Thermal and histological events resulting from soft tissue incision using CO₂ lasers at 9.3 (mu) or 10.6 (mu) , fitted with a hollow wave guide or an articulated arm delivery system respectively, were investigated. In 9 fresh pigs' mandibles, standardized incisions 3 cm in length were made in the oral mucosa. Incisions were performed in the cw mode at 1 W, 4 W, and 12 W. Thermal events were measured in adjacent soft tissues using thermocouples. Incisions were dissected out, fixed, embedded in paraffin wax, sectioned and stained with Serius Red. The Students' t-test for paired data was used to compare zones of necrosis, zones of collagen damage and thermal events. No significant temperature rise was measured during irradiation at any timepoints or power settings (p < 0.05). Results were very similar for the two lasers with significantly different results obtained only at the 12 W setting (p < 0.05). Vertical incision depths and horizontal incision widths did not differ significantly (p < 0.0001) at 12 W and 4 W. Horizontal and vertical zones of necrosis did not differ significantly (p < 0.0001) either between the two lasers at 12 W and 4 W. Thus the thermal and histological events occurring during soft tissue incision were similar using these two lasers, despite the difference in wavelength and delivery system.

The aim of this study was to analyze the ability of CO₂ laser to remove physiologic pigmentation of gingiva. Dogs were chosen for this study because of their intense black pigmentation on the gingiva, similar to what can be found in human negroes and other dark- skinned races. Three specimens were irradiated at the left side of the buccal aspect of the gingiva, while for comparison the right side was used as a control. CO₂ laser in a continuous mode applying 3 watt power was used (Xanar-20, USA). The portion to be irradiated was continuously irrigated with saline solution, to prevent tissue damage from the excessive heat generated. The handpiece device irradiated the target easily and fast, with no bleeding. All the pigmentation could be removed from the portion exposed to the laser beam. A 45th day follow up showed very little repigmentation just in one of the specimens. It could be concluded that CO₂ laser irradiation can be an alternative to remove pigmentation of the gingiva for cosmetic purposes. The risk of repigmentation exists, so the patients should be aware of this inconvenience, sometimes demanding further irradiation.

The aim of this study was to evaluate the clinical aspects of dental pulps submitted to shallow pulpotomy followed by CO₂ laser radiation at five different procedures. For this purpose, initially 66 dogs' teeth were opened and about 2 or 3 mm of coronal dental pulp was removed. Continuous irrigation with saline solution was implemented. The teeth were randomly divided into 6 groups of 11 each. After cessation of bleeding, in group I, CO₂ laser (Xanar-20, USA) was irradiated for 1 second at a power of 5 watts; in group II, 2 seconds at 3 watts; in Group III, 2 seconds at 5 watts; in Group IV, 1 second at 3 watts; in Group V, a continuous mode at 3 watts; Group VI served as a control, with no laser irradiation. The results showed no clinical differences between the 3 W and 5 W powers. Time period of irradiation exposition influenced definitively the clinical appearance of the dental pulps. Groups I and IV (1 second) were unable to stop the bleeding, which persisted over 15 minutes for all teeth. This may be due to the intense heat generated by CO₂ laser, causing vasodilatation. Groups II and III displayed a similar appearance, but bleeding stopped in about 10 minutes. Group V (continuous mode) had no bleeding after irradiation, but a plasma-like liquid would come out for almost 2 minutes. When comparing to the control (Group VI), all the pulps would assume a jelly-like aspect, with black granulated tissue on the surface, covering totally the pulps of Group V and partially the other groups. The histological results will be discussed in a further study. From the data obtained, it seems that CO₂ laser irradiation for pulpotomies should be done in a continuous mode, for clinical convenience in terms of time taken and effective irradiation.

Specimens consisted of 18 extracted single rooted teeth unaffected by periodontal disease. After debriding roots, specimens were randomly divided into 4 treatment groups and subjected to a single pass, at varying energy densities, of a CO₂, Nd:YAG, and Nd:YAG with air/water surface cooling (Nd:YAG-C). The rate of exposure was controlled at 4 mm/sec. Approximate energy densities were: CO₂, 138, 206, 275, and 344 J/cm²; Nd:YAG, 114, 171, 229, and 286 J/cm²; Nd:YAG-C, 286, 343, 514, and 571 J/cm². The CO₂ laser was used both in continuous and pulsed beam modes (20 Hz, 0.01 sec pulse length and 0.8 mm dia spot size) whereas the Nd:YAG and Nd:YAG-C were preset at 50 Hz, 0.08 sec pulse length and 0.6 mm dia spot size. Specimen examination by SEM revealed, for all lasers, a direct correlation between increasing energy densities and depth of tissue ablation and width of tissue damage. However, to achieve the same relative dept of tissue ablation, the Nd:YAG-C required higher energy densities than either the CO₂ or Nd:YAG lasers. The Nd:YAG-C generated a cavitation with sharply defined margins. Furthermore, regardless of energy density, and in contrast with other laser types, areas treated with the Nd:YAG-C did not exhibit collateral zones of heat damaged surface tissue.

This in vitro investigation characterized the chemical structure of lased root surfaces using FTIR photoacoustic spectroscopy. Twelve disks, 6 X 2 mm, were cut from debrided root surfaces of extracted, unerupted human molars. Each specimen was exposed to either the CO₂ Nd:YAG or water cooled Nd:YAG laser at these energy densities: CO₂, 275; Nd:YAG without water 571; Nd:YAG with water 571 and 1429 J/cm². Spectra were recorded using the photoacoustic cell attachment of an Analect RFX 65 FTIR spectrometer. Spectral contributions from protein occur at 1650, 1550, 1240 cm^-1; mineral contributions at 1030 - 1060 cm^-1, 600 - 560 cm^-1, 870 cm^-1. Specimens exposed to the Nd:YAG without water show a substantial reduction in the absorption bands attributable to protein and an additional band at 2015 cm^-1. In the presence of water, the band at 2015 cm^-1 does not appear at the lower energy density but is recorded at an energy density of 1429 J/cm² when the surface is darkened. The spectra of the CO₂ treated specimens, with the char layer present, show a significant reduction in the protein bands and additional bands at 2015 and 2200 cm^-1, that are tentatively assigned to the cyanamide and cyanate ions, respectively (Dowker and Elliott, 1979). These results suggest a reaction of the organic matrix and mineral with laser exposure.

Surface temperatures were monitored using pulsed photothermal radiometry (PPTR) during multiple pulse carbon dioxide laser irradiation ((lambda) equals 9.3, 9.6, 10.3 and 10.6 micrometers ). Permanent changes in the optical properties (reflectance and absorption) were observed at fluences greater than 2 J/cm² for dentin and 5 J/cm² for enamel. The laser irradiation changes the thermal and the optical properties of these tissues, substantially changing the energy deposition for subsequent laser pulses. The temperature response of enamel and dentin and the reflectance of dentin changed considerably with successive laser pulses. After 10 to 50 pulses the surface stabilized and no further changes were noted. Scanning electron micrographs of the laser conditioned surfaces showed large crystals of modified hydroxyapatite (approximately equals 500 nm) devoid of the organic matrix. Presumably, the water and the interwoven biopolymer matrix had been carbonized nd vaporized. Caries inhibition measurements after multiple pulse irradiation of enamel indicate that the stable laser conditioned surface is more resistant to acid dissolution than untreated enamel.

We present time-resolved reflection and surface temperature measurements of dental hard tissue irradiated with 100-microsecond(s) CO₂ laser pluses at two different wavelengths (9.6 and 10.6 micrometers ). The fluences in these single-pulse experiments ranged from 1 to 6 J/cm². Time-resolved temperature measurements indicate enhanced energy coupling (absorption) for the 9.6-micrometers laser light at fluences >= 6 J/cm² compared to irradiation at 1 J/cm². At the same time we observe a marked reduction in surface reflection. These results are consistent with a transition from strong, relatively narrow band absorption at low temperatures (low fluences) to weaker and broader band absorption (lower absorption coefficient) at higher temperatures. Near an absorption resonance the decreased absorption coefficient leads directly to reduced reflection losses and thus increased energy coupling to the target.

Several studies in our laboratories have demonstrated that CO₂ laser treatment of dental enamel can inhibit subsequent caries-like progression from 10 - 85% compared to controls. The reasons for these observed effects are still unclear. The aim of the present study was to combine and interpret results from in vitro caries experiments, single and multiple pulse temperature measurements, SEM observations, and crystallographic measurements, each following CO₂ laser irradiation of dental enamel or synthetic carbonated apatite. Optimum caries inhibition in enamel appears to be achieved by pretreatments that produce surface temperatures in the range of 600 - 1000 degree(s)C. For clinical application the surface enamel heating must not lead to consequent pulp chamber temperature rises of > 4 degree(s)C. To meet these conditions a pulsed laser with a sufficiently high absorption coefficient ((lambda) equals 9.3 or 9.6 micrometers ), pulse width near the thermal relaxation time of enamel (50 - 100 microsecond(s) ), minimum useful number of pulses (approximately 25), low repetition rate (approximately 10 Hz), and low but effective fluence (approximately 1-5 J/cm²/pulse), works well.

Laser energy transmission through hard tissue was investigated using a pulsed Holmium:YAG laser (2.12 micrometers wavelength). The surface of extracted human dental tissue, 200 micrometers to 700 micrometers in thickness, was irradiated by a laser beam of various fluences between 3 J/cm² to 28 J/cm². The transmitted energy through different dentinal components of the tooth was measured. For the mature teeth, the region of the dentinoenamel junction showed the least transmission and the coronal the most; the difference between the two regions could be as large as 20%. The unerupted or young teeth revealed the opposite transmission characteristics. Repeated laser treatment revealed an enhanced transmissibility and the transmitted energy reached a plateau after certain irradiation exposure. Also studied were the effects of various media on the dental transmissibility. For example, surface application of a smear layer of unfilled resin did not change the transmissibility but appeared to slow down the temperature build-up. Visible surface damage -- a yellow or a white spot on the treatment site -- appeared when the fluence reached beyond 20 J/cm². SEM samples revealed three different surface structural changes: melting with tubule closures, surface removal with tubule exposures, and surface cracking with crater formation, depending on the level of irradiation.

The Holmium:YAG laser at 2.12 microns wavelength was used to compare the changes in resistance to demineralization of the dentinal root surfaces of human extracted teeth in vitro. Three protocols were used: Group #1, and application of nonfilled resin/NaF (4%) solution followed by exposure with the Holmium:YAG laser beam; Group #2, an application of an aqueous solution of NaF (4%) only; and Group #3, irradiation with the laser beam only. The teeth were exposed on the root surfaces with untreated control and experimental sites on opposite sides of the teeth. A 3 mm spot size covered an area of 3 X 5 mm with 0.450 (+/- .05) joules at a fluence of 2.66 - 3.3 J/cm². All teeth were decalcified in a 10% Formic acid solution for a timed period. Samples were prepared for staining by sectioning the teeth at the dentoenamel junction and 3 mm apically to produce a cross-section of each tooth root surface. Each sample was placed in toluidine blue dye to observe the depth of dye penetration into the dentin of treated and control sites. Toluidine blue dye showed a consistent greater depth of dye penetration into the dentinal areas of the untreated control sites versus the resin/NaF-lased group. The topical fluoride only group did not appear different than the untreated control sites of the teeth. The lased only group showed areas of dye penetration similar to the untreated control sides with other areas of little or no dye penetration. The finding that HO:YAG laser energy/chemical agent produced increased resistance to demineralization of dentinal surfaces in vitro suggested potential clinical applications of this combined modality.

On the basis of research and analysis into optical properties of teeth, this paper introduces the techniques to transform teeth phosphorescence excited by ultraviolet light into electric signals and following steps for data collection, analysis and processing. Also presented are the methods to diagnose pulp-vitality, decayed teeth, and, especially, infant caries and pre-caries diseases. By measurement of a tooth's temperature, other stomatic illnesses can be diagnosed.

Flexible plastic waveguides were used in several fields of dentistry for treatments in the oral cavity. Soft tissue lesions were treated applying CO₂ laser energy. A new technique for dental implants was suggested using a combination of Er-YAG and CO₂ laser energy. Cavity preparation in the teeth was performed using the Er-YAG laser radiation and CO₂ energy transmitted by the waveguides was used for root canal treatments.

This presentation addresses the interplay between commerce and conscience. The relationship between industry and academia must be free of both true and apparent conflict of interest. Obviously, the matter is of great importance, since as scientists and clinicians, our integrity is our most valuable asset. This is no less true for the manufacturers of dental laser technology. Ethics, then, is a bottom-line issue for all concerned. Often, in spite of good intentions, there has been no clear-cut policy on this issue. Occasionally, when there has been policy, there has been no mechanism for implementation. Universities have conflict-of-interest requirements, while industry and others in the profession do not. In the academic sphere, we are obligated to be open, thorough, honest and scrupulous in our research and educational activities. Recently, the Board of Directors of the Academy of Laser Dentistry unanimously passed a resolution clarifying their position on conflict-of-interest issues. We offer it to SPIE so that ultimately, we may face our profession and business colleagues squarely, and with full and faithful disclosure. Issues of conflict of interest, principal investigators, financial interests, and recommendations for full disclosure are presented.

High-repetition rate, fiberoptic-delivered Nd:YAG lasers have increased oral soft tissue laser applications. This study focused on three parameters: the temperature rise occurring in deeper tissue during excision, the histology of thermal coagulation during excision of oral tissue, and effects of accidental exposure to adjacent hard tissue. Thermocouples were placed 5.0 +/- 0.5 mm in bone below fresh bovine gingiva and at the same depth in tongue; temperatures in the underlying tissue were measured during laser excision. An Nd:YAG laser with 100 microsecond(s) pulse duration was used to excise the tissue using a 200 or 300 micrometers diameter fiber in contact with the tissue. The soft tissue was excised using constant force and rate with laser powers of 1.5, 3, 5, and 10 W, and a variety of pulse rates. The tissue was bioprepared, sectioned and stained with hematoxylin and eosin. The width and depth of the tissue removed as well as lateral and deep thermal coagulation were measured in histologic sections with a measuring microscope (10x). Multifactor randomized ANOVA showed that probe diameter and repetition rates were not significant variables (p <EQ 0.05) but that temperature increased with laser power. Excision began between 2 and 4 W regardless of repetition rate. Excision efficiencies were determined for power and repetition rate. Within the parameters tested in this study, the pulsed fiberoptic-delivered Nd:YAG laser did not cause detrimental temperature rise or deep thermal coagulation in the excision of oral soft tissue.

A smear layer is created during the cleaning and shaping of root canal systems. The Nd:YAG laser has been shown to be effective in removing that smear layer and any tissue remnants from prepared root canal systems suggesting that it may aid in root canal sterilization without detrimental thermal effects to adjacent tissues. The root canal system of 72 single-rooted teeth was conventionally prepared and sterilized using gamma radiation. The teeth were divided into three groups of 24 each, 8 of which were inoculated only with sterile broth and remained as negative controls. Sixteen teeth of each group were inoculated with one of three organisms of 10⁶ to 10¹⁰ CFU/(mu) l: B subtilis (BS), E. coli (EC) and S. marcescens (SM) (10 (mu) l). Eight in each group were not treated further and served as positive controls. Sixteen test teeth were treated with the laser three times using each exposure parameter: 1 W, 10 Hz pulses per second (pps); 2 W, 20 Hz; and 3 W, 30 Hz inserted to the radiographic apex. Laser exposures were completed while withdrawing the fiber from the root canal system. At completion of laser exposure, all teeth were cultured, using sterile paper points and plated on brain heat infusion agar. Three cultures were taken for each tooth, the plates incubated for 72 hours, and read for the presence of growth of colony-forming units. The laser was able to reduce the number of organisms placed in root canal systems, and suggests that the laser may be used in root canal therapy for bacterial reduction and cleaning of the root canal space.

Laser technology is now being clinically investigated for the removal of carious enamel and dentin. This study used an animal model to evaluate histological pulpal effects from laser exposure. The molars of 24 Sprague-Dawley rats (n equals 264) were exposed to either a pulsed 1.06 micrometers Nd:YAG laser (120 microseconds, 320 micrometer diameter fiber), air rotor drill preparation or left untreated as controls. The following treatment conditions were investigated: control group (n equals 54); high speed drill with carbide bur (n equals 39); laser exposure at 50 mJ/p at 10 Hz (n equals 27), 100 mJ/p at 10 Hz (n equals 66) and 100 mJ/p at 20 Hz (n equals 39). A sixth treatment condition was investigated: root surface hypersensitivity, which included incremental laser exposure from 30 to 100 mJ/p at 10 Hz (n equals 39). The animals were euthanized either immediately after treatment, at one week, or at one month. The jaws were fixed and bioprepared. Remaining dentin thickness was measured, and ranged from 0.17 +/- 0.04 mm to 0.35 +/- 0.09 mm. The pulp tissue was examined for histologic inflammatory response. No evidence of pulpal involvement or adverse pulpal effects were found at any time period in teeth receiving 50 mJ/p. When histologic samples were compared with controls, all observations were similar. Of the 210 exposed teeth, 2 teeth receiving 100 mJ/p demonstrated abscess formation and were exfoliated. Further, in the rat molar when remaining dentin thickness was less than 0.5 mm, exposed to 100 mJ/p, threshold pulpal effects occurred. The response of rat pulp to laser exposure indicated no histologically measurable response to pulsed laser energy at 50 mJ/p.

Plaque, calculus and altered cementum removal by scaling and root planing is a fundamental procedure in periodontal treatment. However, the residual smear layer contains cytotoxic and inflammatory mediators which adversely affect healing. Chemical smear layer removal is also problematic. In previous investigations effective smear layer removal was achieved using long pulsed irradiation at 1.06 (mu) . However, laser irradiation was not adequate as an alternative to scaling and root planing procedures and concurrent temperature rises exceeded thermal thresholds for pulpal and periodontal safety. It was the aim of this study to determine whether nanosecond pulsed irradiation at 1.06 (mu) could be used as an alternative or an adjunct to scaling and root planing. Sixty freshly extracted teeth were divided as follows: 5 control, 5 root planed only, 25 irradiated only, 25 root planed and irradiated. Irradiation was performed at fluences of 0.5 - 2.7 J/cm², total energy densities of 12 - 300 J/cm², frequencies of 2 - 10 Hz using the Medlite (Continuum) laser. Irradiation-induced thermal events were recorded using a thermocouple within the root canal and a thermal camera to monitor surface temperatures. SEM demonstrated effective smear layer removal with minimal microstructural effects. Surface temperatures increased minimally (< 3 C) at all parameters, intrapulpal temperature rises remained below 4 C at 2 and 5 Hz, F < 0.5 J/cm². Without prior scaling and root planing, laser effects did not provide an adequately clean root surface.

Lasers are rapidly gaining recognition as an effective tool for dental hard tissue procedures. The prospect of using UV lasers for modifying tooth structure is severely limited by the question of delivery mode. One class of UV laser which can be delivered through optical fibers are the XeCl excimer lasers with a pulse duration of 120 ns which are also used for angioplasty procedures. In this study we compared morphological and thermal characteristics of the two XeCl excimer lasers. The study also shed some light on plasma emission and its role in ablative processes. It is shown that the two lasers exhibit relatively similar characteristics. However, while temperature effects are quite similar and ablation rates are slightly improved during longer pulse ablation, morphological structures as indicated by SEM are quite different, illustrating a different role and effect for the laser plasma.

Previous studies have reported altered dentinal structure and properties after laser irradiation. It was the aim of this investigation to determine the thermal and ablative effects of XeCl irradiation in dentin and then to investigate microstructural and physicochemical changes in the residual dentin structure. Extracted human molar tooth roots were bisected and coated with acid-resistant varnish, leaving a window. After irradiation of one half at 1 Hz, 15 ns pulse durations, fluences of 0.5 - 2 J/cm², both halves were subjected to acidified gelatin gel at pH 4.5. The carious lesions were bisected and used to perform SEM and microhardness measurements.

Caries selective ablation is fixed to a window of fluences predicted by the ablation thresholds of carious and healthy dentin, respectively. The aim of the study was to develop a dental handpiece which guarantees homogeneous fluence at the irradiated tooth surface. Furthermore the point of treatment should be cooled down without energy losses due to the cooling system. We suggest the direct coupling of the laser radiation into a laminar stream of liquid, which acts in turn as a lengthened beam guide. The impacts of the laser radiation and of the cooling medium fall exactly into the same point. Hot ablation debris is removed out of the crater by the flush of the water jet. Fluences are constant if the handpiece is used in contact mode or at a distance. Normally the surface of a bare fiber working in contact mode is destroyed after a few shots. Coupling the laser radiation into a stream of liquid prevents this destruction. Putting together the benefits of this special handpiece short overall treatment times seem to be possible. High average power can be applied to the tooth without the threat of thermal damage. Furthermore no time consuming cutting of the fiber prolongs the treatment time.

In a preceding trial the absorption characteristics of subgingival calculus were calculated using fluorescence emission spectroscopy (excitation laser: N₂-laser, wavelength 337 nm, pulse duration 4 ns). Subgingival calculus seems to contain chromophores absorbing in the ultraviolet spectral region up to 420 nm. The aim of the actual study was the ablation of sub- and supragingival calculus using a frequency doubled Alexandrite-laser (wavelength 377 nm, pulse duration 100 ns, repetition rate 110 Hz). Extracted human teeth presenting sub- and supragingival calculus were irradiated perpendicular to their axis with a laser fluence of 1 Jcm^-2. Using a standard application protocol calculus was irradiated at the enamel surface, at the junction between enamel and root, and at the root surface (located on dentin or on cementum). During the irradiation procedure an effective water cooling-system was engaged. For light microscopical investigations undecalcified histological sections were prepared after treatment. The histological sections revealed that a selective and total removal of calculus is possible at all locations without ablation of healthy enamel, dentin or cementum. Even low fluences provide us with a high effectiveness for the ablation of calculus. Thus, based on different absorption characteristics and ablation thresholds, engaging a frequency doubled Alexandrite-laser a fast and, even more, a selective ablation of sub- and supragingival calculus is possible without adverse side effects to the surrounding tissues. Even more, microbial dental plaque can be perfectly removed.

New possibilities of hard tooth tissues removal efficiency increasing by YAG:Er laser radiation, optimum focusing, reduction of pulse duration, spray and contour method are investigated and demonstrated in the present work.

The erbium:YAG laser coupled with a cooling stream of water appears to be an effective means of removing dental hard tissues. However, before the procedure is deemed clinically viable, there are several important issues of safety and efficacy that need to be explored. In this study we investigated the surface that remains following laser ablation of dentin and compared the results to the use of a dental handpiece. Specifically, we studied the effect the laser radiation had on the bonding of composite to dentin. The crowns of extracted human molars were removed revealing the underlying dentin. An additional thickness of material was removed with either a dental handpiece or an Er:YAG laser by raster scanning the samples under a fixed handpiece or laser. Comparable surface roughnesses were achieved. A cylinder of composite was bonded onto the prepared surfaces following the manufacturer's directions. The dentin-composite bond was then shear stressed to failure on a universal testing apparatus and the maximum load recorded. Preliminary results indicated that laser irradiated samples had improved bond strengths. SEM photographs of the surfaces were also taken to compare the two methods of tooth preparation.

Recently there has been much interest in lasers and their potential use to replace the dental drill. The research has been directed towards vital dental tissues. It must be understood that any laser to be used in dentistry which will replace the dental drill must also ablate and remove existing dental materials. Some concern exists about the ablation products when the Er:YAG laser is used to ablate dental materials. It is incumbent on the professionals using these lasers to understand the materials being produced by these lasers and protect themselves and their patients from possible toxic products. It is the intent of this paper to evaluate the products produced by the ablation of both dental amalgam and composite dental restorative materials and compare them with those produced by the traditional dental handpiece (drill).

The experimental setup of this study is focused on the changes in temporomandibular joint tissue after irradiation with an Erbium:YAG laser. Initially, the free-running beam from the laser was focused onto freshly excised porcine tissue samples, indicating an optimum average energy density and pulse duration for the purpose of temporomandibular joint surgery of about 15 - 60 J/cm² and 120 microsecond(s) - 240 microsecond(s) , respectively. Consecutively, an attempt was made to couple the Erbium:YAG laser beam on the one hand to optical fibers made of infrared-transmitting glasses (fluoride- and chalcogenide-based), on the other hand to a recently developed sapphire and liquid core fiber, respectively. From the preliminary observations of this investigation it appears that both the liquid core and the sapphire fiber are the most promising candidates for delivery of Erbium-YAG laser radiation in arthroscopic surgery of the craniomandibular articulation.

The processes of tissue damage up to destruction under laser radiation action which are characterized by definite dynamics of temperature in the region of laser heating are studied using pulsed photothermal radiometry of tissue (PPTR). The thresholds of the water evaporation from tissue and the tissue destruction for different tissues and wavelengths of incident laser radiation are considered. The difference in dentine temperatures when the tissue destruction starts for CO₂ and Er lasers is discussed. The features of the destruction processes and the difference of the temperatures corresponding to the tissue destruction thresholds under CO₂ laser action for hard and soft tissues are discussed.

The biological action of the laser radiation with the wavelength 2.69 micrometers onto the hard dental tissues and pulp was studied. Modes of laser action, preserving the pulp viability after the odontopreparation of the caries with the various rate, were revealed and clinically evaluated.

We report results of clinical application of the new computer-laser system. The system includes hardware and software means, which are applied for new efficient methods of prevention and treatment of main dental diseases. The hardware includes a laser physiotherapeutic device (LPD) `Optodan' and a fiberoptic laser delivery system with special endodontic rigging. The semiconductor AG-AL-AG laser diode with wavelengths in the spectral range of 850 - 950 nm (produced by Scientific-Industrial Concern `Reflector') is used as a basic unit. The LPD `Optodan' and methods of treatment are covered by Russian patent No 2014107 and certified by the Russian Ministry of Health. The automated computer system allows us to examine patients quickly and to input differential diagnosis, to determine indications (and contraindications), parameters and regimen of laser therapy, to control treatment efficacy (for carious -- through clinical indexes of enamel solubles, velocity of demineralization and other tests; for periodontal diseases trough complex of the periodontal indexes with automated registry and calculation). We present last results of application of the new technique and methods in treatment of dental diseases in Russian clinics.

As will be shown today, it should not follow that extended seniority, often senescence, should warrant the acclaim of a keynote address. There is an impression of a part of the mouth, that I have kept on my desk for some years to show what happens when you do not examine in detail the entire mouth. This impression shows a squamous carcinoma of the posterior aspect of the gum which I missed, because I did not examine closely the posterior oral cavity. So, this bit of an impression serves as a reminder to me of how unlearned I truly am. To assist you in developing some perspectives on the history of lasers in dentistry, the following material will be presented: 1963 - "I Start on the Teeth" from the Laser Laboratory Medical Center, University of Cincinnati. — 1987 "Laser Dentistry" (my current review) from the Laser Laboratory, Medical Center, University of Cincinnati. - 1991 - "NonSurgical Medicine" (my book) with a chapter by G. C. Willenborg, D.D.S.M.M.F.F.I.C.D., Lasers and Electro-optics in Dentistry, a comprehensive article, pages 253-292. - 1995 - "A Future For Laser Dentistry" from the Naval Medical Center, San Diego, California.