The high incidence of patients with clinical and neurological symptoms of lumbar disc herniation has spurred the development of less invasive and more cost efficient methods to treat patients. In this study we evaluated pulsed and continuous wave (cw) 1064 nm Nd:YAG laser ablation and induced thermal damage in sheep intervertebral disc. We used the Heraeus LaserSonics Hercules 5040 (Nd:YAG) laser system and 400 micrometers bare and 600 micrometers ball-tipped fibers in cw and pulsed mode. For the laser parameters and fibers used in this study, ablation of the intervertebral disc was successful and thermal damage did not exceed 0.5 mm. Varying beam diameters and focusing abilities (i.e., bare and ball) did not produce any difference in the coagulation thermal effect.

We investigated the effect of varying Tm:YAG (2.014 micrometers ) and Ho:YAG (2.130 micrometers ) laser parameters on ablation rate and consequent thermal damage. Mid-infrared wavelengths are strongly absorbed by most biological tissues due to the tissue's high water content. The ablation rate of fresh bovine knee joint tissues (fibrous cartilage, hyaline cartilage, and bone) in saline was assessed as a function of radiant exposure (160 - 950 J/cm²), at pulse widths of 200 microsecond(s) ec for Tm:YAG and 250 microsecond(s) ec for Ho:YAG and a repetition rate of 2 Hz. All tissues used in this study could be efficiently ablated using two micron lasers. The mechanism of action is likely related to the formation and collapse of cavitation bubbles, associated with mid-infrared lasers. We concluded that the Tm:YAG and Ho:YAG lasers are capable of effective knee joint tissue ablation.

This paper proves that the application of the photoelastic experiment to studying the mechanical principle of reduction on compression fracture of the spine, for deciding the influence of the location and amount of applied force on vertebras, ligamentum longitudinal anterius, and stress distribution, has certain directive significance in the treatment of spine injury.

Three medical lasers, Argon, CO₂, and Nd:YAG, were studied at power outputs of 5 watts, 5 watts, and 40 watts respectively. Laser irradiation was directed at the pharyngeal mucosa of sagittally split horses heads in a randomized fashion. Areas irradiated were measured immediately using hand held calipers, and after being prepared for microscopic examination to determine width and depth of penetration into the mucosa. The results indicated that tissue destruction produced by the CO₂ laser was predictable compared to the Nd:YAG laser. The Argon laser, between 1 and 6 seconds of exposure, produced only superficial photoablation of mucosal tissue which did not extend into the muscular layer. The conclusion of this in vitro investigation was that the Argon laser irradiation applied transendoscopically may be a reasonable substitute for surgery and electrocautery commonly used to treat follicular lymphoid hyperplasia, a respiratory disease of young horses.

Exotic veterinary practice has evolved in connection with the importation industry, development of zoological collections and rising private pet ownership to the point that laser technology is in demand. The specific needs of the many species presented for surgical care and the expectations of owners are examined in relationship to the currently understood diseases of exotic animals.

This study was done to determine delivery parameters for holmium:YAG laser ablation of alimentary tract mucosa. Cadaveric and in vivo canine stomach studies determined laser energies that could ablate mucosa without irreversibly damaging underlying tissues. In vivo gastric, duodenal and colonic studies were performed to document mucosal ablation efficiency.

The curriculum guidelines for dental laser education were developed through a consensus process with members from dental academia, industry and private practice. This document was developed at a workshop on the development of standards for dental laser education and laser instructor certification held at the University of California, San Francisco on July 25 and 26, 1992. A working draft is currently being circulated among dental laser educators, researchers, practitioners, organized dentistry and members of industry. After further discussion, modification and review, the final document will be widely distributed and updated annually. Any questions concerning the guidelines may be addressed to the authors of this document in care of the organizer. Suggestions for the improvement of this standard and endorsement of this document are invited.

The first generation of dental lasers proved limited to soft tissue applications. Due to the thermal properties of these lasers, drilling of enamel and dentin is harmful to the underlying nerve tissue. As a solution to this problem, more sophisticated solidstate lasers are under commercial development for hard tissue applications. The first of these second generation lasers to emerge is the erbium:YAG now marketed in Europe by KaVo. This system relies on a cumbersome articulated arm delivery device. Other manufacturers have overcome this delivery problem with the introduction of flexible delivery methods. Another hard tissue laser that has been introduced is the short-pulsed Nd:YAG. This laser uses shaped pulses to drill teeth without thermal damage. An overview of these and other second generation dental lasers is presented.

The results of hard tissues of human tooth processed by pulses of Nd, Ho and Er lasers are represented. As examples of interaction of holmium laser radiation with enamel and dentin the principle phenomena of laser tooth damage is shown.

Extracted molars were used in order to study the efficiency of Erbium YAG, Holmium YAG, and Neodymium YAG radiation on the removal of dental enamel, dentin. The hard tissues were penetrated with standard energy and pulse parameters with or without water cooling, laser beam or fiber and black paint. The specimens were analyzed with SEM. Differences between laser wavelengths were observed. Morphologic alterations and crater formation depend directly on the wavelength and energy of the laser beam.

In dentistry, the defect of cementation on the margins of crowns accumulates bacterial plaque easily. This can result in recurrent caries and periodontal disease. In this paper holographic interferometry is applied to study the effect of masticatory force on various complete crowns. Four complete molar crowns made from different casting materials (Au, Pd-Ag, Ni-Cr, and PFM) were tested. The horizontal displacements of two points near the margin, measured by the method of multiple observations, could be as large as 15 micrometers under normal load (25 kgw). However, the marginal discrepancy of all four crowns estimated were quite small (< 0.2 micrometers ). This also indicates that the cementation between the crown and the tooth is quite good. Nevertheless, when the load was increased to 45 kgw, a defect of cementation was found on the Pd-Ag crown.

The aim of the study was to describe the appropriate fluence necessary for the effective removal of dental decay by ablation processes without or with at least minimal removal of healthy dentin. The experiments were conducted at two wavelengths [355 nm (frequency tripled, Q-switched Nd:YAG-laser) and 377 nm (frequency doubled, gain-switched Alexandrite-laser)] found to be close to the maximum of preferential absorption of carious dentin over healthy dentin. Optoacoustic techniques were applied to determine the ablation thresholds of healthy and carious dentin. The ablation efficiencies at characteristic fluences were determined using non-tactile microtopography. During all experiments a fiber optic delivery system was engaged.

The laser induced autofluorescence from carious regions of human teeth was studied using a krypton ion laser at 407 nm as an excitation source, a fiberoptical detection system combined with a polychromator and an optical multichannel analyzer. In addition, time-resolved and time-gated fluorescence measurements in the nanosecond range were carried out. It was found that carious regions contain different fluorophores which emit in the red spectral range. The emission spectra with maxima around 590 nm, 625 nm and 635 nm are typical for metalloporphyrins, copro- and protoporphyrin. During excitation the fluorescence was bleached. Non-carious regions showed a broad fluorescence band with a maximum in the short-wavelength spectral region with shorter fluorescence decay times than the carious regions. Therefore, caries can be detected by spectral analysis of the autofluorescence as well as by determination of the fluorescence decay times or by time-gated imaging.

It seems that the dental profession will not embrace the laser for dentistry until hard tissue applications are developed. To date the lasers that are available for dentists in the clinical setting have little scientific basis for use on dental hard tissues. Before a viable laser method becomes available for dental hard tissues, basic research on the correlation of incident fluence to hard tissue removal must be studied. In this paper we propose a method of determining the exact size and shape of the defect created by an Er:YAG laser and correlate the size, depth, and volume of the defect relative to the fluence, spot size and number of pulses of the Er:YAG laser.

Er:YAG laser ablation was investigated by fast photography in a Schlieren optic setup. The results support the idea of continuous, thermally driven microexplosion type of ablation, which is based on the inhomogeneous distribution of strong (water) and weak absorbers (hydroxyapatite). Sudden vaporization and heating of the water content leads to a very effective material removal by bursting off the solid tissue components. Material is ejected in the form of particles when the threshold energy density for ablation (about 3 J cm^-2) is reached. For high radiant exposure, initial plume velocity is in the order of the speed of sound in air. After leaving the tissue surface, particles are heated by the still incoming laser radiation, causing glowing and melting. No surface plasma and only weak pressure waves caused by individual spikes were observed.

Cylinders of microfil light-cured composite resin were bonded to the labial enamel surface of bovine incisor teeth which had previously been subjected to different laser treatments. One part of the tooth surfaces were laser treated in a defocused way only, another part with a different overlaying pattern of focused laser pulses. Specimens were thermocycled and the adhesion of the composites were determined by tensile strength tests. The best results were obtained by laser conditioning of the enamel surface in a defocused way with an overlaying fine pattern of focused single shots. The tensile strength reached 92.5% of the acid etched bonding.

Enamel and dentin samples were exposed extraorally to pulsed TEA CO₂ lasers with pulse durations of 1 microsecond(s) ec and 0.1 microsecond(s) ec. The ablation rate is for energy densities above 5 J/cm² independent of the CO₂ laser energy. For 1 microsecond(s) long CO₂ pulses the ablation rate is 3 micrometers /pulse for drilling in enamel, and 8 micrometers /pulse for drilling in dentin. Drilling with 0.1 microsecond(s) CO₂ laser results in lower ablation rates of approximately 1 micrometers /pulse in enamel, and 4 micrometers /pulse in dentin. At all experimental energy densities plasma formation is observed, effectively reducing the amount of energy deposition. Compared with these results, experiments with the Er:YAG laser show that 200 microsecond(s) long Er:YAG laser pulses achieve better ablation in the high energy density range because ablation is not diminished as rapidly by the plasma formation. The Er:YAG laser saturated ablation rates are approximately 60 micrometers /pulse for drilling in dentin and 40 micrometers /pulse for drilling in enamel.

CO₂ Lasers at (lambda) equals 9.6 and 10.6 micrometers and pulse lengths in the range of 100 ns to 150 micrometers operating in multimode were used as a drilling instrument with energy densities up to 200 J/cm². The laser light was focused perpendicularly onto the surface of 1 mm slices of dentin and enamel. Different methods of cooling were applied. Temperatures were measured during ablation with thermocouples. The quality of ablation was checked with a stereo microscope and the diameters of the ablated areas were measured. Ablation rates (mm³/s) and ablation efficiencies (mm³/J) were calculated. Best results were obtained with pulse lengths of 100 to 130 micrometers . Ablation without carbonization of the organic matrix of dentin was only possible with water or water/air spray cooling. Ablation rates of up to 0.2 mm³/s and an ablation efficiency of up to 50 X 10^-3 mm³/J were reached.

In this work we update our report about CO₂ laser surgery used to remove hypertrophic gingiva in patients under cyclosporine treatment after heart-transplant. The indications and basic results were confirmed, but we present two cases where a second surgery was needed to remove recurrent overgrowing gingival tissue.

Deep carious decay is still a problem for conservative dentistry. A prototype of a transverse excited atmospheric pressure carbondioxide laser (TEA-CO₂-Laser) was used for testing the properties in selective ablation of softened carious dentin, artificially sclerosing the remaining dentin, and providing thermal damage for the pulp. Using low pulse frequencies of 1 or 2 Hz, pulse durations of 50 ns, and pulse energies of 5 J/cm² the TEA-CO₂- Laser seems to be able to solve the therapeutic problem.

The application of laser technology to endodontics has been studied for some time. At the present time several major problems are being investigated: (1) removal of infected tissues, (2) sterilization of canals, (3) obturation of canals, and (4) preservation of the vitality of supporting tissues. This list is not intended to imply other problems do not exist or have been solved, but it is a starting point. This paper reviews some of the literature that relates to laser applications to endodontics and concludes with some of the findings from our investigation.

In 1993 laser dentistry will be 30 years old. Stem, one of the pioneers of dental laser research, dedicated his activity to the investigation of how a very powerful light interacts with the tooth structure. As we know, laser radiation, or light energy has to be converted into some other form of energy in order to produce a therapeutic tissue effect. The atoms and molecules that comprise biological tissue are ultimately responsible for absorbing laser radiation and converting it into other energy forms. Laser-tissue interactions are often categorized according to whether laser energy is converted into heat, chemical energy or acoustic (mechanical) energy. Today in dentistry, C02 and Nd:Yag lasers are available for clinical applications. Both of them emit an infrared type of radiation which interacts with the tissue through a thermal effect. This type of interaction with the tissue has to be carefully controlled. This thermal effect, however, can cause complications by damaging the pulp or the surrounding tissues of the tooth. In 1972 a report by R. Stern showed that over an applied density Of energy of 25 joules/cm2 from a CO2 laser, enamel shows cracks, microfractures and a crumbly mineralized structure. The water content of tissue usually plays a dominant or important role in the absorption of laser energy, specifically for the C02 laser beam. In vivo studies have shown that because enamel contains only 2.3% water the transfer of heat through the dentinal layer to the pulp chamber occurs very fast and pulpal tissue can be damaged when enamel is irradiated.2 When enamel is exposed to a CO2 laser beam with a density of energy of 20 to 200 joules/cm2 the intrapulpal temperature increased from 5.5°C to 32°C above body temperature.3 The conclusion was that, for cavity preparation, the use of a C02 laser would be limited for sterilization of dentinal surfaces. The Nd:Yag lasers appear to cause less damage to the pulp. Even when the energy was more than twice the maximum energy delivered by a C02 laser, no coagulation or necrosis occurred. This wavelength has also been tested successfully on pits and fissures of monkeys with an energy density of 20 to 120 joules/cm2. Minimal changes on histological examination of the pulp have been found.4'5 In 1987 a remark was made by Launay and Mordon, ",,.medical lasers have been tried on dental tissues, but the effects of the lasers on the pulp have not been studiedt'. Immediately after that, the conclusions were that more research and quantitative analysis of laser thermal effects on the dental tissues was needed6 Since that time, different authors have reported quantitative results of the thermal effects analysis. Our intention was to explore new methods to facilitate dissipation of surface heat generated by laser exposure of enamel to a pulsed Nd:Yag laser beam. The pupose of the study was to compare the elevation of temperature inside the )ulp chamber at different levels of energy, for different methods of cooling and without cooling during the exposure of enamel to a pulsed Nd:YAG laser beam.

The use of laser energy to clean, shape, and sterilize a root canal system space involves the generation of heat due to the thermal effect of the laser on the organic tissue contents and dentin walls of that space. If heat generation is above physiologic levels, irreparable damage may occur to the periodontal ligament and surrounding bone. This study measured temperature rise on the outer root surfaces of extracted teeth during intracanal laser exposure. Thirty single rooted, recently extracted teeth free of caries and restorations were accessed pulps extirpated and divided into three groups. Each root canal system was treated with a 1.06 micrometers pulsed Nd:YAG laser with quartz contact probes. Temperatures were recorded for all surfaces (mesial distal, buccal, lingual, apical) with infrared thermography utilizing a detector response time of 1 (mu) sec, sensitivity range (infrared) of 8 to 12 micrometers and a scan rate of 30 frames/sec.

The aim of this study was to compare the conditions for selective removal of carious lesions by pulsed lasers emitting wavelengths in the near UV in contrast to lasers emitting in the IR spectral region at 2.9 micrometers . Absorption measurements of carious lesions and healthy dentin revealed highest absorption differences at wavelengths between 320 and 520 nm. The effects of a frequency doubled, gain-switched Alexandrite-laser (wavelength 377 nm) and a q- switched Er:YAG-laser (wavelength 2.9 micrometers ) on carious and healthy dentin were studied in comparison. Both lasers emitted pulses of 200 ns duration. The ablation thresholds for the different tooth structures were determined. The ablation threshold of carious lesions is about the same for the Er:YAG as for the second harmonic Alexandrite-laser. For the Er:YAG-laser the ablation threshold of healthy dentin is about 2 times higher than the ablation threshold of carious lesions. In the case of the second harmonic Alexandrite-laser the difference between ablation is 4 times higher. Thus, regarding the window of fluences sufficient for truly caries selective ablation, the conditions for selective removal of carious dentin are better in the near UV than in the IR spectral region at 2.9 micrometers .

The literature indicates that human dental enamel altered by CO₂ laser energy becomes less susceptible to the caries process. In addition, the reported levels of laser radiation required to facilitate this preventative effect do not produce a visible change on the enamel surface. Also, research indicates that laser-induced fluorescence may provide a modality for detecting and quantifying differences in dental enamel. This pilot study, utilizing 3D scanned laser-induced fluorescence images, was designed to determine if laser irradiated enamel could be distinguished from normal enamel. Five third molars were selected for this study (Bu surfaces). Two 1.0 mm² areas were scanned on each tooth using a scanning laser fluorescence spectrophotometer. Each scan area consisted of 20 parallel scan lines, 1.0 mm in length, spaced 50 micrometers apart. Measurements were taken at 50 micrometers intervals for a total of 400 points/scan. The results were stored in a 2D matrix format. Nine windows were then irradiated with a CO₂ laser (3 at 0.5 W, 1.5 W, 2.5 W for 0.15 sec.) and re-scanned. Three-dimensional contour images produced for each scan permitted the irradiated area to be readily identified and isolated. The non-irradiated matrix for each window (baseline) was subtracted from the corresponding irradiated matrix. The resultant image was then summed to produce a `fluorescence volume' representative of the increase in fluorescence due to the laser irradiation. We have observed a distinct fluorescence signature by the laser irradiated area. Results are presented on the correlation of laser power with fluorescence volume.

Laser-induced fluorescence has potential for both caries research and diagnosis. However, research has shown that precise control is necessary for accurate enamel comparisons. Such factors as focus, number of sampling points, scan matrix size and reproducible placement of the scan matrix can all have substantial effects on results. Five noncarious third molars were mounted in acrylic and ground so that a flat Bu enamel surface was created. Each enamel area was covered with acid-resistant varnish except for a window approximately 1.0 mm². Each specimen was mounted in the fluorometer for scanned laser fluorescence analysis using a 1.0 mm² scan matrix. Readings were taken at 50 micrometers intervals for a total of 400 readings per matrix. Each specimen was remounted and reanalyzed in the fluorometer. Each specimen was lased (1.5 W, 1.5 mm f.s., 0.15 sec.) and reanalyzed as per above by fluorometer. Running-sums of line means were calculated for each scan and graphed. In all samples, the curves for nonlased enamel were lower and widely separated from those for lased enamel. In each specimen, the nonlased curves were either coincident or nearly so. The results indicate that ensuring constant focus, repeatable orientation of scan matrices and high sampling frequency collectively can lead to a high degree of scanned laser fluorescence reproducibility.

This study determined the effectiveness of a Neodymium:YAG 1.44 micrometers wavelength laser on human cartilage. This wavelength is strongly absorbed by water. Cadaveric meniscal fibrocartilage and articular hyaline cartilage were harvested and placed in normal saline during the study. A 600 micrometers quartz fiber was applied perpendicularly to the tissues with a force of 0.098 N. Quantitative measurements were then made of the ablation rate as a function of fluence. The laser energy was delivered at a constant repetition rate of 5 Hz., 650 microsecond(s) pulsewidth, and energy levels ranging from 0.5 joules to 2.0 joules. Following the ablation of the tissue, the specimens were fixed in formalin for histologic evaluation. The results of the study indicate that the ablation rate is 0.03 mm/mj/mm² for hyaline cartilage and fibrocartilage. Fibrocartilage was cut at approximately the same rate as hyaline cartilage. There was a threshold fluence projected to be 987 mj/mm² for hyaline cartilage and fibrocartilage. Our results indicate that the pulsed Nd:YAG laser operating at 1.44 micrometers has a threshold fluence above which it will ablate human cartilage, and that its ablation rate is directly proportional to fluence over the range of parameters tested. Fibrocartilage and hyaline cartilage demonstrated similar threshold fluence and ablation rates which is related to the high water content of these tissues.

Using a pulsed Holmium:YAG laser, wavelength 2.1 micrometers , the ablation rate and thermal effect were measured on human meniscal cartilage. Holding the pulsewidth and repetition rate constant, fluences per pulse were varied between 167 - 927 J/cm²/pulse for the penetration rate and between 1.7 - 100 J/cm²/pulse for the mass loss rate. The fastest ablation rate was found at 927 J/cm²/pulse for the penetration rate and at 100 J/cm²/pulse for the mass loss rate. The thresholds were 53 J/cm²/pulse and 1.36 J/cm²/pulse, respectively. The increases in ablation rate were directly proportional to increases in fluences for both methods. Histological examination showed the average lateral thermal change to be 400 - 500 micrometers and 400 - 460 micrometers , respectively, with no relation to level of fluence.

In order to establish a practical way of evaluating the efficiency of an arthroscopic laser system, specifically the new 1.44 micron Neodymium:YAG laser system, a simple experiment was carried out at the Carl Zeiss Laboratory in Princeton, New Jersey. A new parameter, laser efficiency as it applies to tissue ablation is introduced, LE_TA or ablation efficiency.

The XeCl excimer laser was investigated as an ablating tool for human fibrocartilage and hyaline cartilage. Quantitative measurements were made of tissue ablation rates as a function of fluence in meniscal fibrocartilage and articular hyaline cartilage. A force of 1.47 Newtons was applied to an 800 micrometers fiber with the laser delivering a range of fluences (40 to 190 mj/mm²) firing at a frequency of 5 Hz. To assess the effect of repetition rate on ablation rate, a set of measurements was made at a constant fluence of 60 mj/mm², with the repetition rate varying from 10 to 40 Hz. Histologic and morphometric analysis was performed using light microscopy. The results of these studies revealed that the ablation rate was directly proportional to fluence over the range tested. Fibrocartilage was ablated at a rate 2.56 times faster than hyaline cartilage at the maximum fluence tested. Repetition rate had no effect on the penetration per pulse. Adjacent tissue damage was noted to be minimal (10 - 70 micrometers ).

Currently, the clinical indications and results of arthroscopic microdiscectomy and laser disc decompression come close to, but do not exceed, the results of classic discectomy or microdiscectomy for the whole spectrum of surgical disc herniations. However, as minimally invasive techniques continue to evolve, results can be expected to equal or be potentially superior to conventional surgery. This exhibit demonstrates how the use of a vital dye can enhance standard arthroscopic microdiscectomy techniques and, when used in conjunction with KTP/532 laser disc decompression, allows for better arthroscopic visualization, documentation, and extraction of nucleus pulposus, ultimately expanding the current limiting criteria for minimally invasive techniques. When proper patient selection is combined with good clinical indications, the surgical results are rather dramatic, often achieving immediate relief of sciatica in the operating room.

The angular distribution of scattered laser light was measured at 543 nm (HeNe), 632 nm (HeNe), and 1053 nm (YLF) through 50 to 100 micrometers sections of enamel and dentin. The scattering distributions were strongly forward peaked at all three wavelengths, indicating that all samples were highly transmissive. The scattering distributions are very sensitive to surface scattering, and a large percentage of the incident light is internally reflected at the exit surfaces of these materials, masking the true scattering distributions. True bulk scattering distributions were measured in a bath of index-matching fluid. For 1 micrometers radiation there was no measurable absorption and only minimal highly forward-directed scattering in 100 micrometers enamel sections. In dentin there was somewhat more forward-directed scattering with less than 10% absorption in 100 micrometers sections. This information should be taken into consideration in any laser irradiation of dental surfaces at these wavelengths.

In order to serve as supplements to existing mechanical devices and procedures in dentistry, laser systems and laser procedures may not produce any irreversible damages to the dental hard and soft tissues or to the root canals. For the fast and effective removal of caries lesions, enamel and dentin, or for the preparation of root canals, decisive laser parameters which play a dominant role during these non-mechanical treatments are: the laser wavelength, the pulse duration, the fluence, and the pulse repetition rate of the applied laser system. We report here of the advantages and technical features of a compact pulsed and frequency-doubled alexandrite laser system for cutting of enamel and dentin, for vaporization and coagulation of soft dental tissue, for preparation and sterilization of root canals, and for crystallization of composite material.

Previous studies have recorded the reduction of caries-like lesions or demineralization in extracted human teeth that had been irradiated with CO₂ laser, Nd:YAG laser, and Argon laser. This study was conducted to evaluate the effects of three different cw lasers on acid resistance and demineralization of dental enamel. Human enamel was laser irradiated with either Argon, CO₂, or Nd:YAG energy densities of 60 - 65 J/cm² or 120 - 130 J/cm². The amount of demineralization was determined in a rotating disk assembly (0.1 M acetate buffer, pH - 4.5) for 24 hours and the results determined and plotted against the non-lased control using microradiographs and computerized imaging. The amount of dissolution of tooth structure lost to demineralization in 4.5 pH acid bath in a 24 hour period was reduced from approximately 140 microns for the unlased control to approximately 90 microns for the Argon laser and 70 microns for the CO₂ laser at 60 - 65 J/cm². At 120 - 130 J/cm² the results were: 120 microns for the Nd:YAG, 70 microns for the Argon, and 45 microns for the CO₂ laser. This study shows that demineralization is reduced significantly in vitro when human enamel is exposed to Argon and CO₂ laser irradiation.