School of Dentistry, University of Alberta, Edmonton, AB, Canada; Department of Mechanical Engineering, Faculty of Engineering, University of Alberta, Edmonton, Alberta, Canada.
School of Dentistry, University of Alberta, Edmonton, AB, Canada.
Dent Mater. 2020 Dec;36(12):1557-1565. doi: 10.1016/j.dental.2020.09.012. Epub 2020 Oct 3.
The objective was to explore how clinically relevant machining process and heat treatment influence damage accumulation and strength degradation in lithium silicate-based glass ceramics machined in the fully crystallized state.
A commercial zirconia-reinforced lithium silicate (ZLS) glass ceramic with a fully developed microstructure (Celtra® Duo) was studied. Disk-shaped specimens (nominal 10 mm diameter and 1 mm thickness) were fabricated either using a CAD-CAM process, creating a clinically relevant dental restoration surface, or were sectioned from water-jet cut cylindrical blocks with their critical surfaces consistently polished. Bi-axial flexure strength (BFS) was determined in a ball-on-ring configuration, and fractographic analysis was performed on failed specimens. XRD, AFM and SEM measurements were conducted before and after heat treatment. For each sample group, BFS was correlated with surface roughness. A two-way ANOVA and post-hoc Tukey tests were used to determine differences in BFS between machining and heat treatment groups (ɑ = 0.05).
A two-way ANOVA demonstrated that BFS was influenced by fabrication route (p < 0.01) with CAD-CAM specimens exhibiting significantly lower mean BFS. A factorial interaction was observed between heat treatment and machining route (p < 0.01), where a significant strengthening effect of post-manufacture heat treatment was noted for CAD-CAM specimens but not sectioned and polished samples. CAD-CAM specimens exhibited sub-surface lateral cracks alongside radial cracks near fracture origin which were not observed for polished specimens. BFS did not correlate with surface roughness for polished specimens, and no change in microstructure was detectable by XRD following heat treatment.
The mechanical properties of the ZLS ceramic material studied were highly sensitive to the initial surface defect integral associated with manufacturing route and order of operations. CAD-CAM manufacturing procedures result in significant strength-limiting damage which is likely to influence restoration performance; however, this can be partially mitigated by post-machining heat treatment.
本研究旨在探讨临床相关的加工工艺和热处理如何影响完全晶化状态下加工的锂硅基玻璃陶瓷的损伤积累和强度降低。
本研究采用商业氧化锆增强锂硅玻璃陶瓷（Celtra® Duo），该材料具有完全发育的微观结构。通过 CAD-CAM 工艺制作具有临床相关牙体修复表面的圆盘试件（名义直径 10mm，厚度 1mm），或者从水射流切割的圆柱形块体上截取具有一致抛光关键表面的试件。采用球-环配置法测定双轴弯曲强度（BFS），并对失效试件进行断口形貌分析。在热处理前后进行 XRD、AFM 和 SEM 测量。对于每个样品组，将 BFS 与表面粗糙度相关联。采用双向方差分析和事后 Tukey 检验来确定加工和热处理组之间的 BFS 差异（α=0.05）。
双向方差分析表明，BFS 受到制造路线的影响（p<0.01），CAD-CAM 试件的平均 BFS 显著较低。热处理和加工路线之间存在因子相互作用（p<0.01），对于 CAD-CAM 试件，后制造热处理具有显著的增强效果，但对于截取和抛光的试件则没有。CAD-CAM 试件在断裂起源附近的径向裂纹旁出现了亚表面横向裂纹，而抛光试件则没有观察到这种情况。对于抛光试件，BFS 与表面粗糙度不相关，热处理后 XRD 未检测到微观结构的变化。
研究的 ZLS 陶瓷材料的机械性能对与制造路线和操作顺序相关的初始表面缺陷积分非常敏感。CAD-CAM 制造工艺会导致严重的强度限制损伤，这可能会影响修复体性能；然而，这种损伤可以通过后加工热处理部分缓解。
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