Joseph Neev

Ultrashort pulse lasers for hard tissue ablation

To date, lasers have not succeeded in replacing mechanical tools in many hard tissue applications. Slow material removal rates and unacceptable collateral damage has prevented such a successful transition. Ultrashort pulses (<10 ps) have been shown to generate little thermal or mechanical damage. Recent developments now enable such short-pulse/high-energy laser systems to operate at high pulse repetition rates (PRRs). Using proper operating parameters, ultrashort pulse lasers (USPLs) could exceed the performance of conventional tissue processing tools and yield significant material volume removal while maintaining their minimal collateral damage advantages. As such, for the first time, USPLs offer real possibility for practical replacement of the air-turbine dental drill or other mechanical means for cutting hard tissues. In this study, the subpicosecond interaction regime was investigated and compared to nanosecond ablation by using a Titanium:Sapphire Chirped Pulse Amplifier (CPA) system with 1.05-/spl mu/m pulses of variable duration. Both 350-fs and 1-ns pulse regimes were studied. Ablation rates (ARs), ablation efficiency, and surface characteristics revealed through electron micrographs were investigated. The study characterized the interaction with a variety of hard tissue types including nail, midear bone, dentin, and enamel. With 350-fs pulses, tissue type comparison showed a remarkably similar pattern of ablation rate and surface characteristics. Negligible collateral damage and highly efficient per-pulse ablation were observed in this pulse regime. These observations should be contrasted with the 1-ns pulse ablation characteristics where strong dependence on tissue type was demonstrated and ablation efficiency was approximately an order of magnitude smaller. With efficient interaction which minimizes collateral damage, and with both cost and size of ultrashort pulse systems decreasing, the implications of this study are far-reaching for the efficient use of USPLs in several fields of medicine that currently apply traditional surgical methods.

Effects of Nd:YAG laser on apical seal of teeth after apicoectomy and retrofill.

The application of Nd:YAG laser to tooth surface can change its surface permeability. The purpose of this study was to investigate the effects of Nd:YAG laser on the permeability of dentin following apicoectomy and retrofill. Sixty single-rooted teeth were randomly assigned to six groups of 10 teeth each. The six groups were arranged in three pairs, experimental and control groups. The canals of teeth in pairs 1 and 2 were cleaned, shaped, obturated, and their apical 2 mm were resected. A class I preparation was prepared and filled with amalgam in each tooth in pair 1. The apical 2 mm of each tooth in pair 3 was removed, and a class I preparation was prepared and filled with amalgam. The apical surface of resected roots in half of the samples in each pair was lased twice by using Nd:YAG laser. The duration of lasing and the number of pulses were recorded for each tooth. After application of nail polish to the unoperated surface of each tooth, the teeth were placed in 0.5% methylene blue dye for 48 h. The amount of dye penetration in sagittal sections of each tooth was measured. The amount of dye penetration was significantly lower in lased roots than in nonlased ones (p < 0.05). Based on our results, it appears that application of Nd:YAG laser reduces the permeability of resected roots.

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.

Effect of ArF-193 nm excimer laser on human dentinal tubules: A scanning electron microscopic study

The purpose of this study was to evaluate the effects of the ArF-193 nm excimer laser on the dentinal tubules of extracted human teeth under a scanning electron microscope. Fifteen 3 mm thick slices were cut with an electric saw at the cementoenamel junction from 15 extracted human teeth. A diamond bur was used to remove the cementum layer and expose the dentinal tubules. Each slice was scored by a permanent marker into four equal quadrants. The ArF excimer laser was applied for 5 seconds on three of the quadrants with fluences that ranged from 0.2 J/cm2 to 15 J/cm2 and pulse repetition of 25 Hz. The untouched quadrant served as a control. The specimens were mounted on stubs, sputter coated by gold, and examined by a scanning electron microscope. The effects of the ArF excimer laser irradiation varied. Laser fluences of 0.2, 0.5, and 1.0 J/cm2 had no effect. Although fluence of 15 J/cm2 caused significant removal of peritubular dentin, melting and resolidification of the dentinal smear layer was also observed under the scanning electron microscope with a laser fluence of 5 J/cm2.

MICROSCOPE-DELIVERED ULTRAVIOLET-LASER ZONA DISSECTION - PRINCIPLES AND PRACTICES

Journal of Assisted Reproduction and Genetics, Vol. 9, No. 6, 1992 LASER Microscope-Delivered Ultraviolet Laser Zona Dissection: Principles and Practices INTRODUCTION amounts of water, we searched for laser systems emitting radiation where water is characterized by relatively high absorption. While other researchers have elected to pursue wavelengths of high absorption coefficient (8) and have recently reported alternative methods for de- livering these particular laser pulses to the zona target by either using glass micropipettes filled with positive air pressure (with the 193-nm radiation) (9) or using specialized fibers or micropipettes (in the case of the 2.94-txm erbium:YAG laser) (10), we have chosen to focus our attention on other wave- lengths. Possible difficulties with contact methods such as energy delivery to the target, the need for making use of a glass or salt-based instrument (some of them are toxic), and the necessity for maintaining physical contact between the delivery media (pipette or fiber) defeat most of the advan- tages in using laser light and essentially reduce the laser-based techniques to a mechanical/contact mode, similar to conventional PZD methods. Addi- tional complications arise from the need for steril- ization of optical fibers or micropipette tips. This requires constant adjustments in the delivery sys- tem and disposal of relatively expensive fiber seg- ments. The tip quality must also be carefully con- trolled in order to achieve a good beam quality, a consideration which is sure to slow down the pro- cedure. A final problem is due to the fact that some laboratories make extensive use of mineral oil cover over the targeted medium. As we discovered, drop- lets of oil tend to adhere to optical fibers when they are inserted through the oil layer into the host me- dium. These oil droplets, in turn, absorb the fiber output radiation, accumulate heat, expand (thereby mechanically disturbing the micromanipulated ob- ject), and completely block any additional radiation from arriving at its target. Based on the above considerations, we have elected to search for a set of laser parameters which will allow the laser light to be delivered to the Since their introduction, the techniques of zona drill- ing (ZD) and partial zona dissection (PZD) have drawn considerable attention as potential tools in gamete and embryo micromanipulation. ZD in- volves the application of small volumes of acidic Tyrodes medium, which, through its digestive properties, creates small holes in the zona pellu- cida (ZP). This process was originally described by Gordon and Talanski (1). PZD is a mechanical tech- nique for breaching the ZP and was first described by Malter and Cohen (2). It makes use of a pointed micropipette which pierces the ZP and is then sheared against a larger pipette, thus creating a breach in the zona pellucida. Indeed, most cur- rently accepted methods of micromaniputation of oocytes and embryos are based on the use of me- chanical techniques or the use of an acidified me- dium solution (3,4). In 1989, Tadir et al. (5) suggested the incorpora- tion of laser technology to achieve accurate inci- sions in the ZP as well as sperm micromanipulation through the use of optical traps. In addition, laser- induced selective destruction of extra pronuclei was also attempted (6). In these studies, the inter- action of the fundamental wavelength Q-switched Nd:YAG laser (15-nsec pulses of 1.064 ixm), the Nd:YAG harmonics (at 532 and 355 nm), and a nitrogen-pumped dye laser (600-psec pulses, at 366 nm) were all tested. In an effort to determine the most suitable param- eters for selective laser interaction with the various components within oocytes and embryos, we have been studying additional laser systems (7). Since cells in general, and oocytes and embryos in par- ticular, are relatively transparent and contain high The opinions presented in this column are those of its author(s) and do not necessarily reflect those of the journal and its editors, publisher, and advertisers,

Ablation of human nail by pulsed lasers

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.

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.

Surface temperature and thermal penetration depth of Nd:YAG laser applied to enamel and dentin

The determination of the thermal effects of Nd:YAG laser energy on enamel and dentin is critical in understanding the clinical applications of caries removal and surface modification. Recently extracted non-carious third molars were sterilized with gamma irradiation. Calculus and cementum were removed using scaling instruments and 600 grit sand paper. The smear layer produced by sanding was removed with a solution of 0.5 M EDTA (pH 7.4) for two minutes. Enamel and dentin surfaces were exposed to a pulsed Nd:YAG laser with 150 microsecond(s) pulse duration. Laser energy was delivered to the teeth with a 320 micrometers diameter fiberoptic delivery system, for exposure times of 1, 10 and 30 seconds. Laser parameters varied from 0.3 to 3.0 W, 10 to 30 Hz and 30 to 150 mJ/pulse. Other conditions included applications of hot coffee, carbide bur in a dental air-cooled turbine drill and soldering iron. Infrared thermography was used to measure the maximum surface temperature on, and thermal penetration distance into enamel and dentin. Thermographic data were analyzed with a video image processor to determine the diameter of maximum surface temperature and thermal penetration distance of each treatment. Between/within statistical analysis of variance (p <EQ 0.05) determined a difference existed between enamel and dentin in thermal effects from the Nd:YAG laser. Enamel had lower maximum surface temperatures than dentin for all laser powers and times. The surface temperature ranged from 34 +/- 1 degree(s)C to 110 +/- 4 degree(s)C on enamel and 62 +/- 5 degree(s)C to 392 +/- 82 degree(s)C on dentin. As power and time of exposure increased, both the maximum surface temperature and thermal penetration distance increased. The greatest length of thermal effect on the surface (11.0 +/- 0.9 mm) and thermal penetration distance (4.7 +/- 0.4 mm) recorded were caused by the air-cooled turbine drill on dentin. Surface temperatures were much higher for the Nd:YAG laser applied to enamel and dentin than those of the air-cooled turbine drill with carbine bur. Although temperatures created with the laser were higher, the diameter of the hot spot on the surface and the thermal penetration distance in the pulpal direction were significantly less than those of the dental drill. Therefore, the pulsed infrared Nd:YAG laser, with 320 micrometers fiber optic delivery, can be applied to enamel and dentin without detrimental thermal pulpal effects.

Dentin ablation with three infrared lasers

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.

Lasers for gamete micromanipulation: basic concepts

Journal of Assisted Reproduction and Genetics, Vol. I0, No. 2, 1993 LASER Lasers for Gamete Micromanipulation: Basic Concepts for the preferred approach: (i) heat deposition, (ii) DNA absorption, (iii) ablation threshold, and (iv) simplicity in equipment and training. One may sug- gest adding a few more prerequisites such as (v) absorption in water and proteins, (vi) a spot size smaller then the thickness of the zona pellucida (ZP), and (vii) precision of the entire unit. !n a previous study (12) we have discussed the influence of various physical parameters on the ex- pected effects during gamete manipulations (i.e., cutting geometry, ablation beam size, pulse repe- tition rate and duration, and laser fluence, i.e., en- ergy per unit area). It is the intent of this column to discuss some aspects related to the above- mentioned prerequisites in order to take full advan- tage of the laser as light scalpels. Lasers, (an acronym for Light Amplification by Stimulated Emission of Radiation) are electromag- netic waves with unique properties. The beam is collimated, monochromatic, and coherent. Prog- ress in physics and laser technology in recent years has resulted in the introduction of many lasers for biomedical studies. Although lasers differ from each other by the wavelengths, which are in the visible range (red, green, or blue), ultraviolet (UV), or in the infrared (IR) range (Fig. l a), effects may also vary as a result of different application modes as will be discussed later. INTRODUCTION A brief literature search on the key words micro- manipulation (MM) and male factor infertility may highlight the controversy regarding this issue. It has recently been suggested (1) that so inconsistent are the reported results that at present it is pertinent to ask does microsurgical assisted fertilization (MAF) work at all ? The controversies are related mainly to patient selection needed for establishing prognostic criteria and the method of choice (2,3). Gamete manipulations require special equipment and expertise, while the preparation of disposable microneedles for MAF is time-consuming and, thus, expensive (4). In an attempt to increase accuracy and simplic- ity, it has been suggested that the laser might offer several advantages. Since its first introduction for gamete manipulation in 1989 (5) several studies addressed basic questions on its potential role and discussed various methods (6-10). It is beyond the scope of this article to assess the important issues of effectiveness and safety of the laser for gamete manipulations. Several studies and clinical obser- vations are being performed throughout the world and it will take some time until the controversies regarding the future role of MAF will be answered. However, in view of the increasing interest in lasers for gamete MM, some guidelines are needed. Strohmer and Feichtinger have recently presented in abstract form some biophysical criteria for laser MM (11). They suggested four basic requirements HEAT DEPOSITION IN THE OOCYTE OR THE EMBRYO The opinions presented in this column are those of its author(s) and do not necessarily reflect those of the journal and its editors, publisher, and advertisers, Some heat will always be generated in the micro- manipulated oocyte or embryo if the ablation WL is