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Effects of low-power light therapy on wound healing: LASER x LED 617 The therapeutic benefits of LASER light in the treatment of wounds have been reported since the 1960s and those of LED light only since the 1990s.7,8 However, many of the results described show incon- sistency, mainly due to methodology bias or lack of standardization in the studies. Furthermore, the use of LED as a therapeutic resource remains controversial. There are questions regarding the equality or not of biological and therapeutic effects promoted by LED and LASER resources, but also regarding the appro- priate parameters to each of these light sources. This study aimed to determine, through a liter- ature review: 1 - the biological effects that support the use of light sources such as LED in the treatment of wounds and 2 - the light parameters (wavelength and dose) suitable for the treatment of wounds with LED light sources. The biological effects and light parame- ters of LED will be compared to those of LASER in order to verify the similarity (or not) regarding wound treatment. MATERIALS AND METHODS A literature search was performed in Medline, PubMed, SciELO and Science Direct databases. The literature search was restricted to studies published in English and Portuguese in the period of 1992-2012. The keywords used were “low level laser therapy”, “laser”, “light emitting diode”, “LED”, “photothera- py”, “wound healing”, “fibroblast”, “collagen” and “angyogenesis” combined with each other. RESULTS Sixty-eight studies were analyzed, including 48 on LASER light, 14 related to LED light and 6 for both types of light (Tables 1 to 3). According to data pre- sented on table 1, 16 of the 48 studies on the effects of LASER light were in vitro and 32 were performed in animals.9-56 The use of different wavelengths (532-1064 nm) was verified, with the most utilized spectral range being between 632.8 and 830 nm. Doses ranging from 0.09 to 90 J/cm2 were used, predominating the values from 1 to 5 J/cm2. One study did not cite the dose value used.48 The biological effects promoted were reduction of inflammatory cells, increased prolif- eration of fibroblasts, stimulation of collagen synthe- sis, angiogenesis inducement and granulation tissue formation. It was noted in a study that the dose of 4 J/cm2 was more effective than 8 J/cm2.14 Furthermore, doses of 10 and 16 J/cm2 promoted inhibitory effects.20,25,29,34 Eight of the 14 studies on the effects of LED light were in vitro studies and 6 performed in animals, as shown in table 2.57-70 Wavelengths ranging 456-880 nm were used, with spectral range from 627 to 670 nm predominating. Doses ranged from 0.1 to 10 J/cm2, and 4 J/cm2 was the predominant dose. However, not all studies reported the dose applied.64,66,67,68 Biological effects observed were reduction of inflammatory cells, increased fibroblast proliferation, collagen synthesis, stimulation of angiogenesis and granulation tissue formation, these being similar to the ones observed in studies with LASER. Table 3 shows six studies comparing the biolog- ical effects of LASER and LED lights.71-76 Two of the studies were in vitro and 4 were performed in rats. It has been noticed that wavelengths varied from 460 to 950 nm, with the range of 630-790 nm being the most utilized both in LASER and LED studies. Doses rang- ing from 0.1 to 10 J/cm2 were used, with predomi- nance of doses up to 5 J/cm2. All studies reported sim- ilar effects between LASER and LED, such as increased fibroblast proliferation and stimulation of angiogenesis. DISCUSSION Since the introduction of photobiomodulation in healthcare, the effectiveness and applicability of light resources for the treatment of skin wounds have been extensively investigated both in vitro and in vivo. Nevertheless, the biological mechanisms that support the actions of low intensity light in tissues are still not clearly elucidated. While some studies report an increase in cellular proliferation of several cell types including fibroblasts, endothelial cells and keratinocytes, conflict- ing results about the clinical benefits of using light on skin wounds are found in the literature. The way light interacts with the biological tis- sues will depend on the characteristics and parame- ters of light devices, mainly the wavelength and dose, and also the optical properties of the tissue. Regarding the characteristics of light devices, LASER consists of a resonant optical cavity and differ- ent types of active media such as solid, liquid or gaseous materials, in which processes of light genera- tion occur through the passage of an electric current.77 Potency in the range of 10-3 to 10-1 W, wavelength from 300 to 10,600 nm, pulse frequency from 0 (contin- uous emission) to 5,000 Hz, pulse duration and pulse interval from 1 to 500 milliseconds, total radiation from 10-3000 seconds, intensity between 10-2 and 100 Wcm-1 and dose from 10-2 to 102 Jcm-2 characterized LASER as a low potency device.78 On the other hand, LED is a diode formed by p-n junctions (p-positive, n-negative) that, when directly polarized, causes electrons to cross the poten- tial barrier and recombine with holes within the device. After the spontaneous recombination of elec- tron-hole pairs, the simultaneous emission of photons occurs. The physical mechanism by which LED emits light is spontaneous light emission. The light-emitting An Bras Dermatol. 2014;89(4):616-23.PDF Image | Effects of low-power light therapy on wound healing
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