Song Xiao-Fei, Ren Hai-Tao, Yin Ling
Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, School of Mechanical Engineering, Tianjin University, Tianjin 300072, China.
Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, School of Mechanical Engineering, Tianjin University, Tianjin 300072, China.
J Mech Behav Biomed Mater. 2016 Jan;53:78-92. doi: 10.1016/j.jmbbm.2015.08.003. Epub 2015 Aug 12.
Esthetic high-strength lithium disilicate glass ceramics (LDGC) are used for monolithic crowns and bridges produced in dental CAD/CAM and oral adjusting processes, which machinability affects the restorative quality. A machinability study has been made in the simulated oral clinical machining of LDGC with a dental handpiece and diamond burs, regarding the diamond tool wear and chip control, machining forces and energy, surface finish and integrity. Machining forces, speeds and energy in in vitro dental adjusting of LDGC were measured by a high-speed data acquisition and force sensor system. Machined LDGC surfaces were assessed using three-dimensional non-contact chromatic confocal optical profilometry and scanning electron microscopy (SEM). Diamond bur morphology and LDGC chip shapes were also examined using SEM. Minimum tool wear but significant LDGC chip accumulations were found. Machining forces and energy significantly depended on machining conditions (p<0.05) and were significantly higher than other glass ceramics (p<0.05). Machining speeds dropped more rapidly with increased removal rates than other glass ceramics (p<0.05). Two material machinability indices associated with the hardness, Young's modulus and fracture toughness were derived based on the normal force-removal rate relations, which ranked LDGC the most difficult to machine among glass ceramics. Surface roughness for machined LDGC was comparable for other glass ceramics. The removal mechanisms of LDGC were dominated by penetration-induced brittle fracture and shear-induced plastic deformation. Unlike most other glass ceramics, distinct intergranular and transgranular fractures of lithium disilicate crystals were found in LDGC. This research provides the fundamental data for dental clinicians on the machinability of LDGC in intraoral adjustments.
美学高强度二硅酸锂玻璃陶瓷（LDGC）用于牙科CAD/CAM以及口腔调改过程中制作的整体式冠和桥，其可加工性会影响修复质量。已针对使用牙科手机和金刚石车针模拟口腔临床加工LDGC开展了一项可加工性研究，涉及金刚石刀具磨损和切屑控制、加工力和能量、表面光洁度和完整性。通过高速数据采集和力传感器系统测量了体外牙科调改LDGC时的加工力、速度和能量。使用三维非接触式彩色共焦光学轮廓仪和扫描电子显微镜（SEM）对加工后的LDGC表面进行了评估。还使用SEM检查了金刚石车针的形态和LDGC切屑形状。发现刀具磨损最小，但LDGC切屑大量堆积。加工力和能量显著取决于加工条件（p<0.05），且显著高于其他玻璃陶瓷（p<0.05）。与其他玻璃陶瓷相比，加工速度随去除率增加下降得更快（p<0.05）。基于法向力-去除率关系推导出了两个与硬度、杨氏模量和断裂韧性相关的材料可加工性指数，在玻璃陶瓷中LDGC的加工难度最大。加工后LDGC的表面粗糙度与其他玻璃陶瓷相当。LDGC的去除机制以穿透诱导的脆性断裂和剪切诱导的塑性变形为主。与大多数其他玻璃陶瓷不同，在LDGC中发现了二硅酸锂晶体明显的沿晶断裂和穿晶断裂。本研究为牙科临床医生提供了关于LDGC在口腔内调改时可加工性的基础数据。
