الفهرس 
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Abstract
The principal function of human skin is to protect the body from external environment and so it is important that any damage of it is rapidly repaired through cutaneous wound healing process.
Cutaneous wound healing is a complex process involving three overlapping phases. In the initial inflammatory phase, leukocytes limit further tissue damage and platelets form plug to stop bleeding and release several factors that aid in the following phases of healing. In the proliferative phase, keratinocytes proliferate to restore the epidermal barrier and fibroblasts proliferate and deposit new tissue helped by new vessels that are formed by the process of angiogenesis. The last phase is the prolonged remodeling phase where the new tissue is progressively re-built to form a tissue that resembles the original as much as possible and a connective tissue scar is formed.
The process of wound healing can follow primary, secondary or tertiary intention healing. Factors affecting wound healing include systemic factors as malnutrition, debilitating diseases, smoking, systemic medications,
and ionizing radiation. Local factors include local infection, edema,
ischemia, and foreign bodies.
Conditions of impaired wound healing (such as chronic wounds or ulcers) are associated with substantial morbidity and mortality, and impose financial burden upon the world’s health services. Therefore, finding agents that accelerate wound healing is mandatory.
The use of laser as a non-surgical medical treatment modality for assisting the normal processes of healing has increased during the last decades. Laser therapy aims to restore the normal biological function of injured or stressed cells so’ Normalization’ is the keystone of laser therapy The stimulatory effect of laser therapy can be seen in wounded cells or in cells that are growing sub optimally whereas cells that are normal or fully functional remain unaffected and no therapeutic effect can be observed.
Using laser therapy, the laser cure offers hope for wounds that have not responded to conventional treatment. Low level laser therapy (LLLT)has been advocated for its professed anti-inflammatory effects, pain relief and acceleration of the regeneration of damaged tissue.
A low level laser is one that produces an energy density (output powers between 10 - 90 mW) so low that temperature elevations are limited to less that 0.5 - 0.75°C and any observed biological effects are consequently ascribed to non-thermal or photo-chemical events.
LLLT irradiation includes wavelengths of between 500 nm and 1100 nm and typically involves the delivery of 1 - 4 J/ to treatment sites. The effect of LLLT is that photons from a laser probe are absorbed into the mitochondria and cell membrane of target cells and a cascade of metabolic effects results in various physiological changes. One such effect is improved wound healing Some of the physiological effects of LLLT include: promotion of cell proliferation and cell growth, increased cell metabolism, restoration of homeostasis or normalization of cell function, increased production and release of enzymes, acceleration of the healing process by promoting protein synthesis such as collagen, prevention of scarring, and stimulation of lymphatic system activities to prevent swelling and edema.
The LED is based on the semiconductor diode. When a diode is switched on, electrons are able to recombine with holes within the device,
releasing energy in the form of photons. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor.
LEDs produce light with wavelengths similar to those of laser, but they have broader output peaks (they are less monochromatic) and lack of the coherence that is a particular feature of laser light.
Photobiostimulation mechanism is ascribed to the activation of mitochondrial respiratory chain component resulting in the initiation of a cascade of cellular reaction. It has been postulated that photoreceptors in the red to NIR region are the terminal enzyme of the respiratory chain cytochrome c oxidase with 2 copper elements.
In LED-exposed cells like fibroblasts, increased ATP production,
modulation of reactive oxygen species, reduction and prevention of apoptosis, stimulation of angiogenesis, increase of blood flow, and induction of transcription factors are observed. These signal transduction pathways lead to increased cell proliferation and migration, modulation in levels of cytokines, growth factors, and inflammatory mediators, and increase in anti
apoptotic proteins.
Accelerated healing and greater amount of epithelization for wound closure have been demonstrated in human studies. The literature also shows that LED therapy is known to positively support and speed up healing of chronic leg ulcers.