The Comparison of the Efficacy of Blue Light-Emitting Diode Light and 980-nm Low-Level Laser Light on Bone Regeneration.
- 1*Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Eski?ehir Osmangazi University, Eski?ehir†Department of Oral and Maxillofacial Surgery, Faculty of Dentistry‡Department of Pathology, Faculty of Medicine, Akdeniz University, Antalya§Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Istanbul Aydin University, Istanbul, Turkey.
The aim of this study is to histologically compare effects of blue light-emitting diode (LED) light (400-490?nm) and Ga-Al-As low-level diode laser light (980?nm) on bone regeneration of calvarial critical-sized defects in rats. Thirty Wistar Albino rats were included in the study. The experimental groups were as follows: blue LED light (400-490?nm) group (LED); 980-nm low-level laser light group (LL); and no-treatment, control group (CL). A critical-sized defect of 8?mm was formed on calvaria of rats. Each animal was sacrificed 21 days after defect formation. Calvarias of all rats were dissected and fixated for histological examination. Histomorphometric measurements of total horizontal length of the newly produced bone tissue, total vertical length of the newly produced bone tissue, and diameter of the newly produced longest bone trabecula were performed with a computer program in micrometers. There was a statistically significant increase in the total horizontal length and total vertical length in LL and LED groups compared to that in the CL group (P?<?0.05), while there was no statistical difference between LED and LL groups (P?>?0.05). A statistically significant difference was observed in the longest bone trabecula and LL groups compared to that in CL (P?<?0.05), but not between LED-CL and LED-LL groups (P?>?0.05). In conclusion, blue LED light significantly enhances bone regeneration in critical-sized defects when compared with CL group, but does not have a statistically significant effect on bone regeneration when compared with 980-nm low-level laser light
Effects of low-power light therapy on wound healing: LASER x LED*
A wound is characterized by the interruption on the continuity of a body tissue. It can be caused by any type of physical, chemical and mechanical trauma or triggered by a medical condition.1 Cutaneous wounds are relatively common in adults and their incidence seems to increase in parallel with the advances in life expectancy in the population.2
The therapeutic approach to wound healing consists of preventive measures such as health professional continuing education, family counseling and guidelines to a proper patient nutrition. The use of medicinal plants, administration of essential fatty acids, calcium alginate, antiseptics and degerming products, activated carbon, semi-permeable films, biological collagen, cell growth factors, hydropolymer, hydrogel and hydrocolloid substances, proteolytic enzymes, sulfadiazine silver, gauze dressings, bandages for skin protection and compression are also advocated.3 Physical treatments such as therapeutic ultrasound and electrotherapy are cited likewise in the literature as important adjuncts in wound management.4,5 These therapies seem to be advantageous but they have limitations and do not always achieve satisfactory results.
Wounds that are difficult to heal represent a serious public health problem. The lesions severely affect the quality of life of individuals due to decreased mobility and substantial loss of productivity; they can also cause emotional damage and contribute to increase the burden of public expenditures in healthcare.6
The need to care for a population with poorly healing wounds is a growing challenge that requires innovative strategies. An approach that stands out in the treatment of these lesions is low-power light therapy, promoted by light devices such as LASER (Light Amplification by Stimulated Emission of Radiation) and LED (Light Emitting Diode).
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 inconsistency, 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 appropriate parameters to each of these light sources.
This study aimed to determine, through a literature 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 parameters 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”, “phototherapy”, “wound healing”, “fibroblast”, “collagen” and “angyogenesis” combined with each other.
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 3to3). According to data presented 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 proliferation of fibroblasts, stimulation of collagen synthesis, 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 biological 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 ranging from 0.1 to 10 J/cm2 were used, with predominance of doses up to 5 J/cm2 . All studies reported similar effects between LASER and LED, such as increased fibroblast proliferation and stimulation of angiogenesis.
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, conflicting results about the clinical benefits of using light on skin wounds are found in the literature.
The way light interacts with the biological tissues will depend on the characteristics and parameters 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 different types of active media such as solid, liquid or gaseous materials, in which processes of light generation 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 (continuous 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 potential barrier and recombine with holes within the device. After the spontaneous recombination of electron-hole pairs, the simultaneous emission of photons occurs. The physical mechanism by which LED emits light is spontaneous light emission. The light-emitting diodes convert the electrical current in a light spectrum, a process called electroluminescence.79 LEDs usually operate with outputs in the range of milliwatts and therefore are usually set up on small chips or connected to small light bulbs.80
The variable characteristics and parameters of light devices is one of the factors that complicate the interpretation of research results about the effects of low intensity light on skin wounds. As observed in this study, there is discordance between the types of light and parameters used in studies. This fact may limit the decision-making process regarding the role of light in treating wounds since photobiomodulator effects are parameter-dependent.
Energy absorption is the primary mechanism that allows light from LASER or LED to produce biological effects in the tissue. Light absorption is dependent on wavelength and the main tissue chromophores (hemoglobin and melanin) strongly absorb wavelengths shorter than 600 nm. For these reasons, there is a therapeutic window in the optical spectral range of red and near infrared, wherein the efficiency of light penetration in the tissue is maximum (Figure 1).81
Fifty-nine of the 68 studies reviewed applied LASER or LED inside the optical therapeutic window and 9 applied them in the range of blue or green, and even so biological effects were observed. Although light in the blue and green wavelengths range can achieve significant effects in cells, the use of low power light in animals and humans involves almost exclusively light in red and near infrared wavelengths.81 Historical issues, mainly cost and availability may be related to this fact.
As noted in Tables 1, ?,22 and ?and33 studies applied LASER or LED with doses around 0.09 to 90 J/cm2. The most significant biological effects were seen with predominant dose values, i.e. up to 5 J/cm2, which are within the Arndt-Schultz curve (Figure 2). According to Sommer et al, very low doses do not promote biological effects, while higher doses result in inhibition of cellular functions.82 The energetic state of the cell, i.e. the physiological condition of the tissue in treatment is therefore critical to determine which dose to use.
The mechanism of light action on the cellular level that supports its biological effects is based on photobiological reactions. A photobiological reaction involves the absorption of a specific wavelength of light by photoreceptor molecules.83
There is evidence that wavelengths in the spectral range from red to near infrared are absorbed by cytochrome c oxidase.83,84 In the study by Karu and Kolyakov action spectra of monochromatic light from 580 to 860 nm were analyzed.85 The authors noted four active spectral regions, two in the red range (peaks from 613.5 to 623.5 nm and 667.5 to 683.7 nm) and two infrared (peaks from 750.7 to 772, 3 nm and 812.5 to 846.0 nm). In addition, they also observed the absorption by cytochrome c oxidase in these four bands. The authors concluded that cytochrome c oxidase could absorb light in different spectral bands (red and near infrared), probably in the binuclear centers CuA and CuB (oxidized forms).
Photobiological reactions can be classified into primary and secondary. Primary reactions derive from the interaction between photons and the photoreceptor, and they are observed in a few seconds or minutes after the irradiation of light. On the other hand, secondary reactions are effects that occur in response to primary reactions, in hours or even days after the irradiation procedure.84,86
The primary reactions of light action on photoreceptors are not yet clearly established, but there are some hypotheses. After the absorption of light in the irradiated wavelength, cytochrome c oxidase displays an electronically excited status, from which it alters its redox status and causes the acceleration of electron transfer in the respiratory chain.87 Another hypothesis is that a part of the electronically excited status energy is converted into heat, causing a localized and transient heating in photoreceptors.88 A third assumption would be that when enabling the flow of electrons in the respiratory chain by light irradiation, an increase in the production of superoxide anion can be expected.89 A fourth reaction formula assumes that porphyrins and flavoproteins absorb photons and generate reactive species of singlet oxygen.90 It has also been proposed that light can reverse cytochrome c oxidase inhibition through nitric oxide and thereby increase the rate of respiration.91
The mechanism of secondary photobiological reactions is determined by transduction (energy transfer from one system to another) and photosignal amplification leading to photoresponse. This means that effects derived from primary reactions are amplified and transmitted to other parts of the cell, resulting in physiological effects such as alterations in cell membrane permeability with changes in intracellular calcium levels, increased cellular metabolism, DNA and RNA syntheses, fibroblast proliferation, activation of T lymphocytes, macrophages and mast cells, increased synthesis of endorphins and decreased bradykinin.83
Secondary reactions are responsible for the connection between response to light action by photoreceptors located inside the mitochondria and the effects located in the nucleus or different phenomena in other cell components. This process makes it possible to apply a very small amount of light to produce clinically significant effects on tissues.92
In short, light absorption depending on the wavelength, causes primary reactions on the mitochondria. These are followed by a cascade of secondary reactions (photosignal transduction and amplification) that occur in the cytoplasm, membrane and nucleus as shown by the Karu model (Figure 3).
Nevertheless, there is a hypothesis about a modification in the Karu model. It is believed that the red light is absorbed by cytochrome-c oxidase inside the mitochondria, while the infrared wavelength is absorbed by specific cell membrane proteins directly affecting membrane permeability; both pathways lead to the same photobiological end response.93
Sources like LASER differ from LED ones because of a characteristic known as coherence. This feature is related to stimulated emission mechanisms, with LASER light being formed by same frequency, direction and phase waves.94 Some authors believe that coherence plays a role in the production of light therapy derived benefits, and LED (not coherent) would be less efficient than LASER (coherent) or even unable to promote therapeutic effects.95
The reviewed studies, however, have shown that LED light can be as effective as LASER, since both have similar biological effects, with no significant difference between them. The cellular response to photostimulation is not associated with specific properties of LASER light, such as coherence.96 According to Karu, the property of coherence is lost during the interaction of light with biological tissue, not being thus a prerequisite for the process of photostimulation or photoinhibition.86
More clinical studies, especially with LEDs, must be performed in order to assess the adequacy of parameters commonly used experimental in vitro and animal studies to the clinical practice, since, in the relevant literature, there is a diversity in methodology, as well as differences in wavelength, dose and types of study.
The reviewed studies show that phototherapy, either by LASER or LED, is an effective therapeutic modality to promote healing of skin wounds. The biological effects promoted by these therapeutic resources are similar and are related to the decrease in inflammatory cells, increased fibroblast proliferation, angiogenesis stimulation, formation of granulation tissue and increased collagen synthesis. In addition to these effects, the irradiation parameters are also similar between LED and LASER. Importantly, the biological effects are dependent on such parameters, especially wavelength and dose, highlighting the importance of determining an appropriate treatment protocol.
Conflict of interest: None
Financial Support: None
* Work performed at the Bioengineering Laboratory at Universidade Federal de Minas Gerais (UFMG) – Belo Horizonte (MG), Brazil.
How to cite this article: Chaves MEA, Araújo AR, Piancastelli ACC, Pinotti M. Effects of low-power light therapy on wound healing: LASER x LED. An Bras Dermatol. 2014;89(4):616-23.
Effect of frequent laser irradiation on orthodontic pain.
a Former graduate student, Graduate School of Clinical Dental Science, The Catholic University of Korea, Seoul, Korea.
Abstract Objective: To analyze the effect of low-level laser therapy (LLLT) on perception of pain after separator placement and compare it with perceptions of control and placebo groups using a frequent irradiation protocol.
Materials and Methods: Eighty-eight patients were randomly allocated to a laser group, a light-emitting diode (LED) placebo group, or a control group. Elastomeric separators were placed on the first molars. In the laser and LED groups, first molars were irradiated for 30 seconds every 12 hours for 1 week using a portable device. Pain was marked on a visual analog scale at predetermined intervals. Repeated measure analysis of variance was performed for statistical analysis.
Results: The pain scores of the laser group were significantly lower than those of the control group up to 1 day. The pain scores in the LED group were not significantly different from those of the laser group during the first 6 hours. After that point, the pain scores of the LED group were not significantly different from those of the control.
Conclusions: Frequent LLLT decreased the perception of pain to a nonsignificant level throughout the week after separator placement, compared with pain perception in the placebo and control groups. Therefore, LLLT might be an effective method of reducing orthodontic pain.
Laser Med Sci. 2012 Jul 20. [Epub ahead of print]
Effect of laser and LED phototherapies on the healing of cutaneous wound on healthy and iron-deficient Wistar rats and their impact on fibroblastic activity during wound healing.
Center of Biophotonics, School of Dentistry, Federal University of Bahia, Av. Araújo Pinho, 62, Canela, Salvador, BA, 40110-150, Brazil, email@example.com.
Iron deficiency impairs the formation of hemoglobin, red blood cells, as well the transport of oxygen. The wound healing process involves numerous functions, many of which are dependent on the presence of oxygen. Laser has been shown to improve angiogenesis, increases blood supply, cell proliferation and function. We aimed to study the effect of ?660 nm laser and ?700 nm light-emitting diode (LED) on fibroblastic proliferation on cutaneous wounds on iron-deficient rodents. Induction of iron anemia was carried out by feeding 105 newborn rats with a special iron-free diet. A 1?×?1 cm wound was created on the dorsum of each animal that were randomly distributed into seven groups: I, control anemic; II, anemic no treatment; III, anemic?+?L; IV, anemic?+?LED; V, healthy no treatment; VI, healthy?+?laser; VII, healthy?+?LED (n?=?15 each). Phototherapy was carried out using either a diode laser (?660 nm, 40 mW, 10 J/cm(2)) or a prototype LED device (?700?±?20 nm, 15 mW, 10 J/cm(2)). Treatment started immediately after surgery and was repeated at 48-h interval during 7, 14, and 21 days. After animal death, specimens were taken, routinely processed, cut, stained with hematoxylin-eosin, and underwent histological analysis and fibroblast counting. Significant difference between healthy and anemic subjects on regards the number of fibroblast between treatments was seen (p?<?0.008, p?<?0.001). On healthy animals, significant higher count was seen when laser was used (p?<?0.008). Anemic subjects irradiated with LED showed significantly higher count (p?<?0.001). It is concluded that the use of LED light caused a significant positive biomodulation of fibroblastic proliferation on anemic animals and laser was more effective on increasing proliferation on non-anemics.
Lasers Med Sci. 2011 May 31. [Epub ahead of print]
The effect of two phototherapy protocols on pain control in orthodontic procedure-a preliminary clinical study.
Centro de Laserterapia e Fotobiologia, Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911 – Bairro Urbanova, 12244-000, São José dos Campos, SP, Brazil, firstname.lastname@example.org
Phototherapy with low-level coherent light (laser) has been reported as an analgesic and anti-inflammatory as well as having a positive effect in tissue repair in orthodontics. However, there are few clinical studies using low-level LED therapy (non-coherent light). The aim of the present study was to analyze the pain symptoms after orthodontic tooth movement associated with and not associated with coherent and non-coherent phototherapy. Fifty-five volunteers (mean age?=?24.1?±?8.1 years) were randomly divided into four groups: G1 (control), G2 (placebo), G3 (protocol 1: laser, InGaAlP, 660 nm, 4 J/cm(2), 0.03 W, 25 s), G4 (protocol 2: LED, GaAlAs, 640 nm with 40 nm full-bandwidth at half-maximum, 4 J/cm(2), 0.10 W, 70 s). Separators were used to induce orthodontic pain and the volunteers pain levels were scored with the visual analog scale (VAS) after the separator placement, after the therapy (placebo, laser, or LED), and after 2, 24, 48, 72, 96, and 120 h. The laser group did not have statistically significant results in the reduction of pain level compared to the LED group. The LED group had a significant reduction in pain levels between 2 and 120 h compared to the control and the laser groups. The LED therapy showed a significant reduction in pain sensitivity (an average of 56%), after the orthodontic tooth movement when compared to the control group.
Lasers Med Sci. 2009 Nov;24(6):909-16. Epub 2009 Feb 24.
Comparative analysis of coherent light action (laser) versus non-coherent light (light-emitting diode) for tissue repair in diabetic rats.
Dall Agnol MA, Nicolau RA, de Lima CJ, Munin E.
Instituto de Pesquisa e Desenvolvimento (IP&D), Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, São Paulo, Brazil. email@example.com
The already known benefits produced by the interaction of coherent light (laser) with biologic tissues determine its use as an adjuvant in the treatment of several complications associated with diabetes. Non-coherent light, such as that emitted by light emitting diodes (LEDs), becomes a promising alternative, because of its low cost and easy handling in these applications. Thirty-six rats were given surgical dorsum lesions. The lesions for the control group did not receive any supporting therapy. The other groups were irradiated only once, 30 min after the establishment of the lesion, with LED (640 nm with 40 nm full bandwidth at half maximum) or laser (660 nm). The histomorphological and histomorphometrical parameters were quantified. The coherent and non-coherent lights produced similar effects during a period of 168 h after the lesions had been made. For the group composed of diabetic animals, 72 h after creation of the lesion, it was observed that the therapy with LEDs had been more efficient than that with the laser in the reduction of the wounds’ diameters.
Photomed Laser Surg. 2009 Aug;27(4):617-23.
Comparison between single-diode low-level laser therapy (LLLT) and LED multi-diode (cluster) therapy (LEDT) applications before high-intensity exercise.
Leal Junior EC, Lopes-Martins RA, Baroni BM, De Marchi T, Rossi RP, Grosselli D, Generosi RA, de Godoi V, Basso M, Mancalossi JL, Bjordal JM.
Laboratory of Human Movement, University of Caxias do Sul, Caxias do Sul, RS, Brazil. firstname.lastname@example.org
BACKGROUND DATA AND OBJECTIVE: There is anecdotal evidence that low-level laser therapy (LLLT) may affect the development of muscular fatigue, minor muscle damage, and recovery after heavy exercises. Although manufacturers claim that cluster probes (LEDT) maybe more effective than single-diode lasers in clinical settings, there is a lack of head-to-head comparisons in controlled trials. This study was designed to compare the effect of single-diode LLLT and cluster LEDT before heavy exercise. MATERIALS AND METHODS: This was a randomized, placebo-controlled, double-blind cross-over study. Young male volleyball players (n = 8) were enrolled and asked to perform three Wingate cycle tests after 4 x 30 sec LLLT or LEDT pretreatment of the rectus femoris muscle with either (1) an active LEDT cluster-probe (660/850 nm, 10/30 mW), (2) a placebo cluster-probe with no output, and (3) a single-diode 810-nm 200-mW laser. RESULTS: The active LEDT group had significantly decreased post-exercise creatine kinase (CK) levels (-18.88 +/- 41.48 U/L), compared to the placebo cluster group (26.88 +/- 15.18 U/L) (p < 0.05) and the active single-diode laser group (43.38 +/- 32.90 U/L) (p < 0.01). None of the pre-exercise LLLT or LEDT protocols enhanced performance on the Wingate tests or reduced post-exercise blood lactate levels. However, a non-significant tendency toward lower post-exercise blood lactate levels in the treated groups should be explored further. CONCLUSION: In this experimental set-up, only the active LEDT probe decreased post-exercise CK levels after the Wingate cycle test. Neither performance nor blood lactate levels were significantly affected by this protocol of pre-exercise LEDT or LLLT.
Biofizika. 2006 Jan-Feb;51(1):116-22.
A comparison of the effects of laser and light-emitting diodes on superoxide dismutase and nitric oxide production in rat wound fluid
[Article in Russian]
Klebanov GI, Shuraeva NIu, Chichuk TV, Osipov AN, Vladimirov IuA.
The action of laser and light-emitting diode radiation in the visible region on the content of reactive nitrogen species and activity of superoxide dismutase in rat wound fluid was studied, and efficiency of action of coherent laser and incoherent light emitting diode radiations in the red region of the spectrum on the parameters under study was compared. A model of incised aseptic wounds in rats proposed by L.I. Slutskiy was used. A He-Ne laser (632 nm) and a Y-332B light emitting diode served as radiation sources. It was shown that (1) exposure of wounds to the visible light of both laser and light-emitting diodes causes dose-dependent changes in superoxide dismutase activity and production of nitrites and (2) the radiation coherence does not play any significant role in the changes of superoxide dismutase activity or nitrogen oxide formation by wound fluid phagocytes
Biofizika. 2005 Nov-Dec;50(6):1137-44.
A comparative study of the effects of laser and light-emtting diode irradiation on the wound healing and functional activity of wound exudate leukocytes
[Article in Russian]
Klebanov GI, Shuraeva NIu, Chichuk TV, Osipov AN, Rudenko TG, Shekhter AB, Vladimirov IuA.
The effects of coherent He-Ne laser and non-coherent light-emitting diode radiation on rat skin wound healing and functional activity of wound excudate leukocytes were compared. A comparative pathomorphological analysis showed that the He-Ne laser and light-emitting diode irradiation stimulated the transition of the inflammatory phase of the wound healing into the reparative (proliferative) and scarring phases sequentially. It was also detected that the functional activity of leucocytes changed in a dose-dependent manner. The leukocyte activity was found to be similar in the groups with laser and light-emitting diode irradiation. Thus, we can conclude that coherent laser and non-coherent light-emitting diode radiation have very close effects on wound healing and activity of wound exudate leukocytes, and coherence is not required for this activity.
J Clin Laser Med Surg. 2001 Feb;19(1):29-33.
Biostimulatory windows in low-intensity laser activation: lasers, scanners, and NASA’s light-emitting diode array system.
Sommer AP, Pinheiro AL, Mester AR, Franke RP, Whelan HT.
Central Institute of Biomedical Engineering, Department of Biomaterials, University of Ulm, Germany.
OBJECTIVE: The purpose of this study was to assess and to formulate physically an irreducible set of irradiation parameters that could be relevant in the achieving reproducible light-induced effects in biological systems, both in vitro and in vivo.
BACKGROUND DATA: Light-tissue interaction studies focusing on the evaluation of irradiation thresholds are basic for the extensively growing applications for medical lasers and related light-emitting systems. These thresholds are of central interest in the rejuvenation of collagens, photorefractive keratectomy, and wound healing.
METHODS: There is ample evidence that the action of light in biological systems depends at least on two threshold parameters: the energy density and the intensity. Depending on the particular light delivery system coupled to an irradiation source, the mean energy density and the local intensity have to be determined separately using adequate experimental methods.
RESULTS: From the observations of different research groups and our own observations, we conclude that the threshold parameters energy density and intensity are biologically independent from each other.
CONCLUSIONS: This independence is of practical importance, at least for the medical application of photobiological effects achieved at low-energy density levels, accounting for the success and the failure in most of the cold laser uses since Mester’s pioneering work.