Khosroshahi M E, Ghasemi A B
Laser Laboratory, Faculty of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran.
Lasers Med Sci. 2004;18(4):196-203. doi: 10.1007/s10103-003-0283-5. Epub 2004 Feb 11.
The interaction of a multi-line (2.6-3 micro m) HF laser with enamel tissue is reported. The etch rate experiment showed an ablation threshold fluence of 47 Jcm(-2), but using the dispersion theory for optical coefficients of n and k for enamel at dominant laser lines, this value reduced to congruent with 25 Jcm(-2), making it more comparable with other investigations. The main mechanism of enamel ablation at 2.78 microm where its absorption is very high is thought to be due to microexplosive evaporation of water within the enamel matrix, i.e., thermomechanical decomposition. Modelling showed that with 46% reflectivity from the enamel surface, the maximum temperature rise will be about 500 degrees C, which is much less than the melting point of hydroxyapatite. Also, using a photothermal deflection technique showed that, at fluences below threshold a considerable amount of heat was emitted from the surface, which was detected as a single compressive wave. The spectroscopic studies indicated that calcium was the main chemical element observed in the plasma with emission spanning from 420 to 620 nm.
报道了多线（2.6 - 3微米）高频激光与牙釉质组织的相互作用。蚀刻速率实验表明烧蚀阈值通量为47焦耳/平方厘米，但利用牙釉质在主要激光波长处的光学系数n和k的色散理论，该值降至约25焦耳/平方厘米，使其与其他研究更具可比性。在2.78微米处牙釉质吸收非常高，其烧蚀的主要机制被认为是由于牙釉质基质内水的微爆蒸发，即热机械分解。建模表明，牙釉质表面反射率为46%时，最大温度升高约为500摄氏度，远低于羟基磷灰石的熔点。此外，使用光热偏转技术表明，在通量低于阈值时，表面会释放出大量热量，检测为单个压缩波。光谱研究表明，钙是在等离子体中观察到的主要化学元素，发射波长范围为420至620纳米。
