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）对牙齿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）运行的FEL波长从1.0 μm调整到6.0 μm。用LEBRA-FEL辐照人牙切片。先前的研究表明，LEBRA-FEL在波长为2.94 μm的情况下，可以有效地形成与普通牙科Er: YAG激光器相似的凹坑。在本研究中，为了更详细地揭示LEBRA-FEL消融牙齿硬组织的机制，我们在辐照实验中使用石膏样品作为热历史指标。经x射线衍射、差热分析、微红外光谱和微拉曼光谱分析，辐照后未发现热烧蚀作用超过100℃的残留物。通过视频记录辐照过程，微小颗粒从辐照点排出。这些结果表明，这种等离子体消融是可行的。综上所述，激光辐照烧蚀的传统解释是由于材料中含有水分子的微爆裂，这需要重新审视，并寻求另一种可能的理论，以满足本研究的FEL辐照结果。

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.