How Do Lasers Reduce Pain, and What Amount of Treatment Is Necessary?

Praveen R. Arany, DDS, PhD, is an assistant professor of oral biology at the State University of New York at Buffalo.

Scott D. Benjamin, DDS: As a clinical practitioner, managing the patient's discomfort both during and after procedures is a primary concern. The utilization of hard- and soft-tissue lasers has greatly reduced the need for local anesthesia and the collateral trauma to the remaining tissue. For many procedures, lasers have minimized the related discomfort that patients have experienced in the past. However, the pain is not always completely eliminated, especially during the postoperative period after surgical and endodontic procedures have been performed.

Photobiomodulation (PBM) therapy is a type of light therapy that utilizes non-ionizing forms of light, including lasers, LEDs, and broadband light, in the visible and infrared spectrums, to stimulate or inhibit a tissue response to enhance healing, improve tissue performance, and/or reduce pain. In the past, PBM therapy has been referred to by more than 70 different terms (ie, low-level laser or light therapy, phototherapy, photomedicine, soft laser therapy, cold laser therapy, etc). In November 2015, the term photobiomodulation was designated by PubMed as the new subject heading to encompass all of these terms. Extensive research has been done and is continuing to be done in the area of PBM therapy. At the present time, more than 4,000 laboratory studies have been published and more than 500 randomized controlled trials have been conducted on the use of PBM therapy.

PBM therapy significantly helps in controlling inflammation, managing edema, enhancing tissue repair and healing, and improving muscle performance. By controlling these responses, the related pain and discomfort can be meaningfully reduced. Due to the biphasic response of tissue to light energy, with the appropriate dosage of laser energy, PBM therapy can also have an analgesic effect. When properly administered both pre- and postoperatively, PBM therapy has greatly reduced the pain and discomfort that patients experience. This is especially beneficial for more invasive procedures such as periodontal surgery, implant placement, extractions, and endodontic procedures.

A simple way to explain the concept of PBM therapy is to compare it to administering medication. When a pharmaceutical agent is administered, the goal is to use chemical energy to induce a chemical response within the target tissue. During PBM therapy, photonic energy is being delivered directly to the target tissue to elicit a photochemical response at the subcellular level. A primary benefit of PBM therapy is that the energy is applied directly to the region of treatment or area of pathology (eg, temporomandibular joint pain); therefore, there is minimal concern for the systemic side effects and problems that accompany the prescribing of opioids, NSAIDs, and other pain medications.

The non-ablative properties of PBM therapy enable it to be routinely performed by clinical auxiliaries similar to how they administer topical anesthesia. PBM therapy can be performed as soon as the patient is seated, while reviewing the dental procedures to be performed during the appointment, and at the conclusion of the treatment when the postoperative and home instructions are being explained, minimizing the need to expand patient appointment times.

Beyond significantly improving patient satisfaction, PBM therapy offers a financial benefit to clinicians by reducing the time and expense associated with managing postoperative treatment complications.

Arun Darbar, BDS: Pain management with lasers is possible through the concept of PBM therapy. The wavelengths presently used range from 400 nm to 1064 nm. Depending on the dose used, PBM therapy modulates tissue response, inducing biostimulation or bioinhibition. A biphasic dose response is observed with lower doses in the range of 4 to 8 J/cm², which is effective for stimulation, whereas higher doses of 10 to 20 J/cm² result in inhibition.

The subject of pain management is complex depending on the origin (eg, neurogenic, traumatic, or as result of other complications such as infection) and whether it is associated with an acute or chronic condition.

Managing acute conditions such as traumatic ulcers and extraction sockets generally only requires one session at a dosage of 4 to 8 J/cm², and the pain relief is almost instant. This is achieved with an acceleration in the inflammatory process, thereby reducing painful side effects. Provided that postoperative instructions are followed, healing occurs uneventfully.

Simple postsurgical trauma should also only require a single treatment immediately after surgery to reduce the complications, but complex cases need follow-up treatment in 3 to 5 days. A dose of 8 J/cm² around the surgical site and associated lymphatics will elicit an effective response.

Chronic conditions such as recurrent aphthae may require 2 to 3 sessions every 3 to 4 days until healed. Initial inhibition should be attained with a higher dose for pain management, followed by lower doses for repair and regeneration. This is achieved through a local response that reduces edema as well as a systemic immune response.

How lasers are used to treat herpetic lesions depends on the stage they are in. If they are midway in the cycle, one treatment may be provided to reduce the edema for instant pain relief, followed by a supplemental treatment 2 to 3 days later. After a couple of episodes have been treated, the pain and rate of reoccurrence diminishes. If treated at the prodromal stage, the cycle can be aborted. Eventually, these sufferers are free from recurrent episodes as a result of the immune response.

Establishing analgesia requires fairly high and frequent doses, depending on the procedure, with the most important factor being patient attitude and psychology. This involves inhibition of the nerve fibers and delayed conduction.

Facial traumas with various tissues involved and temporomandibular joint disorders will require multiple treatments, depending on the severity of the pain and complications. In cases of paresthesia, prolonged weekly treatment and assessment may be required.

Praveen R. Arany, DDS, PhD: The use of near-infrared heat lamps for localized, controlled heating, leading to focal vasodilation and pain relief is well demonstrated; however, the use of non-thermal light treatments (ie, PBM therapy) has been viewed with skepticism by some clinicians. This treatment involves the non-thermal use of a non-ionizing source of photonic energy to alleviate pain or inflammation and promote tissue healing and regeneration. Pain related to dental ailments has a broad range of underlying pathoses, including trauma due to mechanical, thermal, chemical, or immunological insults; infections; tumors; and anatomical anomalies. A common sequela of these injuries is a robust inflammatory response that creates a local milieu of biochemical and neural overactivity leading to pain.

Although pain has complex physical, psychological, and social facets, clinical management strategies have predominantly focused on peripheral and central mechanisms. The analgesic mechanisms of PBM therapy have been investigated by various researchers who have noted its effect on increasing production of serotonin and β-endorphins as well as modulating acetylcholine esterase and glutamate activity within the synapses. The discrete effects of PBM therapy on the pain-mediating neuron cell membrane receptor TRPV1 and disruption of axonal microtubule β-tubulin have been observed. Other mechanisms include a direct increase in ATP, which is capable of modulating key intracellular and extracellular (purinergic) signaling pathways. It is extremely important to emphasize that many of these studies have noted the transient and reversible nature of these cellular and molecular changes. This lack of any persistent permanent structural or functional neural deficits is particularly relevant when lasers are used with appropriate treatment parameters. Along these lines, a broad range of PBM therapy parameters such as wavelength (ie, visible to near-infrared [435 to 1,064 nm]), mode (ie, continuous versus pulsed), power density (ie, 1 to 3000 mW/cm²), treatment time (ie, 60 to 1,800 seconds) and energy density (5 to 30 J/cm²) have been shown to be effective for pain relief.

PBM therapy has tremendous potential as a noninvasive, non-pharmacological alternative for pain management. This is particularly relevant in the context of the current opioid crisis because dental and craniofacial pain poses a significant health burden. There is an ongoing effort by various national and international organizations that is focused on developing rigorous clinical guidelines for appropriate PBM therapy protocols for specific applications, including analgesia. These guidelines are based on the specific type of pain (ie, acute versus chronic) as well as its anatomical location and underlying etiology. The clinical applications of PBM therapy in dentistry extend from the treatment of routine scenarios, such as aphthous ulcers, extractions (especially third molar), orthodontic tooth movements, oral mucositis, dentin hypersensitivity, and pulpal anesthesia to more complex situations, such as temporomandibular joint disorders, medication-related osteonecrosis of the jaw, burning mouth syndrome, and trigeminal neuralgia, among others. It also has been suggested that tooth preparation with a hard-tissue laser involves an inherent analgesic component that is attributed to the lack of vibratory stimuli associated with conventional mechanical tooth preparations. In summary, PBM therapy offers an innovative tool to manage orofacial pain and improve clinical dental care.