Schoenly Joshua E, Seka Wolf, Rechmann Peter
Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA.
Lasers Surg Med. 2010 Jan;42(1):51-61. doi: 10.1002/lsm.20884.
A frequency-doubled Ti:sapphire laser is shown to selectively ablate dental calculus. The optimal transverse shape of the laser beam, including its variability under water-cooling, is determined for selective ablation of dental calculus.
STUDY DESIGN/MATERIALS AND METHODS: Intensity profiles under various water-cooling conditions were optically observed. The 400-nm laser was coupled into a multimode optical fiber using an f = 2.5-cm lens and light-shaping diffuser. Water-cooling was supplied coaxially around the fiber. Five human tooth samples (four with calculus and one pristine) were irradiated perpendicular to the tooth surface while the tooth was moved back and forth at 0.3 mm/second, varying between 20 and 180 iterations. The teeth were imaged before and after irradiation using light microscopy with a flashing blue light-emitting diode (LED). An environmental scanning electron microscope imaged each tooth after irradiation.
High-order super-Gaussian intensity profiles are observed at the output of a fiber coiled around a 4-in. diameter drum. Super-Gaussian beams have a more-homogenous fluence distribution than Gaussian beams and have a higher energy efficiency for selective ablation. Coaxial water-cooling does not noticeably distort the intensity distribution within 1 mm from the optical fiber. In contrast, lasers focused to a Gaussian cross section (< or =50-microm diameter) without fiber propagation and cooled by a water spray are heavily distorted and may lead to variable ablation. Calculus is preferentially ablated at high fluences (> or =2 J/cm(2)); below this fluence, stalling occurs because of photo-bleaching of the calculus. Healthy dental hard tissue is not removed at fluences < or =3 J/cm(2).
Supplying laser light to a tooth using an optical fiber with coaxial water-cooling is determined to be the most appropriate method when selectively removing calculus with a frequency-doubled Ti:sapphire laser. Fluences over 2 J/cm(2) are required to remove calculus efficiently since photo-bleaching stalls calculus removal below that value.
倍频钛宝石激光可选择性地去除牙结石。为实现牙结石的选择性去除，需确定激光束的最佳横向形状，包括其在水冷条件下的变化情况。
研究设计/材料与方法：通过光学手段观察各种水冷条件下的强度分布。使用焦距为2.5厘米的透镜和光整形漫射器将400纳米激光耦合到多模光纤中。水冷通过围绕光纤同轴供应。在牙齿以0.3毫米/秒的速度前后移动时，垂直于牙齿表面对五个人类牙齿样本（四个有牙结石，一个无结石）进行照射，照射次数在20至180次之间变化。在照射前后，使用带闪烁蓝色发光二极管（LED）的光学显微镜对牙齿进行成像。照射后，用环境扫描电子显微镜对每颗牙齿进行成像。
在缠绕于直径4英寸鼓上的光纤输出端观察到高阶超高斯强度分布。超高斯光束的能量密度分布比高斯光束更均匀，且在选择性消融方面具有更高的能量效率。同轴水冷在距光纤1毫米范围内不会明显扭曲强度分布。相比之下，聚焦为高斯横截面（直径≤50微米）且无光纤传播并通过喷水冷却的激光会严重变形，可能导致消融不均匀。在高能量密度（≥2焦耳/平方厘米）下，牙结石会被优先消融；低于此能量密度时，由于牙结石的光漂白作用，消融会停止。在能量密度≤3焦耳/平方厘米时，健康的牙齿硬组织不会被去除。
当使用倍频钛宝石激光选择性去除牙结石时，确定通过带有同轴水冷的光纤向牙齿提供激光是最合适的方法。由于低于2焦耳/平方厘米时光漂白会使牙结石去除停止，因此需要超过2焦耳/平方厘米的能量密度才能有效去除牙结石。
