Use of Laser Therapy in the Healing Process: A Literature Review

Abstract

Objective: The purpose of this work was to conduct a literature search on the use of laser therapy in the tissue repair process, addressing different lasers and parameters used by the authors. Methods: We conducted a literature review of electronic databases to search for articles that investigate the effects of laser therapy on wound healing in rats, mice, and humans with specific diseases, published from January 2008 to March 2013. Results: In the 31 articles selected, the most frequently used type of laser was gallium-aluminium-arsenium (GaAIAs) in male rats. We noted that the protocol for laser application differed from author to author, making it difficult to compare results regarding the choice of parameters and treatment protocol. Conclusions: Laser therapy had a positive effect on the healing process of cutaneous lesions in rats, which was not observed in humans.

Introduction

Skin lesions are defined as a disruption of normal anatomical structure,¹ and can be caused by physical, chemical, or mechanical traumas, or triggered by a clinic disorder. According to Guo and Dipietro,² wound healing consists of four phases: hemostasis, inflammation, proliferation, and tissue remodeling, which must occur in sequence at a certain time, and continue for a specified time period at an optimal intensity.

The healing process can be affected by either local or systemic factors. Local factors are those that directly affect the characteristics of the lesion, such as tecidual oxygenation and infections. Systemic factors may be the individual's age, stress level, diabetes, medications, obesity, excessive alcohol consumption, smoking, and nutritional status.² Therefore, resources that can help in the healing process are necessary.

Currently, there are numerous physiotherapeutic resources that act in the healing process, among which we highlight the laser (originally an acronym of “light amplification by stimulated emission of radiation”),³ which is the modality to be discussed in this review. Since 1971, laser has been described as one of the most important noninvasive therapeutic modalities used in the treatment of chronic wounds,⁴ becoming nowadays one of the most commonly used methods of physiotherapy.^4a The differences among laser beams are determined by their wavelengths. The shorter the wavelength, the higher its action and power of penetration. The laser can be continuous or pulsed, with its power and energy expressed in Watts (W) and Joules per square centimeter (J/cm²), respectively.⁵

The benefits of the laser in wound healing are well described in the literature. In vivo and in vitro studies have shown that laser treatment accelerates the biochemical reactions, the activity of fibroblasts, collagen metabolism, neovascularization, and mitochondrial adenosine triphosphate (ATP) production, as well as promoting lymphocyte activation and analgesic and anti-inflammatory effects. Moreover, when the appropriate dose laser is applied through tissue biostimulation, this may stimulate the cellular functions that are vital during the process of cicatrization. When laser is applied at an appropriate dose, it can stimulate cellular functions by biostimulation of the tissues, which are vital in the healing process.⁶

Although several studies have shown the effects of laser radiation on tissues, the literature is still rather conflicting regarding the mechanisms responsible for the mitotic⁵ activity and the optimal parameters to stimulate epithelial tissue healing.⁷ More studies are necessary to investigate the best laser intensity in the healing process, as well to understand how this works at the cellular level.

Therefore, the aim of the present study was to conduct a literature search on the use of laser therapy in the tissue repair process, addressing different lasers and parameters used by the authors

Methods

A literature review was conducted to search for articles that investigate the effects of laser therapy on wound healing in rats, mice, and humans, published from January 2008 to March 2013.

The relevant articles were sought and obtained from the research on electronic databases (MEDLINE^® and PubMed), using the following keywords: wound healing, laser therapy, and tissue.

The articles identified by the initial search strategy were assessed independently by two authors, according to the following inclusion criteria: (1) have used laser, (2) have described the wavelength, (3) have at least one outcome or index involving the healing process, and (4) contain studies involving epithelial tissue damage.

Those studies on animals that fulfilled the inclusion criteria were classified into four categories: A, B, C, and D, according to the randomization criteria. Whereas “A” meanst that the random allocation process was adequate, “B” meant that the random allocation was not described, but that it was mentioned in the text that the study was random.“C” meant that the random allocation was inadequate and “D” meant that the study was not randomized. Articles classified into A and B were included in this study.⁸ Human-based studies that met the inclusion criteria were assessed for their methodological quality using the Jadad scale.⁹ The Jadad scale is divided into three items (randomized studies, double-blind studies, and studies with description of losses and exclusions); a maximum of five points can be obtained: three points for each “yes,”one additional point for an appropriate method of randomization, and one point added when the article used an appropriate method of blinding. A study was considered of poor quality if it received two points or fewer after the evaluation. The scale was applied independently by two researchers and then the concordance between them was analyzed. Studies with low methodological quality (Jadad scale score <2) were excluded from this review. We also excluded articles that had not fulfilled the inclusion criteria and the ones that had no clear information with respect to the materials and methods used.

Results

A total of 557 articles were found, of which 31 were selected (n=28 about rats or mice and n=3 about humans). Seven different lasers were used by the authors in the studies: gallium aluminum arsenide (GaAlAs), phosphide indium-gallium-arsenic (InGaAlp), GnbH, helium neon (HeNe), gallium arsenide (GaAs), indium gallium arsenide (InGasAs), and phosphide indium-gallium-aluminum (GaAlInP). The GaAlAs laser was used more often, by 11 authors, all in studies using an animal model. Twenty-five studies were conducted in rats and three were conducted in mice. The main results described and summarized in Tables 1 –7.^{10

–36} The three studies in humans used InGasAs and InGaAlP lasers. The main results of the effects of the laser on the process of healing skin lesions are described and summarized in Table 8.^38
–40

Table 1.

Studies Using Laser GmbH in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated área and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Peplow et al.¹⁰	Diabetic mice (BKS.Cg-m + / + Lepr^db/J)	1 wound in the left flank region	Laser GmbH was applied to the center of the wound; off mode	660 nm	233–313 mW/cm². 116–156 mW/cm². 58–78 mW/cm²	25–100 mW	100 mW-20 sec. 50 mW-40 sec. 25 mW-80 sec	4.7–6.3 J/cm²	Once daily for 7 consecutive days	Optical microscopy. Cuts of 4 mm and stained with hematoxylin and eosin (HE).	The three levels of irradiance influenced the healing of wounds, having no significant difference between the results	Did not use
Chung et al.¹¹	Diabetic and nondiabetic mice (BKS.Cg-m + / + Lepr^db/J)	1 wound diameter of 5 mm was made in the flank of each mouse	Laser GmbH	660 nm	X	18 and 80 mW	20 sec	X	The laser was applied for 8, 10, and 14 days	The wounds were photographed on days 1, 4, 7, 10, and 14. The processed tissue was stained with HE and subsequently analyzed with optical microscopy.	The wound treated with laser 1.6 J/day showed greater re-epithelialization, decrease in inflammatory exudate, and about half had a small amount of edema	Did not use

X, Information was not obtained or was not clear in the text.

Table 2.

Studies Using Laser InGaAlP in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated área and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Tacon et al.¹²	54 female Wistar rats	1 wound 1 cm in diameter in the dorsal neck region	Laser InGaAlP. Positioned directly on the animal to a vertical distance of 1 cm from the edge. Was applied to the wound edge and sweeping. Continuous mode.	660 nm	X	30 mW	X	3 and 6 J/cm²	One application per day on alternate days for 5, 10, and 15 days	Histological slides stained with hematoxylin and eosin (HE) 4 μm and subsequent morphometry and planimetry	There was no significant difference between experimental groups on days 5 and 15 with respect to wound contraction. There was no significant difference between the histological parameters analyzed in 5 days. A significant decrease was observed in the number of polymorphonuclear cells in 10 days.	Did not use
Lacjaková et al.¹³	16 Sprague-Dawley rats	4 wounds 4 mm on the dorsum of the mice	Laser InGaAlP	670 nm	5, 15, and 40 mW/cm²	X	X	5 J/cm²	The animals were treated for 6 days	The tissues were processed and stained with HE and van Gieson and subsequently analyzed with optical microscopy	Only the group treated with 40 mW/cm² density was able to significantly reduce inflammation. In wounds treated with laser density of 15 mW/cm², significant acceleration was observed in re-epithelialization. Laser treatment with density 15 and 40 mW/cm² significantly improved the proliferation of fibroblasts and the formation of new blood vessels.	Did not use

X, Information was not obtained or was not clear in the text.

Table 3.

Studies Using Laser AlGaInP in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated área and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Renno et al.¹⁴	32 male Wistar rats	An instrument 2×2 cm was heated and then applied on the mouse skin to produce a second degree burn	AlGaInP laser. Point application	660 nm	X	100 mW	5 sec	0.5 J/cm²	The groups were irradiated for 7 and 14 days	Analysis of necrosis through the paper-template method. Histologic nalysis by light microscopy and immunohistochemistry.	Positive effects have been observed on the healing of laser 660 nm burns. A significant VEGF immunoreactivity was observed in the laser-treated group.	Did not use
Noudeh et al.¹⁵	19 male Wistar rats	1 wound on the dorsal region of the rat ∼12 mm	GaAlAs laser and GaAlInP. The laser was applied to the wound bed and margins.	670 and 810 nm	500 and 250 mW	X	48 and 50 sec	1.33² and 10 J/cm²	Laser sessions were performed every 3 days, giving a total of seven sessions	The healing of wounds was assessed by digital photography through a digital microscope	The combination of applied lasers 670 and 810 nm showed no significant results in improved healing of epithelial tissue	Did not use
Vasilenko et al¹⁷.	40 Sprague-Dawley rats	1 incision of 4 cm	GaAlAs laser and AlGaInP. Applying continuous manner at a distance of 15 cm.	635 and 670 nm	4 and 15 mW/cm²	X	533 and 1250 sec	5 J/cm²	The laser was applied daily for 7 days	Maximum strength was examined tissue breakdown	Both lasers were able to increase the tensile strength of the wound	Did not use

X, information was not obtained or was not clear in the text.

VEGF, vascular endothelial growth factor.

Table 4.

Studies Using Laser GaAlAs in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated área and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Noudeh et al.¹⁵	19 male Wistar rats	1 wound on the dorsal region of the rat ∼12 mm	GaAlAs and GaAlInP. The laser was applied to the wound bed and margins.	670 and 810 nm	500 and 250 mW	X	48 and 50 sec	1.33 and 10 J/cm²	Laser sessions were performed every 3 days, giving a total of seven sessions	The healing wounds were assessed by digital photography through a digital microscope	The combination of applied lasers 670 and 810 nm showed no significant results in improved healing of epithelial tissue	Did not use
Garcia et al.¹⁷	115 male Wistar rats	1 circular wound of 8 mm diameter in the dorsal region	GaAlAs laser. Was applied in continuous mode and punctual, with laser beam area of the of 0.071 cm²	660 nm	X	30 mW	13 sec	5.57 J/cm²	The laser was applied for 3, 7, and 14 days	Slides were stained with hematoxylin and eosin (HE) and subsequently analyzed by light microscopy	Decrease in inflammatory infiltrate, increased epithelial differentiation, increased collagen deposition and improved wound healing in animals receiving nicotine	Did not use
Gonçalves et al.¹⁸	24 male Wistar rats	5 wounds around the dorsolateral region of 12 mm diameter	GaAlAs laser. Collimated laser beam spot area and irradiation of 0.035 mm².	830 nm	X	9 mW	The application time was set automatically by the instrument	30 and 60 J/cm²	The laser was applied daily for 7 days	Slides were stained with HE and Sirius red and subsequently analysized with optical microscopy	The results showed that laser 60 J/cm² was more effective in stimulating angiogenesis, and 60 and 30 J/cm² were more effective in promoting maturation of collagen in the scar tissue of rats	Did not use
Akyol et al.¹⁹	80 male Wistar rats	3 incisions of 15 mm in the dorsal region	GaAlAs laser. Was applied ∼1 cm from the wound surface.	808 nm	0.1 W/cm²	4 W	20 sec	2 J/cm²	The laser was applied immediately after surgery and on the 2nd, 4th, 6th, and 8th day (5 sessions)	The tissue was processed and stained with HE and subsequently analyzed with optical microscopy	Significant difference in epithelialization and decreased inflammation in 10 days. There was no statistically significant difference between groups in inflammation and epithelialization in 20 days.
Vasilenko et al.¹⁶	40 Sprague-Dawley rats	1 incision of 4 cm	GaAlAs and AlGaInP. Applying continuous manner at a distance of 15 cm.	635 and 670 nm	4 and 15 mW/cm²	X	533 and 1250 sec	5 J/cm²	The laser was applied daily for 7 days	The resistance to rupture of the irradiated tissue was measured for each sample	Both lasers were able to increase the tensile strength of the wound	Did not use
Gϋngörmϋş et al.²⁰	20 Wistar rats	2 incisions 15 mm were made on the backs of mice	Laser GaAlAs	808 nm	0.1 W/cm²	4 W	20 sec	2 J/cm²	The irradiation started immediately after surgery and on the 2nd, 4th, 6th, and 8th day (5 sessions)	The tissue was processed and stained with HE and analyzed with light microscopy	Significant difference in inflammation between the groups at 10 days	Did not use
Gϋngörmϋş et al.²¹	40 female Wistar rats	Two incisions 15 mm were made on the backs of mice	GaAlAs laser. Applying continuous mode.	808 nm	0.1 W/cm²	20 W	20 sec	2 J/cm²	The irradiation started immediately after surgery and on the 2nd, 4th, 6th, and 8th day (5 sessions)	The tissue was processed and stained with HE and analyzed with light microscopy	Significant difference in the process of re-epithelialization between groups.In 20 days no significant difference was observed between groups.	Did not use
Garcia et al.²²	96 male Wistar rats	One of 8 mm circular incision in the dorsal region. One burn in the same region	Laser GaAlAs.Point application in 8 points on the edges of the wound.	685 nm	0.5 W/cm²	X	81 sec	4.5 J/cm²	Animals were euthanized 3, 7, and 14 days after injury	Histological analysis by light microscopy	The results suggested that the laser can be useful for treating skin burns, particularly if initiated at an early stage of healing	Did not use
Ribeiro et al.²³	24 Wistar males	One incision 1 cm² in the dorsum of the rat	Laser GaAlAs.The laser was positioned directly over the wound at a vertical distance of 0.3 cm from the wound edge. Irradiation was performed at four different points.	660 nm	40 mW	X	120 sec	5 J/cm²	Irradiation daily for 7 days	Immunohistochemical analysis and quantitative analysis of lymphoid cells and myofibroblasts	Quantitative analysis of myofibroblasts showed that these cells were significantly more abundant in irradiated wounds in 8 days.T cells were significantly less evident in the irradiated groups.	Did not use
Reis et al.²⁴	32 Wistar males	One incision 6 mm diameter dorsal region	Laser GaAlAs. Applying continuous mode.	670 nm	0.031 W/cm²	X	31 sec	1 J/cm²	X	The tissue was processed and stained with HE and Sirius red and subsequent optical microscopy	The laser improved the process of tissue repair by reducing edema and polymorphonuclear infiltrate and increased collagen production with tissue matrix better organized	Was performed by transmission electron microscopy.
Medrado et al.²⁵	120 Wistar rats of both sexes	One incision 8 mm in the dorsal region	Laser AsGaAl. Application so punctual.	670 nm	31 mW/cm²	9 mW	31 sec	0.5 J/cm²	After the laser treatment the wound tissue was removed on the 3rd, 7th, 10th, 15th, 20th, 30th, and 60th day after treatment	The tissue was processed and stained with HE and Sirius red light microscopy and subsequent fluorescence microscopy and immunohistochemistry.	The laser and the silica were identified as capable of modulating the synthesis of collagen during healing. The laser allowed a better arrangement of collagen fibers, necessary for the development of the tensile strength of the scar tissue.	Was performed by transmission electron microscopy.

X, Information was not obtained or was not clear in the text.

Table 5.

Studies Using Laser GaAs in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated area and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Júnior et al.⁶	30 Wistar rats	One incision 10 mm in the dorsal region	Laser GaAs; pulsed mode	870 nm	15 mW	0.5–3.5 mW	15 sec	3.8 J/cm²	First application immediately after surgery, then 48 h, and 7 days after (3 sessions)	Immunohistochemistry was performed and apoptosis detected	In the laser-treated group the number of apoptotic cells was significantly higher	Did not use
Silveira et al.²⁶	6 male Wistar rats	One wound diameter of 8 mm was brought into the dorsal region of the mice	GaAs laser (pulsed emission) and HeNe (emission continues)	Pulsed mode: 904 nm; continuous mode: 660 nm	0.4 W/cm²	70 W and 30 mW	X	1 and 3 J/cm²	The animals were irradiated 2, 12, 24, 48, 72, 96, and 120 h after the injury	Biochemical analysis was performed: level of hydroxyproline, lipid peroxidation and protein carbonylation, and superoxide dismutase and catalase.	There was significant improvement in the healing of wounds in the groups irradiated with HeNe and GaAs when compared with the control.The laser is beneficial to the healing process, particularly with the HeNe laser 1 and 3 J/cm² and GaAs 3 J/cm²	Did not use

X, Information was not obtained or was not clear in the text.

Table 6.

Studies Using Laser HeNe in an Animal Model

References	Animal	Number, size, and location of the lesion	Irradiated area and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Santuzzi et al.²⁷	20 Swiss mice	One incision 1 cm long on the dorsal-thoracic	Laser NeNe. Application of continuous mode, the scanning method	632 nm	0.5–3.5 mW	5 mW	12 sec	4 J/cm²	Application daily for 3 days	The tissue was processed and subjected to staining with Masson's Trichrome	The combination of He-Ne laser therapy with ICOX2 was able to regulate the effects of both isolated biostimulation treatment	Did not use

ICOX2, cyclooxygenase-2.

Table 7.

Studies Using Laser that Did Not Describe the Type

References	Animal	Number, size, and location of the lesion	Irradiated área and the distance from the laser	Wavelength (nm)	Power density (mW/cm²)	Power (mW)	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results	Using electron microscopy
Dadpay et al.²⁸	18 male Wistar rats	Two wounds, one in the chest and another in the lumbar region, of 1.5 cm thickness each	Infrared diode lasers. The irradiated area including the area of the wound and surrounding skin with laser pen perpendicular to the tissue target at a distance of 1 cm per region.	890 nm	1.08 mW/cm²	1.08 mW	Group 1, 30 sec; groups 2 and 3, 200 sec	Group 1, 0.03 J/cm²; groups 2 and 3, 0.2 J/cm²	Once daily for 15 days	Biomechanical analysis: maximum load, maximum stress, modulus of elasticity, and energy absorption	0.2 J /cm² is capable of increasing the maximum stress and elastic modulus of diabetic rats and nondiabetic	Did not use
Khoshvaghti et al. ²⁹	48 male Wistar rats	The skin of the back was exposed for 2 sec at the edge of a cylinder of 6 mm in diameter connected to a source of boiling water	X	890 nm	1.08 mW/cm²	75 W	856 sec	0.924 J/cm²	The burns were irradiated 4, 8, 13, and 20 days after injury	Morphometric analysis. The tissue was processed and stained with toluidine blue.	The laser significantly decreased the total number of mast cells during proliferation and remodeling phases of wound healing of the burn	Did not use
Sperandio et al.³⁰	100 female Wistar rats	One incision 6 mm in diameter in the dorsal region	Laser applied so punctual	660 nm	X	100 mW	33 sec	117.85 J/cm²	The laser was applied after surgery. The animals were euthanized on the 1st, 3rd, 5th, 7th, and 14th days after surgery.	The wounds were photographed for the analysis of contraction.Histological analysis with optical microscopy.	The laser showed excellent results regarding wound healing	Did not use
Marchionni et al.³¹	80 male Wistar rats	One circular wound on the dorsal region of 6 mm in diameter.	The laser was applied to the wound edges	670 nm	0.31 W/cm²	9 mW	31 sec	1 J/cm²	The laser was applied for 1, 3, 5, 7, and 14 days	The tissue was processed for hematoxylin and eosin (HE), Sirius red, and immunohistochemistry	In the groups treated with laser, significant difference was observed in the reduction of edema and polymorphonuclear cells, in addition to a significant increase in collagen synthesis.	Did not use
Guirro et al.³²	75 male Wistar rats	One wound on the dorsal region of 1 cm²	The laser has been implemented in four points off the edges and noncontact wound in the wound bed	670 nm	X	30 mW	4 J/cm²-134 sec7 J/cm²-234 sec	4 and 7 J/cm²	Lesions were stimulated daily for 7 and 14 days	The tissue was processed and stained with HE for histological analysis.Linear measurements of re-epithelialization were calculated from the edge of the lesion toward the end of the regenerating epithelium along both edges.	A significantly greater reduction in the number of leukocytes was observed in the group treated with 7 J/cm².There was no significant difference between the groups with respect to the results of epithelialization.	Did not use
Cury et al.³³	60 male Wistar rats	One wound (10×4 cm) on the back of each mouse	Twenty four points on the skin flap surface and surrounding it were irradiated through the punctual contact technique	660 and 780 nm	X	40 mW	30 and 40 sec	30 and 40 J/cm²	Irradiation was performed 1–4 days postoperatively	We calculated the percentage of necrotic area on the edge of the wound	There was no significant difference between groups	Did not use
Nussbaum et al.³⁴	70 Sprague-Dawley rats	One incision in the dorsal region	X	808 and 635 nm	0.028 w/cm²	X	36 and 710 sec	1 and 20 J/cm²	Irradiation occurred three times a week for 8 and 19 days	The wound was photographed three times a week and bacterial growth was evaluated.The tissue was processed and stained with HE and Sirius red and analyzed by electron microscopy.	Significant differences in the maximum area of the wound were observed in groups treated with laser.Irradiation using 635 nm resulted in 89% of wounds being sterile.Radiated wounds with 1 J/cm² showed significant tissue repair later.	Did not use
Al-Watban³⁵	893 Sprague-Dawley rats	One incision 102.5±9 mm² or burn 148±12.5 mm²	X	532, 633, 810, 980, and 10,600 nm	20.4 mW/cm², 15.56 mW/cm², 22.22 mW/cm², 66.37 mW/cm², 13.6 mW/cm²	143 mW	75–1350 sec	5, 10, 20, and 30 J/cm²	Three irradiations per week	The injured or burned areas were measured daily, and slope values were obtained	The laser of 633 nm showed the best effects on the healing process of wounds and burns	Did not use
Gál et al.³⁶	48 Sprague-Dawley rats	Four incisions of 4 mm in the dorsal region	Laser 10 cm away from the wound	635 nm	1, 5, and 15 mW/cm²	X	300, 1000, and 5000 sec	5 J/cm²	Irradiation daily up to 6 days	The tissue was processed and stained with HE and van Gieson's and subsequent optical microscopy	The laser group showed a significant difference in the process of re-epithelialization.The 635 nm laser effectively stimulated the healing of wounds	Did not use

X, information was not obtained or was not clear in the text.

Table 8.

Studies Using Laser Therapy in Humans

References	Jadad Scale	Area, size, and location of the wound	Irradiated area and the distance from the laser	Wavelength (nm)	Power	Time (sec)	Energy density (J/cm²)	Days and number of treatments	Methods	Results
Kaviani et al.³⁷	3	Diabetic patients with foot ulcers, stage I and II, according to the Wagner classification	Application contactless at a distance of 1 cm from the surface of the ulcer	685 nm	50 mW	200 sec	10 J/cm²	The ulcers were irradiated six times a week for 2 successive weeks and then to complete the cure	The ulcers were photographed by digital camera according to standard protocol, and peripheral neuropathy was assessed by monofilaments	The laser-treated group showed a significant percentage reduction of the ulcer.After 20 weeks, a greater number of patients showed complete healing and less healing time; however, this was not statistically significant.
Leclère et al.³⁸	3	Patients with ulcers of venous origin with a diameter between 2 and 8 cm	Laser InGasAs	980 nm	15 W	3 sec	90 J/cm²	Patients were examined weekly for 9 weeks	The ulcers were photographed	No significant difference in reducing the size of ulcers
Barreto and Salgado³⁹	3	Patients with neuropathic ulcers	Laser InGaAlP. Continuous mode. Point application and scan	660 nm	40 mW	X	2 and 4 J/cm²	Patients were treated three times per week for 12 weeks	The ulcers were photographed and the Pressure Ulcer Scale for Healing (PUSH) was used	The laser showed no additional benefit in healing of ulcers

X, information was not obtained or was not clear in the text.

Discussion

Most of the authors concluded that laser therapy had positive effects on wound healing.^{10,11,13

–18,20
–22,24

–32,34
–36} However, it was observed that the laser application protocol differs among authors with respect to wavelength, irradiance, output power, application time, energy (dose), and number of applications, confounding direct comparison among studies and establishment of optimal irradiation parameters for the treatment of wounds; for example, recommended dosages for wound healing.

According to Silva,⁷ the average application rate of the laser is 4.2 J/cm²; however, it is important to note that in this review the dosages used by the authors ranged from 0.03 to 117 J/cm² with reported positive results across the spectrum of dosage, making it difficult to discuss the relevance of dose.

The types of lasers most frequently used were GaAIAs,^{15

–19,21

–24,36} InGaAlP,^12,13,39 GnbH,^10,11 GaAs,^5,26 HeNe,^26,27 AsGaAl,²⁵ InGasAs,³⁸ and GaAlInP.^14,15 In animal model studies, GaAlA was the most common type of laser used,^{15

–24,36} which is in accordance with the literature review of Silva.⁷ However, in human studies, different types of lasers were used, including the InGasAs³⁸ and the InGaAlP.³⁹

The GaAIAs laser was used in doses of 1 J/cm²,²⁴ 1,33 J/cm².¹⁵ 2 J/cm²,^19
–21 4.5 J/cm²,²² 5 J/cm²,^16,23,36 5.57 J/cm²,¹⁷ 10 J/cm²,¹⁵ 30 J/cm², and 60 J/cm².¹⁸ Despite the different doses, the results in these studies showed that laser was effective in improving the inflammatory process,^{17,19,20,23,24} stimulation of cicatrization,^{17,19,21
–23,36} deposition of collagen,^17,18,24 angiogenesis, and increased tissue resistance to epithelial tension.¹⁶ Noudeh et al.¹⁵ have not obtained significant results with regard to improved healing using GaAlAs laser (1.33 J/cm²) and GaAlInP (10 J/cm²), possibly because of excessive exposure to laser light, which might have increased the rate of cell apoptosis and caused some genetic lesions, suggesting that laser can have inhibitory effects on the healing process.¹⁵ More studies are necessary to show which dose and time of laser application may have inhibitory effects on the process of wound healing.

InGaAlP laser was used in doses of 2 J/cm²,³⁹ 3 J/cm²,¹² 4 J/cm²,³⁹ 5 J/cm²,¹³ and 6 J/cm².¹² The results showed that the laser had a positive effect on the healing process of cutaneous lesions in rats;^13,29 however, in humans, laser did not show beneficial effects in the healing of neuropathic ulcers.³⁹ According to the authors of this work,³⁹ two biases may have affected the results, which were the small sample and the fact that patients did not use appropriate footwear. However, the studies³⁹ cited here were conducted in the presence of underlying clinically relevant diseases, which does not make it possible to compare the effect of the laser on the normal healing process.

GnBh laser was used by Peplow et al.¹⁰ and Chung et al.¹¹ in mice at a dose of 4.7–6.3 J/cm² and 0.36 and 1.6 J/day, respectively. It was observed that all the doses showed positive results in the healing process, but only at a dose of 1.6 J/day were these results statistically significant. According to the authors, laser treatment with higher power output accelerates the process of wound healing and formation of granulation tissue.¹¹

GaAs laser was used at a dose of 1 J/cm², 3 J/cm²,²⁶ and 3.8 J/cm²,⁵ and in both studies, higher doses showed beneficial effects on the healing process. According to Junior et al.,⁶ where the appropriate dose was used, the laser stimulated mitochondrial ATP production, activation of lymphocytes and mastocytes, and proliferation of fibroblasts, thereby stimulating the healing process.

According to Silveira et al.,²⁶ the HeNe laser is a low-power laser, most often used in physiotherapy to promote wound healing. However, only two studies^26,27 were found that used the HeNe laser with this purpose, and both were in rats. The doses used were 1 J/cm², 3 J/cm²,²⁶ and 4 J/cm²,²⁷ and all had positive effects on the healing process.

InGasAs laserwas used only in one study.³⁸ The InGaSAs laser with a dose of 90 J/cm² applied on venous ulcers in humans showed no significant results on the healing process, probably because of the small number of patients, low treatment frequency, and other factors that may influence the worsening of ulcers.³⁸

Most studies found in this study included only male animals,^{13

–19,21

–24,26

–29,33,36} making it impossible to verify the differences in the healing process between the genders. The same was observed in the review of the literature about laser performed by Peplow et al.,⁴⁰ the existence of studies essentially in male animals, highlighting the need for further studies comparing males and females, and analyzing the effects of sex hormones on the healing process.

The number of human studies was inadequate to make valid interpretations; however, it was noted that only one study³⁷ showed significant laser results on the healing process.

According to Reis et al.,²⁴ there are few reports in the literature about ultrastructural analysis by means of electron microscopy of skin wounds treated with laser. Corroborating this fact, only two studies^24,25 have used transmission electron microscopy as a method of analysis, and in both, the laser had an ultrastructural effect. In one of these studies, the laser showed effects on fibroblasts, which were numerous and have organelles, presenting the Golgi apparatus and the endoplasmic reticulum rough and well developed, with the extracellular matrix organized.²⁴

Conclusions

Most of the analyzed studies reported that laser therapy accelerates the process of wound healing. Nonetheless, the different application protocols found made it difficult to compare results and to select the appropriate treatment parameters. This issue needs to be considered in the development of future research in the area. There are only a few studies in humans; therefore, more research is needed, especially controlled clinical trials, to obtain the appropriate laser parameters for the process of wound healing.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

References

Chen

, Przyborowski

, Berthiaume

. Stem cells for skin tissue engineering and wound healing. Crit Rev Biomed Eng, 2009; 37:4–5.

Guo

, Dipietro

. Factors affecting wound healing. J Dent Res, 2010; 83:219–229.

Regan

, Teasell

, Wolfe

, Keast

, Mortenson

, Aubut

. A systematic review of therapeutic interventions for pressure ulcers following spinal cord injury. Arch Phys Med Rehabil, 2009; 90:213–231.

Mester

, Spiry

, Szende

, Jolan

. Effects of lasers on wound healing. Am J Surg, 1971; 122:532–535.

Silva

, Mendes

, Alves

AMP

, Alves

EPB

, Bertolini

GRF

. Microscopic study of tissue damage in skin of rats treated with low power laser. R Bras Bioci, 2010; 8:264–267.

Demir

, Balay

, Kirnap

. A comparative study of the effects of electrical stimulation and laser treatment on experimental wound healing in rats. J Rehabil Res Dev, 2004; 41:147–154.

Júnior

AMR

, Vieira

, Andrade

LCF

, Aarestrup

. Low-level laser therapy increases transforming growth factor-β₂ expression and induces apoptosis of epithelial cells during the tissue repair process. Photomed Laser Surg, 2009; 27:303–307.

Silva

, Silva

, Almeida

APF

, Junior

, Matos

. Laser therapy in the tissue repair process: a literature review. Photomed Laser Surg, 2010; 28:17–21.

Guidugli

, Castro

, Atallah

. Antibiotics for preventing leptospirosis. Cochrone Database Syst Rev, 2009; 3:CD001305.

10.

Jadad

, Moore

, Carroll

, Jenkinson

, Reynolds

, Gavaghan

. Assessing the quality of reports of randomized clinical trials: is blinding necessary?. Control Clin Trials, 1996; 17:1–12.

11.

Peplow

, Chung

, Ryan

, Baxter

. Laser photobiestimulation of wound healing: reciprocity of irradiance and exposure time on energy density for splinted wounds in diabetic mice. Lasers Surg Med, 2011; 43:843–850.

12.

Chung

, Peplow

, Baxter

. Laser photobiomodulation of wound healing in diabetic and non-diabetic mice: effects in splinted and unsplinted wounds. Photomed Laser Surg, 2010; 28:251–261.

13.

Tacon

KCB

, Santos

HCO

, Parente

LML

, et al. Healing activity of laser AlGaInP (660 nm) in rats. Acta Cir Bras, 2011; 26:373–378.

14.

Lacjaková

, Bobrov

, Poláková

, et al. Effects of equal daily doses delivered by different power densities of low-level laser therapy at 670 nm on open skin wound healing in normal and corticosteroid-treated rats: a brief report. Lasers Med Sci, 2010; 25:761–766.

15.

Renno

ACM

, Iwana

, Shima

. Effect of low-level laser therapy (660 nm) on the healing of second-degree skin Burns in rats. J Cosmet Laser Ther, 2011; 13:237–242.

16.

Noudeh

, Shabani

, Vatankhah

, Hashemian

, Akbari

. A combination of 670 nm and 810 nm diode lasers for wound healing acceleration in diabetic rats. Photomed Laser Surg, 2010; 28:621–627.

17.

Vasilenko

, Slezák

, Kovác

, et al. The effect of equal daily dose achieved by different power densities of low-level laser therapy at 635 and 670 nm on wound tensile strength in rats: a short report. Photomed Laser Surg, 2010; 28:281–283.

18.

Garcia

, Macarini

, Almeida

, et al. influence of low-level laser therapy on wounds healing in nicotine-treated animals. Lasers Med Sci, 2012; 27:437–443.

19.

Gonçalves

, Novaes

, Matta

SLP

, Benevides

, Faria

, Pinto

MVM

. Comparative study of the effects of gallium-aluminun-arsenide laser photobiomodulation and healing oil on skin wounds in wistar rats: a histomorphometric study. Photomed Laser Surg, 2010; 28:597–602.

20.

Akyol

, Gϋngörmş

. The effect of low-level laser therapy on healing of skin incisions made using a diode laser in diabetic rats. Photomed Laser Surg, 2010; 28:51–55.

21.

Gϋngörmϋş

, Akyol

. The effect of gallium-aluminum-arsenide 808-nm low-level laser therapy on healing of skin incisions made using a diode laser. Photomed Laser Surg, 2009; 27:895–899.

22.

Gϋngörmϋş

, Akyol

. Effect of biostimulation on wound healing in diabetic rats. Photomed Laser Surg, 2009; 27:607–610.

23.

Garcia

, Lima

, Tetuo

. Effects of photodynamic therapy on the healing of cutaneous third-degree-burn: histological study in rats. Lasers Med Sci, 2010; 25:221–228.

24.

Ribeiro

MAG

, Cavalcanti

, Ramalho

LMP

, et al. Immunohistochemical assessment of myofibroblasts and lynphoid cells during wound healing in rats subjected to laser photobiomodulation at 660 nm. Photomed Laser Surg, 2009; 27:49–55.

25.

Reis

SRA

, Medrado

, Marchionni

AMT

, Figueira

, Fracassi

, Knop

LAH

. Effect of 670-nm laser therapy and dexamethasone on tissue repair: a histological and ultrastructural study. Photomed Laser Surg, 2008; 26:307–313.

26.

Medrado

, Soares

, Santos

, Reis

SRA

, Andrade

. Influence of laser photobiomodulation upon connective tissue remodeling during wound healing. J Photochem Photobiol B, 2008; 92:144–152.

27.

Silveira

PCL

, Silva

, Freitas

, Latini

, Pinho

. Effects of low-power laser irradiation (LPLI) at different wavelengths and doses on oxidative stress and fibrogenesis parameters in an animal model of wound healing. Lasers Med Sci, 2011; 26:125–131.

28.

Santuzzi

, Buss

, Pedrosa

, Freire

MOVM

, Nogueira

, Gonçalves

WLS

. Combined use of low level laser therapy and cyclooxygenase-2 selective inhibition on skin incisional wound reepithelialization in mice: a preclinical study. An Bras Dermatol, 2011; 86:278–283.

29.

Dadpay

, Sharifian

, Bayat

, Dabbagh

. Effects of pulsed infra-red low level-laser irradiation on open skin wound healing of healthy and streptozotocin-induced diabetic rats by biomechanical evaluation. J Photochem Photobiol B, 2012; 111:1–8.

30.

Khoshvaghti

, Zibamanzarmofrad

, Bayat

. Effect of low-level treatment with an 80-Hz pulsed infrared diode laser on mast-cell numbers and degranulation in a rat model of third-degree burn. Photomed Laser Surg, 2011; 29:597–604.

31.

Sperandio

, Simões

, Aranha

ACC

, Corrêa

, Souza

SCOM

. Photodynamic therapy mediated by methylene blue dye in wound healing. Photomed Laser Surg, 2010; 28:581–587.

32.

Marchionni

AMT

, Medrado

, Silva

TMC

, Fracassi

, Pinheiro

ALB

, Reis

SRA

. Influence of laser (λ670 nm) and dexamethasone on the chronology of cutaneous repair. Photomed Laser Surg, 2010; 28:639–646.

33.

Guirro

ECO

, Montebelo

MIL

, Borlot

, Torres

MACB

, Polacow

MLO

. Effect of laser (670 nm) on healing of wounds covered with occlusive dressing: a histologic and biomechanical analysis. Photomed Laser Surg, 2010; 28:629–634.

34.

Cury

, Bossini

, Fangel

, Crusca

, Renno

, Parizotto

. The effect of 600 nm and 780 nm laser irradiation on viability of random skin flap in rats. Photomed Laser Surg, 2009; 27:721–724.

35.

Nussbaum

, Mazzulli

, Pritzker

KPH

, Heras

, Jing

, Lilge

. Effects of low intensity laser irradiation during healing of skin lesions in the rat. Lasers Surg Med, 2009; 41:372–381.

36.

Al-Watban

. Laser therapy converts diabetic wound healing to normal healing. Photomed Laser Surg, 2009; 27:127–135.

37.

Gál

, Mokrý

, Vidinský

, et al. Effect of equal daily doses achieved by different power densities of low-level laser therapy at 635 nm on open skin wound healing in normal and corticosteroid-treated rats. Lasers Med Sci, 2009; 24:539–547.

38.

Kaviani

, Djavid

, Ataie–Fashtami

, et al. A randomized clinical trial on the effect of low-level laser therapy on chronic diabetic foot wound healing: a preliminary report. Photomed Laser Surg, 2011; 29:109–114.

39.

Leclère

, Puechguiral

, Rotteleur

, Thomas

, Mordon

. A prospective randomized study of 980 nm diode laser-assisted venous ulcer healing on 34 patients. Wound Repair Regen, 2008; 18:580–585.

40.

Barreto

, Salgado

. Clinic-epidemiological evaluation of ulcers in patients with leprosy sequelae and the effect of low level laser therapy on wound healing: a randomized clinical trial. BMC Infect Dis, 2010; 10:1–9.

41.

Peplow

, Chung

, Baxter

. Laser photobiomodulation of wound healing: a review of experimental studies in mouse and rat animal models. Photomed Laser Surg, 2010; 28:291–325.