Objective: To further study the most suitable parameters for automatic full crown preparation using oral clinical micro robot. Its purpose is to improve the quality of automated tooth preparing for the system and to lay the foundation for clinical application. Methods: Twenty selected artificial resin teeth were used as sample teeth. The micro robot automatic tooth preparation system was used in dental clinic to control the picosecond laser beam to complete two dimensional cutting on the resin tooth sample according to the motion planning path. Using the laser scanning measuring microscope, each layer of cutting depth values was obtained and the average value was calculated. The monolayer cutting depth was determined. The three-dimensional (3D) data of the target resin teeth was obtained using internal scanner, and the CAD data of full-crown tooth preparation was designed by CAD self-develged software. According to the depth of the single layer, 11 complete resin teeth in phantom head were automatically prepared by the robot controlling the laser focused spot in accordance with the layer-cutting way. And the accuracy of resin tooth preparation was evaluated with the software. Using the same method, monolayer cutting depth parameter for cutting dental hard tissue was obtained. Then 15 extracted mandibular and maxillary first molars went through automatic full crown tooth preparation. And the 3D data of tooth preparations were obtained with intra oral scanner. The software was used to evaluate the accuracy of tooth preparation. Results: The results indicated that the single cutting depth of cutting resin teeth and in vitro teeth by picosecond laser were (60.0±2.6) and (45.0±3.6) μm, respectively. Using the tooth preparation robot, 11 artificial resin teeth and 15 complete natural teeth were automatically prepared, and the average time were (13.0±0.7), (17.0±1.8) min respectively. Through software evaluation, the average preparation depth of the occlusal surface of 11 resin teeth was approximately (2.089±0.026) mm, the error was about (0.089±0.026) mm; the average convergence angle was about 6.56°±0.30°, the error was about 0.56°±0.30°. Compared with the target preparation shape, the average shape error of the 11 resin tooth preparations was about 0.02-0.11 mm. And the average preparation depth of the occlusal surface of 15 natural teeth was approximately (2.097±0.022) mm, the error was about (0.097±0.022) mm; the average convergence angle was about 6.98°±0.35°, the error was about 0.98°±0.35°. Compared with the target preparation shape, the average shape error of the 15 natural tooth preparations was about 0.05-0.17 mm. Conclusions: The experimental results indicate that the automatic tooth preparation for resin teeth and the teeth were completed according to the specific parameters of the single cutting depth by the micro robot controlling picosecond laser respectively, its preparation accuracy met the clinical needs. And the suitability of the parameter was confirmed.
目的： 应用自行研发的口腔临床微机器人自动化牙体预备系统（简称自动备牙系统），探索全冠预备的适宜参数，以期提高自动化牙体预备的质量，为该系统应用于临床奠定基础。 方法： 取20颗树脂牙，制成树脂牙试件，用自动备牙系统，控制皮秒激光束按规划路径完成树脂牙试件的二维切削，用激光显微镜测量每层切削的深度值，将均值确定为单层切削深度。用口内扫描仪获取另11颗树脂牙三维数据，行全冠预备体计算机辅助设计（computer aided design，CAD），将CAD数据导入自动备牙系统控制软件，以单层切削深度值为参数，用自动备牙系统，按层切方式控制激光聚焦光斑，在仿头模内对置于牙颌模型内的树脂牙行全冠牙体预备。同法获取激光切削天然牙的单层切削深度，在仿头模内对15颗第一磨牙天然牙（北京大学口腔医学院·口腔医院口腔颌面外科门诊提供）进行全冠牙体预备。用口内扫描仪获取树脂牙和天然牙预备体的三维数据，对比分析预备体三维数据与CAD数据的整体平均误差。 结果： 皮秒激光切削树脂牙和天然牙试件的单次切削深度分别为（60.0±2.6）和（45.0±3.6）μm。用自动备牙系统在仿头模内完成了树脂牙和天然牙的全冠牙体预备，分别耗时（13.0±0.7）和（17.0±1.8）min。树脂牙预备体龈向预备深度为（2.089±0.026）mm，误差为（0.089±0.026）mm；轴面聚合度为6.56°±0.30°，误差为0.56°±0.30°；预备体三维数据与CAD数据的整体平均误差为0.02~0.11 mm。天然牙预备体龈向预备深度为（2.097±0.022）mm，误差为（0.097±0.022）mm；轴面聚合度为6.98°±0.35°，误差为0.98°±0.35°；预备体三维数据与CAD数据的整体平均误差为0.05~0.17 mm。 结论： 自动备牙系统可控制皮秒激光，按单次切削深度完成树脂牙和天然牙的自动化全冠牙体预备，预备精度可满足临床需要。.
Keywords: Automation; Crowns; Lasers; Tooth preparation.