Low level lasers in dentistry
Jan Tunér DDS, Grängesberg, Sweden
Per Hugo Christensen, DDS, Copenhagen, Denmark
A wide range of different lasers are used in modern dentistry. The Erbium:YAG laser has a potential of replacing the drill in selected situations; the carbon dioxide laser is a valuable tool in oral surgery; the Argon laser is used in minor surgery and composite curing; the Nd:YAG is used in pocket debridement, tissue retraction and more. This is just to mention a few of the possibilities of the dental laser.
The major drawback so far has been the high cost compared to the conventional therapies and the fast development in the field. The high cost of the investment may not have paid off until the next generation of lasers is on the market. So far the majority of the dentists using lasers are mainly the entrepreneurs and the enthusiasts.
All the above listed lasers are using, or have the possibility of using high powers, ranging from fractions of a watt to 25 watts or more.
Interest from media and patients has been considerable during the last decade, party because of a general interest in "high-tech" and partly because of the eternal dream about an escape from the discomfort experienced in the dental chair.
This article will summarize the physics, science and clinic of a quite different type of dental lasers - the low level laser.
Low level lasers
While the lasers already mentioned can be labeled "High level lasers", there is a less known type of lasers called "Low level lasers". These lasers are generally smaller, less expensive and operate in the milliwatt range, 1-500 milliwatts. The therapy performed with such lasers is often called "Low Level Laser Therapy" (LLLT) or just “laser therapy” and the lasers are called "therapeutic lasers". Several other names have been given to these lasers, such as "soft laser" and "low intensity level laser" whereas the therapy has been referred to as "biostimulation" and "biomodulation". The latter term is more appropriate, since the therapy can not only stimulate, but also suppress biological processes .
Therapeutic lasers generally operate in the visible and the infrared spectrum, 600-900 nm wavelength. However, other wavelengths such as the Nd:YAG at 1064 nm and even the carbon dioxide laser at 10600 nm have been successfully used in laser therapy.
The energy used is indicated in Joule (J), which is the number of milliwatts x the number of seconds of irradiation. Thus, 50 mW x 60 seconds produces an energy of 3000 millijoules, equals 3 J. Suitable therapeutic energies range from 1-10 J per point. The dose is expressed in J/cm2. To calculate the dose, the irradiated area must be known. 1 J over an area of 1 cm2 = 1 J/cm2. 1 J over an area of 0.1 cm2 = 10 J/cm2. There is generally no heat sensation or tissue heating involved in this therapy.
The first laser was demonstrated in 1960. It was a ruby laser, 694 nm wavelength. Interest in the medical implications of laser light was high and already in 1967  some of the first reports appeared on the effects of very low doses of ruby light on biological tissues. In animal studies it was observed that experimental wounds healed better if irradiated and that even the shaved fur of the experimental animals reappeared faster in the irradiated areas. There appeared to be a biological window for the dose. If too low, there was no effect, if too high there was a suppressive effect. Not much later the Helium-Neon laser was introduced in research and the results were similar. Later on diode lasers were introduced and they provided the same results, although some wavelengths appeared to be better for certain indications. In particular, the introduction of infrared lasers improved the optical penetration of the light, reaching deeper lying tissues.
The first commercially available lasers in the early 80ies were extremely low powered, below 1 mW, in spite of the fact that the first scientific reports used 25 mW. This partly explains the initial controversy about LLLT. With the rapid development of laser diodes, the powers of therapeutic lasers have changed dramatically and diode lasers today are typically in the range of 50-500 mW. Increased power has not only shortened the treatment time but also improved the therapeutic results.
Risks and side effects
The only physical risk in laser therapy is the risk of an eye damage. While never reported to have occurred, the risk of an eye damage must be considered, especially when using an invisible and collimated (parallel) beam. Suitable protective goggles should be worn by the patient for extra oral therapy in the face.
Since the therapeutic lasers are well above the ionizing spectrum there is no risk of cancerous changes. Suspected malignancies should of course not be treated by anyone but the specialist.
Among the side effects (rarely) observed are:
- temporary increase of pain in chronic pain conditions. It has been suggested that this is a sign of a transfer of the chronic condition into an acute situation.
- tiredness after the treatment. This is probably a result of the pain relief where the pain previously has prevented a normal relaxation pattern
- redness and a feeling of warmness in the area which is irradiated a result of a increases micro circulation
There are more than 2500 scientific studies in the field of laser therapy, among them more than 100 positive double blind studies . In dentistry alone, the number of studies are some 325, from 82 institutions in 37 countries . The quality of these studies vary but it is interesting to note that more than 90% of the studies report on positive effects of laser therapy.
In total, 30 different dental indications have been reported in the literature. The very variety of indications has been used as an argument against the probability of laser therapy. However, it rather shows the input on general biological systems, such as the immune system, SOD activity, ATP production, cell membrane permeability, release of transmitter substances etc.
Laser therapy science is a complicated matter where a combined knowledge about laser physics, medicine, clinical procedures and scientific rules is essential . Many studies, positive and negative, lack relevant reporting parameters and make a proper evaluation difficult. The existing literature is a sufficient foundation for successful clinical therapy but more research is still needed to find out the optimal parameters.
In two recent US meta analyses ,  there was a high overall significance for wound healing, tissue regeneration and pain.
Treatment is often carried out through local irradiation of the site of injury/pain, but it can also be performed on distal points such as regional lymph nodes, ganglia and cervical nerve roots corresponding to the dermatome in question. Pain release can often be achieved in one or two sessions (especially if the reason for the pain still is in a acute stage) whereas many conditions have to be treated during several sessions. When calculating the dosage, parameters such as pigmentation of the skin, condition of the tissue, acute/chronic stage, depth beneath skin/mucosa, transparence of overlying tissue must be considered.
The therapeutic lasers offer improved possibilities in the treatment of pain, wound healing, inflammation and oedema. However, they also offer the dentist a possibility to treat indications previously not within the capability of the general dentist. In the following some examples will be given, each with a selected reference
With the advent of desensitizing agents, the prevalence of treatment-resistant dentinal hypersensitivity has diminished considerably. On the other hand, the placement of composites and inlays has brought a new reason for the very same. Gershman  has shown that dentinal hypersensitivity can be successfully treated with LLLT. Mild pulpitis requires higher doses than the common dentinal hypersensitivity, and repeated treatments. Frequently a sensitive tooth neck can be treated with only one treatment.
Oral herpes (HSV1) is a common feature in the dental operatory. Instead of being a contraindication for dental treatment during the acute period, an onset of HSV1 can be a good reason for a visit to the dentist. As with any treatment of HSV1 a treatment in the early prodromal stage is most successful. The pain will be reduced immediately and the blisters will disappear within a few days. Repeated treatment, whenever a blister appears will lower the incidence of recurrence. Unlike Acyclovir tablets, there are no side effects . It has been shown  that laser therapy can even be used in the latent period between the attacks to lower the incidence of recurrence.
Patients undergoing radiotherapy  and/or chemoradiotherapy  suffer gravely from the mucositis induced by the therapy. Nutrition is troublesome and therapy regimen may have to be suboptimal for this reason. LLLT can be used not only to treat the mucositis but even to reduce it by mucosal irradiation prior to radiotherapy/chemotherapy.
The most frequent complaint among patients is of course pain. LLLT can reduce or eliminate pain of various origins ]6]. Postoperative discomfort after surgery can be substantially reduced by irradiating the operated area postoperatively before the anesthesia wears off.
After oral surgery paresthesias may occur as a result of the surgery, in particular in the mandibular region. LLLT has been used to eliminate or reduce such complications .
While many cases of sinuitis are "dental", a great number of patients arrive in the dental office with sinuitis of a viral or bacterial background. LLLT will in most cases lead to a fast reduction of the symptoms , making the scheduled treatment easier.
Problems in the temporo-mandibular joint region are quite suitable for LLLT. For arthritic cases the treatment is concentrated to the joint area, in myogenic cases the muscular insertions and trigger points are treated. Laser therapy should always be used in combination with conventional treatment but will improve the outcome of the treatment .
It has been shown  that patients suffering from Ménière's disease (tinnitus/vertigo) have a significantly increased prevalence of problems in the masticatory, neck and trapezius muscles plus problems in the cervical spine, particularly in the transverse processes of the atlas and the axis. Relaxation of the tension in these muscles plus occlusal stabilisation procedures (occlusal adjustment, bite splint) will reduce or eliminate the symptoms of tinnitus and vertigo in this group of patients. Laser therapy can successfully be used to promote muscular relaxation and pain relief in these cases.
Apart from being extremely debilitating, trigeminal neuralgia can sometimes make dental treatment impossible. While no miracle cure, dentists can offer a great deal of comfort to these patients, and with a non-invasive method .
Zoster in the trigeminal nerve should be treated in its early phase. The zoster attack in itself is bad enough, but not too infrequently a postherpetic neuralgia will persist for years or even lifelasting. Laser therapy is a cost-effective, non-invasive method without side effects .
29 different dental indications are described in the literature, some of them being aphtae, bone regeneration, dentitio dificilis and decubitus.
If a dentist is trained in acupuncture, the low level laser will be a very convenient way of replacing the needles in many instances, for corporal or auricular acupuncture. Needles are not too popular with the patients, so the laser will be appreciated. Even for a dentist not practicing acupuncture, there are some well defined acupuncture points which can be used, for instance to reduce nausea .
The clinical results described above may seem impressive, even to the degree of doubts. However, laser therapy is no panacea and should only be used within the limits of its own merits. Correct diagnosis, proper treatment technique and treatment intervals plus sufficient dosage are all essential to obtain good results.
A large number of in vitro studies have reported on the enhanced killing of bacteria using various dyes in combination with low level lasers. The most frequently used dye has been toluidine blue (TBO) and some of the microorganisms studied are streptococcus mutans (20) and staphylococcus aureus (21). The bactericidal effect of TBO is enhanced by low level laser light and the clinical implications of this combination in cariology and periodontology are indeed promising. Low level laser has also been shown to enhance the release of fluoride from lacquers (22) and resin cements (23).
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