Grace Sun, DDS, FAACD, FAGDabcd, and Jan Tunér, DDSefgh
a Private Practitioner, Los Angeles, California
b Educator and Advanced Level Certified with Academy of Laser Dentistry
c Fellow of American Academy of Cosmetic Dentistry
d Fellow of Academy of General Dentistry
e Private Practitioner, Sweden
f Board Member of the World Association for Laser Therapy
g Vice president Swedish Laser Medical Society
h Author of “Laser Therapy - Clinical Practice and Scientific Background” Sweden: Prima Books AB; 2002.
abcd Corresponding author for
Proof and reprints: efgh Coauthor address:
Grace Sun, DDS, FAACD, FAGD Jan Tunér, DDS
462 N. Doheny Drive Spjutvägen 9
Los Angeles, CA 90048 772 32 Grängesberg, Sweden
310-274-4200 Office +46-240-22222 Office
310-274-5901 Fax +46 240 23037 Fax
Low level laser therapy (LLLT) is a newly developing field for most of us, though it has been utilized among medical, dental, physiotherapy and veterinary professions in some parts of the world for decades. LLLT can offer tremendous therapeutic benefits to patients, such as accelerated wound healing and pain relief. There is still much to be learned about the mechanisms, recognition of the therapeutic window and how to properly utilize these cellular phenomenons in a positive way to reach the treatment goals.
LOW LEVEL LASER THERAPY IN DENTISTRY
Grace Sun, DDS, FAACD, FAGD
Jan Tunér, DDS
Therapeutic laser application, also referred to as low level laser offer numerous benefits, including being non-surgical, promotion of tissue healing, and reductions in edema, inflammation and pain. For more than 30 years, low level laser therapy has been an interesting, but not clearly defined area among the medical, dental, physiotherapy and veterinary professions.
The lack of full recognition among clinicians and researchers is due in part to the weakness of published materials. Some studies have ill-defined treatment parameters or poorly designed experiments with no control groups or double blind designs.  A significant amount of research still needs to be learned about working with various wavelengths and creating different treatment effects, and how to establish proper treatment protocol for each different situation. However, a growing number of clinicians consistently utilize the low level laser therapy in treating patients because of the observed success.
Presently, there are 2,500+ scientific studies in the field of light therapy. Among these, there are more than 100 positive double blind studies. In 2001, the dental profession had conducted approximately 350 of these laser-therapy studies, from 98 institutions in 38 countries. Even though the quality of these studies may vary, more than 90 percent report positive effects of laser therapy.
HISTORY AND DEVELOPMENT
The roots of light therapy can be traced back to when our ancestors practiced heliotherapy, which gradually developed into actinotherapy and photomedicine, the utilization of UV (ultra-violet) radiation for sterilization. In 1903, Finsen was awarded the Nobel Prize for developing the carbon arc lamp incorporating lenses and filters for the treatment of lupus vulgaris.
Subsequently, actinotherapy was used for treating tuberculosis, open wounds and rickets. In 1919, x-ray evidence led to support the use of UV in the treatment of rickets. Actinotherapy also stimulates the wound healing of ulcers, boils and carbuncles, the treatment of acne vulgaris, neonatal jaundice and pain relief. ‘’’’ Nevertheless, its potential carcinogenic side effects limit its usage.
After the first laser was developed in 1960 by Theodore Maiman in Los Angeles, there was a rapid development and interest in laser research. During the late 1960s in Budapest, Endre Mester initiated studies on the possible carcinogenic effects of the low-power HeNe and argon laser. Surprisingly, the mice he used in the study regrew hair faster than the controls and the laser had no carcinogenic effect on the experimental group. Mester and his group conducted a series of animal and laboratory studies and the results were published. In 1973, Friedrich Plog in Canada independently began to investigate and discovered the HeNe laser as a viable alternative to needles for acupuncture treatment. During the next decade, many research projects were conducted in Eastern Europe, the Soviet Union and China.
In the 80s, the clinical applications of the low level laser therapy started to appear in the West.’’’ The low level laser started gaining popularity in Europe, Asia, South America and Australia, where they used the less-expensive and higher-powered output (30 mW or less) semiconductor (GaAlAs) (GaAs) devices. In the 90s, industry offered increasingly powerful lasers at reasonable prices and higher doses proved to be more effective. Finally, the most recently FDA approved treatment of carpal tunnel syndrome and “minor chronic neck and shoulder pain of musculoskeletal origin” has also proved to have a positive effect on the awareness and development of the therapeutic laser therapy. Hopefully in the very near future, more patients will benefit from this therapy.
TERMS AND DEFINITIONS
The names to identify and differentiate therapeutic lasers from surgical lasers include soft, cold, low intensity laser therapy (LILT) and low level laser therapy (LLLT). Therapeutic laser classification is Class III medical devices. Surgical lasers are classified as Class IV. The phrases and phenomena describing the biological effects of the therapeutic lasers are: laser photobiostimulation, photobiostimulation or biostimulation. However, since the cellular effects also include bioinhibition, a more appropriate designation of the phenomenon might be laser photobiomodulation. The phrase therapeutic laser has also been employed to suggest the purpose and intent of the treatment.
The LLLT benefits can be carried out with various wavelengths and units with a different output. Usually the therapeutic window for subthermal tissue interaction is 1-500 mW, but surgical lasers can be defocused and used as a “low level” laser. ‘’
The first working laser, presented at a press conference arranged at the Hughes Aircraft Laboratory in Los Angeles, on July 7, 1960, was a Ruby laser, a solid-state laser using a single, rod-shaped ruby crystal. It emits pulsed light at a wavelength of 694 nm (red light). The Ruby laser was also the first to be used in biostimulatory research in the mid 60s. Among its successors was the He-Ne (Helium-Neon) laser, a gas laser emitting at 632.8 nm with a power output of 1-5 mW. The He-Ne laser used predominantly in East Europe and China in the mid to late 1970s.
The most popular lasers are relatively inexpensive diode units that were developed in the 1980s. The GaAs (Gallium-Arsenide, 904 nm) diode laser was developed in the early 1980s and is typically 1-4 mW. Pulse-train modulated GaAs lasers entered the market in the late 1980’s.
The GaAlAs (Gallium-Aluminum-Arsenide, 780-890 nm) was developed in the late 1980s. It originated as 10-30 mW but, since in the late 1990s, has been featured up to 500 mW.
The InGaAlP (Indium-Gallium-Aluminium-Phosphide, 630-700 nm) diode lasers were developed in the mid 1990s. Typically 25-50 mW, they offer an alternative to the HeNe laser for surface wound healing.
The combination probes can be combined into two laser wavelengths or they can combine one or more laser diodes with LEDs of various wavelengths as “cluster probes.” The effect of merging an incoherent LED with the laser also requires to be further research to determine its effectiveness or if it is counterproductive with the design.
The dental therapeutic lasers are usually the size of an electric toothbrush and come with an attachable intraoral probe shaped like the wand used in composite curing light units (Fig. 1). The power of the GaAlAs lasers should not be less than 100 mW to obtain the desired biological effect in a reasonable time.
The principle of using LLLT is to supply direct biostimulative light energy to the body’s cells. Cellular photoreceptors (cytochromophores, antenna pigments) can absorb low level laser light and pass it on to mitochondria, which promptly produce the cell’s fuel, ATP (adenosine triphosphate) (Fig 2). Once the fatigued cells have been energized, they can efficiently proceed in their functions, such as repairing or regeneration.
The most popularly described treatment benefit of LLLT is wound healing. From the studies of Mester et al., the electron microscope examination showed evidence of accumulated collagen fibrils and electron-dense vesicles intracytoplasmatically on the laser-stimulated fibroblasts as compared to untreated areas. Also, the measurement from the incorporation of 3H-thymidin showed the accelerated cell reproduction and increased prostaglandin level following irradiation. The increased microcirculation can be observed with the increased redness around the wound area; during the initial treatment stage, the patient can feel the transient pin-prickling sensation. These occurrences are evidence of the accelerated wound healing.
However, the mechanisms of action underlying the analgesic effects remain unclear, despite the extensively implicit treatment benefits. There is evidence suggesting that LLLT may have significant neuropharmacalogical effects on the synthesis, release and metabolism of a range of neurochemicals, including serotonin and acetylcholine at the central level and histamine and prostaglandin at the peripheral level. The pain influence has also been explained with the LLLT effect on enhanced synthesis of endorphin, decreased c-fiber activity, brady kinine and altered-pain threshold. The analgesic effects have been surrounded with skepticism due to conflicting results, obvious placebo potential and dominating subjective findings, so this is an important field for research and investigation.
The most recognized and dominating theory to explain the effects and mechanisms of therapeutic lasers is the photochemical theory. According to this theory, the light is absorbed by certain molecules, followed by a cascade of biological events. Suggested photoreceptors are the endogenous porphyrins and molecules in the respiratory chain, such as cytochrome c-oxidase and D-NAME, leading to increased ATP production. The photosensitivity of proteins is well known and there are more than 300 photochemically reactive proteins capable of harvesting low light energy. In humans the most well-known photochemically active receptor proteins are rod and cone pigments in the eye. However, other human photoreceptors, such as encephalopsins in the brain and pinopsin in the pineal gland, demonstrate the importance of light for human life. 
It is important to consider the following three points when learning about the mechanisms of low level laser therapy. First, the coherency of the electromagnetic energy plays a role in the efficacy of the treatment. The degree of coherence is related to the spectral narrowness of the light source. While the spectral width of the gas HeNe laser is typically in focus, that of a laser diode is typically 1-10 nanometers and of LED 30-100 nanometers wide. It is obvious that non-coherent LED systems have a significant biological effect; however, these effects seem to be limited to superficial tissues and, in some cases to deeper tissues due to secondary effects through the release of metabolites. Polarization of the light has been shown to be beneficial in wound healing studies.  The polarization of non-coherent light disappears very shortly after entering tissue. The coherent character of the laser light is not lost after penetrating the tissue, but split into small coherent and polarized islands, called speckles. The speckle pattern is maintained through the entire irradiated volume of tissue.  Due to intensity differences within the speckle field, temperature and electric field gradients occur. Such gradients create a force on particles such as cells and organelles but do not affect the motion of atoms and molecules, as is the case in heat therapy. 22,,3 The gradients forces influence organelles such as mitochondria, which may enhance their interaction. This may also explain while so many different lasers, including surgical lasers such as argon, Nd:YAG, diodes and CO2, seem to have a stimulative/regulative effect on tissue, which encompasses pain relief and wound healing. Properties such as penetration characteristics, light configuration and power density are also important factors. There are rather few in vivo studies comparing the effects of coherent and non-coherent light, but in all of them (some 20 studies) coherent light has come out on top.
Additionally, the effect of therapeutic laser irradiation is most prominent in cells in a reduced redox (oxidation-reduction) state. 23’‘ This means that the effect on healthy cells will be less prominent and transient. Nevertheless, some investigators recommend irradiation before as well as after surgical interventions. ‘’28
Lastly, the effect of the laser is localized at the treatment site and can have a more generalized systemic effect. Infrared lasers have greater penetration than lasers in the visible range and are therefore able to affect deeper-lying conditions.  However, the light does not necessarily need to reach the target cells to have the treatment effect. The CO2 laser has been used in the defocused mode as a biostimulator and has been used for deeper-lying conditions such as tendonitis.  Since the light at that wavelength can penetrate skin less than 1 mm, the effect on deeper tissues is supposed to be influenced directly by blood metabolites.  This addresses the systemic effect of the laser therapy. This theory postulates that a condition such as a burn treated on one hand also influences a wound on the other hand, but with less effect. 
CONTRAINDICATIONS AND SAFETY MEASURES
After more than 30 years of use, there are no reports of patients being harmed by therapeutic lasers and the FDA considers Class III lasers as “non-significant risk medical devices”. The risk of eye injury is minimal but must always be considered, especially for high-output lasers in the invisible range. Diode laser light is generally divergent; if the light is collimated, however the risk of eye injury increases significantly. Protective goggles, adapted for the wavelength, are therefore recommended for the patient.
Although there are no contraindications reported for dental therapeutic lasers, some caveats and side effects do exist. Suspected malignancies should never be treated by anyone but the specialist and irradiation of the thyroid should be avoided until more research in this indication is available. Since laser light affects several rheological factors, patients with coagulation disorders merit special attention.31 Anecdotal evidence suggests that pulsating visible light can induce an epileptic seizure. In the realm of side effects, chronic pain patients have reported increased tiredness for a brief period and longstanding pain conditions may transiently increase.
By understanding the basic cellular effects of the lasers and the intended treatment goal of being anti-inflammatory, accelerating the healing process and providing pain relief, the general principles of the application for the various clinical conditions become clear.
The beneficial treatment effects have been applied in dermatological conditions such as wounds and inflammations, neural ailments of painful symptoms in various locations, skeletomuscular ailments of pain, degeneration, spasm, and inflammation in various sites. Veterinary uses of LLLT include treating dogs and horses with nerve injuries, tendonitis, arthritis and trauma from training and competition. The application of LLLT in dentistry is involved in various clinical conditions. The general rule for intra-oral treatments is to use 1-2 J with and the intra-oral probe (Fig. 3) and 4-10 J for extra-oral treatments (Fig. 4).
Post-operative therapy and care
The purpose of using LLLT as part of the post-operative therapy is to provide patients with the highest quality of health care. This includes no or minimal discomfort or pain and a shortened healing period. It can be applied to many dental procedures such as operative fillings, crown and bridge work, non-surgical and surgical endodontic procedures, non-surgical and surgical periodontal treatments, dental implants and oral surgeries or orthodontic adjustments.
Around 2 J of energy will be applied from the wand-like probe to the patient’s injection and operation sites, apical of the apex both buccal and lingual sides, around the CEJ and masticatory muscles. These can be immediate post-operative applications or continuing once-or-twice weekly treatments if the patient has had more extensive surgical procedures or for implant cases. For orthodontic adjustments, the treatment would be for every adjustment visit.
The following briefly summarizes some reported effects:
Diagnosis is essential before any treatment is rendered. The infrared laser is effective for reducing pain and tension in the masticatory muscles, especially in cases of trismus.  Symptoms, tender points and muscle attachments are treated with 6-10 J. After treatment, an increase in the range of movement has been noted. An interesting application is the treatment of somatosensory tinnitus, a condition where TMD therapy can play a vital role. The lateral pterygoid is typically involved in these cases; laser irradiation of this and other involved muscles can more rapidly lead to a reduction of tension and pain in the muscular system. As co-intervention in arthralgic cases, laser can be used to advantage. 
While many desensitizing agents successfully can treat this condition, more difficult cases can be treated by the laser. A review of the literature has been published by Kimura.  A hypersensitive tooth that does not respond to 4-6 J per root in 2-3 sessions is indicated for endodontic treatment. The occlusal scheme should always be evaluated as part of the treatment protocol.
Apart from reducing the initial tension pain, laser therapy can increase the speed of tooth movements by increased osteoclastic cellular activity on the pressure side and increased osteoblastic cellular activity on the tension side. ‘‘ Laser therapy has also been used for oral ulcerations induced by fixed orthodontic appliances.
Herpes simplex virus infection of the lips is the most common among adolescents and adults. Symptoms can range from mild discomfort to extremely painful. The laser has been shown to have a similar effect as Acyclovir and it has even been shown to be effective if given in the silent periods between attacks. If applied in the prodromal stage, the blister is likely to disappear in 2 to 3 days with very little discomfort, rather than 8-14 days. LLLT not only shortens the duration of the onset, but it also reduces the frequency of recurrence and relapse rate. While not appearing very often in the trigeminal area, zosters can also be treated by laser and even post herpetic neuralgia. ‘
Patients undergoing radiation therapy’28 or chemotherapy inevitably develop mucositis. Apart from being very painful, the mucositis may also force the oncologist to reduce the dose or number of sessions. Red laser light has been shown to reduce the severity of mucositis and can be used as a prophylactic prior to radiation. The laser can also treat the dermatitis, which often occurs in radiation therapy.28 This LLLT application offers a tremendous service to cancer patients.
There are always risks of nerve injury and paresthesia associated with dental surgeries, especially with the n. alveolaris inferior. While most of these are of a transient nature, some are longstanding or permanent. Using LLLT not only when the paresthesia has occurred but prophylactically after surgery in a risk-involved zone could reduce these problems. 27’‘
Some colleagues are practice acupuncture, using needles. Although lasers can be used in the place of needles, acupuncture should only be performed by trained individuals. There is, however, a useful and risk-free point on the wrist, known by acupuncturists as the Meridian Point P 6 (Fig. 5). 3-4 J on this point will reduce gagging reflexes in most patients.
The effects in periodontology are not yet well documented but several papers report stimulation of human periodontal fibroblasts, ‘’51 reduced gingivitis index, pocket depth, plaque index, gingival fluid and metalloproteinase-8 levels, 52 as well as positive results after gingivectomies.53
Apart from their ability to treat pain, edema, and inflammation, these lasers have also been used to enhance the fluoride release from cements and varnishes54’55 and kill bacteria in the presence of suitable photosensitizing agents or various dyes. 56’57 The latter is an example of photodynamic therapy, a longtime-practiced therapy in oncology.
This brief introduction of low-level laser therapy explained more than three decades of international experimental and clinical research. No true side effects of utilizing the low-level laser light have been found. When low-level laser light provides the energy that interacts with our cells, it creates a myriad of positive functions, such as accelerated wound healing, pain relief, regeneration and immune enhancement to defend against pathogens. Not only is it non-invasive, but it is also non-pharmaceutical as well as being an economical approach. Hopefully these benefits will help generate the interest of our colleagues, including clinicians, researchers and manufacturers to study and gain more knowledge on how we can utilize this phenomenon. Developing the equipment and, treatment protocols, and training the general educators and health practitioners is essential for improving health services and treatment outcomes. Looking forward, as we move into the next generation of low-level laser therapy we can raise the bar for practicing the optimal healing art as physicians and therapists.
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