Department of Biomedical Materials Science, University of Mississippi Medical Center, MS, USA.
Department of Materials Science and Engineering, Herbert Wertheim College of Engineering, University of Florida, USA.
Dent Mater. 2022 Dec;38(12):1977-1988. doi: 10.1016/j.dental.2022.11.011. Epub 2022 Nov 19.
Previous studies have reported the fractal dimensional increment of glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness.
Bar-shaped specimens were prepared from lithium disilicate (LDS) and nanofluorapatite (NFA) glass-ceramics. One face of each specimen was indented using a Knoop diamond at 25 N (LDS) or 10 N (NFA) followed by loading in 4-point, or 3-point flexure, respectively, until failure. Fracture toughness (K) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm.
Median (25%, 75% quartiles) fracture toughness of LDS bars were 1.62 (1.59, 1.69) MPa m and NFA bars were 0.68 (0.66, 0.74) MPa m, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before noise filtering were 2.16 (2.15, 2.17) and after noise filtering were 2.14 (2.14, 2.15) for LDS and before noise filtering were 2.29 (2.21, 2.38) and after noise filtering were 2.17 (2.17, 2.18) for NFA. Median (25%, 75% quartiles) surface roughness (Ra) before noise filtering were 139 (119, 188) nm and after noise filtering were 137 (118, 187) nm for LDS and before noise filtering were 7 (6, 15) nm and after noise filtering were 7 (6, 15) nm for NFA.
Noise filtering successfully eliminated noise from the material with smooth fracture surfaces (NFA), decreasing the measured fractal dimension. The NFA data fit a K vs. D* statistical model for fused silica previously tested using a similar technique. The equation relating fracture toughness to the fractal dimension was modified, accounting for the toughening mechanisms. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.
之前的研究已经报道了玻璃陶瓷断裂表面的分形维数增量。本研究的目的是确定两种具有不同晶体体积分数和不同断裂表面粗糙度的牙科玻璃陶瓷的断裂韧性与分形维数增量之间的关系。
从锂硅玻璃陶瓷（LDS）和纳米氟磷灰石（NFA）玻璃陶瓷中制备棒状试件。用 Knoop 金刚石在 25N（LDS）或 10N（NFA）下在每个试件的一个面上压痕，然后分别进行四点或三点弯曲加载，直到失效。使用表面裂纹弯曲（SCF）技术（ASTM C1421）计算断裂韧性（K）。用原子力显微镜（AFM）对断裂表面的环氧复制件进行扫描，然后进行噪声滤波。使用 FRACTALS 软件通过 Minkowski 覆盖算法确定分形维数增量（D*）。
LDS 棒的中值（25%，75%四分位数）断裂韧性分别为 1.62（1.59，1.69）MPa·m 和 NFA 棒的为 0.68（0.66，0.74）MPa·m。噪声滤波前中位数（25%，75%四分位数）分形维数（D）值分别为 2.16（2.15，2.17）和 2.14（2.14，2.15），LDS 噪声滤波后分别为 2.14（2.14，2.15）和 2.17（2.17，2.18）。NFA 噪声滤波前中位数（25%，75%四分位数）表面粗糙度（Ra）分别为 139（119，188）nm 和 137（118，187）nm，噪声滤波后分别为 137（118，187）nm 和 137（118，187）nm。NFA 噪声滤波前中位数（25%，75%四分位数）为 7（6，15）nm，噪声滤波后分别为 7（6，15）nm 和 7（6，15）nm。
噪声滤波成功地消除了具有光滑断裂表面（NFA）的材料中的噪声，降低了测量的分形维数。NFA 数据符合以前使用类似技术对熔融二氧化硅进行测试的 K 与 D*统计模型。对考虑增韧机制的关系进行了修改，建立了断裂韧性与分形维数的关系。具有噪声滤波的分形分析可用于估计不表现出裂纹桥接的牙科玻璃陶瓷的断裂韧性。
