Free electron laser ablation effects and its application for dental enamel and dentin

本研究采用波长可调的自由电子激光（FEL）对牙体硬组织进行激光消融。在日本大学电子束研究与应用实验室（LEBRA）工作的自由电子激光器波长从1.0 μm调谐到6.0 μm。用LEBRA-FEL照射人牙切片。上述研究表明，LEBRA-FEL通过照射有效地形成凹坑，几乎类似于通常的牙科Er：YAG激光器，波长为2.94 μm。在这项研究中，揭示LEBRA-FEL消融牙齿硬组织的机制，在更详细的，石膏样品被用来作为在辐照实验过程中的热历史的指示。经X射线衍射、差热分析、显微傅立叶变换红外光谱和显微拉曼光谱分析表明，辐照后没有残留物，表明热烧蚀效应超过100 ℃。通过照射的视频记录，从照射点排出微小颗粒。这些结果表明，这种等离子体烧蚀。因此，传统的激光辐照烧蚀是由于材料中水分子的微爆引起的解释应重新审视，并寻求另一种可能的理论来满足本研究中自由电子激光辐照的结果。

This study aimed to evaluate the laser ablation effect for dental hard tissues, and a free electron laser (FEL) with tunable wavelength was applied. The wavelength of FEL operated at Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, was tuned from 1.0 μm to 6.0 μm. Human tooth sections were irradiated by the LEBRA-FEL. Fore-going studies revealed that the LEBRA-FEL effectively formed pits by irradiation almost similar to the usual dental Er : YAG lasers, wavelength of 2.94 μm. In this study, to reveal mechanism of the LEBRA-FEL ablation for dental hard tissues in more details, a gypsum sample was used as an indicator of thermal history during the irradiation experiment. After the irradiation, there was no remains which indicated the heating ablation effect being over 100 degrees Celsius by means of X-ray diffraction, differential thermal analysis, micro-FTIR and micro-Raman analysis. By video recording of the irradiation, minute particles were discharged from the irradiation spot. These results suggested that the ablation of such a kind of plasma ablation. In conclusion, the traditional explanation of laser irradiation ablation was due to micro-burst of water molecules contained in the materials should be re-examined, and seek another possible theory which may satisfy the FEL irradiation results in this study.