Lased Area Research Articles

Disintegrin-Integrin Binding for Attachment of Polymer Substrate to the Retina.

Objective:We propose a novel attachment method for retinal tissue that utilizes silicone modified with bioactive molecules.Design:This is an experimental study divided into an in vitro section performed in cadaveric pig eyes and an in vivo section performed in rabbits.Subjects:During in vitro experiments 36 cadaveric pig eyes were used. During in vivo experiments 4 rabbits were used.Methods:Different types of silicone went through a laser irradiation process to determine if binding sites for disintegrins could be created. Laser treated silicones that showed disintegrin binding were evaluated with in vitro testing for retina-silicone attachment. The best silicone binding in vitro was implanted into a rabbit’s eye after a full vitrectomy was performed. Post-operative exams were done every two weeks to evaluate placement, attachment and sterilization method. After three months animals were euthanized and eye was enucleated for histology analysis.Main Outcome Measures:Attachment strength between silicone-disintegrin-retina, and signs of endophthalmitis during in vivo studies for biocompatibility purposes.Results:A technique to successfully lase and produce an active area on the silicone surface was described. Scanning electron microscope (SEM) images were evaluated to assess physical ablation/debris field area on the surface, definition of edges, evenness, and symmetry of the lased area allowing us to select MED 4800 silicone family for further testing. Cell culture experiments showed disintegrin binding to the silicone active area. In vitro experiments with cadaveric eyes were performed to test retina-silicone attachment. MED 4860 showed strongest attachment to the retina and it was used during in vivo experiments. A sterilization protocol was tested and proved to be reliable for bioactive materials. Disintegrin coated silicone showed attachment in 2 of 4 rabbits during the 3-month implant period. The adhesion was persistent until reversed with plasmin. All rabbits were implanted for 3 months regardless of attachment, to test the feasibility of the sterilization method. None of the rabbits developed any type of eye infection during the implant period.Conclusion:We successfully lased and produced an active area on the silicone surface to allow disintegrin-silicone binding. Different silicones interact differently with the laser energy, and this is reflected in the strength of the silicone-disintegrin-retina attachment.

Optically pumped lasing in solution-processed perovskite semiconducting materials: Self-assembled Fabry–Pérot microcavity

Optically pumped lasing has been observed in solution-processed perovskite semiconducting materials, CH3NH3PbX3 (X = Cl, Br, I). Self-assembled Fabry–Pérot (FP) cavities have been easily obtained by using a simple “cast-capping method”, where we can obtain single-crystal-like optical cavities. The observed spectra show clear multimode lasing of the FP cavities under pulsed optical excitation. The mode intervals are well explained by the optical constants with large dispersions of the materials. The obtained refractive index around the lasing area coincides with the results in the previous reports.

Subablative Er:YAG Laser Effect on Enamel Demineralization

Objectives: To characterize the cariostatic potential of a low-energy Er:YAG laser treatment. Methods: Twelve sound premolars were selected. Two 2 × 1 mm windows were created on each tooth and randomly assigned to L₁ and L₂ groups. Three sites in each window were chosen with the middle site as the control and the left and right ones receiving Er:YAG laser treatment of 5.1 J/cm² (L₁) or 2.0 J/cm² (L₂), respectively. The teeth were further subjected to 4-day pH cycling to create caries-like lesions. After mineral quantification using a micro-computed tomography scanner, the preventive effects (ΔML = mineral loss of the control area minus that of the lased area) of L₁ and L₂ treatments were calculated based on the difference in the gray value of the control and lased sites. Results: Significant inhibitory effects of L₁ and L₂ on enamel demineralization were demonstrated (both p ≤ 0.001), with the L₁ treatment having a greater effect (45.2%) than the L₂ treatment (25.2%, p = 0.004). Conclusions: Subablative low-energy Er:YAG laser irradiation can significantly prevent enamel demineralization potentially through the retardation of enamel diffusion. This study confirmed that high-energy laser treatment, which may damage the peripheral and underlying tissues, may not be needed for caries prevention.

Thermal alteration and morphological changes of sound and demineralized primary dentin after Er:YAG laser ablation

The purpose of this study was to assess the influence of Er:YAG laser pulse repetition rate on the thermal alterations occurring during laser ablation of sound and demineralized primary dentin. The morphological changes at the lased areas were examined by scanning electronic microscopy (SEM). To this end, 60 fragments of 30 sound primary molars were selected and randomly assigned to two groups (n = 30); namely A sound dentin (control) and B demineralized dentin. Each group was divided into three subgroups (n = 10) according to the employed laser frequencies: I-4 Hz; II-6 Hz, and III-10 Hz. Specimens in group B were submitted to a pH-cycling regimen for 21 consecutive days. The irradiation was performed with a 250 mJ pulse energy in the noncontact and focused mode, in the presence of a fine water mist at 1.5 mL/min, for 15 s. The measured temperature was recorded by type K thermocouples adapted to the dentin wall relative to the pulp chamber. Three samples of each group were analyzed by SEM. The data were submitted to the nonparametric Kruskal-Wallis test and to qualitative SEM analysis. The results revealed that the temperature increase did not promote any damage to the dental structure. Data analysis demonstrated that in group A, there was a statistically significant difference among all the subgroups and the temperature rise was directly proportional to the increase in frequency. In group B, there was no difference between subgroup I and II in terms of temperature. The superficial dentin observed by SEM displayed irregularities that augmented with rising frequency, both in sound and demineralized tissues. In conclusion, temperature rise and morphological alterations are directly related to frequency increment in both demineralized and sound dentin.

Depth of eCO2 Fractional Resurfacing with 3 Different Spot Sizes on Facial Skin in vivo

Introduction: To estimate the depth of laser vaporization of microthermal zones and surrounding thermocoagulation with the eCO2 laser. Materials and Methods: Pretragal skin was lased with 3 spot sizes (120, 300, and 1000 μm), and each spot size was lased at 5 different fluences. The 15 different lased areas were then biopsied. Results: For the 120-μm tip, as the power increases from 80 to 160 mJ, the depth of laser penetration increased from 520 to 900 μm. Total coagulative effect increased from 720 to 1000 μm. For the 300-μm tip, as the power increases from 100 to 180 mJ, the depth of laser penetration increased from 200 to 550 μm. Total coagulative effect increased from 320 to 720 μm. For the 1-mm tip, as power increased from 60 to 220 mJ, the depth of laser penetration hovered around 125 to 150 μm. Total coagulative effect increased from 150 to 350 μm. Conclusion: The 120-μm tip allows for the deepest penetration into facial skin with the least amount of surface area ablated. The 300-μm tip allows for an intermediate level of penetration into the dermis and an intermediate amount of surface ablation. The 1000-μm tip can be used to fully ablate epidermis as in traditional laser resurfacing. Traditional CO2 lasers ablate the entire epidermis, which provides excellent results at the price of prolonged healing times and erythema. These lasers worked with larger spot sizes, often as much as 2.25 mm, and at fluences of about 7–8 J/cm2. Fractional CO2 lasers focus the same amount of energy into the skin in microscopic thermal zones as small as 120 μm, which create fluences of nearly 100 times those of traditional lasers. This results in tissue ablation past the epidermis and through the papillary dermis into the reticular dermis in these narrow zones while leaving the surrounding epidermis intact. These areas of undisturbed tissue allow for more rapid healing. The theory is that the deep penetration into the reticular dermis allows for deep collagen neogenesis, which is good for rhytid improvement while maintaining a rapid healing time.

Enamel diffusion modulated by Er:YAG laser: (Part 1)—FRAP

Several studies have demonstrated the caries protective effect of lasers by strengthening enamel crystalline structure. However, the effect of laser on enamel diffusion (ED) remains unclear. Objectives This study aimed to quantify the laser-induced alteration of diffusion coefficients (DC) in enamel using fluorescence recovery after photobleaching (FRAP). Methods Eleven caries-free enamel sections were characterized morphologically using stereomicroscopy, polarized light microscopy and scanning electron microscopy, before and after laser treatment with Er:YAG laser 50 mJ × 5 s × 5 Hz. With 20 μM fluorescein, DCs were measured ( n = 11) by FRAP coupled with confocal microscopy. Results The DCs measured were 2.89 ± 0.61 × 10 −7 cm 2/s and 4.076 ± 0.73 × 10 −7 cm 2/s, at the lased and unlased areas, respectively ( p = 0.001). Conclusions This study has confirmed the reduction of ED as a potential mechanism involved in laser-induced caries prevention. FRAP was demonstrated to be a promising technique for evaluating diffusion-related phenomenon in enamel.

Surface Properties of Endosseous Dental Implants After NdYAG and CO 2 Laser Treatment at Various Energies

Dental lasers have been used for uncovering submerged implants as well as decontaminating implant surfaces when treating peri-implantitis. The objective of this study was to compare the possible alterations of the smooth surface and resorbable blast material (RBM) surface implants after using NdYAG and CO(2) lasers at various energies. Ten smooth surface implants and 10 RBM surface implants were used. Two smooth surface implants and 2 RBM surface implants served as a control group that was not lased. The remaining implants were treated using NdYAG and CO(2) lasers. The surface of each implant was treated for 10 seconds on the second and third threads. The smooth surface implants (group 1) were treated using a pulsed contact NdYAG laser at power settings of 1, 2, 3.5, and 5 W, which are commonly used for soft tissue surgery; the corresponding energy and frequency were 50 mJ and 20 Hz, 100 mJ and 20 Hz, 350 mJ and 10 Hz, and 250 mJ and 20 Hz, respectively. The group 2 RBM implants were treated using a pulsed contact NdYAG laser. The group 3 smooth surface implants were treated using a pulsed wave non-contact CO(2) laser at 1, 2, 3.5, and 5 W, and the group 4 RBM implants were treated using a pulsed wave non-contact CO(2) laser. Data were analyzed using scanning electron microscopy. The control surface was very regular and smooth. After NdYAG laser treatment, the implant surface showed alterations of all the surfaces. The amount of damage was proportional to the power. A remarkable finding was the similarity of the lased areas on the smooth and RBM surfaces. CO(2) laser at power settings of 1.0 or 2.0 W did not alter the implant surface, regardless of implant type. At settings of 3.5 and 5 W, there was destruction of the micromachined groove and gas formation. This study supports that CO(2) laser treatment appears more useful than NdYAG laser treatment and CO(2) laser does not damage titanium implant surface, which should be of value when uncovering submerged implants and treating peri-implantitis.

Q-switched Versus Free-running Er:YAG Laser Efficacy on the Root Canal Walls of Human Teeth: A SEM Study

Twenty-one teeth with one root canal were prepared by the step-back technique, divided into three groups, and split longitudinally. Group A served as a control. In group B, 20 to 150 pulses of 100 micros, 30 to 70 mJ per pulse at 1 to 4 Hz from a free-running Er:YAG laser were applied to the root-canal dentin. In group C, the Q-switched Er:YAG laser, with the same energy parameters and a 190-ns pulse duration was used. Scanning electron microscopy examination revealed that control specimens had debris and smear layer obscuring the dentinal tubules at all levels in the canals without crack formation. Both groups of laser-treated dentin were clean with opened dentinal tubules except around the lased area in which there was an intact smear layer. Cracks were observed in both laser groups with higher frequency in group C. In group B, craters with different depth levels at the root canal walls were produced and the energy apparently was distributed equally, because craters were well-shaped. In contrast, the ablation efficiency in group C was questionable with the parameters used in this study. Consequently, suitable parameters of the free-running Er:YAG laser must be found before its careful use as an adjunct in endodontic therapy.

Optimal designs for high-power vertical cavity surface emitting lasers

Vertical cavity surface emitting lasers (VCSEL's) lase in a single longitudin al mode, have a circularly symmetric output beam that can be very tightly focused, offer extremely high coupling efficiencies into optical fiber, and can be mas s produced in two-dimensional arrays relative to the conventional edge-emitting semi conductor laser. To obtain a high optical output power, besides enlarging of VCS EL's lasing area, the key points are proper number of quantum wells, homogeneous dist ribution of current density in the active layer and good thermal control. The dependenc e of VCSEL's performance on the number of quantum wells, the active diameter, th e thermal conductivity and the electric resistance of the material; and the dist ance between electri cal contacts are investigated. By optimizing the design parameters for a 980 nm In0.2Ga0.8As/GaAs VCSEL, a maximum continuous wave (cw) output power of 1.95 W at room temperature is obtained, which to our knowledge is the highest cw output power of any single VCSEL so far.

Mid-term results of combined transmyocardial laser revascularization and coronary artery bypass

Background Transmyocardial laser revascularization is increasingly used to treat intractable angina in the absence of graftable vessels; however, its role in combination with coronary artery bypass grafting remains undefined. The aim of this pilot study was to investigate the outcome of the combination therapy at mid-term follow-up. Methods Patients (n = 20) who had elective coronary artery bypass with one or more nongraftable coronary arteries were prospectively randomized to have either coronary artery bypass grafting alone or combination coronary artery bypass grafting plus transmyocardial laser revascularization with a holmium:YAG (yttrium-aluminum-garnet) laser to nongraftable areas. All patients had an exercise tolerance test preoperatively and at 6, 18, and 36 months follow-up. Stress echocardiography was performed on 17 patients at 18 months postoperatively, and regional wall motion score index was calculated in lased and nonlased nonrevascularizable myocardium of the left ventricle at rest and with dobutamine stress. Results Both groups of patients were similar in preoperative demographics and operative data. There was no perioperative death. There was no difference between the two groups in angina scoring at 6, 18, and 36 months follow-up. Exercise tolerance improved by a mean of 46.8 ± 20.0 seconds in the coronary artery bypass grafting group versus 199.2 ± 66.5 seconds per patient in the coronary artery bypass grafting plus transmyocardial laser revascularization group ( p = 1.8 ×10 −6) at 6 months; this benefit was maintained at 18 months (157 ± 46.3 versus 61 ± 39.2 seconds; p = 4 ×10 -4) but was lost at 36 months (57.2. ± 42.1 versus 68.1 ± 46.7 seconds; p = 0.70). The mean values for wall motion score index in the lased and nonlased regions at each stage of dobutamine stress at 18 months after surgery were not statistically significant. Conclusions The combination of coronary artery bypass and transmyocardial laser revascularization improved exercise tolerance in patients in whom complete revascularization could not be achieved by bypass grafting alone in the short term, but this benefit was lost by 36 months postoperatively. The transient improvement in exercise tolerance cannot be explained by changes in contractility in the lased areas.

First Results with Ablating Superficial Cell Layers of the Porcine Vocal Fold Using a Femtosecond Laser

Summary Most of benign, precancerous and malignant epithelial lesions in the human endolarynx, especially the vocal fold require a highly precise and controllable therapy, providing an effective ablation of injured tissue under functional preservation of adjacent structures. The dominant instrument currently used in clinical laser surgery is the CO 2 laser. However, CO 2 laser therapies in the endolarynx may result in severe postoperative risks like impairment of the vocal fold and voice quality. The femtosecond (fs) lasers available today are mainly characterized by extreme short pulses ranging from about 10 fs (10 −14 s) to 1 ps (10 −12 s) and single pulse powers in the range of gigawatts (10 9 W) to terawatts (10 12 W). Thus a fs laser enables the exact ablation of cells or superficial cell layers in target tissue by inducing microplasms during nonlinear absorption processes directly on the target. This process minimizes thermal and mechanical stress into surrounding tissues (“cold ablation”). In this basic study we tried to ablate small volumes of cells from a highly sensitive tissue using an experimental fs laser system without producing secondary damages in the periphery of the lased area. The vocal folds of a porcine larynx were used as a tissue model. First results showed that minimal ablation depths below 200 μm were achieved when a 350 μJ pulse energy and a scan rate of 1mm/s were applied. No defects were observed in the structures beneath the ablated area. Therefore, fs lasers may be suitable for the therapy of superficial small-volume lesions in the endolarynx. This has to be validated in further preclinical studies.

Effects of erbium,chromium:YSGG laser irradiation on canine mandibular bone.

Only relatively few reports have described the morphological effects on bone produced by erbium,chromium: yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser irradiation, and none has investigated the atomic changes or estimated the temperature increases involved. The objectives of this study were to investigate the morphological, atomic, and temperature changes in irradiated areas during and after laser irradiation, and to evaluate the cutting effect on canine mandibular bone in vitro. Two canine mandibular bones were cut into 3 to 5 cm pieces and irradiated by an Er,Cr:YSGG laser utilizing a water-air spray at 5 W and 8 Hz for 10 or 30 seconds. During and after laser irradiation, temperature increases in the irradiated areas were measured by thermography. The samples were then observed by stereoscopy and scanning electron microscopy to determine morphological changes and by energy dispersive x-ray spectroscopy to evaluate atomic alterations. Regular holes or grooves having sharp edges and smooth walls were produced, but no melting or carbonization was observed. The maximum temperature increase was an average 12.6 degrees C for 30-second irradiation. The continuous time of a temperature increase of more than 10 degrees C was consistently less than 10 seconds. An atomic analytical examination revealed that the calcium:phosphorus ratio was not significantly changed between the lased and unlased areas (P>0.0 1). These results showed that the Er,Cr:YSGG laser cuts canine mandibular bone effectively without burning, melting, or altering the calcium:phosphorus ratio of the irradiated bone.

A study on acquired acid resistance of enamel and dentin irradiated by Er,Cr:YSGG laser.

This investigation was performed to evaluate the acid resistance of lased enamel and dentin by Er,Cr:YSGG laser to artificial caries-like lesions by spectrophotometry, and the ultrastructure of lased areas was investigated by scanning electron microscopy (SEM) in vitro. In recent years, many studies have been performed to evaluate the effects of Er,Cr:YSGG laser on dental hard tissues. However, there have been only a few studies to determine if this laser is suitable for caries preventive treatments. An Er,Cr:YSGG laser was used to irradiate the enamel or dentin samples from 30 extracted human molars at 6 W (67.9 J/cm2) or 5 W (56.6 J/cm2) pulse energy, respectively, with or without water mist. Samples were subjected to 2 microl of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometery, and the morphological changes were investigated by SEM. The lowest mean Ca2+ ppm was recorded in the lased samples. SEM observation showed that the lased areas were melted and seemed to be thermally degenerated. After acid demineralization, the thermally degenerated enamel or dentin surfaces were almost unchanged. The results of this study suggested that Er,Cr:YSGG laser irradiation with and without water mist appears to be effective for increasing acid resistance.

Effect of pulsed Nd:YAG laser irradiation on acid demineralization of enamel and dentin.

The purpose of this study was to investigate the effect of Nd:YAG laser irradiation on the acid demineralization of enamel and dentin by spectrophotometry. A mechanism of acquired acid resistance is also proposed. The ability of Nd:YAG laser irradiation to the enhanced resistance to artificial caries formation is still controversial. A pulsed Nd:YAG laser at 1.064-micron wavelength was used to irradiate the human enamel and dentin samples from 20 extracted human molars at the parameters of 1, 2, and 3 W and 20 pps for a total of 9 sec after painting with black ink. Samples were then subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were also investigated by scanning electron microscopy (SEM). The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, in those by irradiated at 2 W and 1 W. The unlased samples showed the highest Ca2+ ppm. SEM observation showed that in the lased areas, the smear layer was partially melted and the underlying primary enamel or dentin seemed to be thermally degenerated. The results of this study suggested that melted smear layer and underlying enamel or dentin degenerated thermally by the heat treatment of Nd:YAG laser might play a major role to enhance resistance to artificial caries-like formation.

Properties of GaN-based laser diodes with a buried-ridge structure

The buried-ridge structure was introduced to GaN-based laser diodes for the purpose of realizing an index-guided structure in order to control the difference of effective refractive indexes between the inside and outside of the lasing area and to stabilize the lasing mode. Low-temperature-grown Al x Ga (1− x) N was used as the burying layer, and it was found that the refractive-index difference can be controlled by adjusting the Al content in the Al x Ga (1− x) N burying layer independent of the ridge dimensions. As a result of fabricating LDs with different Al contents, we found that Al content should be more than 30% in order to form an index-guided structure. The optimum refractive-index difference was estimated by fitting with the calculation. The LD with a buried-ridge structure, in which Al in the burying layer was more than 30%, had desirable properties as an index-guided waveguide.

Effects of the Nd:YAP Laser on Coronal Restorative Materials: Implications for Endodontic Retreatment

With new wavelengths that allow light transmission by optical fibers, the laser is now often used in endodontics either during treatment or retreatment. The aims of this study were to (i) specify the effects of laser irradiation on restorative materials in terms of topographic effects and (ii) describe different protocols for the first steps of retreatment. The laser used in this study was an optical fiber Nd:YAP (Lokki dt, Vienne, France) with a wavelength of 1.34 microns. Samples of the following restorative materials were prepared: amalgam, composite, permanent and temporary cements, and prosthodontic alloy. The handpiece of the Nd:YAP laser was fixed perpendicular to the surface of the different preparations. All trials were performed with the fiber tip either in contact with or at a distance of 2 mm from the material. The surface effects in all cases were (i) the creation of craters in the center of the lased areas, (ii) a border of fusion material at the edge of the craters, and (iii) cracks or fractures at a distance from the target areas. For the cements, amalgam and composite, the effects included a projection of material from the center to the edge of the lased area and/or the apparent photovolatization of light particles. For all materials the laser induced deeper absorption in the areas of direct contact than when it was held at a distance. This suggests that the fiber should be in contact with the restorative material for lasing in the straight part of the canal when the objective is either to pass through the material or alongside it between material and tooth. If the practitioner cannot determine the direction of the curve of the canal, lasing should be performed at a distance to weaken the material and thus permit more efficient use of an ultrasonic device. Lasing should in all cases be performed under close X-ray monitoring. Provided that sufficient caution is used, the laser may be helpful in removing restorative materials during retreatment.

Morphological and atomic analytical studies on enamel and dentin irradiated by an erbium, chromium:YSGG laser.

The purposes of this study were to investigate the morphological and atomic analytical changes and to evaluate the cutting effect on dental hard tissues of this laser in vitro. There have been few reports on morphological and atomic analytical study of dental hard tissues after erbium,chromium:yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser irradiation. Eighteen extracted human molars were sectioned into 3-mm-thick slices, which were irradiated with water-air spray by an Er,Cr:YSGG laser at 6.0 W and 20 Hz for 5 sec for enamel and 5.0 W and 20 Hz for 5 sec for dentin. The samples were then morphologically observed and examined atomic-analytically. Regular holes having sharp edges and smooth walls, but no melting or carbonization, were observed in both samples. An atomic analytical examination showed that the calcium ratio to phosphorus showed no significant changes between the lased areas and unlased areas (p > 0.01). These results showed that the Er,Cr:YSGG laser has a good cutting effect on dental hard tissues and offers advantages of no burning or melting after laser irradiation.

Caries-preventive effect of Er:YAG laser irradiation with or without water mist.

This investigation was performed to evaluate the effect of Er:YAG laser irradiation on the acquired acid resistance of sound dental hard tissues to artificial caries formation by spectrophotometry, and the ultrastructure of lased areas was investigated by scanning electron microscopy (SEM) in vitro. Although an Er:YAG laser has shown the most promise for hard tissue ablation, there have not been any dissolution studies to determine if this laser is suitable for caries preventive treatments. An Er:YAG laser was used to irradiate the enamel and dentin samples from 20 extracted human molars at 400 mJ pulse energy with or without water mist. Samples were subjected to 2 microL of 0.1 M lactic acid solution (pH 4.8) for 24 hours at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were investigated by SEM. The lowest mean Ca2+ ppm was recorded in the samples irradiated without water mist, in those by irradiated with water mist, and in the unlased samples. SEM observation showed that the lased areas had melted and seemed to be thermally degenerated when irradiated without water mist. After acid demineralization, the thermally degenerated enamel or dentin surfaces were almost unchanged. The results of this study suggest that Er:YAG laser irradition with and without water mist appears to be more effective for caries prevention.

Acquired Acid Resistance of Dental Hard Tissues by CO2 Laser Irradiation

This investigation was performed to evaluate the effect of CO2 laser irradiation on the acquired acid resistance of dental hard tissues to artificial caries-like formation and the ultrastructure of lased areas was morphologically investigated in vitro. In recent years, many studies have been carried out to evaluate the effect of the CO2 laser on the enhanced resistance to artificial caries formation of enamel. However, a limited number of papers concerning its effect on dentin have been published. A CO2 laser of 10.6 microns wavelength was used to irradiate human enamel and dentin samples from 20 extracted human molar teeth, and samples were subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were investigated by scanning electron microscopy (SEM). The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, followed by 2 W, 1 W, and unlased samples. SEM observation showed that the lased areas were melting with solidification of the smear layer. Even after acid demineralization, the lased surfaces were almost unchanged. The results of this study suggested that CO2 laser irradiation could sufficiently melt and solidify the enamel and dentin surfaces and thus enhance resistance to artificial caries-like formation.

Evaluation of transmyocardial laser revascularization (TMLR) by gated myocardial perfusion scintigraphy.

TMLR is a novel treatment for patients with coronary artery disease. It comprises the creation of transmyocardial channels thought to improve myocardial perfusion. Gated Tc-99m sestamibi scintigraphy was used to evaluate changes in myocardial perfusion after TMLR. Twelve patients underwent TMLR using a carbon dioxide laser. Sestamibi scans were carried out following a standard protocol prior to and 1, 3, 6, and 12 months after TMLR. Both visual and semi-quantitative assessment showed improvement in 4 patients, deterioration in 2 patients, and no change in the remaining 6 patients each. However, visual and semi-quantitative assessment were concordant in 6 patients and discordant in 6 patients. In 3 of these, semi-quantitative assessment suggested a better outcome, and in 3 patients visual assessment gave better results. Our findings in a small group of patients suggest that about a third benefited from TMLR. Gated myocardial perfusion scintigraphy using technetium-99m sestamibi is suitable for visual evaluation of changes in the lased area over time, but does not allow semi-quantitative evaluation in the patient population typically treated with TMLR. Further investigations using optimized imaging protocols, including positron emission tomography and three dimensional image presentation, are warranted.