Fried Daniel, Ashouri Nahal, Breunig Thomas, Shori Ramesh
Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California 94143, USA.
Lasers Surg Med. 2002;31(3):186-93. doi: 10.1002/lsm.10085.
The mechanism of water augmentation during IR laser ablation of dental hard tissues is controversial and poorly understood. The influence of an optically thick applied water layer on the laser ablation of enamel was investigated at wavelengths in which water is a primary absorber and the magnitude of absorption varies markedly.
STUDY DESIGN/MATERIALS AND METHODS: Q-switched and free running Er: YSGG (2.79 microm) and Er:YAG (2.94 microm), free running Ho:YAG and 9.6 microm TEA CO(2) laser systems were used to produce linear incisions in dental enamel with and without water. Synchrotron-radiation IR spectromicroscopy with the Advanced Light Source at Lawrence Berkeley National Laboratory was used to determine the chemical changes across the laser ablation profiles with a spatial resolution of 10-microm.
The addition of water increased the rate of ablation and produced a more desirable surface morphology during enamel ablation with all the erbium systems. Moreover, ablation was markedly more efficient for Q-switched (0.15 microsecond) versus free-running (150 microsecond) erbium laser pulses with the added water layer. Although the addition of a thick water layer reduced the rate of ablation during CO(2) laser ablation, the addition of the water removed undesirable deposits of non-apatite mineral phases from the crater surface. IR spectromicroscopy indicates that the chemical composition of the crater walls deviates markedly from that of hydroxyapatite after Er:YAG and CO(2) laser irradiation without added water. New mineral phases were resolved that have not been previously observed using conventional IR spectroscopy. There was extensive peripheral damage after irradiation with the Ho:YAG laser with and without added water without effective ablation of enamel.
We postulate that condensed mineral phases from the plume are deposited along the crater walls after repetitive laser pulses and such non-apatitic phases interfere with subsequent laser pulses during IR laser irradiation reducing the rate and efficiency of ablation. The ablative recoil associated with the displacement and vaporization of the applied water layer removes such loosely adherent phases maintaining efficient ablation during multiple pulse irradiation.
红外激光消融牙硬组织过程中水分增加的机制存在争议且了解甚少。研究了在水是主要吸收体且吸收幅度显著变化的波长下，光学厚的外加水层对牙釉质激光消融的影响。
研究设计/材料与方法：使用调Q和连续输出的铒：钇钪镓石榴石（2.79微米）、铒：钇铝石榴石（2.94微米）、连续输出的钬：钇铝石榴石和9.6微米的TEA二氧化碳激光系统，在有水和无水的情况下对牙釉质进行线性切割。利用劳伦斯伯克利国家实验室的先进光源进行同步辐射红外光谱显微镜分析，以10微米的空间分辨率确定激光消融轮廓上的化学变化。
在所有铒激光系统对牙釉质的消融过程中，加水均提高了消融速率并产生了更理想的表面形态。此外，对于添加了水层的情况，调Q（0.15微秒）铒激光脉冲的消融明显比连续输出（150微秒）铒激光脉冲更有效。虽然添加厚水层会降低二氧化碳激光消融过程中的消融速率，但加水可去除弹坑表面不希望出现的非磷灰石矿物相沉积物。红外光谱显微镜显示，在未添加水的情况下，铒：钇铝石榴石和二氧化碳激光照射后，弹坑壁的化学成分与羟基磷灰石有明显偏差。分辨出了以前使用传统红外光谱未观察到的新矿物相。无论有无添加水，钬：钇铝石榴石激光照射后均有广泛的周边损伤，且牙釉质未得到有效消融。
我们推测，在重复激光脉冲后，羽流中的凝聚矿物相沿弹坑壁沉积，这种非磷灰石相在红外激光照射期间会干扰后续激光脉冲，从而降低消融速率和效率。与外加水层的位移和汽化相关的烧蚀反冲可去除此类松散附着的相，在多脉冲照射期间维持高效消融。
