Dentin Ablation Research Articles

A laser‐abrasive method for the cutting of enamel and dentin

Background and Objective This paper introduced a new method for the removal of hard dental tissue based upon the use of particles accelerated by laser irradiation, which the authors have called the laser-abrasive method. Study Design/Materials and Methods The particles used were sapphire as powder or an aqueous suspension. The effect of the products of enamel ablation was also investigated. The particles were accelerated using submillisecond pulses of Er:YAG and Nd:YAG lasers. A strobing CCD camera was used to measure the speed of the ejected particles. The additional contribution of these particles to the efficiency of laser ablation of enamel and dentin was also investigated. Results The results showed that the enamel particles produced by the beam—tissue interaction were also accelerated by this process of ablation and were effective in the removal of enamel and dentin. The use of an aqueous suspension of sapphire particles increased the efficiency of enamel removal threefold when compared with the use of an Er:YAG laser with water spray. Conclusions The laser-abrasive method allowed for the removal of enamel and dentin at speeds approaching those of the high-speed turbine. Lasers Surg. Med. 39:435–444, 2001. © 2001 Wiley-Liss, Inc.

Morphological study of the effects of CO2 laser emitted at 9.3 microm on human dentin.

The purpose of this study was to investigate the effects of dentin ablation using a carbon dioxide (CO2) laser emitted at 9.3 microm by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). There have been no reports on effects of CO2 laser irradiation emitted at 9.3 microm on dentin by SEM and CLSM. Thirty extracted human teeth showing no clinical signs of caries were used. All teeth were horizontally sectioned to approximately 200 microm thickness and sections were irradiated using a 9.3 microm CO2 laser at different parameters as follows: 26 mJ [energy density (ED) 53.0 J/cm2] and 30 mJ (ED 61.1 J/cm2). After laser irradiation, samples were treated with sodium hypochlorite, stained using rhodamine-123, and observed with CLSM followed by SEM procedures. No craters or cracks were observed, but many small molten and rehardened particles were documented on the sample surface using SEM. Some small cracks were seen in the subsurface layer, and some patent dentinal tubules were detected using CLSM. These results suggest that laser irradiation at these parameters affected the sample surface only (less than 20 microm) and would be less harmful to thermal damage of dental pulp for dentin ablation.

Temperature Rise During Er:YAG and Nd:YAP Laser Ablation of Dentin

This in vitro study compared temperature rises during cavity preparation with an Er:YAG laser, Nd:YAP laser, and a high-speed handpiece. Eighteen teeth were sectioned longitudinally and divided into six groups: group 1 was treated with a carbide bur on a high-speed dental handpiece; group 2 was treated with an Er:YAG laser with an energy of 140 mJ, a pulse repetition rate of 4 Hz; and group 3 was treated with an Nd:YAP laser with an energy of 240 mJ, a pulse repetition rate of 10 Hz. In these groups no water cooling was used. Groups 4 to 6 were treated in the same way, but with water spray. Temperature increases were measured at different dentin thicknesses by a microthermocouple attached to the inner side of the pulp chamber. Water cooling was essential to reduce temperature effects in all groups. Nd:YAP laser induced significantly higher temperature rises than Er:YAG or handpiece. Temperature response to the Er:YAG laser and the handpiece seemed to be similar.

Picosecond Laser Ablation of Dentine in Endodontics

. The interaction of picosecond laser radiation with human dental tissue was investigated in this study, in order to determine the ablation rates and the surface characteristics of the dentine by using scanning electron microscopy (SEM). Dentine ablation was performed by using tooth sections of different thicknesses (0.5–2.0 mm). Dental tissue samples were irradiated in air with the fundamental wavelength and first harmonic of a regenerative amplifier Nd:YAG laser system, at 1064 nm and 532 nm, respectively, with a pulse duration of 100 ps and a pulse repetition rate of 10 Hz. The results showed very clean craters surrounded by minimum melting of the surface of dentine when the 1064 nm pulses were used. In contrast, when the first harmonic 532 nm pulses were used, the SEM examinations revealed cracks and melting of dentine with irregular surface modification. Consequently, it seems that cleaning and shaping of the root canal walls during endodontic therapy with the picosecond Nd:YAG laser application may be possible in the future. The, as yet unexplored, field of the picosecond laser interaction with hard dental tissue is expected to be a potential alternative for powerful laser processing of biomedical structures.

Morphological changes of human teeth with Er:YAG laser irradiation.

The purpose of this study was to investigate morphological changes in human enamel and dentin structures irradiated with the use of an Er:YAG laser. Despite the high number of research projects concerned with digital applications of lasers, few studies have targeted the effects of Er:YAG laser irradiation on human enamel or dentin structures. Enamel and dentin surfaces of 40 extracted human teeth were irradiated for 5 seconds with a 2.94 microns wavelength, at an output of 300 mJ. Histological and scanning electron microscope studies were then performed to determine the morphological changes in the enamel and dentin structures of those teeth. The Er:YAG laser beam produced defects without signs of serious thermal damage to enamel or dentin. Undesirable thermal effects such as surface cracking or carbonization were not observed. Histological examinations revealed the presence of a thin basophilic line at the bottom and along the walls of defects in the dentin. These morphological changes were evidence of minimal thermal damage to surrounding tissue. These findings suggest that it is possible to remove the enamel and dentin using Er:YAG laser irradiation with minimal thermal changes. However, the mechanism involved in the ablation of enamel and dentin by Er:YAG laser irradiation has not been clarified in this study. Therefore, more research is necessary before the Er:YAG laser can be used clinically in the future.

Laser ablation as a function of the primary absorber in dentin.

Infrared transmission spectra of dentin reveal a broad absorption band between 6.0 and 7.0 microns composed of absorption peaks of water, collagen and carbonated hydroxyapatite. The nearly constant absorption and the existence of absorption peaks of different tissue components were used to investigate ablation as a function of the primary absorber. Laser ablation of dentin as a function of fluence was studied in the wavelength range between 6.0 and 7.5 microns using the Vanderbilt Free-Electron Laser (FEL). Depth and volume of the ablation crater were determined with a silicon replica method and subsequent confocal laser topometry. SEM investigations were performed on the irradiated surfaces. For the description of the experimental data an ablation model is developed. At all applied wavelengths we found a linear increase of ablation depth as a function of fluence above a threshold fluence. The lower absorption of dentin at 7.5 microns compared to the absorption at 6.0, 6.5 and 7.0 microns results in a greater ablation threshold. At 6.0, 6.5 and 7.0 microns wavelengths the ablation thresholds are comparable. The experimental data are in good agreement with an ablation model using a mean absorption coefficient of the target material. No thermal cracking is observed after ablation in dentin. The post ablative surface structure at 6.0 and 7.0 microns looks similar whereas at 7.5 microns the surface reveals a greater roughness. The ablation efficiency and threshold depend on the mean absorption but do not depend upon the chemical identity of the primary absorber in dentin. Calculations show that heat conduction during the laser pulse leads to a thermal equalization between the heated microstructures and surrounding tissue resulting in an ablation with little dependence on the primary absorber.

Dentin and Pulp Response to Erbium:YAG Laser Ablation: A Preliminary Evaluation of Human Teeth

We determined the real effect of Erbium:YAG laser ablation on human teeth in vivo. We advocated the idea that overheating of teeth, specially pulp damage can be avoided if correct laser parameters are used. We evaluated human premolars scheduled for extraction during orthodontic treatment. Before tooth extraction, an oval cavity preparation was made with a pulsed Er:YAG laser. After extraction, the teeth were decalcified for 6 weeks. Routine staining with haematoxylin and eosin was performed on longitudinal section. One hundred seventy-two sections were prepared and examined in a light microscope. Under Er:YAG laser application, reduction of the dentin layer was observed. Dentinal tubules had a radial course up to the surface. No cracks or structural injury were observed. Inflammatory reaction in the pulp was not found. The vascularity of the pulp was normal. The odontoblasts were of the usual spindle-like or star-like cell shape. The cementum and epithelial attachment were healthy. No changes of structure or indications of inflammation were observed. The results of this in vivo experiment on human teeth confirm safety of Er:YAG laser ablation of enamel and dentin under the conditions described.

ArF excimer laser irradiation of human dentin.

The use of excimer lasers for treatment of dental hard tissues has considerable potential because the combined characteristics of low wavelength and short pulse result in limited heat diffusion and, therefore, tissue ablation without the problems of collateral damage. To date, there are relatively few published studies concerning the effects of excimer laser irradiation on dental hard tissues. Thus the present study was conducted to examine the morphological changes in tooth dentin subsequent to ArF excimer laser irradiation. The morphologic changes induced in normal, nondiseased human dentin following irradiation by an ArF excimer laser at fluences ranging from 1 to 4 J/cm2 and the number of laser pulses ranging from 50 to 1,000 were evaluated by scanning electron microscopy. Two modes of ablation, photochemical at low fluences and thermal at high fluences, were observed. A fluence of 1 J/ cm2 when combined with 50 or 100 pulses produced a uniform ablation of the dentin surface without signs of tissue melting. At fluences > 1.5 J/cm2, the thermal mode of ablation was more efficient at removing intertubular dentin than peritubular dentin. Further, when compared to the lower fluences, the higher settings produced a rougher ablation crater surface. Additionally, the higher fluences produced surface melting with each pulse and sealing of exposed dentinal tubules after irradiation with 100-300 laser pulses. The photochemical and thermal mechanisms of tooth dentin ablation were identified based on significant differences in tissue morphology following laser irradiation. The rates of tissue ablation and the observed morphologic changes indicate that the ArF excimer laser could be useful for caries removal and sealing of exposed dentinal tubules.

Dentin ablation with three infrared lasers

Background and Objective Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics. Study Design/Materials and Methods Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 μm and pulse duration (PD) of 250 μs, HO:YSGG at 2.1 μm and 250 μs and an Nd:YAG with WL of 1.06 μm and PD of 15ns. Results The highest surface temperatures were observed during Er:YSGG treatment (> 300°C), moderate temperatures with the Ho:YSGG (150°C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80°C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 μm). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nano-second system. Conclusion Possible explanation for these observations is given in terms of plasma characteristics. © 1996 Wiley-Liss, Inc.

Light Deposition in Dental Hard Tissue and Simulated Thermal Response

Near-IR (approximately 1 micron) lasers are presently used for a variety of intra-oral applications including dental hard tissue ablation, although the light intensity distribution and subsequent heating of the hard tissue are still poorly understood. This paper presents a detailed numerical study of the scattered light intensity distribution along with the corresponding predicted thermal response. The calculations are based on recently published scattering and absorption data for dental hard tissue around 1 micron. Our simulations indicate strongly enhanced energy deposition and concomitant heating near the dentino-enamel junction (DEJ), mainly due to the higher absorption in dentin. We predict from 10 to 20 times higher internal temperatures near the DEJ compared with the surface. For example, for 50-ms pulses of 5-J energy on a 3-mm-diameter spot (approximately 1 kW/cm2 or approximately 50 J/cm2), one can expect internal temperatures near the DEJ in excess of 100 degrees C. Elevated temperatures are predicted to extend far into the dentin, endangering the vitality of the pulp several millimeters below the surface. Our results are compared with published experimental data taken under similar conditions and are found to be in good general agreement. The results of this study do not contradict recently reported ablation of dentin with Nd:YAG laser radiation by contact fiber probes. In this case, the irradiation intensities are 3 to 4 orders of magnitude higher, so plasma formation and plasma shielding of the interior of the tooth are likely.

Dentin ablation by Ho:YAG Laser: Correlation of energy versus volume using stereophotogrammetry

The future use of lasers in endodontics is dependent upon predictable and consistent ablation of dentin. In this pilot study we used an Ho:YAG laser fiberoptic delivery system to apply laser energy to prepared tooth sections in vitro. Longitudinally sectioned single-rooted human teeth were subjected to single-energy pulses varying from 25 to 1750 mJ at a focal length of 1 mm. At different energy levels we observed changes in the dentin surface ranging from minute surface pitting to the formation of large craters. Scanning electron microscopy and stereophotogrammetry were used to determine the relationship between the amount of energy applied to dentin and the extent of dentin ablation. Dentin crater formation was quantified by determining surface area, depth, and volume of craters produced. Increases in laser energy were compared with increases in surface area, depth, and volume of craters produced within the range of 150 to 1200 mJ. The Ho:YAG laser fiberoptic delivery system used in this study provides an effective means of ablating dentin. Three-dimensional stereophotogrammetry may prove to be a useful method for further studies on the effects of laser energy on mineralized tissues.

Poster clinic #17 — Dentin ablation by laser: energy vs. volume

Poster clinic #17 — Dentin ablation by laser: energy vs. volume

Er:YAG laser ablation of enamel and dentin of human teeth: determination of ablation rates at various fluences and pulse repetition rates.

A pulsed Er:YAG laser (2.94 microns) was used to determine ablation depths per pulse of laser energy at 2 Hz and 5 Hz in human teeth cross sections of enamel and dentin. Ablation depths per pulse at 2 Hz in enamel of intact human teeth were measured and compared to ablation depths per pulse determined in enamel cross sections at 2 Hz. Close correlation was observed for ablation depths per pulse of laser energy between teeth cross sections and intact teeth for enamel. Photographs of lased holes at 2 Hz and 5 Hz indicated minimal thermal effects in enamel at fluences below 80 J/cm2. Minimal thermal effects in dentin were noted below 74 J/cm2. Scanning Electron Microscopy (SEM) pictures of lased dentin showed an irregular serrated surface. Results of this study suggest that the Er:YAG laser can effectively ablate enamel and dentin with minimal thermal effects at 2 Hz and 5 Hz.

Selectivity, efficiency, and surface characteristics of hard dental tissues ablated with ArF pulsed excimer lasers

Lasers are finding expanding applications in the field of dentistry. Cutting in soft tissue, hard dental material ablation, caries removal, and root canal therapy are only a few examples of dental laser uses. In this article, the application of short pulse ArF excimer laser to ablation of dentin and enamel is investigated. In particular, the effect of laser pulse repetition rates (PRR) and fluence levels on the efficiency of the ablation process and on the average thermal response of ablated surfaces is investigated. Ablation of dentin was found to be considerably more efficient than the ablation of enamel and depends exponentially on the laser fluence. Both dentin and enamel surfaces showed an increase in surface temperature with repetition rate. At lower PRR, however, temperature increases are very small. Surface temperature was also found to increase with laser fluence, although this increase is very small at laser PRR of 5 Hz or less. Tissue ablation rates were found to be comparable to or better than other nanosecond lasers, and left smooth surfaces, free of thermal damage. Microscopic examination of the ablated surface shows no crack formation, charring, discoloration, or any other thermal damage. The ablated surfaces appear to be very smooth, highly polished, and glossy looking as if they were subjected to thermal melting. This observation is indeed confirmed under scanning electron microscopy (SEM), where evidence of localized melting of the tissue is observed. Furthermore, a close SEM examination of the dentin surface reveals a selectively ablated intertubular dentin, while the remaining pillar-like dentin tubules are sealed off with fused peritubular dentin. At all fluence levels and PRR, the first three to four pulses impinging on an untreated enamel surface produced unusually large plumes of debris which were different in size, texture, and fluorescence emission characteristics from the ablation products of subsequent pulses. It is believed that these different ablation characteristics are a consequence of the pulsed ArF laser's ability to selectively remove residual matter from the more resistant enamel surface.