Computer-aided design (CAD)/computer-aided manufacturing (CAM) milling and handpiece grinding are critical procedures in the fabrication and adjustment of ceramic dental restorations. However, due to the formation of microfractures, these procedures are detrimental to the strength of ceramics. This study analyzes the damage associated with current brittle-regime grinding and presents a potential remedy in the application of a safer yet still efficient grinding regime known as "ductile-regime grinding." Disc-shaped specimens of a lithium disilicate glass-ceramic material (IPS e.max CAD) were obtained by cutting and crystallizing the lithium metasilicate CAD/CAM blanks (the so-called blue blocks) following the manufacturer's instructions. The discs were then polished to a 1 µm diamond suspension finish. Single-particle micro-scratch tests (n = 10) with a conical diamond indenter were conducted to reproduce basic modes of deformation and fracture. Key parameters such as coefficient of friction and penetration depth were recorded as a function of scratch load. Further, biaxial flexure strength tests (n = 6) were performed after applying various scratch loads to analyze their effects on ceramic strength. Scanning electron microscopy (SEM) and focused ion beam (FIB) were used to characterize surface and subsurface damage. Statistical analysis was performed using one-way analysis of variance and Tukey tests. While the SEM surface analysis of scratch tracks revealed the occurrence of both ductile and brittle removal modes, it failed to accurately determine the threshold load for the brittle-ductile transition. The threshold load for brittle-ductile transition was determined to be 70 mN based on FIB subsurface damage analyses in conjunction with strength degradation studies. Below 70 mN, the specimens exhibited neither strength degradation nor the formation of subsurface cracks. Determination of the brittle-ductile thresholds is significant because it sets a foundation for future research on the feasibility of implementing ductile-regime milling/grinding protocols for fabricating damage-free ceramic dental restorations.

中文翻译：

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尖锐滑动接触下二硅酸锂的脆延性阈值。


计算机辅助设计 (CAD)/计算机辅助制造 (CAM) 铣削和手机磨削是陶瓷牙科修复体制造和调整的关键程序。然而，由于微裂纹的形成，这些过程不利于陶瓷的强度。这项研究分析了与当前脆性区域磨削相关的损坏，并提出了一种潜在的补救措施，即应用一种更安全但仍然有效的磨削方式，即“延性区域磨削”。二硅酸锂玻璃陶瓷材料 (IPS e.max CAD) 的圆盘状样品是按照制造商的说明切割和结晶偏硅酸锂 CAD/CAM 毛坯（所谓的蓝色块）而获得的。然后将圆盘抛光至 1 µm 金刚石悬浮表面。使用锥形金刚石压头进行单颗粒微划痕测试（n = 10），以重现变形和断裂的基本模式。摩擦系数和穿透深度等关键参数被记录为划痕载荷的函数。此外，在施加各种划痕载荷后进行双轴弯曲强度测试（n = 6），以分析它们对陶瓷强度的影响。使用扫描电子显微镜 (SEM) 和聚焦离子束 (FIB) 来表征表面和表面下损伤。使用单向方差分析和 Tukey 检验进行统计分析。虽然划痕痕迹的 SEM 表面分析揭示了延性和脆性去除模式的发生，但它无法准确确定脆性-延性转变的阈值载荷。根据 FIB 地下损伤分析结合强度退化研究，脆性转变的阈值载荷确定为 70 mN。 低于 70 mN，样品既没有表现出强度下降，也没有形成表面下裂纹。脆性-延性阈值的确定非常重要，因为它为未来研究实施延性机制铣削/磨削方案以制造无损伤陶瓷牙科修复体的可行性奠定了基础。