飞秒激光切削牙齿硬组织表面粗糙度和显微形貌观察

Femtosecond pulsed laser ablation of dental hard tissues with numerical control： a roughness and morphology study

目的初步建立飞秒激光数控切削牙齿硬组织模拟实验平台并观察显微形貌，以期为飞秒激光的临床应用提供依据。方法用人离体第三磨牙制备牙釉质和牙本质平面样本各1个；通用运动控制器控制样本在与激光入射方向垂直的焦点平面内做矩形波轨迹运动。激光扫描共聚焦显微镜测量切削面粗糙度，扫描电镜观察显微形貌。结果用实验建立的飞秒激光数控切削平台制备牙釉质和牙本质正方形窝洞各1个。窝洞边界清晰、底平壁直。牙釉质激光扫描线内底部粗糙度7．173μm，侧壁粗糙度2．675μm；窝洞底壁粗糙度13．667μm，侧壁粗糙度33．927μm。牙本质窝洞底壁粗糙度51．182μm，侧壁粗糙度25．629μm。扫描电镜下牙釉质未见微裂隙及碳化，牙本质出现碳化、少量裂隙和结晶颗粒。结论飞秒激光数控切削能实现精确牙体切削，切削面侧壁粗糙度小于底面，可满足临床修复要求。但应针对不同切削对象设置适宜的飞秒激光能量密度，其过高时可造成组织损伤。

Objective To establish the femtosecond laser experimental platform in vitro for numerical controlled cavity preparation, and to evaluate the roughness quantitatively and observe the microscopic morphology of the cutting surface. Methods Enamel and dentin planes were prepared on human third molars. A universal motion controller was used to control the samples to do rectangle wave motion perpendicular to the incident direction of the laser at focus. The surface roughness was observed with confocal laser scanning microscope. Results Precise ablation of the dental hard tissues can be achieved with the established femtosecond laser numerical control platform. For enamel, the surface roughness of the cavity inside laser scanning line was 7. 173 i.Lm at the bottom and 2. 675 i.~m on the wall of the cavity. The surface roughness of the cavity between laser scanning lines was 13.667 ~m at the bottom and 33. 927 ~m on the wall. For dentin, the surface roughness of the cavity bottom was 51. 182 ~m and 25. 629 p.rn for the wall. Scanning electron microscope images showed no micro-cracks or carbonization on enamel, while carbonization, cracks and a small amount of crystalline particles were observed on dentin. Conclusions Precise tooth preparation can be achieved with femtosecond laser numerical control flafform. The surface roughness of cavity wall was less than that of the bottom and can meet the clinical needs. Suitable femtosecond laser output power should be set for different cutting objects, otherwise it may result in tissue damages.