808-nm laser therapy with a flat-top handpiece photobiomodulates mitochondria activities of <Emphasis Type="Italic">Paramecium primaurelia</Emphasis> (Protozoa)

Photobiomodulation is proposed as a non-linear process, and only low-level laser therapy (LLLT) is assumed to stimulate exposed cells, whereas high powered laser and fluences can cause negative effects, exhausting the cell’s energy reserve as a consequence of excessive photon-based stimulation. In our work, we investigated and compared the effects of 808-nm diode laser (CW) with a new flat-top handpiece. To this purpose, we tested the photobiomodulation effects of 1 and 3 J/cm² fluence, both generated by 100 mW or 1 W of laser power and of 64 J/cm² of fluence generated by 100 mW, 1 W, 1.5 W or 2 W, as expressed through oxygen consumption and ATP synthesis of Paramecium. Data collected indicates the incremental consumption of oxygen through irradiation with 3 J/cm²–100 mW or 64 J/cm²–1 W correlates with an increase in Paramecium ATP synthesis. The Paramecium respiration was inhibited by fluences 64 J/cm²–100 mW or 64 J/cm²–2 W and was followed by a decrease in the endogenous ATP concentration. The 1 J/cm²–100 mW or 1 W and 3 J/cm²–1 W did not affect mitochondrial activity. The results show that the fluence of 64 J/cm²–1 W more than the 3 J/cm²–100 mW causes greater efficiency in Paramecium mitochondria respiratory chain activity. Our results suggest that thanks to flat-top handpiece we used, high fluences by high-powered laser have to be reconsidered as an effective and non-invasive therapy. Possible associated benefits of deeper tissue penetration would increase treatment effectiveness and reduced irradiation time.     

ArF-excimer laser–induced secondary radiation in photoablation of biological tissue

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200–800 nm. The intensity of secondary radiation in the range of 200–315 nm (UVC and UVB) is ∼20% of the total intensity at high laser fluences (>2 J/cm²), and ∼50% at moderate laser fluences (<500 mJ/cm²); 10 μJ/cm² in the UVC and UVB were measured at the sample surface, at fluences (<1J/cm²) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (>5 J/cm²) are required. As a consequence, laser–induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field. © 1994 Wiley-Liss, Inc.     

The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro

Summary The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin ether (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50–100 mW/cm² and exposure times (2–15 s), representing incident pulse energy fluences of 2.5–5 mJ/cm² and energy densities of 0.1–1.5 J/cm². The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm² (LD₉₀=0.54 J/cm²). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm²).     

Red and infrared laser therapy inhibits in vitro growth of major bacterial species that commonly colonize skin ulcers

Low-level laser therapy (LLLT) is used in chronic wounds due to its healing effects. However, bacterial species may colonize these wounds and the optimal parameters for effective bacterial inhibition are not clear. The aim of this study was to analyze the effect of LLLT on bacterial growth in vitro. Bacterial strains including Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were suspended in saline solution at a concentration of 10³ cells/ml and exposed to laser irradiation at wavelengths of 660, 830, and 904 nm at fluences of 0 (control), 3, 6, 12, 18, and 24 J/cm². An aliquot of the irradiated suspension was spread on the surface of petri plates and incubated at 37 °C for quantification of colony-forming unit after 24, 48, and 72 h. Laser irradiation inhibited the growth of S. aureus at all wavelengths and fluences higher than 12 J/cm², showing a strong correlation between increase in fluence and bacterial inhibition. However, for P. aeruginosa, LLLT inhibited growth at all wavelengths only at a fluence of 24 J/cm². E. coli had similar growth inhibition at a wavelength of 830 nm at fluences of 3, 6, 12, and 24 J/cm². At wavelengths of 660 and 904 nm, growth inhibition was only observed at fluences of 12 and 18 J/cm², respectively. LLLT inhibited bacterial growth at all wavelengths, for a maximum of 72 h after irradiation, indicating a correlation between bacterial species, fluence, and wavelength.     

Soft and hard tissue ablation with short-pulse high peak power and continuous thulium-silica fibre lasers

Thulium lasers operating near 2 m are the subject of interest for various medical applications. The newly developed Tm³⁺ silica fibre laser in Q-switched and CW operation was investigated to determine its efficiency in the interaction with soft and hard tissues. The interaction was investigated using a free-running continuous (CW) Tm³⁺-doped fibre laser (wavelength 1.99 m, with self-pulsation ranging over 1 to few tens of microseconds) and for novel Q-switched operation of the same fibre laser (pulse durations from 150 to 900 ns and pulse repetition rates from 100 Hz to 17 kHz). Residual damage and affected zones using the Q-switched laser were nearly six times smaller than using the CW fibre laser for about 50 s of exposure time, and increased with pulse repetition rate. The energy required to ablate tissue with the Q-switched fibre laser ranged from 0.2 to 0.6 kJ/cm³ and was significantly smaller than that for the CW fibre laser of 153 to 334 kJ/cm³. Under both high-resolution reflected optical microscopy and histological examination, tissue crater depths were observed as cleanly cut with smooth walls and minimal charring in the case of Q-switched operation of the fibre laser. This study is the first direct comparison of tissue interaction of short-pulse (Q-switched) and CW Tm³⁺-doped silica fibre lasers on crater depth, heat of ablation and collateral damage. The Q-switched Tm³⁺-doped silica fibre laser effectively ablates tissue with little secondary damage.AcknowledgmentThis work was supported by the Engineering and Physical Sciences Research Council.     

Pulsed carbon dioxide laser ablation of burned skin: In vitro and in vivo analysis

Pulsed lasers produce efficient and precise tissue ablation with limited residual thermal damage. In this study, the efficiency of pulsed CO₂ laser ablation of burned and normal swine skin was studied in vitro with a mass loss technique. The heats of ablation for normal and burned skin were 2,706 and 2,416 J/cm³ of tissue ablated, respectively. The mean threshold radiant exposures for ablating normal skin and eschar were 2.6 J/cm² and 3.0 J/cm², respectively. Radiant exposures greater than 19 J/cm² produced a plasma, which decreased the efficiency of laser ablation. Thus the radiant exposures for efficient ablation range from 4 to 19 J/cm², and within this radiant exposure range 20–40 μm of tissue are ablated per pulse. We also examined, on a gross and histo-pathologic basis, in vivo burn eschar excision with a pulsed CO₂ laser. The laser allowed bloodless excisions of full thickness burns on the backs of male hairless rats. The zone of thermal damage was approximately 85 μm over the subjacent fascia. The pulsed CO₂ laser can ablate burn eschar efficiently, precisely, and bloodlessly and may prove valuable for the excision of burned and necrotic tissue.     

Low-level infrared laser modulates muscle repair and chromosome stabilization genes in myoblasts

Infrared laser therapy is used for skeletal muscle repair based on its biostimulative effect on satellite cells. However, shortening of telomere length limits regenerative potential in satellite cells, which occurs after each cell division cycle. Also, laser therapy could be more effective on non-physiologic tissues. This study evaluated low-level infrared laser exposure effects on mRNA expression from muscle injury repair and telomere stabilization genes in myoblasts in normal and stressful conditions. Laser fluences were those used in clinical protocols. C2C12 myoblast cultures were exposed to low-level infrared laser (10, 35, and 70 J/cm²) in standard or normal (10 %) and reduced (2 %) fetal bovine serum concentrations; total RNA was extracted for mRNA expression evaluation from muscle injury repair (MyoD and Pax7) and chromosome stabilization (TRF1 and TRF2) genes by real time quantitative polymerization chain reaction. Data show that low-level infrared laser increases the expression of MyoD and Pax7 in 10 J/cm² fluence, TRF1 expression in all fluences, and TRF2 expression in 70 J/cm² fluence in both 10 and 2 % fetal bovine serum. Low-level infrared laser increases mRNA expression from genes related to muscle repair and telomere stabilization in myoblasts in standard or normal and stressful conditions.     

Ti:sapphire femtosecond laser ablation of dental enamel, dentine, and cementum

This paper reports an investigation into the characteristics of femtosecond laser (800-nm central wavelength) in the ablation of human dental enamel, dentine, and cementum at various laser fluences from 0.2 to 3.68 J/cm² with single and multiple pulses. The femtosecond laser interaction with cementum is reported for the first time. Ablation thresholds were determined to be 0.58, 0.44, and 0.51 J/cm² for enamel, dentine, and cementum, respectively. Under the average laser fluences of 1.13 to 3.68 J/cm², clean ablated surfaces without debris and microcracks were obtained. Laser fluence was found to influence the ablated diameter and depth, whereas under a certain fluence, pulse number only affects the depth, without affecting the diameter. The ablation mechanism is found to be based on multi-photon absorption, not previously known for femtosecond laser ablation of dental materials. The low thermal loads of 0.708, 1.44, and 0.404 J/cm³ required for ablating enamel, dentine, and cementum, determined for the first time, are beneficial for minimizing the heat-affected zones and micro-damage. The Raman spectroscopic analysis of phosphate shows that the chemical components of the tooth remain intact before and after the fs-laser ablation. It also shows that different dental tissues respond differently to the laser irradiation.     

Ablation of porcine ligamentum flavum with Ho:YAG,q‐switched Ho:YAG,and quadrupled Nd:YAG lasers

Background and Objectives

Ligamentum flavum (LF) is a tough, rubbery connective tissue providing a portion of the ligamentous stability to the spinal column, and in its hypertrophied state forms a significant compressive pathology in degenerative spinal stenosis. The interaction of lasers and this biological tissue have not been thoroughly studied. Technological advances improving endoscopic surgical access to the spinal canal makes selective removal of LF using small, flexible tools such as laser‐coupled fiber optics increasingly attractive for treatment of debilitating spinal stenosis. Testing was performed to assess the effect of Ho:YAG, Q‐switched Ho:YAG, and frequency quadrupled Nd:YAG lasers on samples of porcine LF. The objective was to evaluate the suitability of these lasers for surgical removal of LF.

Study Design/Materials and Methods

LF was resected from porcine spine within 2 hours of sacrifice and stored in saline until immediately prior to laser irradiation, which occurred within an additional 2 hours. The optical absorbance of a sample was measured over the spectral band from 190 to 2,360 nm both before and after dehydration. For the experiments using the Ho:YAG (λ = 2,080 nm, t_p = 140 µs, FWHM) and Q‐Switched Ho:YAG (λ = 2,080 nm, t_p = 260 ns, FWHM) lasers, energy was delivered to the LF through a laser‐fiber optic with 600 µm core and NA = 0.39. For the experiment using the frequency quadrupled Nd:YAG laser (λ = 266 nm, t_p = 5 ns FWHM), rather than applying the laser energy through a laser‐fiber, the energy was focused through an aperture and lens directly onto the LF. Five experiments were conducted to evaluate the effect of the given lasers on LF. First, using the Ho:YAG laser, the single‐pulse laser‐hole depth versus laser fluence was measured with the laser‐fiber in direct contact with the LF (1 g force) and with a standoff distance of 1 mm between the laser‐fiber face and the LF. Second, with the LF remaining in situ and the spine bisected along the coronal plane, the surface temperature of the LF was measured with an IR camera during irradiation with the Ho:YAG laser, with and without constant saline flush. Third, the mass loss was measured over the course of 450 Ho:YAG pulses. Fourth, hole depth and temperature were measured over 30 pulses of fixed fluence from the Ho:YAG and Q‐Switched Ho:YAG lasers. Fifth, the ablation rate and surface temperature were measured as a function of fluence from the Nd:YAG laser. Several LF staining and hole‐depth measurement techniques were also explored.

Results

Aside from the expected absorbance peaks corresponding to the water in the LF, the most significant peaks in absorbance were located in the spectral band from 190 to 290 nm and persisted after the tissue was dehydrated. In the first experiment, using the Ho:YAG laser and with the laser‐fiber in direct contact with the LF, the lowest single‐pulse fluence for which LF was visibly removed was 35 J/cm². Testing was conducted at 6 fluences between 35 and 354 J/cm². Over this range the single‐pulse hole depth was shown to be near linear (R² = 0.9374, M = 1.6), ranging from 40 to 639 µm (N = 3). For the case where the laser‐fiber face was displaced 1 mm from the LF surface, the lowest single‐pulse fluence for which tissue was visibly removed was 72 J/cm². Testing was conducted at 4 energy densities between 72 and 180 J/cm². Over this range the single‐pulse hole depth was shown to be near linear (R² = 0.8951, M = 1.4), ranging from 31 to 220 µm (N = 3). In the second experiment, with LF in situ, constant flushing with room temperature saline was shown to drastically reduce surface temperature during exposure to Ho:YAG at 5 Hz with the laser‐fiber in direct contact with the LF. Without saline, over 1 minute of treatment with a per‐pulse fluence of 141 mJ/cm², the average maximum surface temperature measured 110°C. With 10 cc's of saline flushed over 1 minute and a per‐pulse laser fluence of 212 mJ/cm², the average maximum surface temperature was 35°C. In the third experiment, mass loss was shown to be linear over 450 pulses of 600 mJ from the Ho:YAG laser (212 J/cm², direct contact, N = 4; 108 J/cm², 1 mm standoff, N = 4). With the laser‐fiber in direct contact, an average of 53 mg was removed (R² = 0.996, M = 0.117) and with 1 mm laser‐fiber standoff, an average of 44 mg was removed (R² = 0.9988, M = 0.097). In the fourth experiment, 30 pulses of the Ho:YAG and Q‐Switched Ho:YAG lasers at 1 mm standoff, and 5 Hz produced similar hole depths for the tested fluences of 9 J/cm² (151 and 154 µm, respectively) and 18 J/cm² (470 and 442 µm, respectively), though the Ho:YAG laser produced significantly more carbonization around the rim of the laser‐hole. The increased carbonization was corroborated by higher measured LF temperature. In all tests with the Ho:YAG and Q‐Switched Ho:YAG, an audible photo‐acoustic affect coincided with the laser pulse. In the fifth experiment, with the frequency quadrupled Nd:YAG laser at 15 Hz for 450 pulses, ablation depth per pulse was shown to be linear for the fluence range of 0.18 – 0.73 J/cm² (R² = 0.989, M = 2.4). There was no noticeable photo‐acoustic effect nor charring around the rim of the laser‐hole.

Conclusion

The Ho:YAG, Q‐Switched Ho:YAG, and frequency quadrupled Nd:YAG lasers were shown to remove ligamentum flavum (LF). A single pulse of the Ho:YAG laser was shown to cause tearing of the tissue and a large zone of necrosis surrounding the laser‐hole. Multiple pulses of the Ho:YAG and Q‐Switched Ho:YAG lasers caused charring around the rim of the laser‐hole, though the extent of charring was more extensive with the Ho:YAG laser. Charring caused by the Ho:YAG laser was shown to be mitigated by continuously flushing the affected LF with saline during irradiation. The Nd:YAG laser was shown to ablate LF with no gross visible indication of thermal damage to surrounding LF. Lasers Surg. Med. 47:839–851, 2015. © 2015 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.     

Effect of low-level laser therapy on types I and III collagen and inflammatory cells in rats with induced third-degree burns

Low-level laser therapy (LLLT) has been increasingly used to accelerate wound healing in third-degree burns. This study investigated the effects of lasers on the tissue repair process of third-degree burns. Burns were produced on the backs of male Wistar rats. The animals were divided into four groups (n?=?12): control, injury, LLLT 3 J/cm², and LLLT 4 J/cm². Each group was further divided into two subgroups; the rats in one subgroup were killed on day 8 and those in the other, on day 16 after injury. The animals in LLLT 3 J/cm² and LLLT 4 J/cm² were irradiated 1 h after injury, and irradiation was repeated every 48 h. Laser (660 nm, 35 mW) treatment at fluences of 3 and 4 J/cm² were used. After killing the rats, tissue fragments from the burnt area were removed for histological analysis. The LLLT-treated groups showed a significant decrease (p <0.05) in the number of inflammatory cells and increased collagen deposition compared to the injury group. Laser irradiation (both 3 and 4 J/cm²) resulted in reduction in the inflammatory process and improved collagen deposition, thereby ameliorating the healing of third-degree burns.     

Experimental photoablation of meniscus cartilage by excimer laser energy

Summary Excimer lasers have been demonstrated to provide a very precise and circumscribed ablation of synthetic polymers and biological tissues. We investigated in vitro the use of ultrashort pulsed ultraviolet excimer-laser energy for controlled removal of meniscus cartilage under the aspects of arthroscopic meniscectomy. A krypton-fluorine gas mixture was used to achieve laser emission of 248-nm wavelength. A total of 22 human menisci obtained either by operation or necropsy were irradiated over a range of energy fluence (2.15–3.07 J/cm²/pulse), repetition rates (5–20 Hz), and exposure time (15–60 s). Ablation rates of 4.00–5.76 m per pulse were obtained. Light-microscopic examinations demonstrated tissue ablation without any evidence of pathological changes associated with continuous-wave laser irradiation. Effects of laser energy were clearly limited to the target of the laser beam, and tissue removal proceeded without production of heat or smoke. Due to the lack of pathological alterations observed, excimer-laser irradiation of meniscus cartilage may prove to be advantageous for precisely cutting and removing menisci without injury to the surrounding normal tissue. Clinical application of excimer-laser irradiation includes the development of suitable fiberoptics and laser coupling, as well as modification of fiber tips.Funds were received from theFonds zur Förderung der wissenschaftlichen Forschung (Ministry of Science and Research, Austria)     

Low-level laser therapy prevents degenerative morphological changes in an experimental model of anterior cruciate ligament transection in rats

The aim of this study was to analyze the effects of low-level laser therapy (LLLT) on the prevention of cartilage damage after the anterior cruciate ligament transection (ACLT) in knees of rats. Thirty male rats (Wistar) were distributed into three groups (n?=?10 each): injured control group (CG); injured laser-treated group at 10 J/cm² (L10), and injured laser-treated group at 50 J/cm² (L50). Laser treatment started immediately after the surgery and it was performed for 15 sessions. An 808 nm laser, at 10 and 50 J/cm², was used. To evaluate the effects of LLLT, the qualitative and semi-quantitative histological, morphometric, and immunohistochemistry analysis were performed. Initial signs of tissue degradation were observed in CG. Interestingly, laser-treated animals presented a better tissue organization, especially at the fluence of 10 J/cm². Furthermore, laser phototherapy was able of modulating some of the aspects related to the degenerative process, such as the prevention of proteoglycans loss and the increase in cartilage area. However, LLLT was not able of modulating chondrocytes proliferation and the immunoexpression of markers related to inflammatory process (IL-1 and MMP-13). This study showed that 808 nm laser, at both fluences, prevented features related to the articular degenerative process in the knees of rats after ACLT.     

Low-intensity red and infrared lasers affect mRNA expression of DNA nucleotide excision repair in skin and muscle tissue

Lasers emit light beams with specific characteristics, in which wavelength, frequency, power, fluence, and emission mode properties determine the photophysical, photochemical, and photobiological responses. Low-intensity lasers could induce free radical generation in biological tissues and cause alterations in macromolecules, such as DNA. Thus, the aim of this work was to evaluate excision repair cross-complementing group 1 (ERCC1) and excision repair cross-complementing group 2 (ERCC2) messenger RNA (mRNA) expression in biological tissues exposed to low-intensity lasers. Wistar rat (n?=?28, 4 for each group) skin and muscle were exposed to low-intensity red (660 nm) and near-infrared (880 nm) lasers at different fluences (25, 50, and 100 J/cm²), and samples of these tissues were withdrawn for RNA extraction, cDNA synthesis, and gene expression evaluation by quantitative polymerase chain reaction. Laser exposure was in continuous wave and power of 100 mW. Data show that ERCC1 and ERCC2 mRNA expressions decrease in skin (p?<?0.001) exposed to near-infrared laser, but increase in muscle tissue (p?<?0.001). ERCC1 mRNA expression does not alter (p?>?0.05), but ERCC2 mRNA expression decreases in skin (p?<?0.001) and increases in muscle tissue (p?<?0.001) exposed to red laser. Our results show that ERCC1 and ERCC2 mRNA expression is differently altered in skin and muscle tissue exposed to low-intensity lasers depending on wavelengths and fluences used in therapeutic protocols.     

Photodynamic therapy: Optimal treatment parameters in murine fibrosarcoma

We have investigated the efficacy of photodynamic therapy (PDT) by using two preparations of haematoporphyrin derivative (HPD) that demonstrated different biological activities against experimental murine fibrosarcoma RIF-1 in C3H/He mice. We have been able to demonstrate a minimum clonogenic survival rate of 0.25% by using the more active HPD at 20 mg/kg with a 40-h retention time and a total laser light dose of 100 J/cm². Further, we noted that clonogenic survival rates of 21.6% and 25.0% respectively could be achieved by using the less active HPD (at 20 mg/kg) with a laser light dose of 150 J/cm², or the more active HPD (at 20 mg/kg) with a laser light dose of 20 J/cm². In both cases necrosis of the surrounding normal tissue was absent. Necrosis of the normal tissue surrounding the tumour was shown to be associated with high laser energy (100 J/cm² and higher) in conjunction with a high dose (20 mg/kg) of the more active HPD. A comparison of survival curves as a function of laser energy for the RIF-1 cells following PDT with the two different preparations of HPD showed a difference in the kinetics of cell death. A curve with a shoulder region and aD _o (mean lethal dose) of 41 J/cm² was obtained when the less active HPD was used, whereas PDT using the more active HPD resulted in a curve with no shoulder and aD _o of 16 J/cm².     

Idiopathic Flushing with Dysesthesia: Treatment with the 585nm Pulsed Dye Laser

Objective: The purpose of this study was to analyze the efficacy and safety of the 585nm pulsed dye laser for the treatment of idiopathic flushing with dysesthesia. Design: This was a retrospective study of patients treated with a 585nm pulsed dye laser with fluences ranging from 3.5 to 7.5J/cm² (purpura threshold fluences), a pulse duration of 450μsec, and a spot size of 5 or 10mm. Setting: The Ronald 0. Perelman Department of Dermatology at New York University Medical Center. Participants: Ten adult subjects who presented with flushing with dysesthesia. Measurements: Participants subjectively evaluated the decrease in dysesthesia and the number of flushing episodes. The objective response to treatment was evaluated by a single physician using pre- and postoperative photographs. The severity of postoperative erythema was compared with baseline using an ordinal scale ranging from zero (resolution of erythema) to four (76-100% of baseline erythema). Results: The mean number of treatments received by the subjects was seven. The mean fluence was 6.66J/cm². Subjectively, 100 percent of subjects reported a decrease in dysethesia and the number of flushing episodes. Objectively, subjects demonstrated at least a 62.5-percent reduction in erythema. Conclusion: Laser surgery provided subjective relief of dysesthesia and decreased the number of flushing episodes with a greater than 62-percent objective reduction in the severity of erythema. The 585nm pulsed dye laser is a safe, efficacious treatment for the signs and symptoms of idiopathic flushing with dysesthesia.Flushing is a transient, episodic redness of the face, neck, upper chest, and/or epigastric area that is associated with certain diseases, ingestion of certain drugs or other substances, heat, emotional factors, or physical exertion.1 Blushing is flushing exclusively provoked by an emotional stimulus.2,3 Dysesthesia is defined as an unpleasant, abnormal sensation that is produced by normal stimuli.4Idiopathic flushing is a diagnosis of exclusion.3,5-8 In a subset of patients with idiopathic flushing, dysesthesia may be noted, and patients describe this symptom as a warm, unpleasant, burning sensation. Patients with this constellation of signs and symptoms, which is henceforth referred to as idiopathic flushing with dysesthesia, consistently deny concomitant pruritus. Furthermore, associated signs and symptoms, such as bronchospasm, abdominal cramps, diarrhea, headache, hypotension, or tachycardia, are rare in these patients.The objectives of this study were to define the characteristics of a poorly defined disorder, idiopathic flushing with dysesthesia, and to evaluate the treatment of subjects with this disorder using the 585nm pulsed dye laser.     

The relevance of pulse repetition rate and radiant exposure to the neurophysiological effects of low-intensity laser (820 nm/pulsed wave) irradiation upon skin temperature and antidromic conduction latencies in the human median nerve

The effects of low-intensity near-infra-red laser irradiation (820 nm; 1.5 and 9.0 J cm^–2; pulsed at 12 Hz, 73 Hz and 5 kHz) upon peripheral neurophysiology and skin temperature were investigated using antidromic conduction studies in the human median nerve in vivo. Healthy human volunteers (n = 90) were recruited and allocated randomly to either a control group (n=10) or one of eight experimental groups (two radiant exposures, 1.5 J cm^–2 and 9.0 J cm^–2 at one of three pulse repetition rates, 12 Hz, 73 Hz or 5 kHz, in addition to a placebo group for each radiant exposure;n = 10 all groups). Analysis of variance (ANOVA) demonstrated a significant (p0.05) decrease in skin temperature following irradiation at the lowest radiant exposure (1.5 J cm^–2) combined with pulse repetition rates of 73 Hz and 5 kHz, with the greatest effect at 73 Hz. These changes in skin temperature were coupled with increases in negative peak latency (NPL); ie changes in NPL were inversely related to changes in skin temperature. However, in contrast to the authors' previous findings using continuous wave (CW) laser irradiation, differences in NPL were not found to be significant. These findings, therefore, provide little evidence of the neuro-physiological effects of low-intensity infra-red irradiation at the dosage levels and pulse repetition rates used here.     

A thermal appraisal of the ablation process in canine aorta in vivo using a 100 μm pulsed Nd-YAG laser

A model has been developed to calculate distal tissue necrosis in vascular tissue after application of a 100 laser pulse from a Nd-YAG laser (5 kW peak pulse power on a 0.13 mm² spot size). The model assumes that the temperature profile in the tissue is proportional to the laser light fluence rate and that the distal tissue necrosis depth is that depth in the tissue where there is a temperature increase of 42 °C minus the etch rate (ablation depth per laser pulse). The fluence rate has been calculated using the diffusion approximation to the radiative transport equation. The tissue optical parameters (absorption and reduced scattering coefficients) have been derived from published data. The etch rate used (10m per pulse) is derived from in vivo experimental results. The model predicts a damage depth varying between 0 and 2.33 mm (mean 1.10 mm) and this is compared with an experimental result (0.77 mm) in dog aorta.     

Sustained effects of blue light on <Emphasis Type="Italic">Streptococcus mutans</Emphasis> in regrown biofilm

In prior studies, exposure of Streptococcus mutans in biofilm to blue light using high fluences of up to 680 J/cm² did not interfere with bacterial capability to reform an initial biofilm; however, a delayed antibacterial effect was observed. Our aim was to determine the sustained effecttts of blue light-emitting diode (LED) curing light on the pathogenicity of the newly formed biofilm. S. mutans were grown to form biofilm that was exposed to blue light (wavelengths, 460–480 nm) for 1, 3, and 7 min (equivalent to 37, 112, and 262 J/cm², respectively). Then, bacteria were suspended and allowed to regrow into new biofilms. The regrown biofilms were assessed for bacterial quantification by optical density (OD) measurement and quantitative polymerase chain reaction (qPCR), bacterial viability and extracellular polysaccharide production by fluorescent staining using confocal scanning laser microscopy, acid production by bacteria (acidogenicity), and bacterial survival at low pH (aciduricity) using qPCR. Bacterial growth in the regrown biofilms was increased when samples were previously exposed to light; however, under the confocal microscopy, a higher proportion of dead bacteria and a reduction in polysaccharide production were observed. The acidogenicity from the regrown biofilm was lowered as fluences of light increased. The aciduricity of the regrown biofilm was decreased, meaning less growth of bacteria into biofilm in low pH with increasing fluences. Blue light has sustained effects on S. mutans bacteria grown into new biofilm. Although bacterial growth in biofilm increased, bacterial viability and virulence characteristics were impaired. The cariogenic potential over time of S. mutans previously exposed to blue light when grown on tooth surfaces is yet to be determined.     

Fluoride uptake and acid resistance of enamel irradiated with Er:YAG laser

This study evaluated the resistance to demineralization and fluoride incorporation of enamel irradiated with Er:YAG. A total of 110 bovine teeth were selected and divided into eight groups: unlased, 37% phosphoric acid, and samples irradiated with the Er:YAG laser at several fluences (31.84 J/cm², 25.47 J/cm², 19.10 J/cm², 2.08 J/cm², 1.8 J/cm², and 0.9 J/cm²). The application of acidulated phosphate fluoride was performed after treatments. All samples were immersed in 2 ml of 2.0 M acetic–acetate acid solution at pH 4.5 for 8 h, and fluoride, calcium, and phosphorus ions dissolved were analyzed by atomic absorption spectrometry and spectrophotometry. The phosphoric acid and 31.84 J/cm² groups presented the lowest dissolution of calcium and phosphorus ions. Higher fluoride incorporation was observed on 1.8 J/cm² and 0.9 J/cm² groups. Based on these results, Er:YAG laser was able to decrease acid dissolution and increase fluoride uptake and can be a promissory alternative for preventive dentistry.     

In vitro Alexandrite laser angioplasty: A study on fibre conduction and tissue effects

Pulsed ultra-violet excimer laser radiation is capable of tissue ablation with only minimal thermal injury of adjacent tissue structures. Since difficult fibre optic coupling of energy was observed, alternative Q-switched laser sources capable of ablation of atherosclerotic plaque are under current investigation. To evaluate tissue effects of Alexandrite laser radiation, 160 arterial segments with macroscopic evidence of atherosclerotic disease were treated. The laser light was transmitted via silica based quartz fibres with different diameters. Using the Q-switched Alexandrite laser at the fundamental wavelength (748 nm) with a pulse duration of 300 ns the energy density threshold for tissue ablation was found to be in the range of 63 to 126 J cm^–2 using a 300m fibre. On macroscopic examination only limited thermal and acoustic injury was found in crater adjacent tissue structures. Crater edges were even and did not reveal signs of crater charring or debris in the crater lumen. However, the histological cross-sections revealed thermal injury extending from 100 up to 200m lateral into adjacent tissue. The crater margins revealed fissuring as a result of shock wave injury. Thermal damage was most evident if irradiation of atherosclerotic tissue was performed in blood.