Enhancement of transepidermal skin clearing agent delivery using a 980 nm diode laser.

BACKGROUND AND OBJECTIVES: Patient compliant optical skin clearing requires non-invasive topical delivery of clearing agents such as glycerol. This requires reducing the skin barrier function by disrupting stratum corneum integrity, which was achieved using a 980 nm diode laser with artificial absorption substrates on the skin surface. Reduction of light scattering has the potential to improve many current and novel diagnostic and therapeutic applications of lasers in medicine. STUDY DESIGN/MATERIALS AND METHODS: In vivo hamster and rat skin was used to test optical skin clearing. Absorption substrates were applied to the skin after shaving. These included black ink, dark children's rub-on tattoo, and carbon paper. 980 nm cw laser light was used to ablate these substrates and to heat the skin surface to enhance the diffusion of topically applied glycerol for optical skin clearing. Increased light penetration was determined from amplitude optical coherence tomography data. RESULTS: Results indicate an improvement of the ability to measure an OCT signal at a wavelength of 1,290 nm up to 42% deeper into in vivo rodent skin using a 980 nm laser with a fluence of less than 0.96 J/mm(2) to alter the stratum corneum. CONCLUSIONS: The use of an inexpensive diode laser can significantly enhance the delivery of topically applied glycerol for optical skin clearing. The laser use involves application of an absorption substrate onto the skin surface. Using carbon paper left no unwanted residue behind and is considered optimal for this purpose.

Measurement of Acoustic Transients During Pulsed Holmium:YAG Laser Ablation of Cadaveric Human Temporal Bone.

Pulsed infrared (IR) and ultraviolet (UV) lasers have been suggested for use in middle ear surgery due to potential fiberoptic delivery, decreased thermal trauma and precise ablation characteristics. Although attention has been focused on the thermal and photoacoustic events that occur during pulsed laser ablation of hard tissue, there are few studies which evaluate the acoustic energy generated from these devices from an audiological standpoint. In this study, the mastoid cavities of cadaveric human temporal bones were irradiated with a holmium: yttrium aluminium garnet (Ho:YAG) laser (λ=2.12 µm) using the following parameters: 5, 10, and 15 Hz pulse repetition rate and 1, 2, 4, 6, 8, and 10 W average power. During ablation, acoustic measurements were made using a sound level meter positioned 5 cm away from the target site. With each set of laser parameters, the sound intensity exceeded 85 dB (dBA scale). Peak intensities of 125 dB were measured, and a saturation effect noted above 4 W or 500 mJ/pulse. The clinical significance of these findings is discussed and the acoustical aspects of middle ear function and noise trauma are reviewed.

XeCl laser surgery of the vocal cords: a histologic comparison with CO2 laser in a porcine model.

Fresh cadaveric pig larynxes were ablated with a CO2 (lambda = 10.6 microm) and a XeCl excimer (lambda = 308 nm) laser. Histologic comparison of the ablation craters created by the two lasers was performed, and ablation crater depth and marginal tissue damage were measured. Crater depth for both laser treatments is correlated with energy deposition and exposure time. The CO2 laser creates three times more nonspecific, marginal tissue damage than the XeCl laser at the ranges of total energy and exposure times used. This study demonstrates the potential of the XeCl laser as an alternative to the CO2 laser in microlaryngeal surgery.

Surface temperature distributions in carbon dioxide, argon, and KTP (Nd:YAG) laser ablated otic capsule and calvarial bone.

HYPOTHESIS: The spatial and temporal surface temperature distribution was measured after laser irradiation in fresh porcine otic capsule and calvarial bone tissue using an HgCdTe (mercury-cadmium-tellurium) infrared camera. BACKGROUND: Carbon dioxide (CO2) (lambda = 10.6 mm), argon (lambda = 514 nm), and Potassium-Titanyl-Phosphate Neodynium: Yttrium-Aluminum-Garnet (KTP[Nd:YAG]) (lambda = 532 nm) lasers are used for stapes surgery and in the treatment of chronic ear disease. Despite extensive clinical use, little is known about the thermal perturbations in otic capsule calcified tissues and what are safe energy parameters for laser use. METHODS: A microspot manipulator, lens, and microfiber were used for continuous wave (CW) and super-pulse (SP) CO2, argon, and KTP(Nd:YAG) lasers, respectively. Peak temperatures after ablation were measured simultaneously along with the full-width--half-maximum of the thermal disturbance and fitted to a Gaussian distribution. The cooling time for the hot spot to return to ambient temperature also was recorded. RESULTS: Temperature changes with CW CO2 irradiation were markedly elevated relative to SP mode and also required longer to cool. The KTP and argon-treated bone were irradiated in the presence and absence of an initiator (black ink): minimal surface temperature elevation was recorded in the absence of an initiator. Further, no surface modification was observed. In contrast, the addition of an initiator resulted in marked temperature elevations and significant surface carbonization with these two visible wavelength lasers. Cooling times varied from 10-40 seconds. No consistent relation to the measured thermal values and tissue microarchitecture was observed. CONCLUSIONS: The measured cooling times and Gaussian distribution of surface temperatures serve as empiric guidelines for minimizing thermal injury to critical structures during laser surgery in the middle ear.

The influence of laser parameter configurations at 9.3 microns on incisional and collateral effects in soft tissue.

These investigations were performed to determine histologic and incisional consequences of varying pulse duration, duty cycle, and average powers during laser incision at 9.3 microns in soft tissue. In 19 fresh pigs' jaws six standardized incisions 3 cm long were made per parameter with a template and motorized jig. Laser parameters investigated were average power: 1 to 9 W, duty cycle: 10% to 80%, and pulse duration: 1 to 200 msec. The gated Cw mode was used. Incision width and depth and collateral tissue effects were assessed statistically with general linear procedures. Multiple factors were found to influence the outcome of laser irradiation. Depth of incision correlated positively with average power. Tissue damage correlated strongly and negatively with all three variables. These results demonstrate that a wide range of surgical and collateral effects can be achieved with one specific laser device depending on the parameter configuration selected.

Ablation of human nail by pulsed lasers.

BACKGROUND AND OBJECTIVE: The hard and resistant structure of the nail plate forms a natural barrier that limits the penetration of topical drugs. To overcome this barrier, the use of pulsed laser systems has been suggested. The purpose of this study was to evaluate the effect of four laser systems on nail plate ablation rates, ablation efficiencies, and subsequent craters morphology. STUDY DESIGN/MATERIAL AND METHODS: Solid state Er:YAG (2.94 microns, 250 microseconds), a Ho:YSGG (2.08 microns, 250 microseconds), a XeC1 Excimer (308 nm, 15 ns), and a novel solid-state ultrashort pulse laser (1.05 microns, 350 fs) were used. Ablation rates, surface morphology, and extent of collateral damage were evaluated using light and electron microscopy. RESULTS: Best ablation efficiencies were demonstrated with the ultrashort pulsed laser (1 micron/mJ), whereas maximum material removal per pulse was obtained with the Er:YAG laser (80 microns/ pulse). Scanning electron microscopy showed cracking damage with both Ho:YSGG and Er:YAG. XeC1 and the ultrashort pulse system left tissue surfaces free of cracks or thermal damage. CONCLUSION: With its minimal acoustical and mechanical impact, high efficiency, and negligible collateral damage, the ultrashort pulse laser at 3 J/cm2 was found to be the optimal laser system for nail ablation.

Thermal imaging of the temporal bone in CO2 laser surgery: an experimental model.

The unique properties of lasers create an enormous potential for specific treatment of chronic ear disease. Despite the widespread acceptance and use of the laser, however, a complete understanding of the time- and space-dependent temperature distribution in otic capsule bone immediately after pulsed laser exposure has not been elucidated. Using a liquid nitrogen-cooled mercury-cadmium telluride infrared detector, the temperature distribution in human cadaveric otic capsule bone was determined immediately after pulsed (100 msec) carbon dioxide laser exposure (0.3 to 4.0 W; 200 microm spot diameter). The time- and space-dependent temperature increases and thermal diffusion were determined as a function of the laser power density and were found to vary linearly.

Effect of XeCl-308nm excimer laser on the mineral content of human dentin.

The effect of the XeCl-308nm excimer laser on the mineral content and surface morphology of cut dentin was examined in ten extracted human teeth. Each dentin specimen was lased for 4 s at a fluence of 1 J/cm2 and a frequency of 25 Hz. Non-lased area of the same specimen served as control. Scanning electron microscopy and energy dispersive spectrometry revealed a significant decrease in the phosphorus levels following laser treatment. A decrease in calcium levels also occurred but was not statistically significant. Nonsignificant changes in sulphur and potassium levels were also noted. Morphologically, the lased dentin showed an apparently melted surface with partial obstruction of the dentin tubules as well as cracks along the lased surface. Therefore, it appeared that laser treatment may alter the chemical structure as well as the surface morphology of the dentin.

Identification of photoacoustic transients during pulsed laser ablation of the human temporal bone: an experimental model.

Laser ablation of hard tissues during neurotologic operations has been accomplished with continuous-wave (CW) lasers in the visible and midinfrared spectrum. The mechanism of ablation at these wavelengths is secondary to photothermal-induced tissue destruction. As a result, significant thermal damage to surrounding tissue may occur. Pulsed ultraviolet (UV) lasers have been suggested as an alternative to the argon, KTP-532, and CO2 lasers currently used in clinical practice. The pulse length of Excimer lasers are considerably shorter than the thermal diffusion time of bone tissue, and as a consequence thermal injury is minimal. This makes pulsed lasers an attractive tool for tissue ablation in the ear: in essence a "cold knife." However, the short pulse width of Excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen. This study identifies the presence of these photoacoustic waves during the Excimer laser treatment of the cadaveric human temporal bone. A XeCl (lambda = 308 nm, tau p = 12 ns) excimer laser was used to ablate hard tissue surrounding the oval window and facial ridge with energies of 75, 45, 25, and 12 mJ/pulse. Spot size was estimated to be 0.5 mm2. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the promontory, round window niche, and facial ridges. The signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope. Photoacoustic waves were clearly identified. Notably, large acoustic waves were measured on the promontory and on both sides of the facial ridge. The implications and clinical relevance of these findings is discussed and compared to findings obtained from a model system.

Dentin ablation with three infrared lasers.

BACKGROUND AND OBJECTIVE: Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics. STUDY DESIGN/MATERIALS AND METHODS: Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns. RESULTS: The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system. CONCLUSION: Possible explanation for these observations is given in terms of plasma characteristics.

Two-lasers assisted ablation: a method for enhancing conventional laser ablation of materials.

A new method for enhanced ablation by pulsed laser radiation has been demonstrated. The method utilizes an "impulse" ablation laser in conjunction with cyclical heating of the tissue by an auxiliary source: the "primer." In this study we use an auxiliary laser as the "primer" heat source, which sets up a thermal and stress field modulation in the target material. The cyclical stress associated with the thermal modulation reduces material strength thus enhancing ablation (larger mass removed per pulse) by the "impulse" laser. Ablation rate enhancement of more than twice the single-laser value is demonstrated.

Efficacy of XeCl-308 excimer laser in fusing hydroxyapatite to seal the root apex.

Sealing the root apex during apical surgery is important for a successful outcome. The effect of XeCl-308 nm excimer laser irradiation on the fusion and seal of hydroxyapatite to the root apex was tested in extracted human teeth. Twenty-four roots of intact single-rooted premolars were instrumented to size 30 K-file at the apex leaving a patent apical foramen. The apex of each tooth was covered with a freshly prepared paste of hydroxyapatite powder mixed with saline. The samples were then divided into two groups. In 12 teeth, the apical area was irridiated with XeCl-308 nm excimer laser at a fluence of 0.7 J/cm2 for 5 s with pulse repetition rate of 25 Hz and a spot size of 0.13 cm2 immediately after the hydroxyapatite application. In the other 12 teeth, no laser treatment was performed after the hydroxyapatite application. The roots were mounted on a model for the detection of radicular leakage of hydrogen peroxide. The hydrogen peroxide leakage of each sample was measured and the difference between the test groups compared. The ability of the hydroxyapatite plug to prevent hydrogen peroxide leakage at the apex was also tested by applying compressed air from the triple syringe on the coronal access preparation for 2 min. Apical leakage was found in four teeth in the lased group and in eight teeth in the non-plased group. However, the difference between the groups was not statistically significant. Compressed air applied to the coronal access caused hydrogen peroxide leakage in all the teeth.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental competence of mouse embryos following zona drilling using a non-contact holmium:yttrium scandian gallium garnet (Ho:YSGG) laser system.

The purpose of this study was to assess the efficacy of the holmium:yttrium scandian gallium garnet (Ho:YSGG) laser, operating in a pipette-free, non-contact mode, to assist hatching and sustain normal embryonic development. Two-cell mouse embryos were recovered and assigned to laser-assisted hatching (LAH) treatment or control human tubal fluid (HTF) culture with or without serum (HTF-s, HTF-o) or with late serum supplementation (HTF-o/s). The basic experimental apparatus for LAH consisted of a stationary 2.1 microns Ho:YSGG laser beam directed through a mechanical shutter into an input port of a Zeiss Axiomat inverted microscope. Fewer (P < 0.05) embryos developed to the blastocyst stage in the HTF-s group (81%) than in the LAH (90%), HTF-o (94%) and HTF-o/s (92%) groups. The level of hatching was significantly increased (P < 0.01) after the LAH treatment (57%) compared to HTF-o/s (32%), HTF-s (18%) or HTF-o (5%). Implantation rates were not significantly impaired following the LAH treatment (21%). These data demonstrate that LAH using the Ho:YSGG laser is a simple, accurate and effective procedure for assisted hatching.

Efficacy of XeCl 308-nm excimer laser in reducing dye penetration through coronal dentinal tubules.

The efficacy of XeCl excimer laser irradiation in reducing dye penetration through human coronal dentinal tubules was studied. The roots of 20 freshly extracted human molars were resected, and the apical aspect of the crowns was ground until the pulp chamber was completely exposed. Following total removal of the pulp chamber and further grinding of the occlusal and apical surfaces up to the intact dentin, the teeth were randomly divided into experimental and control groups of 10 each. The teeth in the experimental group were completely coated with nail polish and then irradiated with XeCl 308-nm excimer laser at a fluence of 0.7 J/cm2 to form an elliptical lased area. The teeth in the control group were also coated with nail polish, but with a similar elliptical spot of exposed dentin corresponding to the irradiated spot created in the lased teeth left uncoated. All specimens were placed in 0.5% methylene blue dye for 48 h, rinsed, and air-dried. The specimens were then ground to reach the experimental area in order and photographed. The total area of penetrated dye was determined by three independent evaluators and then measured with a computerized planimeter. The mean total areas (mm2) measured in the lased specimens were significantly smaller than those in the controls (p = 0.012).

Assisted hatching in mouse embryos using a noncontact Ho:YSGG laser system.

PURPOSE: A noncontact holmium:yttrium scandium gallium garnet (Ho:YSGG) laser system has been designed and tested for the micromanipulation of mammalian embryos. The purpose of this preliminary investigation was to determine the effectiveness of this laser for assisted hatching and evaluate its impact on embryo viability. The Ho:YSGG system, utilizing 250-microsecond pulses at a wavelength of 2.1 microns and 4 Hz, was used to remove a portion of the zona pellucida (ZP) of two- to four-cell FVB mouse embryos. RESULTS: In the first experiment there was no difference in blastocyst production or hatching rates following laser or conventional assisted hatching (LAH or AH, respectively) in contrast to control embryos cultured in a 5% CO2 humidified air incubator at 37 degrees C. In the second experiment a blastocyst antihatching culture model was employed and LAH-treated embryos were cultured in a serum-free HTF medium (HTF-o). Blastocyst formation was not influenced by LAH treatment and hatching was increased (P < 0.01) from 4 to 60% compared to HTF-o control group. CONCLUSIONS: These preliminary data demonstrate the utility and nontoxic properties of the Ho:YSGG laser system for quick and precise ZP drilling.

Opening of the mouse zona pellucida by laser without a micromanipulator.

A contact-free laser system is described for ablation of the embryonic mouse zona pellucida using a pulsed excimer 308 nm laser. Effects on further embryonic development were evaluated. Zonae of 8- to 16-cell mouse embryos were either lased (n = 189), zona-drilled with acidified Tyrode's solution (n = 183) or left zona-intact (n = 188). Blastocyst formation (99-100%) was similar in the three groups. Hatching occurred earlier in lased embryos compared to those of the control group. These blastocysts hatched through the laser ablated area. Significantly more embryos were hatching on day 4 in the conventionally drilled group when compared to the laser treated group (50% versus 24% respectively). On day 7 of development, significantly (P < 0.05) more embryos conventionally zona-drilled (37%) were intact than those which were previously laser treated (10%). Abnormal development was also noted in a small group of embryos which were lased just on the outside of the zona in comparison to 1/3 of an embryonic width away from the zona. The current results suggest that apparently precise zona laser ablation with an excimer laser at 308 nm may have potential adverse effects which may only be manifested after a prolonged period of culture past the cavitation stage. However, implantation rates of morphologically normal laser abalated embryos were not impaired when compared to control embryos.

Sealing of human dentinal tubules by XeCl 308-nm excimer laser.

Root hypersensitivity occurs as a result of exposed dentinal tubules. Various methods and materials have been tried in an attempt to occlude these tubules. The purpose of this investigation was to study by scanning electron microscope the effects of XeCl excimer laser on exposed dentinal tubules of human extracted teeth. Fifteen 3-mm-thick slices were cut at the cementoenamel junction from 15 extracted human teeth by an electric saw. By using a diamond bur to remove the cementum layer the dentinal tubules were exposed. Each slice was scored by a permanent marker into four equal quadrants. Three of the quadrants were lased for 4 s by XeCl excimer laser with fluences ranging from 0.5 to 7.0 J/cm2 and pulse repetition of 25 Hz. The unlased quadrant served as control. The specimens were mounted on a stub, sputter coated by gold, and examined by scanning electron microscope. Nonlased surfaces showed numerous exposed dentinal tubules. In contrast, all specimens lased at fluences of up to 1 J/cm2 showed the presence of melted dentin which closed the dentinal tubules. At fluences of 4 J/cm2 and higher, rupture of molten materials and exposure of dentinal tubules were noted. The results indicate the application of XeCl excimer laser at specific fluences can cause melting of dentin and closure of exposed dentinal tubules.

Effects of the XeCl excimer laser on Streptococcus mutans.

The effect of XeCl excimer laser irradiation on the growth of Streptococcus mutans in liquid media and on agar plates was studied. Bacterial suspensions of S. mutans were placed in 96 wells of well culture plates. The contents of 72 wells (three experimental groups of 24 wells each) were lased for different time durations (2, 4, and 8 s). The remaining 24 wells were left unlased to be used as controls. Samples were withdrawn from all wells and examined for surviving bacteria. In addition, blood agar plates were inoculated with S. mutans and were lased with different energy densities (fluences). Zones of bacterial inhibition were measured. Analysis of variance test was used to determine statistical differences. The bactericidal effect of the laser applications was directly related to the amount of radiation time. Laser irradiation for 4 and 8 s resulted in bactericidal effect that was statistically significant compared with no treatment or to 2-s exposure. The effect of different energy levels was studied by irradiating inoculated blood agar plates. The zones of inhibition produced by higher energy levels (0.5 J/cm2, 0.7 J/cm2, and 1.0 J/cm2) were larger in comparison to the lowest fluence used (0.1 J/cm2). Application of the laser to the surface of the agar plates produced an indentation with a surrounding halo. The indentations and the zones of inhibition were more pronounced as the fluences increased. Based on our results it appears that the XeCl 308-nm excimer laser can kill S. mutans. This effect should be tested on other bacteria commonly present infected root canals.

Microinjection of FITC-dextran into mouse blastomeres to assess topical effects of zona photoablation.

The objective of the current experiments was to investigate whether all or only some blastomeres from precompacted mouse embryos were affected by zona photoablation. The microbeam of xenon chloride excimer laser (308 nm) was guided through an inverted microscope (non-contact system). Topical effects of lasing were determined by microinjection of a vital fluorescent dye of high molecular weight (fluorescein isothiocyanate [FITC] dextran) into the cell immediately adjacent to the site of zona photoablation. This dye is only passed onto daughter blastomeres and therefore allows study of specific cell lines. Embryonic growth was assessed following cell separation at the morula and blastocyst stage. Four-cell embryos treated with the laser had significantly fewer cells 12 h after zona photoablation than control embryos. A similar effect was noted after 24 h between dye injected embryos and those injected and lased simultaneously, indicating potential toxic effects of the laser treatment on the embryo. Effects on the blastomere closest to the site of ablation were evaluated by calculating the ratio of dyed cells to the total number of cells at specific time intervals. The ratios were similar in the dye and laser+dye groups of treated 4-cell embryos 36 h after treatment (0.22 and 0.23, respectively), indicating that the dye was still present in approximately 25% of the cells and that the negative effect of photoablation was evenly distributed among the blastomeres. It is concluded that zona photoablation may have long-term detrimental effects of a non-topical nature on precompacted mouse embryos in spite of the apparent precision of the laser spot size.