Low-level CO2 laser–induced release of 51chromium from canine 2C5 gliosarcoma cells

Recently, interest has grown in the area of low-power laser effects upon tissues. We used a ⁵¹Cr cell labeling technique with glioma tissue to better understand these effects. Canine 2C5 gliosarcoma cells with intracellular ⁵¹Cr were exposed to CO₂ laser in the range of 0.2 to 3.0 J/cm². Correlative analysis of the data indicated that there is a strong direct relationship between laser fluence and the percent of total intracellular ⁵¹Cr released from the glioma cells with a coefficient of correlation (r) of +0.93. The calculated standard error of the correlation coefficient was ± 0.06 and the coefficient of determination (r²) was 0.86. These results indicate that the ⁵¹Cr cell labeling technique is a useful method for quantifying the low-power laser effects on the integrity of the cell membrane of gliosarcoma cells in vitro. However, further investigation is needed to clarify the specific mechanisms by which the CO₂ laser induces changes upon these cells. © 1993 Wiley-Liss, Inc. © 1993 Wiley-Liss, Inc.     

Biological effect of low-power helium-neon (HeNe) laser irradiation

The functional effects (activation and cell damage) of low-power, continuous-wave HeNe laser irradiation were studied in different in vitro cultured cell lines. A characteristic dose-dependence was observed between 0.14 and 28.0 J/cm². The functional activation (increased phagocytic activity, immunoglobulin secretion) or cell destruction could not be detected after irradiation by normal monochromatic light of the same wavelength and energy output. The experiments suggested that low-power laser irradiation has a specific influence on the cells which depends on the coherent and polarized physical features of the laser light.     

Effects of the helium-neon laser on rat kidney epithelial cells in culture

The cellular mechanisms of action of low power lasers are only partially understood. Therefore, we have studied effects of helium-neon (He−Ne) laser irradiation in a cell culture model. The studies were performed with the permanent rat kidney cell line RK-L. By electron microscopy, significant ultrastructural changes of the cells were seen after He−Ne irradiation at 40 mW/cm² for 4h (569 J/cm²), including detritus-like formations of the cell organelles close to the nucleus. While such changes were not observed after 1 h irradiation (142 J/cm²), the number of cells in mitosis increased under this condition. In addition, the rate of incorporation of³H-thymidine into DNA decreased transiently 6–9 h after 1 h He−Ne irradiation of the cells. The consumption of glucose was also lowered for 10 h after irradiation, while the production of lactate increased. Finally, the synthesis of prostaglandin E₂ was reduced following irradiation. These results show that the He−Ne laser induces significant effects at the cellular level. In addition, our findings support the concept that the biological effects of low power laser treatment involve changes in the cell cycle.     

Effect of low-energy laser irradiation on colony formation capability in different human tumor cells in vitro

Fibroblasts and lymphocytes are the most widely used cells for studying the so-called biostimulative effect of low-power laser in vitro. In contrast, stimulation of cancer cells by laser light has not been investigated extensively. The present study attempted to evaluate whether or not human tumor cells could exhibit an increase in colony-forming capability following low-watt laser irradiation. LoVo and HT29 (colon carcinoma), MCF7 (breast carcinoma), M14 and JR1 (malignant melanoma) cell lines were irradiated at different doses of light delivered from an argon or an argon-dye laser. Radiant exposures between 4.2 and 150 kJ/m² at irradiances ranging from 35 to 500 W/m² were delivered. Results were mixed. Of the 41 experiments performed, five showed a significant statistical increase in the number of colonies (P< 0.05), whereas three showed a decrease (P < 0.05). Nevertheless, the trend of most data was toward an increase in colony formation, and Wilcoxon's signed-ranks test suggested that light increases tumor cell culture growth (P < 0.03).     

Central nervous system transplantation benefitted by low-power laser irradiation

The effect of low-power laser irradiation on mammalian central nervous system (CNS) transplantation is reported. Fetal brain allografts were transplanted into the brain (fornix region) of 20 adult rats and spinal cord allografts were transplanted into the spinal cord of eight dogs. For 21 days, the closed operated wounds of 10 rats and four dogs were exposed daily to transcutaneous low-power laser irradiation cw HeNe laser (16 mW, 632.8 nm, spot size 2 mm², energy density of 30 J cm⁻² for rats and 70 J cm⁻² for dogs). This study shows that the low-power laser irradiation prevents extensive glial scar formation (a limiting factor in CNS regeneration) between neural transplants and host brain or spinal cord. Abundant capillaries developed in the laser-irradiated transplants, this being of crucial importance for their survival. The results of the present study and our previous investigations suggest that low-power laser irradiation is a novel tool for treatment of CNS injuries and disorders.     

Comparison of the photodynamic fungicidal efficacy of methylene blue, toluidine blue, malachite green and low-power laser irradiation alone against Candida albicans

This study was to evaluate specific effects of photodynamic therapy (energy density 15.8 J/cm², 26.3 J/cm² and 39.5 J/cm²) using methylene blue, toluidine blue and malachite green as photosensitizers and low-power laser irradiation on the viability of Candida albicans. Suspensions of C. albicans containing 10⁶ cells/ml were standardized in a spectrophotometer. For each dye, 120 assays, divided into four groups according to the following experimental conditions, were carried out: laser irradiation in the presence of the photosensitizer; laser irradiation only; treatment with the photosensitizer only; no exposure to laser light or photosensitizer. Next, serial dilutions were prepared and seeded onto Sabouraud dextrose agar for the determination of the number of colony-forming units per milliliter (CFU/ml). The results were subjected to analysis of variance and the Tukey test (P < 0.05). Photodynamic therapy using the photosensitizers tested was effective in reducing the number of C. albicans.. The number of CFU/ml was reduced by between 0.54 log₁₀ and 3.07 log₁₀ and depended on the laser energy density used. Toluidine blue, methylene blue and malachite green were effective photosensitizers in antimicrobial photodynamic therapy against C. albicans, as was low-power laser irradiation alone.     

Longterm comparison of soft palate scars after UPPP made by CO2, contact Nd-YAG or combined CO2 and Nd-YAG laser beams

C0₂ laser, contact Nd-YAG laser and Combolaser (combined CO₂ and Nd-YAG laser beam) vary distinctively in the way they interact with target tissue. To study the quality of mature scars produced by these lasers, the ultrastructure and amount of collagen in soft palate scars after 60 uvulopalatopharyngoplasty (UPPP) operations were analysed. The CO₂ laser was used in 19, contact Nd-YAG in 21 and Combolaser in 20 operations. At a clinical follow-up examination carried out, on average, 51 (range 34–74) months postoperatively, a specimen was obtained from the soft palate scar for collagen analysis. Postoperative complaints of the patients were acknowledged. No differences between the laser groups were observed concerning the gross appearance of the scars or the amount and ultrastructure of collagen. Neither the frequency nor the quality of post-operative symptoms showed any differences between the lasers. Although the initial tissue effects are different, long-term remodelling produces nearly identical soft palate scars after the use of CO₂, contact Nd-YAG and Combolaser beams.     

Effect of Helium-Neon (He-Ne) Laser Irradiation on Dog Neoplasm Cells in Culture

The effects of laser light on the cellular proliferation have been extensively characterised. Low-power laser sources, such as the helium–neon (He-Ne) laser irradiation with a wavelength of 632.8 nm, have been found to produce photobiological and photodamaging effects with evidence of interference with cell proliferation functions. The present study has investigated the in vitro effect of He-Ne laser irradiation on the proliferative action of dog tumour cells in culture. Dose–response studies showed that repeated He-Ne irradiation (irradiance 12.8 mW/cm²) once a day for 4 consecutive days in a dose range between 0.13 and 2.08 J/cm² significantly increased with increasing energy density up to a laser dose of 0.26 J/cm², whereas at >1.04 J/cm², the cell proliferation decreased with increasing energy densities. It is concluded that the application of He-Ne laser irradiation at energy densities ranging from 0.13 J/cm² to 2.08 J/cm² produced different effects on cell proliferation in dog tumour cells in culture. Paper received for publication 27 June 1997; accepted following revision 6 February 1998.     

Uvulopalatopharyngoplasty with CO2, contact ND-YAG or combined CO2 and ND-YAG laser beams

Three different surgical lasers, ie CO₂, contact Nd-YAG and Combolaser (combined simultaneous and co-axial CO₂+Nd-YAG laser beam), were used for 76 uvulopalatopharyngoplasty (UPPP) operations. The effects of different lasers on intra-operative bleeding, operation time and post-operative pain were compared. Sixty patients with obstructive sleep apnoea syndrome (OSAS) and 16 patients with socially disturbing snoring were operated on. The CO₂ laser was used in 24 patients, contact Nd-YAG was used in 27 patients and Combolaser was used in 25 patients. The Combolaser was associated with significantly less intra-operative bleeding and a shorter operation time. During the immediate recovery period, post-operative pain was most mild after operations with the CO₂ laser when graded according to need for analgesics, or by the patients' subjective evaluation. Concerning possible post-operative complaints or overall outcome of the UPPP operation, no differences were found between the lasers.     

Effects of low-power laser irradiation on survival of random skin flap in rats

This research was designed to study the effects of low-power helium–neon (He–Ne) laser irradiation on random skin flap survival in rat. Fifty 50 male rats were randomly divided into five groups. On the dorsum of each rat, one full thickness random skin flap which contained no specific vessel was elevated. Groups 1 to 4 were exposed to different models of a low-power He–Ne laser. Group 5 rats received no laser treatment and were considered as the control group. The energy density of the He–Ne laser used was 0.2 J/cm². Immediately after surgery and at day 7, the surface area of all flaps was determined. Histological and tensiometrical studies on the surviving part of the flaps were also performed. The data obtained were analyzed by ANOVA. The results showed a significant difference in the surface area of survival parts of flaps and density of blood vessels on day 7 between group 3 rats and the other groups (P=0.0188, P=0.0455). Low-power He–Ne laser irradiation of flaps without recognized blood vessels in rats, reduced vasospasm, produced vasodilation, and caused a significant increase in the surviving surface area.Presented at the 14th World Congress of the International Society for Laser Surgery and Medicine, India, 27–30th August, 2001     

Effects of cavity preparation using a nanosecond-pulsed Nd-YAG laser on tooth-restoration interface

This study evaluated the tooth-restoration interface between composite resin or glass ionomer cement and the tooth surface in teeth where caries removal and cavity preparation were performed either with the dental drill, the dental drill and laser irradiation, or laser irradiation alone. A nanosecond-pulsed Nd-YAG laser was used at energy densities of 2–8 J cm^-2. After tooth restoration, microleakage tests were performed using methylene blue. Using general linear model procedures, no significant differences in microleakage were determined between ‘drill’ and ‘drill and laser’-prepared groups (p< 0.01) in resinand in glass-ionomer-restored teeth. These specimens showed significantly less dye penetration than the ‘laser only’ group (p< 0.0001). No correlation was found between fluence and microleakage using either restorative material (p = 0.8). Dye penetration was significantly greater in the composite-filled than in the glass-ionomer group (p< 0.05). Mechanisms influencing laser effects on bonding require further investigation before clinical application of lasers as an alternative to the dental drill can become viable.     

The effect of near-infrared MLS laser radiation on cell membrane structure and radical generation

The therapeutic effects of low-power laser radiation of different wavelengths and light doses are well known, but the biochemical mechanism of the interaction of laser light with living cells is not fully understood. We have investigated the effect of MLS (Multiwave Locked System) laser near-infrared irradiation on cell membrane structure, functional properties, and free radical generation using human red blood cells and breast cancer MCF-4 cells. The cells were irradiated with low-intensity MLS near-infrared (simultaneously 808 nm, continuous emission and 905 nm, pulse emission, pulse-wave frequency, 1,000 or 2,000 Hz) laser light at light doses from 0 to 15 J (average power density 212.5 mW/cm², spot size was 3.18 cm²) at 22 °C, the activity membrane bound acetylcholinesterase, cell stability, anti-oxidative activity, and free radical generation were the parameters used in characterizing the structural and functional changes of the cell. Near-infrared low-intensity laser radiation changed the acetylcholinesterase activity of the red blood cell membrane in a dose-dependent manner: There was a considerable increase of maximal enzymatic rate and Michaelis constant due to changes in the membrane structure. Integral parameters such as erythrocyte stability, membrane lipid peroxidation, or methemoglobin levels remained unchanged. Anti-oxidative capacity of the red blood cells increased after MLS laser irradiation. This irradiation induced a time-dependent increase in free radical generation in MCF-4 cells. Low-intensity near-infrared MLS laser radiation induces free radical generation and changes enzymatic and anti-oxidative activities of cellular components. Free radical generation may be the mechanism of the biomodulative effect of laser radiation.     

Effect of CO2 laser irradiation on experimental fracture healing: a transmission electron microscopic study

The healing of standardized fracture of rabbit radius was expedited as a result of treatment with low-power CO2 laser irradiation. Observation with transmission electron microscope revealed the following favorable effects of CO2 laser irradiation: The red blood cells were induced to disintegrate, thus promoting the absorption of the hematoma. The macrophages emerged early and increased in number so that debridement of the necrotic tissues was enhanced. The fibroblasts were more active in producing the fibrous callus. The chondrocytes were unusually active in forming bone tissues. The early and sustained appearance of osteoclasts favored the bone remodeling process. Increased capillary formation endowed the fracture healing with rich blood supply. Deposition of calcium salts took place early.     

Investigation of carcinogenic effects of in Vitro Argon and CO2 laser exposure of fibroblasts

Mouse heteroploid fibroblasts were grown nine future generations in vitro tissue culture. The cells were exposed to argon laser, CO₂ laser, and x-ray. Results of scoring for mangnant transformation foci were tabulated and compared. Lasers did not produce a significant malignant transformation. Clinical laser use is reviewed and histology as well as long-term clinical experience confirms the safety of lasers.     

Adhesion after erbium, chromium:yttrium-scandium-gallium-garnet laser application at three different irradiation conditions

The aim of this study was to investigate whether distinct cooling of low fluence erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation would influence adhesion. Main factors tested were: substrates (two), irradiation conditions (three), and adhesives (three). A 750 μm diameter tip was used, for 50 s, 1 mm from the surface, with a 0.25 W power output, 20 Hz, energy density of 2.8 J/cm² with energy per pulse of 12.5 mJ. When applied, water delivery rate was 11 ml/min. The analysis of variance (ANOVA) showed that laser conditioning significantly decreased the bond strength of all adhesive systems applied on enamel. On dentin, laser conditioning significantly reduced bond strength of etch-and-rinse and one-step self-etch systems; however, laser irradiation under water cooling did not alter bonding of two-step self-etching. It may be concluded that the irradiation with Er,Cr:YSGG laser at 2.8 J/cm² with water coolant was responsible for a better adhesion to dentin, while enamel irradiation reduced bond strength, irrespective of cooling conditions.     

Low power laser irradiation alters the rate of regeneration of the rat facial nerve

Low power laser irradiation has been reported to cause biological effects due to the photochemical and/or photophysical action of the radiation. This study determined quantitatively if transcu-taneous low power laser irradiation can affect the regeneration of the rat facial nerve. The facial nerve was crushed unilaterally in anesthetized rats and transcutaneously irradiated daily with a laser beam directed at the area of the crush injury. Laser treatment began on the day of the crush injury and was continued daily for 7, 8, or 9 days. Preliminary experiments determined the most effective wavelength, laser power, length of irradiation, and treatment schedule. The wavelengths examined were 361, 457, 514, 633, 720, and 1064. The laser powers and lengths of irradiation examined ranged from 8.5 to 40 mW and 13 to 120 min. Irradiation treatment was done daily, on alternating days and on the first 4 days postcrush. The most effective laser parameters for the low power treatment included daily irradiation with a helium-neon (HeNe) or argon pumped tunable dye laser a wavelength of 633 nm, with a power of 8.5 mW for 90 minutes (45.9 J, 162.4 J/cm²). The number of horseradish peroxidase (HRP) labeled neurons in the facial motor nucleus was used as an assay of the degree of regeneration. In rats in which the facial nerve was crushed but not irradiated, the average number of HRP labeled neurons in the facial nucleus was 22 on day 7 postcrush, 54 on day 8, 116 on day 9, and 1,149 on day 10. After HeNe or argon pumped tunable dye laser irradiation, the average number of HRP-labeled neurons increased to 34 on day 7 postcrush, 148 on day 8, and 1,725 on day 9. There was a statistically significant difference between the control and irradiated rats on day 9 post-crush (P < 0.01). These data indicate that transcutaneous low power irradiation with the lasers and parameters involved in this study increased the rate of regeneration of rat facial nerve following crush injury. © 1993 Wiley-Liss, Inc.     

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 (～ 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 (～ 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. © 1993 Wiley-Liss, Inc.     

Helium-Neon laser irradiation inhibits the growth of kidney epithelial cells in culture

We have investigated the in vitro action of helium-neon (He-Ne) laser light on the cell cycle and the growth of rat kidney epithelial cell cultures. Dose-response studies showed that repeated He-Ne irradiation (dose rate 40 mW/cm²) once a day in a dose range between 11.9 and 142 J/cm² significantly inhibited cell growth, while daily irradiation with 4.7 J/cm² had no effect. Microscopic examination of nuclear spreads revealed an increased number of cells in mitosis after a single irradiation with 142 J/cm². These results support previous observations suggesting that laser light of low thermal energy interferes with cell cycling and may inhibit cell growth when irradiation is performed at doses of 11.9 J/cm² or more.     

Microtensile bond strength of composite resin to glass-infiltrated alumina composite conditioned with Er,Cr:YSGG laser

Tribochemical silica-coating is the recommended conditioning method for improving glass-infiltrated alumina composite adhesion to resin cement. High-intensity lasers have been considered as an alternative for this purpose. This study evaluated the morphological effects of Er,Cr:YSGG laser irradiation on aluminous ceramic, and verified the microtensile bond strength of composite resin to ceramic following silica coating or laser irradiation. In-Ceram Alumina ceramic blocks were polished, submitted to airborne particle abrasion (110 μm Al₂O₃), and conditioned with: (CG) tribochemical silica coating (110 μm SiO₂) + silanization (control group); (L1-L10) Er,Cr:YSGG laser (2.78 μm, 20 Hz, 0.5 to 5.0 W) + silanization. Composite resin blocks were cemented to the ceramic blocks with resin cement. These sets were stored in 37°C distilled water (24 h), embedded in acrylic resin, and sectioned to produce bar specimens that were submitted to microtensile testing. Bond strength values (MPa) were statistically analyzed (α ≤0.05), and failure modes were determined. Additional ceramic blocks were conditioned for qualitative analysis of the topography under SEM. There were no significant differences among silicatization and laser treatments (p > 0.05). Microtensile bond strength ranged from 19.2 to 27.9 MPa, and coefficients of variation ranged from 30 to 55%. Mixed failure of adhesive interface was predominant in all groups (75–96%). No chromatic alteration, cracks or melting were observed after laser irradiation with all parameters tested. Surface conditioning of glass-infiltrated alumina composite with Er,Cr:YSGG laser should be considered an innovative alternative for promoting adhesion of ceramics to resin cement, since it resulted in similar bond strength values compared to the tribochemical treatment.