<b>Background and Objective</b>: 6.05-μm-laser is strongly absorbed by means of both the OH bending of water and
the amide-I of proteins. In order to prove the usefulness of dentin ablation by laser irradiation with λ = 6.05 μm, we
investigated an ablative behavior of bovine dentin without a water spray.
<b>Study Design/Materials and Methods</b>: The dehydrated bovine dentin was irradiated without a water spray by the
mid-infrared Free Electron Laser at λ = 6.05 μm and λ = 9.7 μm, while varying the laser parameters, such as the
incident fluence and the number of pulse. We observed the configurational changes in the irradiated dentin surface
using a scanning electron microscope and estimated the removed volume using a laser confocal microscope. Also,
we measured the temperature rise using a radiation thermometer and the emission spectrum using a fiber optics
spectrometer during laser irradiation.
<b>Results</b>: We found the followings: (1) the dentin was ablated by the evaporation of proteins at the maximum
temperature rise of ~400 degC; (2) the irradiated dentin surface had dentinal tubules and was not melted; (3) the
extent of the ablative behavior was proportional to the laser parameters used; (4) the tensile bonding strength
between the irradiated dentin surface and the composite resin was significantly higher than that for Er:YAG laser
<b>Conclusion</b>: We can conclude that 6.05-μm-laser can thermo-mechanically excise dentin by the evaporation of proteins even without a water spray. We showed the applicability of a 6.05-μm-laser to a non-invasive laser treatment.
Ultrashort-pulsed laser (USPL) can ablate various materials with precious less thermal effect. In laser dentistry, to solve
the problem that were the generation of crack and carbonized layer by irradiating with conventional laser such as
Er:YAG and CO<sub>2</sub> laser, USPL has been studied to ablate dental hard tissues by several researchers. We investigated the
effectiveness of ablation on dental hard tissues by USPL. In this study, Ti:sapphire laser as USPL was used. The laser
parameter had the pulse duration of 130 fsec, 800nm wavelength, 1KHz of repetition rate and the average power density
of 90~360W/cm<sup>2</sup>. Bovine root dentin plates and crown enamel plates were irradiated with USPL at 1mm/sec using
moving stage. The irradiated samples were analyzed by SEM, EDX, FTIR and roughness meter. In all irradiated
samples, the cavity margin and wall were sharp and steep, extremely. In irradiated dentin samples, the surface showed
the opened dentin tubules and no smear layer. The Ca/P ratio by EDX measurement and the optical spectrum by FTIR
measurement had no change on comparison irradiated samples and non-irradiated samples. These results confirmed that
USPL could ablate dental hard tissue, precisely and non-thermally. In addition, the ablation depths of samples were
10&mgr;m, 20&mgr;m, and 60&mgr;m at 90 W/cm<sup>2</sup>, 180 W/cm<sup>2</sup>, and 360 W/cm<sup>2</sup>, approximately. Therefore, ablation depth by USPL
depends on the average power density. USPL has the possibility that can control the precision and non-thermal ablation
with depth direction by adjusting the irradiated average power density.
The violet diode laser (405nm) has recently begun to be studied for surgical use and authors reported the soft tissue
could be effectively incised by irradiation power of even less than 1W. The wavelength of this laser is highly absorbed
by hemoglobin, myoglobin or melanin pigment. Cutting or ablating soft tissues by lower irradiation power might be
preferable for wound healing. The CO<sub>2</sub> laser is known to be preferable for low invasive treatment of soft tissues and
widely used. The CO<sub>2</sub> laser light (10.6μm) is highly absorbed by water and proper for effective ablation of soft tissues.
In this paper, we report the comparison of the violet diode laser with the CO<sub>2</sub> laser in surgical performance of soft
tissues. Tuna tissue was used as an experimental sample. In the case of the violet diode laser, extensive vaporization of
tissue was observed after the expansion of coagulation. Carbonization of tissue was observed after the explosion. On the
other hand, consecutive vaporization and carbonization were observed immediately after irradiation in the case of CO<sub>2</sub>
laser. The violet diode laser could ablate tissue equivalently with the CO<sub>2</sub> laser and coagulate larger area than the CO<sub>2</sub>
laser. Therefore the violet diode laser might be expectable as a surgical tool which has excellent hemostatis.
In the field of dentistry, effectiveness of USPL irradiation is researched because USPL has less thermal side effect to dental hard tissue. In this paper, we observed morphological change and optical change of dental hard tissue irradiated by USPL for discussing the safety and effectiveness of USPL irradiation to dental hard tissues. Irradiated samples were crown enamel and root dentin of bovine teeth. Lasers were Ti:sapphire laser, which had pulse duration (<i>P</i><sub>d</sub>)of 130 fsec and pulse repetition rate (<i>f</i>) of 1kHz and wavelength (<i>l</i>) of 800nm, free electron laser (FEL), which had <i>P</i><sub>d</sub> of 15 μsec and <i>f</i> of 10Hz and wavelength of 9.6μm, and Er:YAG laser, which had <i>P</i><sub>d</sub> of 250 μsec and <i>f</i> of 10Hz and wavelength of 2.94μm. After laser irradiation, the sample surfaces and cross sections were examined with SEM and EDX. The optical change of samples was observed using FTIR. In SEM, the samples irradiated by USPL had sharp and accurate ablation with no crack and no carbonization. But, in FEL and Er:YAG laser, the samples has rough ablation with crack and carbonization. It was cleared that the P/Ca ratio of samples irradiated by USPL had same value as non-irradiated samples. There was no change in the IR absorption spectrum between samples irradiated by USPL and non-irradiated sample. But, they of samples irradiated by FEL and Er:YAG laser, however, had difference value as non-irradiated samples. These results showed that USPL might be effective to ablate dental hard tissue without thermal damage.
A violet laser with an oscillating wavelength of 405 nm has recently been developed in industry. Laser irradiation at this wavelength penetrates tissue less aggressively than Nd:YAG and diode laser irradiation at wavelengths of 810 nm, and more aggressively than irradiation by carbon dioxide laser. Further, protein is reported to absorb this 405 nm wavelength at high rates. This study was conducted to evaluate the effect of the violet laser on soft tissue in vitro. A prototype violet diode laser produced by Sumitomo Electric Industries was used. This laser irradiates with a continuous wave at a wavelength of 405 nm. Soft tissue samples were irradiated by the device at output powers in a range from 850 mW to 2400 mW as the irradiated samples were conveyed at a scanning speed of 1 mm/sec. The beam diameter was about 270 μm. The irradiated samples were observed by a stereoscopic microscope, fixed with a 10% neutral formalin aqueous solution, and histologically examined. Irradiation by the device vaporized a U-shaped section of tissue to a depth of about 350 to 900 μm. A denatured layer measuring 300 to 450 μm in width was observed under the carbonization layer. The depth of vaporization increased in proportion to the power. These results indicate that a violet laser has good potential to become an effective laser for the cutting and coagulation of soft tissue.
Mucocele is an oral soft tissue cyst caused by the disturbance of saliva flow. Mucocele is widely observed in child patients and recurrence is high. The objective of this study was to clarify the effect of CO<sub>2</sub> laser irradiation in the case of mucocele. A CO<sub>2</sub> laser was used on 45 subjects, aged between 0 to 15 years, having mucocele on lip, lingual, or buccal mucosa. Our procedure in using CO<sub>2</sub> laser was not to vaporize the mucocele but to remove the whole mucocele mass. The border of mucocele was firstly incised by laser following defocusly ablating the root or body of mucocele separating from sorrounding tissue. As a result, mucocele was easily and completely removed without breaking the wall of mucocele. None of the cases required suturing. The results were as follows. 1. The mucocele of lip or lingual mucosa with a rich blood supply, was efficiently removed, without bleeding, giving a clear operative field during the operation. 2. The surgery itself was simple and less time-consuming. 3. After two or three weeks the wound was completely healed without almost any discomfort in all patients 4. Wound contraction and scarring were decreased or eliminated. 5. The reoccurrence of mucocele was not seen, except only in one case of lingual mucocele. In conclusion the use of CO<sub>2</sub> laser proved to be a very safe and effective mode for the removal of mucocele, especially in small children.
Several lasers have been used for clinical treatment in dentistry. Among them, diode lasers are attractive because of their compactness compared with other laser sources. Near-infrared diode lasers have been practically used for cutting soft tissues. Because they penetrate deep to soft tissues, they cause sufficiently thick coagulation layer. However, they aren't suitable for removal of carious dentin because absorption by components in dentin is low. Recently, a violet diode laser with a wavelength of 405nm has been developed. It will be effective for cavity preparation because dentin contains about 20% of collagen whose absorption coefficient at a violet wavelength is larger than that at a near-infrared wavelength. In this paper, we examined cutting performance of the violet diode laser for dentin. To our knowledge, there have been no previous reports on application of a violet laser to dentin ablation. Bovine teeth were irradiated by continuous wave violet diode laser with output powers in a range from 0.4W to 2.4W. The beam diameter on the sample was about 270μm and an irradiation time was one second. We obtained the crater ablated at more than an output power of 0.8W. The depth of crater ranged from 20μm at 0.8W to 90μm at 2.4W. Furthermore, the beam spot with an output power of 1.7W was scanned at a speed of 1mm/second corresponding to movement of a dentist's hand in clinical treatment. Grooves with the depth of more than 50μm were also obtained. From these findings, the violet diode laser has good potential for cavity preparation. Therefore, the violet diode laser may become an effective tool for cavity preparation.