Effect of semiconductor GaAs laser irradiation on pain perception in mice

Factors affecting Low Level Laser Therapy

Low Level Laser Therapy has been reported as causing many therapeutic reactions within living tissue, yet research studies have not been able to support conclusively the results which appear to occur clinically. If the physiotherapist accepts that light quality may have been a variable overlooked in previous studies, it is necessary to consider whether there are other factors which may have contributed to the variable and, at times, conflicting results. These factors include depth of penetration and resultant absorption. Factors such as power output, dose, pulse frequency and frequency of treatment will also influence the therapeutic action of laser. This review evaluates parameters common to most therapeutic lasers as well as other features including the multiple-diode probe. Issues which may help clinicians optimise their treatment when using Low Level Laser Therapy will be addressed.

Does low-level laser therapy have an antianesthetic effect? A review

Because local anesthetics are vasodilators, they tend to be absorbed into the bloodstream from the operative field as a result of the vasodilation of peripheral arterioles. To counteract this vasodilation, vasoconstrictive agents are often included in local anesthetic solutions to provide a longer duration of anesthesia. Low-level laser therapy (LLLT) has the same benefits, such as microcirculation activation and more-efficient tissue metabolism, analgesic effects, and vasodilatation. If LLLT is used to prevent pain postoperatively, improvements in local circulation and increased vasodilatation may increase the absorption of a local anesthetic agent. This may reduce the duration of the anesthesia, thereby allowing postoperative pain management to begin sooner. The maximal intensity of pain occurs during the first hours after surgery, when the local anesthetic has worn off. Theoretically, postoperative pain control can be increased with the use of a local anesthetic with a more-prolonged action. If a treatment method has both analgesic and antianesthetic effects, then the method may block its own effects. We review whether LLLT applied postoperatively to operated-on areas has an antianesthetic effect, that is, whether pain in the first hours after surgery was greater for patients who received LLLT than for control patients. Not too much evidence supports the antianesthetic effects of LLLT. However, additional experimental and clinical studies must be performed to investigate the effects of LLLT on the duration of anesthesia.

Treatment of burning mouth syndrome with a low-level energy diode laser

OBJECTIVE

To test the therapeutic efficacy of low-level energy diode laser on burning mouth syndrome.

BACKGROUND

Burning mouth syndrome is characterized by burning and painful sensations in the mouth, especially the tongue, in the absence of significant mucosal abnormalities. Although burning mouth syndrome is relatively common, little is known regarding its etiology and pathophysiology. As a result, no treatment is effective in all patients. Low-level energy diode laser therapy has been used in a variety of chronic and acute pain conditions, including neck, back and myofascial pain, degenerative osteoarthritis, and headache.

METHODS

A total of 17 patients who had been diagnosed with burning mouth syndrome were treated with an 800-nm wavelength diode laser. A straight handpiece was used with an end of 1-cm diameter with the fiber end standing 4 cm away from the end of handpiece. When the laser was applied, the handpiece directly contacted or was immediately above the symptomatic lingual surface. The output used was 3 W, 50 msec intermittent pulsing, and a frequency of 10 Hz, which was equivalent to an average power of 1.5 W/cm(2) (3 W × 0.05 msec × 10 Hz = 1.5 W/cm(2)). Depending on the involved area, laser was applied to a 1-cm(2) area for 70 sec until all involved area was covered. Overall pain and discomfort were analyzed with a 10-cm visual analogue scale.

RESULTS

All patients received diode laser therapy between one and seven times. The average pain score before the treatment was 6.7 (ranging from 2.9 to 9.8). The results showed an average reduction in pain of 47.6% (ranging from 9.3% to 91.8%). The burning sensation remained unchanged for up to 12 months.

CONCLUSION

Low-level energy diode laser may be an effective treatment for burning mouth syndrome.

Effect of low-power pulsed laser on peripheral nerve regeneration in rats

The purpose of this study was to determine whether low-power pulsed laser irradiation could affect the regeneration of a 10-mm gap of rat sciatic nerve created between the proximal and distal nerve stumps, which were sutured into silicone rubber tubes. After 8 weeks of recovery, pulsed laser-irradiated groups at frequencies of 5 kHz and 20 kHz both had significantly lower success percentages of regeneration (50% and 44%, respectively) compared to sham-irradiated controls (100%). In addition, qualitative and quantitative histology of the regenerated nerves revealed a less mature ultrastructural organization with a smaller cross-sectional area and a lower number of myelinated axons in both pulsed laser-irradiated groups than in controls. These results suggest that pulsed laser irradiation could elicit suppressing effects on regenerating nerves.

Cranial irradiation with Gaalas laser leads to naloxone reversible analgesia in rats

Laser irradiation of the rat cranium can produce analgesia. The present experiment investigated the mechanism of such action. 27 rats received all possible combinations of laser (0, 6.4, and 12J/cm2) and naloxone (0, 5, and 10 mg/kg) prior to a hot plate test. Laser (820 nm, KHz pulsing, Omega Laser Systems, London) was applied to the rats' skulls and hind paw lick latencies (in seconds) were recorded immediately, 30 min., and 24 hr. after the administration of treatment. When animals were tested immediately following laser irradiation at 12J/cm2 significant analgesia resulted. Treatment with naloxone at either dose antagonised this effect, but naloxone produced no significant hyperalgesia when given alone. This suggests that opioid peptide mechanisms mediate the analgesic action of low-intensity laser irradiation of the cranium.

Laser irradiation abates neuronal responses to nociceptive stimulation of rat-paw skin

The effects of diode laser irradiation on peripheral nerves was examined by monitoring neuronal discharges elicited by application of various stimuli to the hind-paw skin of rats. Neuronal discharges elicited by brush, pinch, cold, and/or heat stimulation, as well as chemical stimulation by injection of turpentine (0.1 ml, SC) were recorded from L5 dorsal roots in urethane-anesthetized rats. Diode laser irradiation (830 nm, 40 mW, 3 min, continuous wave) of the saphenous nerve exposed from the muscle of the lower leg significantly inhibited neuronal discharges elicited by pinch (68.4 +/- 6.5%), cold (45.4 +/- 9.2%), and heat stimulation (49.2 +/- 11.3%). Neuronal discharges induced by brush stimulation (104.3 +/- 4.7%) were not affected by laser irradiation. Injection of turpentine, a chemical irritant, into the hind-paw skin (0.1 ml, SC) elicited neuronal discharges in the ipsilateral dorsal root, and these discharges were significantly inhibited or abolished by laser irradiation. In 6- to 7-week-old rats treated neonatally with capsaicin (10 mg/kg, SC), injection of turpentine into the hind-paw skin did not elicit neuronal discharges and laser irradiation did not affect the background discharges. These data suggest that laser irradiation may selectively inhibit nociceptive neuronal activities.

Evidence for the existence of low-energy laser bioeffects on the nervous system

The reported effects of low-energy laser irradiation on the nervous system are manifested in alterations in cellular and extracellular biochemical constituents and reactions, as well as in changes in cell division rates. These bioeffects were observed in both in vivo and in vitro experiments. Other observed phenomena relate to the function of the nervous system and consist mainly of induced alteration in electrical conduction, stimulation thresholds, and behavioral effects. Clinical aspects of low-energy laser bioeffects relate mainly to pain mitigation and postponement of the posttraumatic neural degeneration processes. Many of the reported observations were obtained by experiments apparently conducted according to less than rigorous scientific criteria, and some could not be duplicated. On the whole, however, there is little doubt that low-energy laser irradiation exerts some effects on the nervous system under specific conditions of irradiation and tissue exposure via a mechanism which is probably photochemical in nature.

Effect of irradiation by semiconductor laser on responses evoked in trigeminal caudal neurons by tooth pulp stimulation

The effect of irradiation with a gallium-aluminum-arsenide semiconductor laser on responses evoked in trigeminal subnucleus caudal neurons by tooth pulp stimulation was investigated electrophysiologically in Wistar rats anesthetized with urethane plus alpha-chloralose. The pulp of lower incisor was electrically stimulated and the evoked action potentials were extracellularly recorded in the ipsilateral caudal neurons. The laser beam was applied on the cervical surface of the stimulated incisor. The rate of firing discharges and the numbers of spikes evoked in the caudal neurons were compared before and after laser irradiation. Laser irradiation suppressed the late discharges in the response of the caudal neurons which were evoked by excitatory inputs from C-fiber afferents, but did not suppress the early discharges evoked by inputs from A delta-fiber afferents. This indicates that low power laser irradiation (semiconductor laser: 830 nm, 350 mW, CW, through the tooth structures, for 120 s) inhibited the excitation of unmyelinated fibers of the pulp without affecting fine myelinated fibers. These results suggest that low power laser irradiation has a suppressive effect on injured tissue by blocking the depolarization of C-fiber afferents.

Analgesic effect of Ga-Al-As diode laser irradiation on hyperalgesia in carrageenin-induced inflammation

This study concerned the effect of Ga-Al-As diode laser irradiation (780 nm, continuous wave, 31.8 J/s/cm2, spot size od 0.2 mm, 3 minutes/dose) on hyperalgesia induced in the hind paw of rats by injecting carrageenin. The pressure-pain thresholds of hind paws were measured by the Randall-Selitto test for evaluation of hyperalgesia. Two doses of laser irradiation, given to the inflamed region immediately before and after the injection of carrageenin, partially (approximately 50%) inhibited the occurrence of hyperalgesia accompanied with a progression of inflammation. This analgesic effect was equal to that of indomethacin (4 mg/kg, i.o.). In another group, the hyperalgesia was removed almost completely for at least 24 hours by one dose of laser irradiation, which was given 3 hours after the carrageenin injection, whereas the edema was not inhibited. This analgesic effect, however, was partially (approximately 50%) antagonized with a dose of 10 mg/kg (i.p.) of naloxone and totally inhibited with 30 mg/kg. These results suggest that low-power laser irradiation on inflamed regions of carrageenin-treated rats has a marked analgesic effect and that certain mechanisms that are not related to endogenous opioids are involved in a part of the mechanisms of the analgesic effects.