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

为评价激光对牙体硬组织的消融效果，采用波长可调的自由电子激光(FEL)。日本大学电子束研究与应用研究室工作的自由电子激光波长从1.0μm调到6.0μm。前人的研究表明，LEBRA-FEL通过与通常的牙科Er：μ激光相似的方式有效地形成凹坑，波长为2.94μm。在本研究中，为了更详细地揭示LEBRA-FEL对牙齿硬组织的消融机理，使用了一个石膏样品作为辐照实验中的热历史指示器。X射线衍射、差热分析、显微傅里叶变换红外光谱和显微拉曼分析表明，辐照后未发现热烧蚀效应大于100℃的残留物。通过对照射过程的录像，微小颗粒从照射点排出。这些结果表明，这种消融是一种等离子体消融。综上所述，激光辐照烧蚀的传统解释是材料中所含水分子的微爆发，应重新审视，并寻求另一种可能的理论来满足本研究中的自由电子激光辐照结果。

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.