We report on the use of a blue laser diode to excite natural fluorescence from a range of dental samples. Sixty teeth with naturally occurring lesions were examined. The lesions were classified on visual inspection as falling into three classes as shiny lesions, dull lesions and brown lesions. The resulting fluorescence was then examined using a fibre optically coupled spectrometer in a series of wavelength bands. By examining the intensity ratios in the two wavelength bands 480-500nm and 620 to 640nm we were able to classify the lesion types and thus provide a quantifiable measurement of lesion types. This method has application for detection of dental caries as well as demonstrating potential application to evaluate lesions which may represent different degrees of caries activity.

Polarization Sensitive Optical Coherence Tomography (PS-OCT) was used to monitor the progression of simulated caries lesions on occlusal surfaces and image the lesions underneath composite sealants. The polarization sensitive system, recording images in both the parallel and perpendicular axes, was useful for enhancing the image contrast of the artificial caries and minimizing the interference of the strong reflections at surface interfaces. Using the perpendicular axis signal, the mean integrated reflectivity increase from day 0 to day 14 was 5.1 dB (p<0.01, Repeated-Measures ANOVA, Tukey-Kramer). For imaging the lesions underneath sealants, the mean integrated reflectivity of the enamel underneath 250, 500, 750 and 1000 μm of composite was calculated for the demineralized and control samples. The artificial lesions could be detected under 750 μm of visibly opaque sealant, with a 5.0 dB difference from the control samples (t-test, p<0.001). Tooth colored sealants allowed deeper imaging depth. The artificial lesions could be detected under 1000 μm of sealant, with a 6.6 dB difference from the control samples (t-test, p<0.001). This study demonstrated that PS-OCT can be used to track lesion progression on occlusal surfaces non-destructively with or without sealants.

New imaging technology is needed for the early detection of dental caries (decay) in the interproximal contact sites between teeth. Previous measurements have demonstrated that dental enamel is highly transparent in the near-IR near 1310-nm making that wavelength range ideal for the transillumination of interproximal lesions. However, imaging at 1310-nm involves the use of expensive InGaAs technology. The purpose of this study was to compare the performance of a low cost near-IR sensitive imaging system employing a CCD camera with enhanced near-IR sensitivity operating at 830-nm with the 1310-nm InGaAs system. Images of simulated caries lesions were acquired through tooth sections of varying thickness and whole teeth in order to demonstrate the utility of a near-IR dental transillumination system for the imaging of early dental caries (decay). Simulated lesions, representing the optical scattering of natural dental caries, were placed in plano-parallel dental enamel sections and whole anterior teeth. The contrast ratio between the simulated lesions and surrounding sound enamel was calculated from analysis of the respective spatial intensity profiles in the acquired projection images. This study shows that near-IR transillumination at 830-nm offers significantly improved image contrast over the visible range, but less image contrast than at 1310-nm.

Neodimium laser treatment has several drawbacks when used in the hard tissue cutting, because of the low absorption of the dental tissues at its wavelength. This investigation proved that the Nd:YAG radiation is a powerful ablation tool if it is used with the dye assisted method. Several in vitro tests on enamel and dentin were accomplished changing some laser parameters to have different pulse shapes and durations from 125μs up to 1.4ms. The importance of short time high power peaks, typical of crystal lasers, in the ablation process was investigated. The pulse shapes were analyzed by their intensity in space and time profiles. A first set of results found the optimum dye concentration be used in all the following tests. Furthermore the ablation threshold for this technique was found for each different pulse shapes and durations. A low energy ablation method was found to avoid temperature increase and surface cracks formation. In vitro temperature analysis was reported comparing the differences between no dye application laser treatment and with a dye spray applied. A strong reduction of the temperature increase was found in the dye assisted method. A discussion on the general findings and their possible clinical applications is presented.

It is necessary to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. The overall objective of this study was to test the hypothesis that lasers resonant to the specific absorption of water, collagen, and hydroxyapatite with pulse durations less than the thermal relaxation times at each respective laser wavelength will efficiently remove dentin with minimal peripheral thermal damage. Precise incisions were produced in 3 x 3 mm² blocks of human dentin using CO₂ (9.6 μm), Er:YSGG (2.79 μm), and Nd:YAG (355 nm) lasers with and without a computer controlled water spray. Polarization-sensitive optical coherence tomography was used to obtain optical cross-sections of each incision to determine the rate and efficiency of ablation. The peripheral thermal damage zone around each incision was analyzed using polarized light microscopy (PLM) and Synchrotron-Radiation Fourier Transform Infrared Spectro-microscopy (SR-FTIR). Thermally induced chemical changes to both mineral and the collagen matrix was observed with SR-FTIR with a 10-μm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10-μm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr ) of the deposited laser energy, with and without applied water at 9.6 um and only with applied water at 2.79 μm. For pulse durations greater than Tr, significantly greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water spray. There was minimal thermal damage for 355-nm laser pulses, however extensive mechanical damage (cracks) was observed. High resolution SR-FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub-microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone.

The sealing cements used in endodontics are commonly of the type activated by chemical reactions. During polymerization, mechanical contractions are not uncommon, leading to non-perfect sealing or treatment failure. Photopolymerizable cements usually presents superior performance as compared to those chemically activated. However, difficulties in carrying-up the light to difficult-to-reach regions like the dental apex preclude those material of being accepted in the dental office routine. Recently, a novel technique for the light curing of photopolymerizable cements in endodontic applications has been proposed. Such a technique makes use of a polymeric light guide to deliver the curing light to the apex region, for a single step polymerization of the canal filler. For this work, a 28 mm long polymer light-guide, has been produced. The polymer surface was roughened to produce light scattering and allow the light to escape from the guide. The light scattering profile along the body of the guide is an important property for the proposed application. We used an integrating sphere to measure the irradiation profile for the proposed endodontic device. It was found that the experimental data for the amount of light coupled into the integrating sphere as a function of the length of the cone inside the sphere fits to a double exponential model.

The success of endodontic treatment depends on the methods used for shaping, cleaning, disinfecting, and sealing of a root canal. In the last few decades, big progress has been achieved in the application of the following methods: manual instrumentation, sonic and ultrasonic devices, and rotary instruments. The procedures used in the root canal system preparation result in a smear layer creation. The aim of this study was to give more precision to the smear layer removal using laser radiation. The root canal systems of 20 human teeth were treated endodontically. As laser radiation sources, Er:YAG laser system generating a wavelength of 2940 nm (rep. rate 1.5 Hz, spot size diameter 320 um, number of pulses 55, energy 100 mJ) and Alexandrite laser system generating a wavelength of 375 nm (rep. rate 1 Hz, spot size diameter 320 um, number of pulses 200, energy 1 mJ) were used. As a delivery system, a hollow glass waveguide with the special X-ray contrast cover was used. The flexible waveguide was moved via root canal and the laser radiation cleaned the wall surface. After application of Er:YAG laser radiation, the smear layer was fully removed, the surface was clean and smooth, and in the SEM investigation the open dentinal tubules were visible. No cracks were determined. The surface modifications were also not observed after endodontic preparation as well as Alexandrite laser radiation therapy. The whole treatment can be checked by X-ray machine.

It is often necessary to replace pit and fissure sealants and composite restorations. This task is complicated by the necessity for complete removal of the remaining composite to enable suitable adhesion of new composite. Previous studies have shown that lasers pulses from a frequency-tripled Nd:YAG laser (355-nm) can selectively remove residual composite after orthodontic bracket removal on enamel surfaces. UV laser light is preferentially absorbed by polymeric resins and the organic content of the tooth enamel. The objective of this study was to determine if such laser pulses are suitable for selective removal of the old composite from pit and fissure sealants and restorations without damaging surrounding sound tissues. Optical coherence tomography was used to acquire optical cross sections of the occlusal topography and peripheral tooth structure non-destructively before application of the sealants, after sealant application, and after sealant removal with 355-nm laser pulses with intensities ranging from 0-10 J/cm². Thermocouples were used to monitor the temperature in the pulp chamber during composite removal under clinically relevant ablation rates, i.e., 30 Hz and 30 mJ per laser pulse. At an irradiation intensity of 1.3 J/cm² pit and fissure sealants were completely removed without visible damage to the underlying enamel. At intensities above 1.5 J/cm², the laser removes the resin layer while at the same time preferentially etching the surface of the enamel. Temperature excursions in the pulp chamber of extracted teeth was limited to less than 5°C if air-cooling was used during the rapid removal (1-2 min) of sealants, water-cooling was not needed. This is the first presentation of a method for the selective removal of composite restorative materials without damage to the underlying sound tooth structure.

Previous studies have shown that during IR laser irradiation at CO₂ and Er:YAG laser wavelengths, residual particles of fused non-apatite calcium phosphate phases accumulate that may inhibit adhesion to restorative materials. A layer of water added to the enamel surface before ablation prevents the accumulation of such phases. The objective of this study was to investigate the influence of laser pulse duration and wavelength with and without the added water layer on the bond strength of composite to laser prepared enamel surfaces. The surfaces of bovine enamel were irradiated by three lasers systems: a 0.5-μs Er:YSGG laser. a 25-μs Er:YAG laser and a 5-μs TEA CO₂ laser operating at 9.6-μm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. There was no significant reduction in the shear-bond strength of enamel to composite for the shorter erbium laser pulses if a water-spray was not used, in contrast to previous results for the 200-μs free-running Er:YAG laser in which the water-spray resulted in significantly higher bond-strengths. Shear-bond strengths for both erbium laser systems were significantly higher than for the CO₂ laser irradiated samples and the negative control (no acid-etch) but significantly lower than the positive control group (phosphoric acid-etch). The application of the water-spray markedly influenced the surface morphology for all three laser systems with the most uniform surface preparation being produced by the 25-μs Er:YAG laser and the 5-μs CO₂ laser with the water-spray.

Teeth-bleaching is an initial phase in the reproduction of an aesthetic smile; thus, it is very important that the dentist knows how to diagnose the causes of color changes and indicate whitening before proposing dental treatment. Technological advances in teeth-whitening lead to the development of new techniques, improving comfort, security and decreasing time of execution: argon laser, diode laser, LED whitening, xenon light whitening. The clearing agent used in all techniques, including home whitening, is hydrogen peroxide (H₂O₂) in different concentrations. In this study, the authors describe mechanisms of gel activation, the use of Laser and LED's for teeth-bleaching, the importance of diagnosis and the comfort of the patient in in-office teeth-bleaching techniques.

Dental ceramic:Duceram porcelain(Ducera,Dental-Gesellschaft mbH, FrankFurt, Germany) low fusing dental porcelain was subjected in this investigation to different types of laser radiations: a) Nd:YAG laser pulses o 8 ns, 200mJ/pulse for 5&10 minutes b) Tsonamy 70 fs laser pulses for 1 & 5 minutes c)193 nm Excimer laser pulses 6 &13 mJ/pulse for 5 & 10 minutes and finally d) 0.1, 0.3, 0.5 and 1 MRad of Gamma radiations using 10 samples for each type of radiation. Knoop hardness values of test samples were measured using a knoop hardness tester(KHN-Ernst Leitz Wetzlar Germany)showing increased hardness values for all test irradiated samples as compared with the control. Highest hardness value were recorded for Excimer laser 13 mJ/pulse-10 minutes(670kg/mm2 as compared with 410kg/mm2 for the control. On the other hand, the highest value for the transverse strength was obtained for Excimer laser 3.8mJ/pulse-10 minutes). To account for the structural changes occurring due to laser irradiations and leading to the detected here improvement in the mechanical properties we used several techniques which are known to be sensitive to any structural changes such as: x-ray diffraction, SE-Microscopy, FTIR & Raman spectroscopy. Our observations showed series of variations indicating good accordance in the introduced here results. A reasonable interpretation is given here for the effects and variations observed in our measurements and spectra as a result of both Gamma and Laser irradiation. Finally, the given here results indicated that Laser irradiation can be used as a powerful tool for improving the hardness and transverse strength of dental ceramic.

The aim of this study was to determine the appropriateness of Nd:YAG laser irradiation for root canal preparation. Tooth crowns were removed from single-rooted human teeth and a quartz optical fiber (diameter 400 μm) was inserted into the root canal orifice towards the apical foramen. The length of the fiber within the root canal was measured, and the irradiating length determined. Root canals were then filled with 3% TiO₂ emulsion solution (a photosensitizer) and irradiated using a pulsed Nd:YAG laser at 600 mJ/pulse (pulse frequency; 5 or 10 pps). During laser irradiation, the fiber was moved coronally from the apical region towards the canal orifice at a rate of 1 mm/s. Contact microradiographs (CMR) were taken before and after laser irradiation. Each root was then halved longitudinally, and the root canal surface observed by scanning electron microscopy (SEM). The CMR images of the tooth revealed that the root canal was slightly enlarged as a result of treatment. Carbonization of the root canal dentin was not seen, but a smear layer and melted dentin were observed by SEM. Nd:YAG laser irradiation using TiO₂ emulsion solution appears to be a useful tool for root canal preparation.

Apicoectomy is a surgical procedure that consists of radicular apex resection, eliminating periapical lesion. This study evaluated the effect of CO₂ and Nd:YAG lasers on root dentine permeability after apicoectomy with Er:YAG laser. Forty-four single-rooted teeth, obtained from the Endodontic Laboratory stock from the Faculty of Dentistry of Ribeirao Preto, University of Sao Paulo, were used. The teeth were instrumented with the step-back technique, irrigated with 1.0% sodium hypochlorite and sealed with Sealer 26 (Dentsply, Brazil) and lateral condensation. The samples were divided into four groups of 11 teeth each that had the root sectioned 2mm from the apex: G1 - roots were sectioned with a 4138 diamond bur with cooling; G2 - roots were sectioned with pulsed Er:YAG laser at the following parameters: 15 Hz and 250 mJ; G3 - roots were sectioned with pulsed Er:YAG laser and Nd:YAG laser (10 Hz, 100 mJ, and 1 W) was app0lied on the sectioned surface; G4 - roots were sectioned with pulsed Er:YAG laser and CO₂ laser (5 W, 10 seconds ON and 20 seconds OFF) was applied to the sectioned surface. The teeth were then impermeabilized with cyanoacrylate and placed in 0.5% methylene blue for 7 days. The proximal surface of the samples was removed for exposure of the sealed root canal and dye penetration was measured by means of microscopic evaluation. The results showed a statistically significant difference at the level of 1%. We conclude that all treatments presented microleakage and can placed in increasing order: Er:YAG (G2), Bur (G1), Er:YAG + Nd:YAG (G3); Er:YAG laser presented the lowest microleakage values, showing its viability for clinical use in apicoectomies.

The knowledge about and control of thermal energy produced by Er:YAG laser after irradiating hard dental tissues and compound resin is important because the pulp, like all vital biological tissue, has a certain capacity for supporting stimulus. The objective of this study was to analyze the thermal variation generated by Er:YAG laser (λ=2.94μm) during the preparation of a Class I cavity in the dental structure and in the removal of microhybrid Z100 (3M) compound resin. An evaluation was made of 30 maxillary human pre-molar teeth from the bank of the Endodontic Laboratory Center of Ribeirao Preto Dental School, Brasil. The sample was divided into 6 groups of 5 teeth each: Group 1, preparation of Class I cavity with Er:YAG laser (350mJ, 3Hz, 343 impulses, 120J, 113 seconds); Group 2, preparation of Class I cavity with Er:YAG laser (350mJ, 4Hz, 343 impulses, 120J, 81 seconds); Group 3, preparation of Class I cavity with Er:YAG laser (350mJ, 6Hz, 343 impulses, 120J, 58 seconds); Group 4, removal of compound resin from Class I preparation with Er:YAG laser (350mJ, 3Hz, 258 impulses, 90J, 85 seconds); Group 5, removal of compound resin from Class I preparation with Er:YAG laser (350mJ, 4Hz, 258 impulses, 90J, 67 seconds); Group 6, removal of compound resin from Class I preparation with Er:YAG laser (350mJ, 6Hz, 258 impulses, 42 seconds). The laser used was KaVo Key 2 (Biberach, Germany), λ=2,94μm, P=3 Watts, pulse duration of 250μs, with air-water cooling. The increase in temperature during dental preparation and the removal of the compound resin was evaluated by means of a Tektronix DMM916 Thermocouple (Consitec, Brasil). The results showed that the application of laser for the removal of the hard dental tissues and for the removal of compound resins with the pulse frequencies 3, 4 and 6 Hz did not generate heating greater than 3.1°C and remained within the histopathological limits permitted for pulp tissue (5.5°C) and there was a significant statistical difference between the heat generated by the application of laser in the removal of the hard dental tissues and in the removal of compound resins (p<0.01). The average increase in temperature of the compound resin component was greater than the tooth.

This study evaluated radicular dentine permeability of root canal walls when using different irrigating solutions associated or not with Er:YAG laser. Fifty human maxillary incisors, obtained from laboratory stock, were randomly divided into ten groups of five teeth each. External surfaces of the teeth were impermeabilized with cyanoacrylate (Super Bonder). After chamber access, the root canals were instrumented with the step-back technique. Ten ml of irrigating solution was used in each root canal. Group I: irrigated with distilled and deionized water; Group II: irrigated as Group I and irradiated with laser; Group III: irrigated with 0.1% laurel diethyleneglycol ether sodium sulfate; Group IV: irrigated as Group III and irradiated with laser; Group V: irrigated with 1% sodium hypochlorite; Group VI: irrigated as Group V and irradiated with laser; Group VII: irrigated with 15% EDTA; Group VIII: irrigated as Group VII and irradiated with laser; Group IX: irrigated with 10% citric acid; Group X: irrigated as Group IX and irradiated with laser. Laser (KaVo Key Laser II) was applied with the following parameters: 15 Hz, 300 pulses, 42 J total energy, and 140mJ input and 51mJ ouput. The fiber optic tip was introduced until the apex and the laser was activated. The tip was withdrawn gently with helicoidally movement from the apex until the cervical portion. After preparation of the root canals, the root were immersed in 10% copper sulfate for 30 minute and then immersed in 1% rubeanic acid alcohol solution for the same period. The roots were sectioned transversally into 150μm slices, sanded, washed, dehydrated, cleared and mounted on glass slides for microscopic examination. The quantification of the penetration of copper ions was done by morphometric analysis. Results showed that distilled and deionized water + laser and 1% sodium hypochlorite presented the highest dentine permeability (p>0.05) and was statistically different from the other groups (p<0.05). The use of 0.1% laurel diethyleneglycol ether dodiu7m sulfate and distilled and deionized water showed less of an increase in dentiene permeability than the other studied solutions and were statistically similar. One percent sodium hypochloroite +laser, EDTA + laser, citric acid + laser, 0.1% laurel diethyleneglycol ether sodium sulfate + laser and EDTA, citric acid were statistically similar (p>0.05) and showed intermediate values of dentine permeability when compared to the other treatments.

The first step towards the development of clinically useful optical diagnostic systems is achieving a fundamental understanding of how light propagates through the tooth. The optical properties of dental hard tissue needed to describe light propagation in those tissues have not been determined in the near-IR. Although it is well known that the overall magnitude of light scattering increases due to demineralization of tooth enamel and dentin, the specific nature of those changes, namely quantitative changes in the optical constants and the scattering phase function have not been determined. The objective of this study was to determine the changes in the optical constants and the scattering anisotropy of dental enamel after artificial demineralization at 1310-nm. During the caries process micropores are formed in the lesion due to partial dissolution of the individual mineral crystals. Such small pores are likely to behave as scattering centers, strongly scattering visible and near-IR light. In this study, demineralization increased the scattering coefficient more than two orders of magnitude at 1310-nm and the scattering due to the scattering centers (micropores) is highly forward directed.

Previous studies have shown that during the laser irradiation of dentin and bone, thermal damage can be minimized by using a highly absorbed laser wavelength, laser pulses shorter than the thermal relaxation time of the deposited laser energy at that wavelength, and the addition of a layer of water to the tissue surface before ablation. The objective of this study was to investigate the influence of laser pulse duration and wavelength with and without the added water layer on the bond strength of composite to laser prepared dentin surfaces. The specific hypothesis that was tested was that thermal damage to the collagen matrix in dentin compromises the bond strength to composite restorative materials. Three laser systems were employed that were tuned to water, collagen and mineral absorption with pulse durations less than the thermal relaxation time of the deposited energy. The surfaces of human dentin were irradiated by laser irradiation from free-running and Q-switched Er:YSGG lasers (2.79-μm), pulsed CO2 lasers operating at 9.6-μm and a Q-switched Nd:YAG laser operating at 355-nm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to access the suitability of laser treated surfaces for bonding. All the laser groups had significantly lower bond strengths than the positive acid etch control group. The highest bond strengths were for the short (<5-μs) Er:YSGG and CO₂ groups with water. Laser groups without water had significantly reduced bond strengths.

Previous studies have shown that laser irradiation of dental enamel by a pulsed carbon dioxide laser can inhibit subsequent acid dissolution of the enamel surface. The aim of the present study was to determine the influence of an applied water layer before laser irradiation by a 9.6-μm TEA laser on the dissolution kinetics of the dental enamel surface. Recent studies have shown that residual non-hydroxyapatite particles accumulate on the enamel surface if a water layer is not present before laser irradiation. Such non-hydroxyapatite mineral phases are expected to profoundly influence the surface dissolution rate. Bovine enamel blocks (3x3 mm²) were irradiated at 9.6-μm wavelength with a 5-8 μs pulse duration laser and a fluence of 20 J/cm². A motion control system and a liquid spray system were used to ensure uniform water application and uniform irradiation of the entire enamel surface. Surface acid dissolution profiles following irradiation were acquired with and without the water spray. Dissolution profiles without the water-spray manifested higher initial dissolution rates than the non-irradiated control group, followed by later rates lower than the control group. In contrast, dissolution rates with the applied water layer produced early low dissolution rates, lower than the control group, followed by a more rapid dissolution rate, similar to the control group. This study demonstrates that the application of a water layer before laser irradiation significantly alters the surface dissolution kinetics of dental enamel.

Raman Spectroscopy was used to examine the distribution of the organic components in the human dentin before and after the chemical and thermal etching process. Polished dentin disks (n = 6/group) with 4mm thickness from twelve third molars were irradiated with Er:YAG laser. The dentin disks were prepared by polishing through a series of SiO₂ papers with water and cleaned by ultrasonic system. Four pretreatment were performed. The disks were etched with 37% phoshporic acid for 15 s (group 1), Er:YAG laser 80 mJ, 3Hz, 30s. (group II), Er:YAG laser 120 mJ, 3Hz, 30s. (group III) and Er:YAG laser 180mJ, 3Hz, 30s. (group IV). The Raman spectra obtained from normal and treated dentin were analyzed. Attention was paid to the organic component (1453cm^-1). Raman spectroscopy showed that the organic dentin content were more affected in autoclaved teeth than in the specimens treated by Thymol. Peak area reduction in the specimens treated by Thymol in group I and II showed to be the most conservative procedures regarding to changes in organic dentin components. Pulse energies of 120 and 180 mJ showed to preduce more reduction in the organic content associated with more reduction in the peak areas at 1453 cm^-1.

It has been shown that both pulsed Nd:YAG (1064nm) and continuous diode (810nm) dental lasers kill pathogenic bacteria (laser antisepsis), but a quantitative method for determining clinical dosimetry does not exist. The purpose of this study was to develop a method to quantify the efficacy of ablation of Porphyromonas gingivalis (Pg) in vitro for two different lasers. The ablation thresholds for the two lasers were compared in the following manner. The energy density was measured as a function of distance from the output of the fiber-optic delivery system. Pg cultures were grown on blood agar plates under standard anaerobic conditions. Blood agar provides an approximation of gingival tissue for the wavelengths tested in having hemoglobin as a primary absorber. Single pulses (Nd:YAG: 100- ìs; diode: 100-msec) of laser energy were delivered to Pg colonies and the energy density was increased until the appearance of a small plume was observed coincident with a laser pulse. The energy density at this point defines the ablation threshold. Ablation thresholds to a single pulse were determined for both Pg and for blood agar alone. The large difference in ablation thresholds between the pigmented pathogen and the host matrix for pulsed-Nd:YAG represented a significant therapeutic ratio and Pg was ablated without visible effect on the blood agar. Near threshold the 810-nm diode laser destroyed both the pathogen and the gel. Clinically, the pulsed Nd:YAG may selectively destroy pigmented pathogens leaving the surrounding tissue intact. The 810-nm diode laser may not demonstrate this selectivity due to its longer pulse length and greater absorption by hemoglobin.