Shu Sano

Real-time monitoring of the surface modification of root dentin using photoacoustic spectroscopy and photothermal radiometry

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.

Comparison of Acid Resistance of Root Dentin after Treatment with a Mid-Infrared Free Electron Laser at between λ=9.0 and 9.7 µm

The purpose of this study was to compare the acid resistance of root dentin treated with a free electron laser emitting at between λ=9.0 and 9.7 µm, corresponding to the absorption peaks due to the phosphate ions. In order to obtain the optimum irradiation time for effective surface modification in the acid resistance test, we measured the temporal behaviors of acoustic wave emission and temperature rise. Lased and unlased samples were immersed in 0.1 M lactic acid, and the amount of Ca dissolved in the solution was determined after immersion times of 1–22 h. The acid resistances for λ=9.0 and 9.7 µm increased only until ~3 h. We conclude that the surface modification of root dentin leads to improved acid resistance, but that this only persists for a few hours. Subsurface modification but not surface modification would be effective in the treatment of root surface caries.

Development of CW CO2 Laser Percussion Technique

Biological tissue has a complex structure consisting of various kinds of tissues. CO2 laser radiation is strongly absorbed by the water in biological tissue. It is thus used to make incisions in biological tissue. However, the desired incision cannot be made when the state of the biological tissue (especially, its water content) varies during irradiation. It is thus necessary to monitor the state of tissue during laser irradiation. The present study considers laser-induced sound. When a laser beam is used to irradiate biological tissue, the water in the tissue absorbs the laser energy. The temperature of the irradiated region increases, causing the tissue to expand rapidly and eventually explode. Laser-induced sound is simultaneously generated. Laser scalpels are currently used as a form of laser treatment. This laser-induced sound is thought to contain information about the kind of biological tissue being irradiated and its state. In the present study, the kind of the sample and information about its state are obtained by irradiating simulated body tissues by a CW (Continuous Wave) CO2 laser beam and analyzing the generated laser-induced sound. The results reveal that it should be possible to identify the sample being irradiated in real time by analyzing the laser-induced sound characteristics, which differ according to the kind and the state of the tissue.

Laser Ablation of Biological Tissue Using Pulsed CO{sub 2} Laser

Laser scalpels are currently used as a form of laser treatment. However, their ablation mechanism has not been clarified because laser excision of biological tissue occurs over a short time scale. Biological tissue ablation generates sound (laser‐induced sound). This study seeks to clarify the ablation mechanism. The state of the gelatin ablation was determined using a high‐speed video camera and the power reduction of a He‐Ne laser beam. The aim of this study was to clarify the laser ablation mechanism by observing laser excision using the high‐speed video camera and monitoring the power reduction of the He‐Ne laser beam. We simulated laser excision of a biological tissue by irradiating gelatin (10 wt%) with radiation from a pulsed CO2 laser (wavelength: 10.6 μm; pulse width: 80 ns). In addition, a microphone was used to measure the laser‐induced sound. The first pulse caused ablation particles to be emitted in all directions; these particles were subsequently damped so that they formed a mushroom cloud....

Comparison of the acid resistance of root dentin after treatment with an MIR-FEL emitting at λ=9.0 μm and λ=9.7 μm

Background and Objective: The surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is a potential candidate for non-invasive treatment to prevent root surface caries. The purpose of this study is to compare the relative acid resistance of root dentin treated with an MIR Free Electron Laser emitting at between 9.0 μm and 9.7 μm. Study Design/Materials and Methods: The average power density was varied over the range 7.5-51.5 W/cm2. After irradiation, the samples were immersed in a 0.1 M lactic acid solution. Acid resistance was estimated as the quantity of Ca dissolved in the solution after immersion times (tim) of 1-22 h. Results: The acid resistance of all samples increased markedly, but only until tim = ~3 h. It did not depend significantly on the laser parameters used. Conclusion: The surface modification of root dentin leads to improved acid resistance, but this only persists for a few hours and therefore represents a poor treatment for root surface caries.