reduced release of Histamine, Bradykinins, Substance P and Acetylcholine
Decreased Pain, Redness and Swelling during the inflammatory response
Increased activity of Neutrophils and Macrophages
Aids in Immune Response and Growth Factor Release
Increased Collagen Formation and Fibroblast Stimulation
Stimulation of Wound and Tissue Healing
Increased Collateral Circulation and Microcirculation
Important for Wound Healing and Tertiary Effects
Reduced Conduction of c-fibres
Decreased Dental Pulp Pain
Stimulation of Osteoblasts
Stimulates the Production of Bone
Stimulation of Odontoblasts
Stimulates the Production of Dentin
 One common finding in the research is that there are no side effects associated with laser irradiation. In 2007, Tiina Karu reported that the effects of PBM are dependent on the initial redox status of a cell. If a cell is damaged, or in a reduced redox state, the cellular response will be stronger. Conversely, a cell which is at an optimal redox potential will have a weak or absent cellular response.Thus, cells that are damaged or sick will respond to PBM better than cells that are healthy and functioning normally.

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What are Therapeutic Lasers? 

Therapeutic Lasers
The most common types of therapeutic lasers are Helium Neon (HeNe), Gallium Aluminum Arsenide (GaAlAs), and Gallium Arsenide (GaAs). The name of the laser is determined by the solid, liquid or gas element that is in the lasing medium. The radiation from a laser always has a fixed wavelength, as determined by the structure of the lasing medium.
Therapeutic lasers generally range from 600-950 nm on the electromagnetic spectrum. In general, the longer the wavelength, the deeper the light will penetrate. However, the penetration of laser light can depend not only on wavelength, but also on whether the laser is super-pulsed, power output, technical design of laser and treatment technique.

A 660nm laser will not penetrate deeply and will be most effective for wound healing or treatment of shallow muscles. An 830nm laser will penetrate more deeply into tissue and underlying structures, making it an ideal laser for wound healing, muscle attachments, pain and various oral conditions. Low Level Lasers in the wavelength region of 900-980nm will penetrate deeply, but have very little effect on the mucous membrane. It is important when purchasing a laser unit that you evaluate where you will be treating to determine the most effective unit for you or your clinic.
Summary of Laser Types
 Helium Neon (HeNe) or Indium Gallium Aluminum Phosphide (InGaAlP):
Wavelength - 633nm – 660n
Pulsed or Continuous - Generally continuous but can be mechanically pulsed
Penetration Depth – Shallow, ~1-2cm
Ideal treatment applications – Wound healing, shallow muscles
Benefits – Benefical effect on mucous membrane and skin
               - Minimal risk of injury to the eyes (visible light will elicit a blink reflex)
Gallium Aluminum Arsenide (GaAlAs)
Wavelength – 780-870nm
Pulsed or Continuous – Continuous, but can be mechanically pulsed
Penetration Depth - ~2-3cm
Ideal treatment applications – Wound healing, muscle attachments, muscles, oral applications
Gallium Arsenide (GaAs)
Wavelength – 904nm
Pulsed or Continuous  - Always pulsed
Penetration Depth - ~3-4 cm (although dependent on dose, power and application mechanism)
Ideal treatment applications – Deep muscle and inflammation treatments

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