The most critical part of PBM is determining the optimal dosage. The tissue dosage is expressed in fluence, or energy density, measured in joules per square centimeter (J/cm²). The total produced energy is determined by multiplying the output power of the laser in milliwatts by the time of exposure in seconds; for example, 50 mW × 40 sec = 2000 millijoules (mJ), or 2.0 J.

Low-level laser therapy follows the Arndt-Schulz law: Too small a stimulus does not trigger any effect. Increased stimulation augments the effect up to an optimal dose level. Increasing the dose even further means that the stimulation is gradually reduced, and at very high doses, stimulation is inhibited. The quest for the “optimal dose” is still not exact, but much is known about therapeutic windows for this modality. In some patients, the goal is inhibition rather than stimulation, especially for pain management. High doses of laser light will inhibit the pain signals, partly by creating transient varicosities along the neurons, impeding signal transmission.⁷ Opioid-related mechanisms also have been reported,⁸ as well as a reduction in the compound action potential⁹ (Figures 15-4–15-6). Dosages may need to be modified throughout the course of the treatment as the desired outcome changes. Such a flexible approach is indicated during orthodontic treatments, for example. During application of the required force to the tooth, pain reduction is the primary goal, so a bioinhibitory dose is used. At subsequent visits, the aim is to stimulate the osteoblast-osteoclast turn over, so a lower dose is applied.¹⁰

The general rule is to apply high doses of laser energy for acute conditions that manifest with inflammation and edema, while treating chronic conditions (e.g., wounds, paresthesias, pain) more conservatively. Initially, acute conditions often can be treated until they resolve and the pain is no longer present, whereas chronic conditions should be treated two to three times weekly.

The importance of pulsing the light is obvious when the laser is applied to cell monolayers in the laboratory.^11–13 The pulse repetition rate (PRR) also helps in the clinical setting, although little is known about pulsing in vivo and animal/clinical studies are inconclusive. It is not yet known how to control these mechanisms through use of different PRRs. Also, the biologic effects of a “chopped” continuous-wave laser beam and a superpulsed beam are different. At present, use of a continuous beam is therefore recommended in units that have continuous-wave emission. The 904-nm gallium arsenide (GaAs) laser does not have a continuous-wave mode, so determination of the optimal PRR must rely on anecdotal evidence for selection of pulse parameters.

Acute conditions can be resolved with a single PBM session, but many conditions require repeated irradiation for optimal results. Dental treatments often create acute injuries, so repeated irradiation is not necessary. As an example, in an extraction, irradiation of the site at the time of the procedure often is sufficient to reduce pain and inflammation. Other treatments, such as for facial pain or orthodontic discomfort, will require more sessions over a longer period of time. In many cases, follow-up visits requiring irradiation can be delegated to the dental assistant or the dental hygienist. Regulations vary in different areas, so clinicians should confirm local regulations before delegating. In some situations the patient can borrow, rent, or buy a simple low-power laser or LED device (even a traditional 5-mW laser pointer) for a period to optimize the treatment by applying daily doses according to the dentist’s instructions (Figure 15-8).

Doses of laser energy near the therapeutic window will not cause negative effects. The worst result with PBM is that nothing happens. There are few absolute contraindications to PBM, but a few caveats follow.

Because of the complex mechanisms involved in PBM, most of the literature is still not at an evidence-based level, except for a few indications. Still, research at more than 100 dental institutions worldwide is represented in the literature, comprising more than 4000 studies. Annually, approximately 250 papers on PBM appear on PubMed, many on dental issues and most reporting positive results. Reports of no effect from PBM often can be attributed to very low doses, miscalculation of the supposed dose, and ineffective treatment applications.¹⁷ Nevertheless, some qualified negative studies underline that PBM is not a “hit and run” therapy but depends on knowledge of all relevant parameters. A correct diagnosis and sufficient dosage are key to success.

Therapeutic lasers with wavelengths of less than 500 mW generally are harmless and classified as “low-risk devices” by the U.S. Food and Drug Administration (FDA).

Lasers and LEDs are available with different wavelengths and also different combinations of wavelengths, powers, and probe sizes. The choice of device is therefore not “one size fits all.” Any therapeutic light device can be used for many indications, but some combinations of wavelength and power are optimal for selected indications; clinicians should focus on their special interests. When choosing a device, other practical considerations include probe sterilization, education, technical service, and guarantee period.

During the past decade, stronger lasers have been advocated as more effective, so therapeutic lasers with output of 500 mW or more are now commercially available. For musculoskeletal conditions and pain therapy, high-output lasers may be useful, but for processes such as wound healing and bone regeneration, use of lower power over a longer time is more effective. Availability of power adjustments in a therapeutic laser, as with a surgical laser, is therefore helpful. Applying 5 J in 10 sec with a 500-mW laser is quite different from applying the same 5 J with a 50-mW laser in 100 sec. The 500-mW laser would work better for pain but might be less effective for treatment involving tissue regeneration.¹⁹ This divergence of effect reemphasizes the importance of adequate and appropriate training in the decision-making process.

Some therapeutic lasers have a removable, sterilizable probe, similar to that of the dental curing light; if it will not affect the optics, the probe should go through a heat sterilizer and the handle should be covered with a disposable barrier. If the tip cannot be sterilized, the whole unit should be covered in a disposable barrier. Sterilizing requirements vary, so familiarity with and understanding of local regulations are imperative.

Although dental lasers such as the Nd:YAG, CO₂, and erbium family are considered “hard” or “surgical” lasers, various studies indicate that they also can produce a degree of biostimulation in the areas peripheral to the focal spot, where the energy is reduced to stimulatory levels (Figure 15-9).

There is a growing interest in the combination of different dyes with therapeutic lasers. Neither the dyes nor the therapeutic lasers used alone will have an effect on bacteria, but in combination, singlet oxygen will be produced, which has a strong bactericidal effect.

All dentists have in their armamentarium a composite curing light, typically with a wavelength peak of approximately 470 nm. Energies delivered are within the low-level laser therapeutic window, but studies of the photobiologic effect on the surrounding tissues are largely lacking.

Laser light is coherent and is delivered as a collimated beam, whereas light from an LED light is noncoherent, without collimation. The subject of whether one is more efficacious than the other is a topic of controversy, often resulting in very heated discussion. Many research studies have investigated the effect on tissue with LEDs and lasers, with differing outcomes. A study by Nishioka et al. in 2012, however, investigated the effect of laser and LED irradiation using the same total energy deposited in tissue and found that both resulted in a significant decrease in the necrosis of the skin flap, which indicated that the light source consistency was not essential for successful results.³⁰

Few dentists use acupuncture, but several acupuncture points can be used in low-level laser applications by all dentists. Therapeutic lasers produce effects similar to those of acupuncture needles and are safer to use. For example, P6 (i.e., Neiguan) on the wrist is an excellent point for use in reducing nausea and vomiting.³¹ The location of this point is 2.5 cm up from the wrist and 0.5 to 1.0 cm deep. The point is between two tendons. Delivery of 3 to 4 J to P6 often allows a more relaxed environment for taking impressions or working in the molar area, especially in patients with a heightened gag reflex. Another easily accessible point is the Li4 (i.e., Hegu), a pain-reducing point located in the middle of the second metacarpal bone on the radial side (Figures 15-10 and 15-11).

Because PBM can influence so many pathologic conditions, the use of the therapeutic laser is not limited to the following indications. More than 30 conditions have been described in the dental literature; the most important are briefly described here. As more research is conducted, the number of indications for use based on peer-reviewed literature will undoubtedly increase.

Applying PBM to the mucosa, but not the hard palate, before an injection results in a slight anesthetic effect.³³ PBM applied before the injection also will improve healing, should the needle cause trauma to a vessel or nerve. PBM improves local microcirculation,³⁴ so the effect of the numbness can be shortened if PBM is applied to the site after completion of the dental procedure. Energy of 4 to 6 J is needed in both cases.

The healing time of aphthous ulcers can be shortened and the immediate pain reduced by administering 4 to 6 J over the lesion and 4 J to the submandibular lymph nodes on the affected side^35,36 (Figure 15-12). Patients prone to development of aphthous ulcers should avoid toothpastes containing sodium lauryl sulfate, which may trigger these lesions in predisposed persons.

The lymphatic system plays an important role in the inflammatory process, and PBM applied over the involved lymph nodes decreases edema. Irradiation should start over the most distal nodes of the chain involved and proceed toward the focus of the swelling, using 4 J per node. The permeability of the lymph vessels will be reduced and lumen size increased, and repeated irradiation will stimulate growth of collaterals^37–41 (Figure 15-13). The lymphatic system also brings the lymphocytes and natural killer cells to fight infection. Meneguzzo et al.⁴¹ reported that irradiation with an 810-nm laser reduced rat paw edema whether it was performed in the paw itself or over the inguinal lymph nodes.

PBM does not have a bactericidal effect, and surgical lasers are the preferred instruments to reduce bacteria in infected root canals. Few manufacturers of therapeutic lasers offer probes that could reach the root canals. However, infrared light can reach all apices, and visible red light can reach the more superficial apices through the mucosa, to produce an antiinflammatory and pain-reducing effect.

Nontraumatic approaches and good postoperative procedures are the key to satisfactory healing after extractions. However, the occasional complication is unavoidable. Adding PBM after the extraction will reduce the inflammatory phase, induce pain reduction, stimulate the fibroblasts in the wound periphery, and stimulate the osteoblasts in the socket.^50–55 High doses of laser energy applied directly into the socket will reduce postoperative pain and inflammation (Figures 15-14 and 15-15).

Patients with a herpes simplex virus type 1 (HSV-1) eruption may be reluctant to visit the dentist. However, PBM is the most efficient method of treating this infection.^36,56–58 In particular, if it is treated during the initial prodromal stage (when the patient feels the initial tingling), healing will take only a few days, or the symptoms may even disappear within hours. Of importance, in patients with recurrent HSV-1 attacks, longer intervals between the outbreaks are typical after PBM treatment.^59,60

A single high dose of irradiation after implant placement will reduce postoperative pain, inflammation, and edema. Repeated sessions at a lower dose will stimulate osseointegration by stimulating the osteoblasts. As with all healing processes, repeated irradiation is necessary; 4 to 6 J over each implant is recommended, with the laser tip in slight contact.^62–66 PBM also is a useful additional therapy in the control of periimplantitis. The effect is most prominent if PBM is applied immediately after surgery and then two or three times per week for 2 weeks.

PBM will shorten the course of the inflammatory process, and it is important to recognize that acute pain reduction requires high doses, whereas reduction of the inflammatory period requires less dosage. Reducing the pain may satisfy the patient but may prolong the inflammatory process. The infrared laser dose for inflammation reduction is 8 to 12 J/cm².