Increased fluoride uptake in human dental specimens treated with diode laser

The hypothesis of this study was the fact that diode lasers can increase the fluoride uptake in dental structures. The main objectives were: (1) to evaluate the effect of diode laser–NaF varnish combination on binding fluoride to dental enamel in an in vitro model and (2) to analyse outer enamel surface changes produced by the laser energy. After NaF enamel varnish and laser irradiation at different levels of energy, specimen surfaces were examined by environmental scanning electron microscopy. The incorporation of F⁻ ion into the dental structure was quantitatively determined by using a fluoride ion-selective electrode. Results showed that the laser treatment significantly increased the binding of fluoride to the enamel surface without damaging it. The amount of F⁻ estimated was 37 ± 7 mg/l to the power of 5 W and 58 ± 12 mg/l to the power of 7 W. These increases were significantly greater than the ones achieved by conventional topical fluoridation. The results were analysed and compared by Kruskal–Wallis and Dunn’s multiple comparison tests, and significant statistical differences were found. These suggest that the NaF varnish–diode laser combination may be a useful option for the effective fluoridation of teeth.     

Temperature change during non-contact diode laser irradiation of implant surfaces

A temperature increase of more than 10°C can compromise bone vitality. Laser radiation with different wavelengths has been used for the treatment of peri-implantitis, but little is known about the effect of laser irradiation on temperature rise on the implant surface. In this study, the temperature gradient (∆T) generated by laser irradiation of implant surface using two diode lasers (810 nm and a 980 nm) with 2 W of power has been recorded by two thermocouples (one in the cervical area and one in the apical area) and studied. The 810-nm diode laser showed the following results: after 60 s of irradiation with 2 W of continuous mode the temperature gradient in the cervical area of the implant (∆Tc) was 37.2°C, while in the apical area (∆Ta) was 27.2°C. The 980-nm diode laser showed the following results: after 60 s of irradiation with 2 W continuous mode ∆Tc was 41.1°C, and ∆Ta was 30.6°C. The 810-nm diode laser with 2 W continuous mode generated a temperature increase of 10°C after only 14 s. The 980-nm diode lasers groups produced a much more rapid temperature increase. In only 12 s, the continuous wave of 980 nm reached the 10°C temperature rise. From the present in vitro study it was concluded that the irradiation of implant surfaces with diode lasers may produce a temperature increase above the critical threshold (10°C ) after only 10 s.     

Effects of different setting of diode laser on the mRNA expression of growth factors and type I collagen of human gingival fibroblasts

The aim of this study was to analyze the influence of non-surgical applications of diode laser (940 nm) on the cell proliferation and mRNA expressions of type I collagen and growth factors in human gingival fibroblasts (GF). Gingival fibroblasts were isolated from human gingival connective tissue of systemically healthy individuals. Cells were treated with different laser parameters as follows; (1) Infected pocket setting (power: 2 W, pulse interval: 1 ms, pulse length: 1 ms, 20 s/cm²); (2) Perio-pocket setting (power: 1.5 W, pulse interval: 20 ms, pulse length: 20 ms, 20 s/cm²); and (3) Biostimulation setting (power: 0.3 W in continuous wave, 20 s/cm²). Proliferation of GF was evaluated after different laser applications using a real-time cell analyzer. Total RNA was isolated on day 2 and cDNA synthesis was performed. Type I collagen, insulin-like growth factor (IGF), vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-β) mRNA expressions were determined with quantitative RT-PCR. In a proliferation experiment, no significant differences were observed in the different laser applications when compared to the control group. Statistically significant increases in IGF, VEGF, and TGF-β mRNA expressions were noted in the laser groups when compared to the untreated control group (p < 0.05). A significant increase in collagen type I mRNA expression was noted in only biostimulation set-up of diode laser (p < 0.05). The results of this study demonstrate that non-surgical laser applications modulate behavior of gingival fibroblasts inducing growth factors mRNA expressions and these applications can be used to improve periodontal wound healing.     

Preserving the Integrity of Oesophageal Stents with Laser Therapy and Argon Plasma Coagulation: An In Vitro Study

. Thermal lasers and argon plasma coagulation are widely used in the treatment of stent overgrowth in patients with advanced oesophageal malignancy. The aim of treatment is to achieve patency while avoiding damage to the prosthesis. This experimental study was designed to determine the power and duration of application that can be safely tolerated by four different types of oesophageal prostheses. Five stents were studied: wall stent; open metal mesh stent (uncovered Ultraflex); covered metal mesh stent (covered Ultraflex); Gianturco (Z-stent); Esophagocoil. Nd-YAG Laser, GaAlAs diode laser and argon plasma coagulation were applied in non-contact mode at gradually increasing power levels and duration and the effects were observed. The use of argon plasma coagulation on Esophagocoil stent seems safe in power settings of 100 W up to 10 s. The diode laser is intermediate in that Gianturco and Esophagocoil stents can withstand pulses of up to 50 W for about 2 s. The Nd-YAG laser is detrimental to most stents at power levels of 20 W. Only the Esophagocoil withstands Nd-YAG pulses of 60 W but only up to 1 s. Wallstent, open and membrane-covered mesh stents perform poorly in that they can only tolerate up to 1.5 s of power at 25 W with the Diode and 1.0 s of power at 20 W with Nd-YAG laser. The use of different thermal modalities on the five stents has indicated safe power limits and duration. Membrane-covered stents are always damaged by thermal laser application unless the membrane is truly transparent. Paper received 23 February 2000; accepted after revision 24 March 2000.     

High-power diode laser at 980 nm for the treatment of benign prostatic hyperplasia: ex vivo investigations on porcine kidneys and human cadaver prostates

Diode laser systems at 980 nm have been introduced for the treatment of lower-urinary-tract-symptoms (LUTS) suggestive of benign prostatic enlargement (BPE). However, the coagulation and vaporization properties are unknown. We therefore aimed to evaluate these properties in ex vivo models in comparison with the kalium-titanyl-phosphate-(KTP) laser. The diode laser treatment was applied to isolated, blood-perfused porcine kidneys and fresh human cadaver prostates (HCPs) at different generator settings. We performed histological examination to compare the depth of coagulation and vaporization. The diode laser showed larger ablation and coagulation characteristics than the KTP laser did. Ablation of the diode laser was found to be 1.79-times (120 W in porcine kidney, P < 0.0001) and 3.0–5 times (200 W in HCP, P < 0.0005) larger. The diode laser created a nine-times (120 W in porcine kidney, P < 0.0001) and seven-times (200 W in HCP, P < 0.0001) deeper necrosis zone. The diode laser vaporization was highly effective ex vivo. Owing to the laser’s deep coagulation zones, in vivo animal experiments are mandatory before the diode laser (980 nm) is applied in a clinical setting, so that damage to underlying structures is prevented.     

Transmission of laser energy and assessment of target temperature in an experimental model of laser balloon angioplasty

The potential application of laser balloon angioplasty (LBA) is limited because of difficulties in temperature control and dosimetry during trans-balloon laser irradiation. An experimental model of LBA was designed to help understand the polymer membrane effects of two materials on tissue temperature. The durability of two types of polymer films with different optical properties, polyethylene terephthalate (PET), a low scattering polymer and polyetheretherketone (PEEK), a high scattering polymer, were examined as potential balloon material. The PEEK film (thickness: 50 μm) was melted and perforated by light from a diode laser (wavelength: 808±10 nm, irradiance: 1469 W cm⁻², mean exposure time: 30±7 s). On the other hand, the PET film with the same thickness was completely intact after 1 min exposure at the same irradiance. Diode laser irradiation was applied to indocyanine green stained human aortic media in three different exposure methods; directly, through the free PET and through the pressed PET film. Temperatures of laser-irradiated specimens were measured using an infra-red thermal camera with an 8–12 μm bandwidth, and corrected for the emissivity of the tissue and the PET film. Results demonstrated underestimation of surface temperature because of low transmittance of radiated intensity through the free PET film and a significant (p<0.001) increase of corrected temperature (δT=169±32°C) through the pressed-PET exposure compared with the direct exposure (ΔT=81±7°C), even though the same laser irradiance (18.6W cm⁻²) was applied for 5s. That is, the tightly PET-covered tissue develops a significantly higher temperature during diode laser irradiation, and this increased thermal effect can be advantageous for laser welding with less power in laser balloon angioplasty.     

Ex vivo and in vivo investigations of the novel 1,470 nm diode laser for potential treatment of benign prostatic enlargement

Perioperative haemorrhage is still the major complication of transurethral resection of the prostate (TURP) for benign enlargement of the prostate. Photoselective vaporisation of the prostate (PVP) with the potassium–titanyl–phosphate (KTP) laser has been shown to achieve instant tissue ablation with excellent haemostatic properties. Our aim was to determine the tissue removal capacity, coagulation and haemostatic property of the novel 1,470 nm diode laser, ex vivo and in vivo. We evaluated two prototype diode laser systems at 1,470 nm in an ex vivo, isolated, blood-perfused, porcine kidney model (n = 5; 10 W–50 W) and in an in vivo investigation of beagle prostate (n = 4; 100 W) to assess vaporisation capacities and coagulation properties at different generator settings. The diode laser evaluation was compared with an 80 W KTP laser in the porcine model. After the laser treatment we performed a histological examination to compare the depth of coagulation and vaporisation. The diode laser system (50 W) showed significantly lower (P < 0.0001) capacities for tissue removal than the 80 W KTP laser (0.96 mm ± 0.17 mm and 5.93 mm ± 0.25 mm, respectively, P < 0.0001), while coagulation zones were significantly (P < 0.001) larger in diode laser-treated kidneys (3,39 mm ± 0.93 mm and 1.27 mm ± 0.13 mm, respectively). In vivo, the diode laser displayed rapid ablation of prostatic tissue with no intraoperative haemorrhage. Histological examination revealed coagulation zones of 2.30 mm (±0.26) at 100 W in the diode laser-treated prostates.     

Comparison of effects of diode laser and CO<Subscript>2</Subscript> laser on human teeth and their usefulness in topical fluoridation

Various authors have reported more effective fluoridation from the use of lasers combined with topical fluoride than from conventional topical fluoridation. Besides the beneficial effect of lasers in reducing the acid solubility of an enamel surface, they can also increase the uptake of fluoride. The study objectives were to compare the action of CO₂ and GaAlAs diode lasers on dental enamel and their effects on pulp temperature and enamel fluoride uptake. Different groups of selected enamel surfaces were treated with amine fluoride and irradiated with CO₂ laser at an energy power of 1 or 2 W or with diode laser at 5 or 7 W for 15 s each and compared to enamel surfaces without treatment or topical fluoridated. Samples were examined by means of environmental scanning electron microscopy (ESEM). Surfaces of all enamel samples were then acid-etched, measuring the amount of fluoride deposited on the enamel by using a selective ion electrode. Other enamel surfaces selected under the same conditions were irradiated as described above, measuring the increase in pulp temperature with a thermocouple wire. Fluorination with CO₂ laser at 1 W and diode laser at 7 W produced a significantly greater fluoride uptake on enamel (89 ± 18 mg/l) and (77 ± 17 mg/l) versus topical fluoridation alone (58 ± 7 mg/l) and no treatment (20 ± 1 mg/l). Diode laser at 5 W produced a lesser alteration of the enamel surface compared to CO₂ laser at 1 W, but greater pulp safety was provided by CO₂ laser (ΔT° 1.60° ± 0.5) than by diode laser (ΔT° 3.16° ± 0.6). Diode laser at 7 W and CO₂ laser at 2 W both caused alterations on enamel surfaces, but great pulp safety was again obtained with CO₂ (ΔT° 4.44° ± 0.60) than with diode (ΔT° 5.25° ± 0.55). Our study demonstrates that CO₂ and diode laser irradiation of the enamel surface can both increase fluoride uptake; however, laser energy parameters must be carefully controlled in order to limit increases in pulpal temperature and alterations to the enamel surface.     

Metrical and histological investigation of the effects of low-level laser therapy on orthodontic tooth movement

The aim of this study was to evaluate the effects of 820-nm diode laser on osteoclastic and osteoblastic cell proliferation-activity and RANKL/OPG release during orthodontic tooth movement. Thirty-eight albino Wistar rats were used for this experiment. Maxillary incisors of the subjects were moved orthodontically by a helical spring with force of 20 g. An 820-nm Ga-Al-As diode laser with an output power of 100 mW and a fiber probe with spot size of 2 mm in diameter were used for laser treatment and irradiations were performed on 5 points at the distal side of the tooth root on the first, second, and 3rd days of the experiment. Total laser energy of 54 J (100 mW, 3.18 W/cm², 1717.2 J/cm²) was applied to group II and a total of 15 J (100 mW, 3.18 W/cm², 477 J/cm²) to group III. The experiment lasted for 8 days. The number of osteoclasts, osteoblasts, inflammatory cells and capillaries, and new bone formation were evaluated histologically. Besides immunohistochemical staining of PCNA, RANKL and OPG were also performed. No statistical difference was found for the amount of tooth movement in between the control and study groups (p > 0.05). The number of osteoclasts, osteoblasts, inflammatory cells, capillary vascularization, and new bone formation were found to be increased significantly in group II (p < 0.05). Immunohistochemical staining findings showed that RANKL immunoreactivity was stronger in group II than in the other groups. As to OPG immunoreactivity, no difference was found between the groups. Immunohistochemical parameters were higher in group III than in group I, while both were lower than group II. On the basis of these findings, low-level laser irradiation accelerates the bone remodeling process by stimulating osteoblastic and osteoclastic cell proliferation and function during orthodontic tooth movement.     

Lipolysis Using a 980-nm Diode Laser: A Retrospective Analysis of 534 Procedures

Background  The safety and efficacy of the 980-nm diode laser for laser lipolysis were evaluated in different body areas. Methods  From June 2005 to June 2007, 334 subjects underwent laser lipolysis. The treatment was performed using a 980-nm diode laser (OSYRIS, Hellemmes, France). After tumescent anesthesia, a 1-mm-diameter microcannula housing a 600-μm optical fiber was inserted into the subcutaneous fat. The cannula was moved back and forth in a predetermined manner to get a homogeneous distribution of energy at the treated area. Laser settings (power and cumulative energy) were selected in relation to individual body areas: 6 W (chin, arm, knee), 10 W (abdomen, back), and 15 W (thigh, hips, buttock). Patient satisfaction was evaluated and side effects were recorded. The laser energy counter incrementally counted the energy used; then the cumulative energy used for each treatment was recorded. Ultrasound imaging was used to control tumescent anesthesia infiltration, cannula position prior to laser emission,and postoperative fat liquefaction. Results  Five hundred thirty-four (534) laser lipolysis procedures were performed on 334 patients. Different areas were treated: hips (197), inner thighs (86), abdomen (86), knees (61), flanks (57), buttocks (28), chin (22), arms (18), back (4). Mean cumulative energy was area–dependent, ranging from a minimum of 2200 J (knee) to a maximum of 51,000 J (abdomen). Contour correction and skin retraction were observed almost immediately in most patients. There was no scarring, infection, burns, hypopigmentation, bruising, swelling, or edema. Ecchymoses were observed in almost all patients but resolved in under 1 week for 322 patients. Patient satisfaction was very high. Because laser lipolysis is an outpatient procedure, patients were able to resume normal daily activities after 24 h. Ultrasound imaging confirmed that the thermal effect generated by the laser results in melting and rupture of the collagenous and subdermal bands. Conclusion  This clinical study demonstrates that the removal of small volumes of fat with concurrent subdermal tissue contraction can be performed safely and effectively using a 980-nm diode laser. Additional benefits include excellent patient tolerance and quick recovery time. This study also confirms that enough accumulated energy must be delivered to achieve sufficient lipolysis throughout different fat layers.     

Experimental Study of Different Laser Systems for PMMA Extraction Within the Scope of Revision Hip Arthroplasty

. Cement removal at revision hip arthroplasty forms a critical step for a successful operation. The removal of polymethymethacrylate (PMMA) with curet and chisel can cause major damage to the femoral shaft. The use of ultrasound or lithotripsy can cause perforation and microfractures to bone tissue. The goal of our study was to evaluate the application and practicability of different laser systems for cement removal. We examined and compared the effects of a diode laser (wavelength λ=800 nm), a Nd:YAG laser (λ=1064 nm), and an Er:YSSG laser (λ=2780 nm) on PMMA and the PMMA–bone interface. Whereas the Nd:YAG laser with a high ablation rate led to severe bone damage with extensive carbonisation, the Er:YSSG laser with a low ablation rate produced a defined cut at the PMMA–bone interface (max. depth 3.70 mm at 6.0 W laser power). Using the diode laser a defined high quality ablation of PMMA at the PMMA–bone interface was possible without any visible damage of adjacent tissue (max. depth 2.75 mm at 2.9 W laser power). However, sufficient ablation in an adequate operating time could not be realised with this power. The use of a laser tool for cement removal is insufficient. It only facilitated the manual removal of the remaining cement with chisel and curet. Paper received 5 November 1999; accepted after revision 27 April 2000.     

Microarterial anastomosis using a noncontact diode laser versus a control study

A series of direct carotid end-to-end laser anastomosis vs. direct manual suture was carried out on a series of 70 Wistar rats (mean weight 260 g). Both common carotids (0.8–1.2 mm) were sectioned and repaired. The left side (n = 70) was submitted to laser-assisted microvascular anastomosis (LAMA) performed by means of a diode laser device (wavelength 830 nm and power output 3 W in continuous wave) without chromophore. The right side (n = 70) underwent a control manual suture (CMA). The diode laser energy was delivered into a micromanipulator coupled to a Zeiss operating microscope with a focused spot of 300 μm in diameter. After placement of three 10.0 stitches for edge coaptation, the LAMA was achieved using laser shots (average 3) of 500 mW power, 4.5 s duration, and 700 W/cm² irradiance each. The CMA was performed by means of six 10.0 stitches. The good vascular flow was confirmed by Doppler spectral analysis (n = 466) carried out from day 0 to day 90. Light and scanning electron microscopy (n = 82) showed that re-endothelialization after LAMA was gaining ground on day 3, whereas collagenous network developed in the media scar by day 10. In contrast, after CMA the arterial repair was delayed on day 20, inducing a media fibrotic scar. The patency rate was 93% in both anastomoses. The shorter operating time (13 min for LAMA vs. 22 min for CMA) and the noncontact laser technique are the main intraoperative advantages. The technical benefits of the diode laser are pointed out. © 1994 Wiley-Liss, Inc.     

Effects of diode laser therapy on blood flow in axial pattern flaps in the rat model

. Axial pattern skin flaps are a very important reparative tool for the plastic and reconstructive surgeon in the reconstruction of tissue defects. From whatever unfortunate reason, part or all of such flaps occasionally suffers from irreversible ischaemia with loss of the flap. Infrared diode laser therapy has been shown to improve local and systemic circulation. The present study was designed to assess the effect of an 830 nm diode laser (power density, 18.5 W/cm², energy density 185 J/cm²) on the blood flow of axial pattern flaps in the rat model and their survival, compared with unirradiated controls. The flaps were raised in all animals (n=40), and blood flow assessed with laser speckle flowmetry (LSF). In the experimental groups (3 groups, n=10 per group), the flaps were irradiated either directly over the dominant feeder vessel (iliolumbar artery), at the proximal end or at the distal end of the flap itself and blood flow assessed during irradiation. Flowmetry was performed again in all animals at 5 and 10 min postirradiation, and the flaps sutured back in position. The unirradiated controls were handled in exactly the same way, but the laser was not activated. The survival rate of the flaps was assessed on the fifth postoperative day. LSF demonstrated significant increased blood flow in the flaps at 5 and 10 min postirradiation in all experimental groups compared with the control animals. At five days postirradiation, there was significantly better survival of the flaps in all the experimental groups compared with the controls (p<0.01), but no significant difference was seen between any of the experimental groups. We conclude that laser therapy increases the blood flow and perfusion of transferred flaps, and that this has significant effects on the survival of the flaps. One possible mechanism of modulation of the autonomic nervous system is discussed. Paper received 19 March 2001; accepted after revision 28 September 2001.     

Temperature evolution on human teeth root surface after diode laser assisted endodontic treatment

The thermal rise threshold of an 810-nm semi-conductor diode laser on the root surface when used in root canals in vitro for laser assisted root canal treatment is investigated in this study. A total of 50 human single-rooted extracted teeth were included. For this study, the canals were enlarged up to an apical size of ISO#50 file. Laser irradiation was performed with six different settings. Specimens were irradiated at 0.6–1 W output power at the distal end of the fiber and about 1–1.5 W output power in the continuous mode (CW) as two groups. In the third group, 0.6–1 W output power, 10 ms pulse length (PL) and 10 ms interval duration (ID) were selected. In three other groups 1–1.5 W output power were used with different PL and ID as following: PL 10 and ID 10 ms, PL 10 and ID 20 ms and PL 20 and ID 20 ms. The total irradiation time was from 5 to 20 s per canal with a 200 m in diameter and 25 mm long tip. After laser treatment, the temperature changes at the outer root surface were registered by means of NiCr-Ni measuring sensors and a T 202 thermometer. The safe temperature threshold for applying this diode laser in root canal is considered as 7°C increase. To avoid increasing the temperature changes at the outer root surface related to this threshold, following total irradiation times were found: 0.6–1 W output power (10 ms PL/10 ms ID): 20 s (s), 1–1.5 W output power (10 ms/10 ms and 20 ms/20 ms): 15 s, 0.6–1 W output power CW and 1–1.5 W output power (20 ms PL/10 ms ID): 10 s and 1–1.5 W output power CW: 5 s. In the first three groups, 5 s irradiation and 5 s rest period avoided a temperature increase above the threshold of 7°C).     

Laser phototherapy effect on protein metabolism parameters of rat salivary glands

The aim of this study was to evaluate the effects of infrared diode laser phototherapy (LP) on tissues of the submandibular gland (SMG) and parotid gland (PG). Wistar rats were randomly divided into experimental (A and B) and control (C) groups. A diode laser, 808 nm wavelength, in continuous wave mode, was applied to the PG, SMG and sublingual gland in the experimental groups on two consecutive days. The doses were 4 J/cm² and 8 J/cm², and total energy was 7 J and 14 J, respectively. The power output (500 mW) and power density (277 mW/cm²) were the same for both experimental groups. In order to visualize the area irradiated by the infrared laser, we used a red pilot beam (650 nm) with 3 mW maximum power for the experimental groups. For the control group, the red pilot beam was the only device used. The SMG and PG were removed after 1 week of the first irradiation. Total protein concentration, amylase, peroxidase, catalase and lactate dehydrogenase assays were performed, as well as histological analysis. Statistical tests revealed significant increase in the total protein concentration for groups A and B in the parotid glands (P < 0.05). Based on the results of this study, LP altered the total protein concentration in rats’ parotid glands.     

Influence of different power densities of LILT on cultured human fibroblast growth

The aim of this in vitro study was to analyze the influence of different power densities of low-intensity laser therapy (LILT) on the biomodulation of human gingival fibroblasts. The cells were cultured in nutritional deficit. Laser irradiation was carried out with a GaAlAs diode laser (λ-660 nm, 2 J/cm²). The irradiation was done twice with 12-h interval using the punctual technique, at continuous mode and in contact. The experimental groups were: I, control, nonirradiated; II, power of 10 mW and intensity≅142.85 mW/cm²; III, 29 mW and 428.57 mW/cm². Growth curves were obtained by using the trypan blue dye exclusion assay. The cell growth of the irradiated groups was significantly higher than control group (P≤0.05). The cultures of Group II presented cell growth superior to that of Group III. Based on the conditions of this study, we concluded that the power density influences cell growth in an inversely proportional manner.     

Near infra-red diode laser for photodynamic tumour therapy using bacteriochlorina

Clonogenic cell survivals were performed in order to assess the feasibility of tumour cell kill with an experimental diode laser emitting 250 mW of light at λ = 779 nm using the photosensitizer bacteriochlorina(BCA). The AlGaAs diode laser is based on organometallic vapour epitaxial crystal growth technology. The electrical to optical conversion efficiency amounts to 21% and the beam divergence is 47° by 7.0° full width at half maximum. BCA was proved to be an effective non-toxic photosensitizer in vitro and in vivo. It has a major absorption peak at 760 nm where tissue penetration of light is optimal. Clonogenic T24 human bladder carcinoma cell survivals were photosensitizer concentration and light dose dependent. A 0.1% survival rate was obtained with an illumination intensity of 50 mWcm⁻² for 90 s (4.5 Jcm⁻²) and a BCA concentration of 6 μgml⁻¹. Illumination without BCA at energy levels exceeding the PDT levels with a factor 10, or BCA alone without illumination had no effect on the cells in the clonogenic cell survivals. The combination of BCA with a near infra-red diode laser is most promising for photodynamic tumour therapy as a result of the reliability, compactness and relatively low price of the illumination device, the high transmittance of near infra-red light in tissue and the tumour killing potential of BCA.     

Atomic force microscopy and transmission electron microscopy analyses of low-temperature laser welding of the cornea

Low-temperature laser welding of the cornea is a technique used to facilitate the closure of corneal cuts. The procedure consists of staining the wound with a chromophore (indocyanine green), followed by continuous wave irradiation with an 810 nm diode laser operated at low power densities (12–16 W/cm²), which induces local heating in the 55–65 °C range. In this study, we aimed to investigate the ultrastructural modifications in the extracellular matrix following laser welding of corneal wounds by means of atomic force microscopy and transmission electron microscopy. The results evidenced marked disorganization of the normal fibrillar assembly, although collagen appeared not to be denatured under the operating conditions we employed. The mechanism of low-temperature laser welding may be related to some structural modifications of the nonfibrillar extracellular components of the corneal stroma.     

Laser-induced thermotherapy for lung tissue—evaluation of two different internally cooled application systems for clinical use

Thermal ablation techniques like radiofrequency or laser-induced thermotherapy (LITT) are increasingly used to treat tumors of parenchymatous organs. Minimal access, parenchymal preservation, and a low complication rate render them suitable for pulmonary tumors as well. Their successful clinical application depends on the induction of sufficiently large lesions and a knowledge of the energy parameters required for complete thermal ablation. The aim of this study was to establish a dose–response relationship for a percutaneous and an intraoperative system for LITT of lung tissue. Thermal lesions were induced in healthy porcine lungs using an Nd:YAG laser (1,064 nm). LITT was performed with a percutaneous application system in group I (n = 18) and an intraoperative application system in group II (n = 90). Laser energy was applied for 600–1,200 s in a power range of 20–32 W (12,000–38,400 J). The lesions were longitudinally and transversally measured, and the volume was calculated after the intervention. Furthermore, an open application system was used to perform LITT under in vivo conditions during lung perfusion and ventilation in domestic pigs. Lesion volumes in both groups showed a plateau-like curve when the laser power increased from an initial level of 25 W. With the percutaneous puncture system (group I), the application of 28 W (16,800 J) for 10 min generated the largest lesions with a volume of 12.54 ± 1.33 cm³, an axial diameter of 39.33 ± 2.52 mm, and a diametrical diameter of 24.67 ± 1.15 mm. A longer application time was not possible due to thermal instability of the applicator. Moreover, group I started developing extensive carbonizations at a laser power of 22 W (13,200 J). The intraoperative application system (group II) achieved the largest lesion volumes of 11.03 ± 2.54 cm³ with diameters of 34.6 ± 4.22 mm (axial) and 25.6 ± 2.51 mm (diametrical) by an exposure time of 20 min and a power of 32 W (38,400 J). Here extensive carbonizations only started to occur at 28 W (33,600 J). Under in vivo conditions, all pigs tolerated the LITT procedure well without complications. Besides a typical cooling effect in the vicinity of blood vessels, the thermal lesions were about three times smaller than the ex vivo lesions. Both the percutaneous and the open LITT application system induced reproducible, clinically relevant lung lesions. The percutaneous puncture set generated large relevant lesions, although its usability is limited by its restricted capacity and high carbonization risk. It is suitable for powers up to 22 W. The intraoperative application system allows higher energy exposure to induce larger lesion volumes. This study elucidates the dose–effect relation of two clinically relevant puncture sets.     

Muscular Trauma Treated with a Ga-Al-As Diode Laser: In Vivo Experimental Study

The aim of the study was to verify in an experimental model the effects of laser therapy performed with Ga-Al-As diode lasers (780 nm, 2500 mW) on traumatised muscles. Forty adult New Zealand male rabbits were divided into four groups (A, B, C and D) of ten animals each. Each group of animals was further divided into two subgroups of five animals each. The animals were submitted to muscular trauma for 7 min by clamping the posterior muscles of the left thigh under general anaesthesia. Four days later, the rabbits in the B₁, B₂, C₁, C₂, D₁ and D₂ subgroups started daily laser therapy. The parameters utilised were: 150 J/cm² energy density, 3 W, 50 Hz in group B; 250 J/cm², 3 W, 100 Hz in group C; and 800 J/cm², 3 W, 0 Hz (continuous output) in group D. The animals in subgroups A₁ and A₂ were used as untreated controls and allowed to heal spontaneously. In order to prepare samples for histological, histochemical and histomorphometrical studies, dissection of the posterior muscle of the thigh was performed under general anaesthesia and before sacrifice, after five days of laser therapy in the subgroups B₁, C₁ and D₁ and after ten days of laser therapy in subgroups B₂, C₂ and D₂. The samples of untreated subgroups A₁ and A₂ were subjected to the same procedure and at the same times as the corresponding laser-treated groups. The following parameters were analysed on muscular samples: qualitative histological aspect (lactate dehydrogenase (LDH), cytochrome oxidase, acid phosphatase and alkaline phosphatase concentration with histoenzymatic methods) and quantitative histomorphometric evaluation of muscular damage and tissue repair. Blood samples were drawn from each subgroup before the trauma and again before sacrifice to measure the creatine phosphokinase (CK) and LDH levels. The results obtained in the tables are shown. Analysis of the results showed a better qualitative and quantitative healing process in traumatised muscles treated with Ga-Al-As diode laser therapy than in spontaneously healed ones. The results obtained with laser therapy were confirmed as haematic, histoenzymatic and histomorphometric values. According to these results, there is a positive relationship between the biostimulation properties of the laser and the healing of traumatised muscular tissue. Received for publication 15 August 1997; accepted following revision 17 March 1998