Institute of Stomatological Research, Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China.
Department of Prosthodontics, Guanghua School of Stomatology, Sun Yat-sen University; Guangdong Engineering Research Center of Technology and Materials for Oral Reconstruction, Guangdong Provincial Key Laboratory of Stomatology, Guangzhou, China.
Dent Mater. 2019 Apr;35(4):e83-e95. doi: 10.1016/j.dental.2019.01.016. Epub 2019 Feb 8.
To identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure.
Thirty standardized molar crowns (IPS e.max Press) were fabricated and microCT scanned to 3D-analyze the size, morphology and distribution of pores in veneering porcelain, followed by in vitro fracture test and SEM fractographic observation. Finite element analysis (FEA) of the microCT reconstructed models was used to evaluate the stress state.
The volumes of pores in samples ranged from 3241μm to 1.29×10μm with the equivalent radius between 10μm to 680μm. Deviation of sphericity of pores ranged from 0.10 to 0.81 and the average of 99.97% pores was near 0.63. For the smaller pores their distribution tended to be uniform, while the larger pores were irregular with elongated ellipsoidal form and located at or near the veneer-core interface. During wedge loading blunt contact fracture testing 21 crowns failed from the fissure on the occlusal surface, of which 16 failed from surface or near surface pores, 2 from the midpoint of the oblique ridge, and 7 from larger interfacial pores. FEA analysis indicated that defects were detrimental to veneer integrity only in regions of tensile stress and where the pore radius associated with crack initiation ranged from 30 to 50μm. Pore morphology appeared to have only a minor effect on fracture.
Within the limitation of the microCT resolution and FEA, it suggests that pores radius large than 30-50μm and located in the tensile stress area like grooves and fissures on the occlusal surface or near surface as well as cervical margins of veneering porcelain will jeopardize the bilayered structure and mechanical integrity of LDG.
确定在双层锂硅玻璃陶瓷（LDG）冠层的饰面瓷中出现伪造孔隙缺陷的情况下，哪些条件会影响并危及结构的机械完整性。
制作 30 个标准化的磨牙冠（IPS e.max Press），并进行微 CT 扫描以对饰面瓷中的孔隙大小、形态和分布进行 3D 分析，然后进行体外断裂试验和 SEM 断口观察。使用微 CT 重建模型的有限元分析（FEA）来评估应力状态。
样品中的孔隙体积范围为 3241μm 至 1.29×10μm，等效半径在 10μm 至 680μm 之间。孔隙的球形度偏差范围为 0.10 至 0.81，平均 99.97%的孔隙接近 0.63。对于较小的孔隙，其分布趋于均匀，而较大的孔隙呈拉长的椭圆形且位于或接近饰面-核心界面处。在楔形加载钝接触断裂试验中，21 个牙冠从牙合面的裂隙处失效，其中 16 个从表面或近表面的孔隙处失效，2 个从斜嵴的中点处失效，7 个从较大的界面孔隙处失效。FEA 分析表明，缺陷仅在拉伸应力区域和与裂纹起始相关的孔隙半径范围从 30 到 50μm 的区域对饰面完整性有害。孔隙形态似乎对断裂只有很小的影响。
在微 CT 分辨率和 FEA 的限制内，这表明孔隙半径大于 30-50μm 且位于拉伸应力区域，如牙合面或近表面的裂隙和沟槽以及饰面瓷的颈缘，将危及 LDG 的双层结构和机械完整性。
