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 CO2 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/cm2. 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/cm2, 180 W/cm2, and 360 W/cm2, 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.
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 (Pd)of 130 fsec and pulse repetition rate (f) of 1kHz and wavelength (l) of 800nm, free electron laser (FEL), which had Pd of 15 μsec and f of 10Hz and wavelength of 9.6μm, and Er:YAG laser, which had Pd of 250 μsec and f 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.
Transdermal drug delivery system (TDDS), which is one of drug delivery system (DDS) for increasing the effectiveness of drugs, is enhanced absorption of drugs by laser irradiation. The purpose of this study is to investigate the optimum laser parameter for enhancing TDD and to examine the mechanism of TDD enhancement. In this study, hairless mouse skins (in vitro) were irradiated with Er:YAG laser, Nd:YAG laser and free electron laser (FEL), which were set up energy density of 0.5 J/cm2/pulse and exposure time of 5 second. We examined the flux (μg/cm2/h) of lidocaine (C14H22N2O, FW: 234.38) through the skins using high pressure liquid chromatography (HPLC), observed cross section of the irradiated samples using light microscope, and measured electrical resistance of the surface of skins. The HPLC results demonstrated that the TDD of the irradiated samples was enhanced 200-350 times faster than it of the non-irradiated samples. It of Nd:YAG laser, however, had no enhancement. The observation of cross section and the electrical resistance of skins were found to not remove the stratum corneum (SC), completely. These results show that laser irradiations, which has the strong absorption to skins, enhance TDD dramatically with low invasive.
It is necessary to control enhancement of transdermal drug delivery with non-invasive. The present study was investigated to assess the effectivity of enhancing the drug delivery by irradiating 6-μm region mid infrared free electron laser (MIR-FEL). The enhancement of transdermal drug (lidocaine) delivery of the samples (hairless mouse skin) irradiated with lasers was examined for flux (μg/cm2/h) and total penetration amount (μg/cm2) of lidocaine by High performance Liquid Chromatography (HPLC). The flux and total amount penatration date was
enhanced 200-300 fold faster than the control date by the laser irradiation. FEL irradiating had the stratum corneum, and had the less thermal damage in epidermis. The effect of 6-μm region MIR-FEL has the enhancement of transdermal drug delivery without removing the stratum corneum because it has the less thermal damage. It leads to enhancement drug delivery system with non-invasive laser treatment.
For non-invasive laser dental treatmet, a real-time and non-contact monitoring technique is needed. We have investigated the extent of the surface modification of root dentin using photoacoustic spectroscopy (PAS) and pulsed-photothermal radiometry (PPTR), and have discussed the applicability of each technology to in vivo monitoring during laser treatment. Root dentins were used as specimens. The wavelength, average power density, and exposure time used were varied within the ranges λ = 9.0-10.6 μm, Pav = 7-28 W/cm2, and τ = 0-10 s respectively. The temporal behaviors of the laser-induced acoustic waves and the temperature rise were measured with an audible microphone and a radiation thermometer, respectively. The extent of the surface modification was evaluated by using information on the ablation depth and the absorption spectrum of the irradiated dentin. The morphological and chemical changes of the irradiated dentin can be made available to assist in dentinal tubule sealing and increased acid resistance for root surface caries therapy. It was found that time-resolved measurements of the acoustic waves and the temperature are useful for a real-time understanding of the extent of the morphological and chemical changes, respectively. We have demonstrated that applicability of an in vivo monitoring technique using PAS and PPTR for root surface caries therapy.