Objectives

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.

Methods

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).

Results

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.

Significance

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.

中文翻译：

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在完全结晶状态下加工的CAD-CAM氧化锆增强硅酸锂陶瓷中的强度极限损伤及其缓解

目标

目的是探索临床相关的加工工艺和热处理如何影响在完全结晶状态下加工的硅酸锂基玻璃陶瓷的损伤累积和强度降低。

方法

研究了具有完全发达的微观结构的商用氧化锆增强硅酸锂（ZLS）玻璃陶瓷（Celtra®Duo）。圆盘状样品（标称直径为10毫米，厚度为1毫米）可以通过CAD-CAM工艺制造，创建具有临床意义的牙齿修复表面，或者从水刀切割的圆柱块上切下，并对其关键表面进行连续抛光。以环上球的配置确定双轴弯曲强度（BFS），并对失效的样品进行分形分析。在热处理前后进行XRD，AFM和SEM测量。对于每个样品组，BFS与表面粗糙度相关。使用双向ANOVA和事后Tukey测试来确定机加工和热处理组之间的BFS差异（ɑ= 0.05）。

结果

双向方差分析表明BFS受制造工艺的影响（p <0.01），CAD-CAM标本的平均BFS明显较低。在热处理和加工路径之间观察到阶乘相互作用（p <0.01），其中对CAD-CAM标本注意到了制造后热处理的显着强化效果，但对切片和抛光的样品却没有发现。CAD-CAM样品在断裂起点附近显示了次表面横向裂纹以及径向裂纹，而抛光样品则未观察到。BFS与抛光试样的表面粗糙度无关，热处理后用XRD检测不到微观结构的变化。

意义

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高度敏感。CAD-CAM制造程序会导致严重的强度极限损坏，这很可能会影响修复性能。但是，通过机加工后热处理可以部分缓解这种情况。