University of Alberta, School of Dentistry, Edmonton, AB, Canada.
Materials Science Unit, Dublin Dental University Hospital, Lincoln Place, Dublin 2, Ireland.
Dent Mater. 2019 Jan;35(1):98-104. doi: 10.1016/j.dental.2018.11.004. Epub 2018 Nov 16.
The fabrication of all-ceramic restorations using Computer Aided Design and Computer Aided Manufacturing (CAD-CAM) most commonly involves subtractive machining which results in strength-limiting, surface and sub-surface damage in the resultant prosthesis. The objective was to explore how clinically relevant machining-process variables, and material variables, affect damage accumulation in lithium silicate glass-ceramics.
Three commercial lithium silicate glass-ceramics (IPS e.max CAD, Celtra Duo and Vita Suprinity) were selected. For each material, two groups of disk-shaped specimens were fabricated (n=15), using a CAD-CAM process, creating surfaces equivalent to those generated for a dental restoration, or alternatively, using a highly controlled laboratory process generating disk-shaped test specimens with a consistent polished surface. Bi-axial flexure strength (BFS) was determined in a ball-on-ring configuration and fractographic analyses performed. For each material BFS was correlated with machining sequence and with surface roughness.
BFS was significantly influenced by material substrate (p<0.01) and by fabrication route (p<0.01). A significant factorial interaction (p<0.01) identified that the magnitude of changes in BFS when comparing the two specimen fabrication routes, was dependent on substrate type. The polished control specimens exhibited a significantly increased BFS when compared with the CAD-CAM counterparts for all materials. IPS e.max CAD and Celtra Duo showed a 44 and 46% reduction in mean BFS for the CAD-CAM specimens when compared with the polished counterparts, respectively. In contrast, Vita Suprinity showed the least disparity in mean BFS (21%) but the greatest variance in BFS data.
All CAD-CAM specimens showed evidence of machining introduced damage in the form of median and radial cracks at sites either coincident with, or peripheral to the failure origin. Subtractive machining introduced significant strength limiting damage that is not eliminated by heat treatments applied for either microstructure development (IPS e.max CAD and Vita Suprinity) or annealing/crack blunting (Celtra Duo).
使用计算机辅助设计和计算机辅助制造（CAD-CAM）制造全陶瓷修复体最常涉及减法加工，这会导致在最终修复体中产生强度限制、表面和次表面损伤。本研究旨在探讨临床相关加工工艺变量和材料变量如何影响锂硅玻璃陶瓷的损伤积累。
选择了三种商业锂硅玻璃陶瓷（IPS e.max CAD、Celtra Duo 和 Vita Suprinity）。对于每种材料，使用 CAD-CAM 工艺制作两组圆盘状试件，制作表面相当于为牙修复体生成的表面，或者使用高度受控的实验室工艺制作具有一致抛光表面的圆盘状测试试件。在球对环配置下测定双轴弯曲强度（BFS）并进行断口分析。对于每种材料，将 BFS 与加工顺序和表面粗糙度相关联。
BFS 显著受材料基质（p<0.01）和制造途径（p<0.01）影响。显著的因子相互作用（p<0.01）表明，比较两种试件制造途径时，BFS 变化的幅度取决于基质类型。与 CAD-CAM 对应物相比，抛光对照试件的 BFS 显著增加。与抛光对应物相比，IPS e.max CAD 和 Celtra Duo 的 CAD-CAM 试件的平均 BFS 分别降低了 44%和 46%。相比之下，Vita Suprinity 的平均 BFS 差异最小（21%），但 BFS 数据的差异最大。
所有 CAD-CAM 试件均显示出加工引入的损伤的证据，表现为在失效起源处或其周围出现的中位和径向裂纹。减法加工引入了显著的强度限制损伤，即使应用于微结构发展（IPS e.max CAD 和 Vita Suprinity）或退火/裂纹钝化（Celtra Duo）的热疗也无法消除。
