Effects of low-level laser therapy on wound healing

Objective: To gather and clarify the actual effects of low-level laser therapy on wound healing and its most effective ways of application in human and veterinary medicine. Methods: We searched original articles published in journals between the years 2000 and 2011, in Spanish, English, French and Portuguese languages, belonging to the following databases: Lilacs, Medline, PubMed and Bireme; Tey should contain the methodological description of the experimental design and parameters used. Results: doses ranging from 3 to 6 J/cm appear to be more effective and doses 10 above J/cm are associated with deleterious effects. The wavelengths ranging from 632.8 to 1000 nm remain as those that provide more satisfactory results in the wound healing process. Conclusion: Low-level laser can be safely applied to accelerate the resolution of cutaneous wounds, although this fact is closely related to the election of parameters such as dose, time of exposure and wavelength.


INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION
T he incorporation of laser as a therapeutic tool has been accompanied in the biomedical field since 1960 by Theodore Maiman.One of the first published experiments on the effects of low-level laser dates from 1983, with HeNe (Helium Neon) laser irradiation of wounds in rats for 14 consecutive days 1 .
The effects of low-level laser can be observed in the behavior of lymphocytes, increasing their proliferation and activation; on macrophages, increasing phagocytosis; and on fibroblasts, increasing the secretion of growth factors and enhancing the uptake of both fibrin as collagen.In addition, it contributes to increase the motility of epithelial cells, the amount of granulation tissue and may reduce the synthesis of inflammatory mediators [2][3][4][5] .Its action can be observed on the reduction of the area of skin wounds in humans and animals, although the adoption of physical variables involved in the treatments is still not a consensus among authors [6][7][8][9] .
Regarding the irradiation protocol, the use of lasers may differ in the type of activation means, the power and dose, and also on the manner and time of irradiation and number of applications 3 .
From the above, and with the growing interest in alternatives to conventional drug therapies, the objective of this was to gather and clarify the actual effects of low-level laser therapy on wound healing and its most effective ways of application in human and veterinary medicine.

METHODS METHODS METHODS METHODS
This was a qualitative study from original articles published in journals indexed in the following databases: Lilacs, Medline, PubMed and Bireme.We included all original articles whose publication occurred between the years 1984 and 2011 in Spanish, French, English and Portuguese languages and provided methodology containing the parameters used by the applied laser mode.We excluded the research articles that did not contain the methodology regarding the description of the parameters used in their work.

LITERATURE REVIEW LITERATURE REVIEW LITERATURE REVIEW LITERATURE REVIEW LITERATURE REVIEW
The acronym LASER has its origin in the English language, abbreviating "light amplification by stimulated emission of radiation".The word laser is established by usage and defines a source of monochromatic, intense, coherent and collimated light, whose emission of radiation is done by stimulating the external field, with varied and growing applications in industry, engineering, human medicine and more recently, veterinary medicine 10,11 .In the latter, the rat has been used to study the different aspects involved in cutaneous healing process, being the elected experimental model due to ease of handling 12 .
Lasers are classified into high and low power.The first is generally applied for the removal, cutting and coagulating of tissues, while the low-power ones are more commonly applied in the processes of tissue repair, such as muscle, joint, nerve, bone and skin injuries 6,13,14 .
The photobiological effects of laser radiation can be conventionally divided into short and long term.The responses in the short term are those in which the effect can be observed in a few seconds or minutes after irradiation.The effects observed in the long term are those that occur hours or even days after the end of irradiation and usually involve new cell biosynthesis, especially in the proliferative phase of inflammation 12,15,16 .
A wide variety of lasers that promote wound healing can be found in the literature, including:.Helium-Cadmium, Argon, Helium-Neon, Krypton, Gallium Arsenide and Aluminium and CO 2

DISCUSSION DISCUSSION DISCUSSION DISCUSSION
The repair process is complex and comprises vascular and cellular alterations, epithelial and fibroblasts proliferation, synthesis and deposition of collagen, elastin and proteoglycan production, revascularization and wound contraction 8 .Noteworthy still are the trophic-regenerative, anti-inflammatory and analgesic effects 2,8,24 .It is also claimed that the low-level laser therapy can lead to increased mitochondrial activity, with a consequent increase of adenosine triphosphate (ATP), vasodilation, protein synthesis, decrease in prostaglandin levels, presence of cellular mitosis, migration and proliferation of keratinocytes and neoangiogenesis 18,19,23,25 .
In this sense, a study with HeNe laser, applied at the rate of 4J/cm 2 showed better effects in the production of collagen type III.In another, it was observed that doses between 7 and 9 J/cm 2 caused the opposite effect, reducing the production of collagen fibers 2,18 .
It is understood that the increased collagen production occurs through photostimulation mechanisms on which certain frequencies/doses may act, thereby modulating cellular proliferation and increasing the amount of fibroblast growth factors.Another possible explanation for this, according to the authors above, would be the better absorption of such energy by the mitochondria and consequently increased production of ATP and nucleic acid, the result being an increase in collagen production, accelerated epithelial repair and facilitated growth of granulation tissue 26 .
According to Zanotti et al. 9 , excitatory doses (up to 8J/cm 2 ) are indicated when the goal of the intervention includes the enhancement of the sodium/potassium pump; stimulating production of ATP; restoration of the membrane potential; increased metabolism and cell proliferation.
Laser therapy has been administered with the aim of promoting better resolution of inflammation, reducing pain, preventing the occurrence of edema and preserving tissues and nerves adjacent to the site of injury.Such effects can be achieved via wavelengths between 600 and 1000nm and power from 1mW to 5 W/cm 2 .The authors also emphasize that very low (2.5W/cm 2 ) or very high (25 W/ cm 2 ) power can cause the opposite effect 27 .
In a study treating the inflammatory process present in induced arthritis of the knee joint of rats with anti-inflammatory and low-level laser therapy, beneficial effects have been observed both at a dose of 3J/cm 2 and 30J/cm 2 , although the latter proved more effective in reducing the painful area over 120 hours after the start of treatment, when associated with lower power and applied for ten minutes 19 .Bashardoust Tajali et al. 3 reported that the wavelength of 632nm improved resolution of fractures, thereby demonstrating that there are many results for the use of this therapy.
Although laser has been successfully applied on the symptoms of various diseases, investigators showed that malignant melanoma cells irradiated by Indium-Gallium-Aluminum-Arsenic-Phosphorus (InGaAlAsP) laser at 660nm wavelength and dose of 1050J/cm 2 revealed worsening behavior 17 .Furthermore, the use of laser is contraindicated in cases of localized or irradiated malignant tumor; epilepsy; on the thyroid gland; on pregnant abdomen; high hypersensitivity; and thrombosis of pelvic or deep leg veins 28,29 .

FINAL CONSIDERATIONS FINAL CONSIDERATIONS FINAL CONSIDERATIONS FINAL CONSIDERATIONS FINAL CONSIDERATIONS
It is concluded that low-level laser therapy, when applied to skin wounds, is able to promote major physiological effects, such as anti-inflammatory resolution, neoangiogenesis, epithelial and fibroblasts proliferation, collagen synthesis and deposition, revascularization and wound contraction.It is also possible to say that doses of 3-6 J/cm 2 appear to be more effective and doses above 10 J/ cm 2 are associated with deleterious effects.The wavelengths between 632.8 and 1000 nm remain as those having more satisfactory results in the wound healing process.

Treatment Treatment Treatment Treatment Treatment
HeNe with power 4J/cm 2 applied for 12 seconds per wound site in continuous mode, 5mW, wavelength of 632.8 nm and the laser beam area of 0.015 cm 2 .
Application of laser once a day on tumor cells, for three consecutive days, with the following parameters: 632nm, 50 mW, 2mm 2 pointer, irradiation area of 2.5 W/cm 2 and times of 60 and 420 seconds at doses of 150J/cm 2 (group 1, in vitro) and 1050J/cm 2 (group 2, in vivo), respectively.The third group was not irradiated (control group).
Application of AlGaInP laser (658 nm, 4J/cm 2 ) in a localized and scanned manner on human decubitus and venous ulcers.
He-Ne laser on skin wounds in diabetic rats, with a wavelength of 632.8 nm and doses of 3-9J/cm 2 , five days / week until complete healing.
HeNe laser used in doses of 3 and 6J/cm 2 , 45 W of power and wavelength of 632nm and a control group, for surgical wounds of healthy rabbits.The animals were evaluated at 7, 14 and 21 days.
Low power laser with a wavelength of 585 nm and a dose of 7J/cm 2 on skin wounds of rats.
First week twice with an interval of 48 hours in the weeks following 1x/week, in a localized manner and without the use of additional medication.
Arthritis in rats treated for five days with 810nm, power 79 and 790mW, doses of 3 and 30J/cm 2 and intensities of 5 and 50mW/cm 2 .
Twelve animals divided into two groups: control and experimental.Wound treated for seven days with GaAs laser, pulsatile dose 3.8 J/cm 2 and power of 15mW time for 15 seconds.
Abrasive damage induced in non-dominant upper limb in two groups of healthy people.One group was treated with a dose of 8J/cm 2 , wavelength 820nm and two minutes exposure.The other group was treated under the same parameters for five seconds.A third group was not treated.
HeNe laser (632nm / 5mW and 904 nm/60W; 4 J/cm 2 ) associated with topical hyperbaric oxygen supply for 20 minutes per session on diabetic foot ulcers over 14 weeks.HeNe (632.8 nm wavelength, dose of 5 J/cm 2 and power of 10.53 mW/cm 2 ), applied three times per week in in vivo cells until complete healing of the wound.

Resiults Resiults Resiults Resiults Resiults
Increase of type III collagen, decreased inflammatory infiltrate and early resolution of wound inflammatory phase.
The dose of 4J/cm 2 differed significantly from the others concerning the reepithelialization process.
Between the in vitro and the control group, there was no statistically significant difference in the growth of tumor cells.Comparing group 2 and control, there was significant growth of mass and volume to the tumor, as well as a large number of blood vessels in the in vivo group.
Reduction of the wounds area.
Increased production of granulation tissue in the animals that received doses of 4-5J/ cm 2 , especially on the fifth day of treatment.
Observed the presence of mature granulation tissue at 14 days and absence of hemorrhage and exudate at day 21.
Permanent vascular proliferation after the fifth day of application.
The results revealed granulation tissue, reducing inflammation and pain relief from the first application.
Increase of adenosine triphosphate (ATP) and improved inflammatory process.Tissue repair significantly larger and more organized in the experimental group.
The groups treated with low level laser showed a statistically significant reduction in the wound when compared to the control group at the 6th, 8th and 10th days of treatment.Improvement of wound healing for both wave lengths adopted, though the latter presented more pronounced findings.
Complete healing of ulcers after 25 sessions and only 4% of recurrence.
Increased cell proliferation (fibroblasts and mitochondria), as well as microcirculation, with a consequent increase in cellular metabolism.