Effect of the ArF excimer laser on human enamel.

Human enamel surface was irradiated with ArF excimer laser and examined under light microscopy and scanning electron microscopy (SEM). Enamel surface was irradiated at three different areas with different energy fluences. It is demonstrated that the ArF excimer laser causes ablation of the calcified hard enamel tissue. Ablation curves were measured. There was no significant difference found in the etch depth between the three different areas of enamel surface. The morphology of the irradiated areas seen under the SEM was found to be dependent on energy fluence. It changed with increase in energy fluence from being etched to forming a smooth, fused, glaze-like surface and then at very high energy fluences producing a rough surface. The influence of the laser irradiation was confined to the irradiated area only, with no visible heat damage to the surroundings. These results suggest that excimer laser could be applied in a controlled and defined manner for tooth enamel treatments in dentistry.     

Effect of excimer laser radiant exposure on uniformity of ablated corneal surface

The argon fluoride (193 nm) excimer laser is being used to change the anterior corneal curvature for correction of refractive errors. Uniformity of the surface following laser ablation may play an important role in the rate of epithelial healing and amount and type of stromal scarring. To test the effect of radiant exposure (fluence) on surface smoothness, we ablated rabbit corneas with the 193 nm argon fluoride excimer laser at nine radiant exposures from 50 to 850 mJ/cm2. A total energy of 100 J/cm2 was used for each ablation at a frequency of 1 Hz. Scanning electron microscopy demonstrated progressive improvement of surface smoothness with increasing radiant exposures. Transmission electron microscopy demonstrated no consistent increase in thickness to the surface condensate (pseudomembrane) with increasing radiant exposure. Improvement in surface quality associated with increasing radiant exposures may result from a more uniform depth of ablation per pulse in the corneal lamellae that absorb laser wavelengths differently. Radiant exposures at levels where the depth of ablation is the same regardless of increasing energy densities achieve a more uniform surface because inhomogeneities in the beam and variation in energy from pulse to pulse do not affect the ablation rate.     

Experimental study of application of excimer laser to laser angioplasty

The possible application of excimer laser to laser angioplasty was studied. In the first experiment, the ablative effects of excimer laser at wavelengths of 248 nm and 308 nm on the pig myocardium were examined in vitro at an air-tissue interface. Crater depth increased with total delivered energy and energy per pulse. Very clear cuts could be observed by histological examination. There was no evidence of thermal damage at a wavelength of 248 nm, at 10 pps. Above 10 pps, a thin bordering zone of suspicious thermal damage was noted with the wavelengths of 248 nm and 308 nm. Thermal damage increased with pulse repetition rate. In the second experiment, the effects of excimer laser irradiation on blood were examined. Five vials, each of which contained 3 ml of blood, were exposed to 37.5 mJ laser beam at 10 pps in repetition rate for 10, 20, 30, 40, 50 seconds. One vial was left untreated as a control. No change in hematocrit value was observed after excimer laser irradiation. In contrast, the level of plasma free hemoglobin rose progressively with each increased duration of exposure. This result indicates that the lysis of erythrocytes does not occur in the laser-exposed cells. However, the damage to erythrocyte membrane took place as it was evidenced by progressive hemoglobin leakage into plasma. In the third experiment, the excimer laser was coupled to a 400 microns quartz optical fiber and the laser energy transmitted through the fiber was measured. At a wavelength of 308 nm, pulse energies up to 9 mJ were noted at the tip of the fiber. At a wavelength of 248 nm, the fiber tip was destroyed. In the fourth experiment, acute and chronic healing responses of normal canine arteries to excimer laser irradiation were studied in 4 mongrel dogs. The artery healed completely at the 18th day after the excimer laser irradiation. There was no evidence of thrombus formation and intimal hyperplasia in these arteries. The results suggest the applicability of excimer laser to laser angioplasty.     

Improved excimer laser photorefractive keratectomy system

An improved 193 nm excimer laser photorefractive keratectomy system is described here. The delivery system was optimised to produce a smooth keratectomy bed, to minimise the healing response, and to reduce the regression of the refractive result. A spatial filtering system was used to smooth the energy distribution within each pulse, and the iris was adjusted for every pulse, to eliminate steps and other irregularities from the keratectomy profile. An image rotator was used to average out any remaining non-uniformities in the energy distribution. The results from the first 39 eyes treated with this laser system with a maximum follow-up of 18 months, are summarised. No epithelial healing problems were noticed, and little or no loss of corneal clarity was noted at any stage during healing. Twenty of the keratectomy procedures were normally sighted myopic corrections, with a maximum follow-up of 5 months. Minimal regression of the refractive correction was seen during the first 8 weeks. © 1993 Wiley-Liss, Inc.     

193 nm excimer laser ablation of bone

The argon fluoride excimer laser is investigated as a cutting-ablating tool for bone surgery. Quantitative measurements are presented for various fluences of laser energy and number of pulses. Histological data are presented that demonstrate the minimal damage to the surrounding material from the laser interaction. Comparisons are made for non-decalcified and decalcified bone. The differences observed, as a function of decalcification in the fluences required for specified depth penetration, are noted and a possible explanation is suggested.     

Cytotoxicity and mutagenicity of excimer laser radiation

Excimer laser radiation at 193 nm, 248 nm and 308 nm cause DNA photochemistry. The photobiological effects resulting from exposure of cells to 308 nm and 248 nm radiation appear to be the same as those obtained using low irradiance CW sources at similar wavelengths. This indicates that the high irradiances available from the excimer laser cause the same DNA photochemistry as the lower-irradiance CW sources. Excimer laser radiation at 193 nm causes less cytotoxicity than predicted based on the DNA absorption spectrum. This may result from absorption of 193 nm radiation by protein present between the cell surface, and nuclear DNA, or from less efficient DNA photochemistry using 193 nm radiation. In vitro assays indicate that DNA-damaging effects resulting in cytotoxicity decrease in the order 248 nm greater than 308 nm greater than 193 nm.     

Intraoperative coronary artery endarterectomy with excimer laser

Compared with continuous-wave lasers, excimer lasers exhibit several in vitro advantages: nonthermal ablation process and linear relation between the number of pulses and the depth of the crater. A 308 nm, 20 nsec pulse duration, 1 to 5 repetition rate laser was specifically designed for clinical application. At the time of cardiopulmonary bypass in 10 symptomatic patients, before bypass grafting, a 1 mm diameter core specifically ultraviolet-tipped fiberoptic scope was introduced via the coronary arteriotomy and placed upstream (seven patients) and downstream (three patients) in contact with the stenosis. Laser power was increasingly delivered up to the clearing of the stenosis or occlusion. Quality of angioplasty was controlled by calibration of the neolumen, cardioplegic solution output through the laser-treated segment, and an eighth day or sixth month coronary arteriogram. In the first three patients studied on the eighth day, all laser-treated coronary artery segments showed an early parallel-linked patent neolumen despite competitive bypass graft flow. In the patients studied after 6 months, all recanalized segments were patent except one; in one patient the venous graft was occluded, but the upstream laser angioplasty was patent. The main limitation of the method lies in the fact that laser coronary recanalization is confined to the fiber core diameter. We conclude that (1) excimer laser angioplasty may be safe and efficient during surgical procedure and (2) as catheter flexibility remains the most critical problem, we are now assuming an appropriate tool with a multifiber system that is suitable for intraoperative as well as percutaneous routes.     

The 308 nm excimer laser in dermatology

THE EFFICACY OF THE 308 NM EXCIMER LASER in the treatment of common psoriasis has been demonstrated. THE DOSES USED have progressively decreased, hence, limiting the adverse events that appear redhibitory with high doses. THE ADAPTATION OF THE DOSES not to the patients themselves but to each of the plaques treated should reduce the number of sessions and the cumulated close necessary to obtain clinical remission. THE 308 NM EXCIMER LASER is effective and tolerance is good in the treatment of vitiligo. It should be proposed for limited vitiligo and essentially of the "UV sensitive" areas, which have shown aesthetically correct percentage of repigmentation. THE PLACE AND INTEREST of its association with other treatments, notably with topical tacrolimus, remains to be defined. Although the results obtained in the treatment of vitiligo are promising, they have to be confirmed in larger cohorts and ensure the absence of median and long term side effects. This therefore limits its use in combined treatments in the context of controlled clinical traits. THE 30 NM EXCIMER LASER IS AN EFFECTIVE AND WELL TOLERATED TREATMENT in localised and non-nodular forms of mycosis fungoid (MF). Although the number of patients treated is limited, the clinical and histological cure observed demonstrates the interest of this new technique in the treatment of MF. These results must be confirmed in a greater number of patients. THE 308 NM EXCIMER LASER is an interesting therapeutic alternative in the treatment of plaques of alopecia areata, erosive oral lichen planus, post-surgical hypopigmentation, vergetures and localised forms of atopic dermatitis. Because of the sparcity of data and in the absence of long term follow-up, it must not be proposed in first intention.     

308 nm准分子激光治疗白癜风

白癜风是一种常见的后天色素脱失性皮肤粘膜病，光疗对白癜风有明确的疗效。新近进入临床应用的308nm准分子激光，安全、高效、副作用小，在白癜风治疗中取得了令人瞩目的成就。本文就308nm准分子激光的作用原理及其在白癜风治疗中的应用综述如下。     

Recanalisation of occluded peripheral arteries by excimer laser

Laser recanalisation was attempted in 24 patients with total segmental occlusions of the lower extremity arteries and the aortic arch branches. All patients were men aged 40-82 years, in 20 the lesions were caused by atherosclerosis, in three by Buerger's thromboangiitis and in one by postembolic occlusion. Angioplasty was performed using excimer lasers with a wavelength of 308 nm and with monofiber waveguides in the transcutaneous transcatheter mode. Recanalisation of the vessel throughout the length of the obliterated segment was successful in 13 out of 24 patients. In all patients with thromboangiitis, energy losses were less than in atherosclerotic occlusions and no problems were experienced in patients with severe calcification. A high percentage of failures is a result of imperfect technology and low effectiveness of control, this must be improved. The Vishnevsky Institute of Surgery in collaboration with the Institute of General Physics has been developing a method of recanalisation of occluded arteries using excimer laser radiation. This paper is a preliminary analysis of our first clinical results.     

Effects of excimer laser on healing of articular cartilage in rabbits

This study examined healing of 1.0 mm diameter defects in rabbit knee articular cartilage for as long as 14 weeks after creation of the defects by either laser or drilling. The purpose of the research was to determine the effects of laser debridement of cartilage on the intrinsic biomechanical properties of the repair tissue. We therefore imitated chondral shaving and subchondral abrasion of cartilage by creating partial-thickness and full-thickness cartilage defects of standardized size with both excimer laser and drilling. Light and scanning electron microscopic examinations of the repair tissue showed that healing of osteochondral defects created by laser may be delayed compared with defects created by drilling, for at least 6 weeks postoperatively. Even though there initially was a considerable delay in healing in the laser group, neither laser nor drilling had any appreciable effects on the mechanical properties of the repair tissue, as demonstrated by biomechanical testing at 14 weeks. Specifically, the repair cartilage in the defects in the laser group had the following material properties (mean ± SD): aggregate modulus, 0.40 ± 0.24 MPa; Poisson's ratio, 0.37 ± 0.08; permeability, 3.72 ± 4.28 × 10^?15 m⁴/N.s; and thickness, 0.20 ± 0.06 mm. The corresponding values for the defects in the drilling group were 0.39 ± 0.23 MPa, 0.34 ± 0.09, 3.82 ± 3.44 × 10^?15 m⁴/N.s, and 0.22 ± 0.09 mm. The repair tissue from both types of defects was pooled, and the values were compared with those for contralateral (control) tissue. The control tissue had a 51% greater aggregate modulus (0.59 ± 0.18 MPa, p = 0.0001), 34% less Poisson's ration (0.23 ± 0.25, p = 0.0001), 48% less permeability (1.94 ± 0.96 × 10^?15 m⁴/N.s, p = 0.0001), and was 29% thicker (0.27 ± 0.08 mm, p = 0.0001). Thus, as evidenced by biomechanical testing at 14 weeks, neocartilage in both superficial and osteochondral defects, created by either laser or a drill, exhibited structural integrity inferior to that of normal control tissue.     

An experimental study of excimer laser angioplasty]

An excimer laser, which is a pulsed ultraviolet laser and ablates tissue precisely with no thermal injury, is expected to coronary laser angioplasty. We transmitted XeCl excimer laser (308 nm) via a 400 microns fused silica fiber. In the first experiment, we studied about excimer laser ablative effects to normal canine arteries and atherosclerotic rabbit aortas, and about healing responses following excimer laser irradiation in both models. Surfaces after excimer laser ablation were slightly rough but no thermal injury was found in the media. And for healing process of normal canine arteries, endothelial cells appeared at 3 weeks and completely covered surfaces with fibrointimal ingrowth at 3 months. In the rabbit aortas, at 3 weeks there was reconstruction of the surface. At 2 months no accelerated atherosclerotic or aneurysmal changes were observed. In the second, with this excimer laser (short pulse) and 400 microns fused silica fibers (distal fiber-end power: 3-6 mJ/pulse), we performed transluminal laser angioplasty to recanalize totally occluded canine femoral arteries under an angioscopic guidance. We cold recanalize 8 of 9 totally occluded arteries with no thermal injury of adjacent tissue, though perforations were observed in 7 of 9 arteries. In the third, we used a newly-developed long pulse excimer laser, with which distal fiber-end energy was about 3 to 4 times as much as the short pulse one, to recanalize totally occluded canine arteries. In result, recanalization was performed in 6 of 8 arteries rapidly with little thermal injury. However, we observed perforations in 6 of 8 arteries like the short pulse one. Multifiber catheter ("over the wire system") coupled with this long-pulse excimer laser was used to reconstruct stenotic iliac arteries of atherosclerotic rabbit models. The procedure was successful in all the 5 rabbits. In conclusion, our preliminary results suggested that further developments of a more powerful and longer pulse-duration excimer laser, optic delivery system and guidance system would make excimer laser angioplasty safer and more effective method in the near future.     

Pulsed excimer laser angioplasty of human cadaveric arteries

Laser angioplasty has been limited by the lack of precise control of thermal and acoustic vascular injury. Pulsed excimer lasers, by contrast, have a capacity to affect target tissue without heat dispersion or damage to surrounding structures. The ablative properties of three excimer wavelengths, krypton fluoride (249 nm), xenon chloride (308 nm), and xenon fluoride (351 nm), were investigated with the use of fresh human cadaveric normal and atherosclerotic femoral arteries. Light and electron microscopy demonstrated clean cuts with histologically normal edges. There was no evidence of either thermal or acoustic damage with any of the wavelengths studied. The depth of ablation varied directly with the number of pulses and inversely with tissue density while the incision width remained constant. The excimer laser appears to offer significant advantages over its conventional counterparts for the ablation of atherosclerotic plaque.     

Photoablation of bone by excimer laser radiation.

BACKGROUND AND OBJECTIVES: The aim of the present study was to compare the usefulness of mechanical osteotomy tools and common laser systems with the ultraviolet (UV) laser in the field of the central nervous system and its bony capsule. STUDY DESIGN/MATERIALS AND METHODS: The cranial bones of 42 living rats were treated with UV laser radiation with wavelengths of 193 nm and 248 nm. The morphology and physical effects were evaluated by means of optical and scanning electron microscopy. RESULTS: This study shows the special characteristics of excimer versus infrared lasers or mechanical tools, such as high precision, no thermic damage, little depth effect, and no delay of healing processes. CONCLUSION: The excimer laser is an interesting instrument for microsurgery of bones in orthopaedics, neurosurgery, and otolaryngology.     

Clinicopathologic study of healing excimer laser radial excisions

Four radial linear excisions were created by an argon fluoride (193 nm) excimer laser in the edematous cornea of a blind eye of a diabetic human patient. Partial thickness corneal trephinations were performed at 3, 7, and 18 months after surgery for histopathologic examination. At 3 months, a wide gap in Bowman's layer permitted extension of an epithelial plug to a depth of 0.35 mm; at 7 and 18 months, the depth of the epithelial plug was decreased to 0.29 mm and 0.01 mm, respectively. With wound healing, excision width decreased and the two cut ends of Bowman's layer were almost reapposed by 18 months, suggesting wound contraction. Linear excisions with the excimer laser appear to be wider than incisions made with a diamond blade, but the pattern of wound maturation appears to be similar.     

Effect of gallium arsenide diode laser on human periodontal disease: a microbiological and clinical study

BACKGROUND AND OBJECTIVE: The present study is aimed to describe short-term results on selected microbiological and clinical parameters obtained by treatment with soft laser in conjunction with methylene blue and/or mechanical subgingival debridement in human periodontal disease. STUDY DESIGN/MATERIALS AND METHODS: Ten patients, in whom each dental quadrant was randomly designated to receive one of four types of treatment procedures, were included in the study. Groups of quadrants received: scaling/root planing (SRP); laser application (L); SRP combined with L (SRP/L); oral hygiene instructions (OHI). Four single rooted teeth (one in each quadrant), having an interproximal site with a probing depth of 4 mm mesio-buccally, were selected in each patient. The selected teeth were first assessed for microbiological (one site/tooth) and then for clinical variables (six sites/tooth). Supragingival irrigation with methylene blue was performed prior to laser application. The microbiological (proportions of obligate anaerobes) and clinical measurements (plaque and gingival indices, bleeding on probing, probing pocket depth) were evaluated over a period of 32 days. RESULTS: Only the SRP/L and SRP groups provided significant reductions in the proportions of obligate anaerobes before and after treatments with no significant differences in between. Parallel to the microbiological changes, both SRP/L and SRP resulted in similar clinical improvements, whereas L alone revealed a limited effect similar to OHI. CONCLUSION: Within the limits of this study, methylene blue/soft laser therapy provided no additional microbiological and clinical benefits over conventional mechanical debridement.