The effect of Nd:YAG laser on tissue is dependant on treatment power, times and frequencies. In order to determine the biologic effect Nd:YAG laser radiation on dental pulp tissue, human dental pulp fibroblasts were obtained from extracted human teeth, and grown in DME containing 10% FBS and used as passage 6 - 7. Confluent cells were exposed to defocused laser energy (1 W, 10 Hz) using a pulsed (120 microsecond(s) ) fiberoptic delivered (320 micrometers fiber) Nd:YAG for 1 - 5 minutes. The cells were labeled with 10 (mu) Ci/ml of ³H proline for 16 hours. Untreated cultures were used as controls. Collagen synthesis was expressed as DPM X 10^-3 mg/protein. The purpose of these measurements was to ascertain whether these radiation levels may induced a reparative response resulting in enhanced collagen synthesis. The results showed that at 1 - 5 minutes there was not significant effect. The tested lasing doses apparently did not cause any injurious effect to the fibroblasts, hence no increase in collagen synthesis.

The effects of the Holmium:YAG irradiation on the pulpal tissues and surface topography on root surface dentin in human teeth in vivo were studied. The exposed root surfaces of seventeen pre-immediate denture patients were scaled and root planed with a Gracey 3 - 4 curette apical to the dentinoenamel junction until smooth and hard. The prepared root surfaces of two teeth per patient were exposed with Holmium:YAG laser energy after an application of nonfilled resin/fluoride mixture. The laser exposed areas were below the dentinoenamel junction around one-half of each root surface. The opposing sides of each of the teeth received resin/fluoride but no laser energy. A third tooth was identified as a nontreated control. The HO:YAG at 2.12 microns wavelength with a defocused beam size of 3 mm was used. The amount of laser energy delivered per 3 X 5 mm area was 0.450 (+/- .05) joules with a fluence of 2.66 - 3.30 J/cm². The teeth were extracted after periods of 45 - 120 days. The specimens were fixed in formalin and prepared for histological examination using hematoxylin and eosin stains. Microscopic evaluation of room surfaces showed increased smoothness on the laser treated sites compared to their opposing non-lased sides. Histological examination of the pulpal tissues exhibited no abnormal changes. No clinical symptoms of pulpal pathology were produced. HO:YAG laser energy proved safe for treating room surfaces of human teeth in vivo under conditions presented in this study.

These investigations were performed to determine thermal, histological and incisional effects in soft tissue of laser irradiation at 9.3 um. Specifically, the consequences of varying pulse duration, interval and frequency, peak and average powers and energy densities were studied. In fresh pig's jaws, 6 standardized incisions, 3 cm in length, were made per parameter using a template and motorized jig. Incisions were made at various standardized anatomical sites, and surface thermal events monitored using an IR camera. Laser parameters investigated: power: 1 - 11 W, duty cycle: 10 - 90%, Pulse duration: 1 - 200 ms, at gated continuous wave. Superpulse and OptiPulse^TM modes with 300 us pulses were also investigated. Incision width and depth as well as collateral tissue effects were assessed statistically. They were directly related to the parameters used. Ease of incision and effects on underlying bone were also parameter-related.

The last five years have represented a great advance in relation to laser development. Countries like Japan, United States, French, England, Israel and others, have been working on the association of researches and clinical applications, in the field of laser. Low power lasers like He-Ne laser, emitting at 632,8 nm and Ga-As-Al laser, at 790 nm, have been detached acting not only as a coadjutant but some times as an specific treatment. Low power lasers provide non thermal effect at wavelengths believed to stimulate circulation and cellular activity. These lasers have been used to promote wound healing and reduce inflammation edema and pain. This work presents a five year clinical study with good results related to oral tissue healing. Oral cavity lesions, like herpes and aphthous ulcers were irradiated with Ga-Al- As laser. In both cases, an excellent result was obtained. The low power laser application decrease the painful sintomatology immediately and increase the reparation process of these lesions. An excellent result was obtained with application of low power laser in herpetic lesions associated with a secondary infection situated at the lip commissure covering the internal tissue of the mouth. The healing occurred after one week. An association of Ga-Al-As laser and Nd:YAG laser have been also proven to be good therapy for these kind of lesions. This association of low and high power laser has been done since 1992 and it seems to be a complement of the conventional therapies.

A prototype of Er:Tm:Ho:LiYF₄ (Ho:YLF) laser, emitting at 2,065 micrometers , 1,25 J 5 Hz, with pulsewidth of 250 microsecond(s) was developed for biomedical applications. In order to verify the possibility of using this laser for cavities preparation in vivo, temperature rise in the pulp chamber must be known. Temperature changes were measured during Ho:YLF irradiation with 500 mJ/pulse, 30 pulses/position with energy density of 2079 J/cm²/pulse. Two groups of teeth were used: group I with pulp chamber empty and group II with pulp chamber filled with phase change material. In both cases, there were no temperature rise above 3,8 degree(s)C in the pulp chamber.

The aim of this study was to investigate the impact of 2nd harmonic Alexandrite-laser radiation (wavelength 380 nm, pulse duration 100 ns) on the growth of bacteria. Bacteriodes vulgatus was chosen as typical and easy to handle anaerobic germ. Escherichia coli wild-type was chosen as a control germ, which is well investigated by many other groups at a wide range of different irradiation conditions. All germs were cultured on agar plates, suspended and irradiated in an optical transparent irradiated medium, and afterwards plated on agar again. An optical transparent irradiation medium minimizes photothermal and photochemical side effects onto the bacteria, which otherwise would be induced by absorption of the laser radiation in an optical opaque culture medium. Imaging of a quartz fiber surface onto the bacterial suspension guaranteed homogeneous irradiation of the sample. Different total energies were achieved by different numbers of pulses. Inhibition of bacterial growth could be observed for both germs. The effectiveness is depending on the type of bacteria and on total energy applied.

The purpose of our research is to determine the effects of KTP laser on root cementum and fibroblast attachment. Initial work has been completed in testing the effect of different energy levels on root surfaces. From these studies optimal energy levels were determined. In subsequent studies the working distance and exposure time required to obtain significant fibroblast attachment to healthy cementum surfaces were investigated. Results showed that lased cemental surfaces exhibited changes in surface topography which ranged from a melted surface to an apparent slight fusion of the surface of the covering smear layer. When the optimal energy level was used, fibroblasts demonstrate attachment on the specimens, resulting in the presence of a monolayer of cells on the control surfaces as well as on the surfaces lased with this energy level. The present study investigates the treatment of pathological root surfaces and calculus with a KTP laser utilizing these optimal parameters determine previously. Thirty single rooted teeth with advanced periodontal disease and ten healthy teeth were obtained, crowns were sectioned and roots split longitudinally. Forty test specimens were assigned into 1 of 4 groups; pathologic root--not lased, pathologic root--lased, root planed root and health root planed root. Human gingival fibroblasts were seeded on specimens and cultured for 24 hours. Specimens were processed for SEM. The findings suggest that with the KTP laser using a predetermined energy level applied to pathological root surfaces, the lased surfaces provided an unacceptable surface for fibroblast attachment. However, the procedural control using healthy root planed surfaces did demonstrate fibroblast attachment.

The concept of guided tissue regeneration (GTR) allowing cells from the periodontal ligament and alveolar bone to repopulate the treated root surface has shown the ability to obtain periodontal new attachment. Healing studies have also shown that conventional GTR therapy still does not exclude all the epithelium. This epithelial proliferation apically interferes with the establishment of the new connective tissue attachment to the root surface. The objective of this research study was to examine whether controlled de-epithelialization with the carbon dioxide laser during the healing phase after periodontal surgery, would retard the apical migration of the epithelium and thereby enhance the results obtained through guided tissue regeneration. Eight beagle dogs were used, the experimental side received de-epithelialization with the CO₂ laser in conjunction with flap reflection and surgically created buccal osseous defects. Selected defects on each side were treated with ePTFE periodontal membranes. The laser de-epithelialization was repeated every 10 days until removal of the membranes. The control side received the same surgical treatment without laser application. This experimental design allowed histologic study of the new attachment obtained in defects treated with flap debridement with or without laser de-epithelialization and with or without ePTFE membranes. A statistical analysis was performed on the histometric data from 48 teeth in the 8 dogs after 4 months of healing. The results showed significant amounts of new attachment obtained from all four treatment modalities with no statistically significant differences for any one treatment. However, the trend towards enhanced regeneration with the combined treatment of laser and membrane vs. membrane alone or debridement alone was evident. The histologic analysis revealed a significant amount of newly formed `fat cementum' seen only on the laser treated teeth. This feature was the most remarkable finding of the study and warrants further research to understand the origin of this phenomenon.

In this study, a fluorescence technique was developed for visualization of dentin using confocal laser scanning microscopy (CLSM). Eighteen extracted human teeth were used: 13 showing no clinical signs of caries and 5 with visually apparent decay. Preliminary study: All teeth were horizontally sectioned to approx. 200 micrometers thickness and pre-treated as follows: no pretreatment; vacuum only; ultrasonication only; sodium hypochlorite (NaOCl) only; vacuum and NaOCl; ultrasonication and NaOCl; or vacuum, ultrasonication and NaOCl. Samples were stained with Rhodamine 123 fluorescent dye at a concentration of 10^-5 M in phosphate buffer saline for 1 to 24 hours. Caries study: Dentin surfaces, some with pre-existing caries, were visualized using CLSM. Most dentin tubules in sound dentin appeared open using CLSM, but most dentin tubules in carious dentin appeared closed or narrowed. Surface images obtained using CLSM were similar to those seen by SEM, but additional subsurface imaging was possible using CLSM at depth intervals of 1 micrometers to a depth of 30 - 50 micrometers . This technique shows good potential for non-invasive surface and subsurface imaging of dentin structures.

Dental hard tissues can be ablated efficiency by (lambda) equals 3 micrometers laser irradiation with minimal subsurface thermal damage. However, the potential of lasers operating in the region of the infrared for caries preventive treatments has not been investigated. In this study, the caries inhibition potential of Er:YAG ((lambda) equals 2.94 micrometers ) and Er:YSGG ((lambda) equals 2.79 micrometers ) laser radiation on dental enamel was evaluated at various irradiation intensities. Pulsed IR radiometry and scanning electron microscopy (SEM) were used to measure the time-resolved surface temperatures during laser irradiation and to detect changes in the surface morphology. The magnitude and temporal evolution of the surface temperature during multiple pulse irradiation of the tissue was dependent on the wavelength, irradiation intensity, and the number of laser pulses. Radiometry and SEM micrographs indicated that ablation was initiated at temperatures of approximately 300 degree(s)C for Er:YAG and 800 degree(s)C for Er:YSGG laser irradiation, well below the melting and vaporization temperatures of the carbonated hydroxyapatite mineral component (m.p. equals 1200 degree(s)C). Nevertheless, there was marked caries inhibition for irradiation intensities below those temperature thresholds, notably 60% and 40% inhibition was achieved after Er:YSGG and Er:YAG laser irradiation, respectively. These results indicate that the Er:YSGG laser can be used effectively for both preventive dental treatments and for hard tissue removal.

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 roles of several of the laser parameters in the observed inhibition are still unknown. The aim of the present study was to examine the roles of pulse duration and repetition rate by the use of in vitro caries experiments, single and multiple pulse temperature measurements, and SEM observations, each following CO₂ laser irradiation of dental enamel. We used pulse durations of 100 and 500 microsecond(s) at wavelengths of 9.3, 9.6, 10.3 and 10.6 micrometers , fluences of 2.5 or 5 J/cm² per pulse, and 25 pulses per treatment window on human enamel. To study repetition rate we used 26 pulses, wavelength of 9.3 micrometers , at 1, 10, 25 or 40 Hz, with a fluence of 2.5 or 3.5 J/cm² per pulse. A complex relationship among pulse duration, wavelength and fluence was demonstrated. Increasing the repetition rate improved the inhibition up to a plateau at 25 Hz. Optimum caries inhibition in enamel appears to be achieved by pretreatments that produce surface temperatures in the range of 800 - 1000 degree(s)C. Optimization of pulse duration, wavelength and repetition rate should allow for effective clinical caries inhibition with short treatment times and minimal change to surface topography of enamel.

A set of interrelated physical models has been developed for use in the rational design of laser irradiation regimens for improving the resistance of tooth enamel to dental caries. Taken together, these models describe (1) the formation of subsurface lesions in dental enamel; (2) the dependence of this lesion formation on micro-environmental solution chemistry variables such as pH and concentrations of calcium, phosphate and fluoride; (3) the dependence of this lesion formation on the metastable equilibrium solubility; (4) the alteration of the MES of enamel by exposure to elevated temperatures and (5) the time-temperature profiles achieved by laser irradiation of enamel. Appropriate laboratory procedures have been developed and carried out to determine the values of the relevant parameters of each of the above models. Key findings are: (1) the onset of dissolution is controlled by the micro-environmental solution ion activity product (IAP) for fluorapatite; (2) the value of this threshold IAP can be shifted significantly by laser irradiation; (3) this IAP shift corresponds to a lowering of the threshold pH for onset of demineralization by about 0.7 pH units; and (4) the set of models listed above can be used together in an integrated approach for the rational design of laser irradiation regimens for improving resistance to dental caries.

The paper summarizes the results of the experiments on the study of the changes in tooth and its pulp, caused by the odontopreparation by the pulsed erbium laser in comparison with the conventional and turbine dental drills. The results evident for the advantages of the laser dental drill application in some cases.

Previous studies have demonstrated the ability of the argon laser to polymerize light activated materials and improve enamel shear bond strengths. This study was conducted to evaluate the effects of the argon laser on dentin shear bond strengths of current dentin bonding systems. Argon laser (HGM Model 8) at 231 mw and 280 mw, 5 second bonding agent, 10 seconds composite and a conventional curing light (Translux EC/Kulzer) at 10 seconds bonding agent, 20 second composite were used to polymerize samples of dentin bonding systems: Scotchbond Multi-Purpose Plus (3M) and Prime Bond (Dentsply/Caulk), both with TPH (Dentsply/Caulk) composite. A flat dentin bonding site (600 grit) was prepared on the buccal surface of extracted human teeth. Twelve samples were made for each set of parameters for both laser and conventional light totaling 60 samples. Samples were stored in distilled water in light- proof containers for 24 hours at 37 degree(s)C. Shear bond strengths (MPa) were determined for each sample on the Instron testing machine. Mean values were calculated for each set of data and ANOVA with Fisher PLSD were used for statistical analysis. The argon laser provided bond strengths that were 21 - 24% greater than those of the conventional curing light system.

Laser modification of the dentin may increase the mechanical retention of composite resin restorations. The purpose of this study was to evaluate the effect of the Nd:YAG laser on dentin bonding. 170 dentin specimens were prepared by horizontal sectioning through the middle coronal third of molars. A 5 mm area of 140 samples were treated at powers of 0.3 to 3.0 W, pulse frequencies of 10 to 30 Hz, and energies of 30 to 150 mJ/pulse. The remaining 30 were untreated dentin sections. Samples were pumiced and bonded with Scotchbond 2 and Silux Plus composite, then light cured and stored at 100% humidity for 24 hours prior to debonding. Shear bond strength was measured and the type of failure was determined. Laser modification of the dentin improved bond strength by 68% compared with the controls. Microscopic examination of the lased samples after debonding showed that 5% failed adhesively at the dentin-resin interface, while 95% failed cohesively within the resin. Therefore, lasers increased dentin bond strengths by improving micromechanical retention.

The aim of present study was to experimentally evaluate osteointegration of the KrF laser diamond-like carbon coated titanium alloy Ti6Al4V cylindrical implants in a preliminary study in vivo. The films were created on cylindrical titanium substrates. Substrates were heated to 70 degree(s)C or 100 degree(s)C by resistively heated holder positioned 17 mm from sample. Target substrate distance was 5 cm, energy density of KrF laser beam on the target was 15 Jcm^-2. Deposition chamber was evacuated to 10^-2 Pa. Film various thickness were created. Control group contained the two samples of Ti6Al4V and two samples from sapphire. Ten rats Wistar were used in this investigation. The cylindrical implants were placed horizontally into the host bone. The position of implant in femur was controlled with radiograph. The implants were retrieved for 6 weeks. 70-nm thick sections (from 2 to 4 sections from each implant) were cut. The section were viewed using a polarized light photomicroscope Nikon. The percentage of bone/implant contact were determined. The level of osteointegration of the host bone were observed. The bone-implant femur and control femur were measured. Total or partial osteointegration was seen and measured depending on deposition conditions.

We review the basic laser ablation processes of dental hard tissue for wavelengths ranging from the IR to the UV. The underlying tissue removal mechanisms extend from water- mediated explosive, to thermomechanical, to plasma-mediated processes. This discussion is based on a literature review of the current state of hard tissue removal under various irradiation conditions combined with some new data using surface temperature measurements. The most effective tissue removal mechanism is the water-mediated explosive process in the IR at wavelengths between 3 and 10 micrometers . Highly controlled tissue removal at low ablation rates can be obtained in the near IR (around 1 micrometers ) using plasma-mediated ablation, provided the irradiation parameters are chosen appropriately. Similarly small ablation rates combined with good tissue specificity characterize the ablation in the UV region of the spectrum. The ablation mechanism in the UV is largely dominated by photothermal processes, although photochemical and thermomechanical processes may contribute.

A wide range of lasers have been investigated for their ability to ablate healthy and carious hard dental tissues.7'28 However, before laser ablation of hard dental tissues can become clinically viable, several issues pertaining to safety and efficacy of procedures need to be resolved. Thermal effects of laser irradiation must be quantified, due to pulpal sensitivity to fairly low levels of heat'8 and to thermally-induced structural changes and damage in hard dental tissues. 13,l216 j general, longer pulse durations are less desirable from the thermal aspect, as they produce greater intra-pulpal temperature rises than comparable shorter pulses.27 Thermal studies performed during laser ablation of dentin using the Q-switched nano-second pulsed Nd:YAG laser have demonstrated the capability of this laser for removal of decayed dentin with minimal thermal effects in adjacent dental tissuesJ821 Another issue involves potential deleterious laser-induced alterations in the tooth surface which may, for example, prevent successful bonding of restorative materials to the irradiated surfaces. Such factors include irradiation-induced melting, craterinc, charring or cracking. 22,23,25,26,29,42 Reports of chemical changes in surface composition. 22,3,24,25 Several researchers have investigated the use of lasers for intentional modification of tooth surfaces to improve the tooth surface/restoration interface. In these studies, lasers were usually used solely for surface treatment after conventional cavity preparation. 3334 '35, 3641, 30 31 32,43,44Most of these investigations were performed using fairly long-pulsed or Cw Nd:YAG, C02 or Argon lasers, which would tend to induce significant temperature increases during irradiation, giving rise to concerns about pulpal tolerance of such procedures. Moreover, the results obtained in these studies varied enormously, ranging from laser-enhanced bonding of dentin with composite resins 3 1 to marginal microleakage attributed to the laser tooth surface preparation. 34 33 This wide range of results demonstrates that further investigation and quantification of the issues involved is necessary prior to clinical application of lasers to restorative procedures. Cost/benefit factors should also be considered: dental lasers are currently still fairly expensive devices. Therefore it may be more useful to investigate the tooth/restoration interface after laser use for actual cavity preparation, instead of merely using such a costly device as an adjunct for minor modification of the surface of conventionally prepared cavities. This study was performed to evaluate the tootWrestoration interface created between a composite resin and the tooth surface in teeth where caries removal and cavity preparation were performed either conventionally or using the Q-switched nanosecond pulsed Nd:YAG laser. Microscopic evaluation of the laser-prepared surfaces was performed.

Absorption spectra of 0.1 - 0.2 mm thick, dehydrated sections of human teeth were measured in the transmission mode with a Bruker FT-IR spectrometer from 2.5 - 20 micrometers . Absorption peaks for amide I, II and III, carbonate and phosphate were identified. Craters were ablated in dentin and enamel using a tunable FEL at 6.45 micrometers at various fluences. Pulse duration: 3 microsecond(s) ; spot size (Gaussian, FWHM): 300 micrometers ; repetition rate: 10 Hz. Crater depth and width were measured from digitized optical images. Ablation rates were computed from crater depth and volume data. Selected specimens were examined with scanning electron microscopy to determine ablation surface characteristics. Depth of thermal damage and dentinal tubule morphology were estimated from SEM examination of fractures through ablation sites. Functions describing crater depth vs. number of pulses (quadratic function) were not the same as crater volume vs. number of pulses (linear function). Crater depth decreases with successive pulses, concurrently, the crater width increases. Thus, each pulse removes approximately a constant volume. Material was observed to flow through the dentinal tubules during and after ablation. Patent tubules on crater walls and floor were observed with SEM. Ablation rates in dentin were approximately 3X those in enamel at 6.45 micrometers . Ablation rates and surface characteristics varied across wavelengths from 5.8 to 8.0 micrometers .

During prior studies it could be demonstrated while engaging a frequency doubled Alexandrite-laser (wavelength 380 nm, pulse duration 100 ns, fluence 1 J/cm², pulse repetition rate 110 Hz) a fast and strictly selective ablation of supra- and subgingival calculus is possible. Even the removal of unstained microbial plaque was observed. First conclusions were drawn after light microscopical investigations on undecalcified sections of irradiated teeth. In the present study the cementum surface after irradiation with a frequency doubled Alexandrite-laser was observed by means of a Scanning Electron Microscope. After irradiation sections of teeth were dried in alcohol and sputtered with gold. In comparison irradiated cementum surfaces of unerupted operatively removed wisdom teeth and tooth surfaces after the selective removal of calculus were investigated. A complete removal of calculus was observed as well as a remaining smooth surface of irradiated cementum.

Pulsed IR laser ablation on dental hard substances was studied in the wavelength range between 9.5 and 11.5 micrometers with the Free-Electron Laser (FEL) in Nieuwegein/NL and between 6.0 and 7.5 micrometers with the FEL at Vanderbilt University in Nashville/TN. Depth, diameter and volume of the ablation crater were determined with a special silicon replica method and subsequent confocal laser topometry. The irradiated surfaces and the ejected debris were examined with an SEM 9.5 - 11.5 micrometers : depth, diameter and volume of the ablation crater are greater and the ablation threshold is lower for ablation with a wavelength corresponding to the absorption max. of hydroxyapatite (9.5 micrometers ), compared to ablation at wavelengths with lower absorption (10.5 - 11.5 micrometers ). For all wavelengths, no thermal cracking can be observed after ablation in dentine, however a small amount of thermal cracking can be observed after ablation in enamel. After ablation at 9.5 micrometers , a few droplets of solidified melt were seen on the irradiated areas, whereas the debris consisted only of solidified melt. In contrast, the surface and the debris obtained from ablation using the other wavelengths showed the natural structure of dentine 6.0 - 7.5 micrometers : the depth of the ablation crater increases and the ablation threshold decreases for an increasing absorption coefficient of the target material. Different tissue components absorbed the laser radiation of different wavelengths (around 6.0 micrometers water and collagen, 6.5 micrometers collagen and water, 7.0 micrometers carbonated hydroxyapatite). Nevertheless the results have shown no major influence on the primary tissue absorber.

The cavity surface and shape after Er:YAG laser ablation at different energies, number of pulses and at a different repetition rate were observed. Longitudinal sections of extracted human incisors and transverse sections of ivory tusk were cut and polished to flat and glazed surfaces. The samples thickness was from 3 to 5 mm. The Er:YAG laser was operating in a free-running (long pulse) mode. The laser radiation was focused onto the tooth surface by CaF₂ lens (f equals 55 mm). During the experiment, the teeth were steady and the radiation was delivered by a special mechanical arm fixed in a special holder; fine water mist was also used (water-mJ/min, a pressure of two atm, air-pressure three atm). The shapes of the prepared cavities were studied either by using a varying laser energies (from 70 mJ to 500 mJ) for a constant number of pulses, or a varying number of pulses (from one to thirty) for constant laser energy. The repetition rate was changed from 1 to 2 Hz. For evaluating the surfaces, shapes, and profiles, scanning electron microscopy and photographs from a light microscope were used. The results were analyzed both quantitatively and qualitatively. It is seen that there is no linear relation between the radiation pulse energy and the size of the prepared holes. With increasing the incident energy the cavity depth growth is limited. There exists some saturation not only in the enamel and dentin but especially in the homogeneous ivory.

Laser energy transmission through enamel and dentin may effect pulpal safety. In this research, energy transmission was measured by placing enamel and dentin samples directly on an optical detector (both specular and diffuse transmission). Recently-extracted non-carious third molars were cut at thicknesses of 0.5, 1.0, 1.5, and 2.0 (+/- 0.25) mm. Laser exposure was effected using a pulsed contact-delivered infrared Nd:YAG laser with 320 micrometers fiberoptic probe, moved continuously across the surface for 30 seconds per measurement. Transmitted energy was measured following every 50 pulses; three replications were performed per treatment condition. Power was applied on enamel and dentin at 8 parameters: 0.3, 0.5, 0.7 and 1.0 W with frequency of 10 Hz and at 1.0, 2.0, 2.5, and 3.0 W with frequency of 20 Hz (total measurements n equals 864). Multifactor ANOVA confirmed that transmission through enamel was greater than through dentin. Energy transmission increased with both power and frequency. In enamel, transmission decreased as thickness increased. The most significant determinant of energy transmission was the incident surface energy per pulse. Means for samples 0.5 mm thick, at 1 W, 10 Hz: in enamel, 53% of the laser energy was transmitted through the sample, compared with 14% through dentin. For samples 2.0 mm thick: in enamel, 38% of the laser energy was transmitted compared with 17% in dentin.

In spite of intensive research, lasers have not replaced conventional tools in many hard tissue applications. Ultrashort pulse lasers offer several advantages in their highly per-pulse-efficient operation, negligible thermal and mechanical damage and low noise operation. Possible development of optimal laser systems to replace the high-speed dental drill is discussed. Applications of ultrashort pulse systems for dental procedures are outlined. Selection criteria and critical parameters are considered, and are compared to the conventional air-turbine drill and to long and short pulsed systems.

An overview of the physics of dental tissue processing with ultra-short pulse lasers is presented. Due to the small ablation rate per pulse, multiple pulses are necessary for macroscopic material removal. The paper discusses the cumulative effect of multiple pulse processing. Experimental data and calculation of thermal loading are presented, and the optimal laser system repetition rate is estimated. Modeling of the crater produced by multiple pulses is presented and possibilities to control the crater shape are discussed.

A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10¹² W/cm² are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

Ultrashort laser pulse tissue ablation has demonstrated advantages of greatly reduced required energy and collateral damage. These advantages stem directly from the fact that laser energy is absorbed nonlinearly in a time too short for significant thermal and hydrodynamic response. The high peak power and short pulse duration both have implications for practical fiber delivery systems.

Lasers are currently limited in their ability to remove hard tissue. Furthermore, many laser systems, such as the long pulse infrared lasers used to ablate bone or hard dental tissue, also generate unacceptable heat levels and cause collateral tissue damage. Ultrashort pulse lasers, however, are highly efficient, quiet, and relatively free of charge. With recent developments now allowing operation at high pulse repetition rates, ultrashort pulse systems can yield significant material volume removal which can potentially match or even exceed conventional technology while still maintaining the minimal collateral damage characteristics. In this paper, the interaction characteristics of two pulse regimes with enamel and dentin: 350 fs pulse ablation of hard dental tissues is compared to the interaction with one nanosecond pulses. Ablation rates were characterized and surface morphology, and structure were evaluated using a scanning electron microscope.

In spite of intensive research, lasers have not replaced conventional tools in many hard tissue applications. Low removal rates, loud operation noise, and mechanical and thermal damage are among the main obstacles to successful application of lasers. Ultrashort pulse lasers offer several advantages in their high per-pulse-efficiency, negligible thermal and mechanical damage and low noise operation. Practical applications of these devices, however, depends critically on sufficiently high volume removal which should match or even exceed the high speed drill. In our study, acoustical output of the USPL is compared to the low and high speed dental drill, Er:YAG, and Ho:YSGG lasers. Noise levels of the USPL are shown to be negligible in comparison with all other tested system. In addition, thermal characteristics of hard dental tissue ablation by ultrashort pulse laser of low and high pulse repetition rates are presented. Encouraging results showing temperatures increases smaller than 10 degree(s)C even at the highest pulse repetition rates (1 KHz) are presented. A simple model for heat diffusion is discussed.

The effectiveness of the Er:YAG laser for caries removal was evaluated in vitro and in vivo. As the in vitro study, thirty-two extracted human teeth with cervical root caries were used. An axially divided half of each caries lesion was treated with the Er:YAG laser, and the other was removed with round steel burs mounted on a micromotor or was left untreated as a control. Laser irradiation was performed in contact and non-contact mode at 145 mJ/pulse (51.3 J/cm²/pulse) and 10 pps under water spray. Conventional micromotor treatment was performed at 10,000 rpm using some different size of round steel burs. Measurement of time required for caries removal, histological observation of decalcified serial sections, SEM observation and hardness measurement of the cavity floor dentin were conducted with both laser and conventional treatments. In addition to the above in vitro study, the usefulness of root caries treatment with the Er:YAG laser was assessed in vivo as a clinical trial. The results indicated that removal of carious dentin using the Er:YAG laser was completed effectively to the same extent as the conventional treatment and thermal damage of the lased cavity was minimum. The Er:YAG laser treatment diminished unpleasant sound and vibration, when compared with the conventional rotary technique. We conclude that the Er:YAG laser possesses the promising characteristics for caries removal.

A great deal of discussion has taken place regarding how to properly polymerize light activated resins. Claims are made that effective testing can be made by using surface hardness tests on samples with various dental instruments. Although these tests would probably identify a material that had been very poorly polymerized it would not identify materials that were properly polymerized. The lack of consistent, reproducible forces and evaluation of the results make these test practically worthless. Surface hardness which is important clinically has value when combined with evaluation of the surface immediately adjacent to the light source and the surface adjacent to the tooth. Also immediate and 24 hour testing to allow for continued polymerization is helpful in determining how to achieve best results for our patients. A variety of new light sources have been introduced to dentistry with claims of faster and better polymerizations. The visible light units are also undergoing improvements to include built in meters to monitor light output. The purpose of this study was to evaluate the top and bottom surface hardness of a composite resin using the following light sources: argon, xenon, and two visible light sources.

We have proposed and experimentally demonstrated a new configuration of laser Doppler flowmetry for dental pulpal blood flow measurements. To date, the vitality of a tooth can be determined only by subjective thermal or electric tests, which are of questionable reliability and may induced pain in patient. Non-invasive techniques for determining pulpal vascular reactions to injury, treatment, and medication are in great demand. The laser Doppler flowmetry technique is non-invasive; however, clinical studies have shown that when used to measure pulpal blood flow the conventional back-scattering Doppler method suffers from low signal-to-noise ratio (SNR) and unreliable flux readings rendering it impossible to calibrate. A simplified theoretical model indicates that by using a forward scattered geometry the detected signal has a much higher SNR and can be calibrated. The forward scattered signal is readily detectable due to the fact that teeth are relatively thin organs with moderate optical loss. A preliminary experiment comparing forward scattered detection with conventional back- scattered detection was carried out using an extracted human molar. The results validated the findings of the simple theoretical model and clearly showed the utility of the forward scattering geometry. The back-scattering method had readings that fluctuated by as much as 187% in response to small changes in sensor position relative to the tooth. The forward scattered method had consistent readings (within 10%) that were independent of the sensor position, a signal-to-noise ratio that was at least 5.6 times higher than the back-scattering method, and a linear response to flow rate.

The purpose of this in vitro study was to investigate and compare effects of currently available laser systems at different wavelengths (XeCl excimer laser, Holmium:YAG laser, Erbium:YAG laser) on porcine articulating facets, capsule and meniscus of the temporomandibular joint via photomacroscopy, light and scanning electron microscopy. From a critical review of the relevant literature and the preliminary observations of this investigation, it appears that the Neodymium:YAG laser is inappropriate for TMJ arthroscopic surgery with regard to the huge thermal injury caused to the remaining tissue. The Holmium:YAG laser suffers from remarkable photomechanical and photothermal side effects, whereas the Erbium:YAG laser ablates temporomandibular joint tissue efficiently with minimal adjacent damage--similar to the XeCl excimer laser, without entailing the risk of potential mutagenity. To sum up, it can be concluded that there is a clinical need for laser- assisted arthroscopic surgery of the craniomandibular articulation. Nevertheless, at present none of the available laser systems meet the medical demands completely. Currently, the Erbium:YAG laser seems to be the most suitable for TMJ arthroscopic surgery.