de Jager N, Feilzer A J, Davidson C L
ACTA, Department of Dental Materials Science, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.
Dent Mater. 2000 Nov;16(6):381-8. doi: 10.1016/s0109-5641(00)00030-0.
In order to adjust occlusion, the functional surfaces of porcelain restorations are often ground and mechanical machining is even an essential part of the CAD-CAM process for these restorations. The aim of this study was to investigate the influence of the finishing procedures on the biaxial flexure strength of four commercial porcelains.
Four commercial porcelains of which two are used for metal-ceramic restorations (Flexo Ceram Dentine and Vita VM K68) and two for veneers and inlays (Duceram LFC Dentine and Cerinate BODY) are used in this study. For each porcelain, sixty discs (Ø = 22 mm, h = +/- 2.0 mm) were produced using twelve different finishing procedures. Twenty discs were left untreated, twenty discs were milled, using a high-speed diamond disc, and twenty discs were machined in a high-speed grinding/polishing device. Half of the samples were glazed. In each of these six groups, half of the samples were stored for 16 h at 80 degrees C in a 4% acetic acid solution. The biaxial flexure strength was determined using the ball-on-ring method. In each group the roughness of the surface was determined and examined via SEM.
With the exception of Flexo Ceram Dentine, a significant correlation was found between the roughness of the surface and the biaxial strength: the smoother the surface, the stronger the sample. The differences in biaxial strength may be attributed to the stress concentration of an applied load due to the roughness of the surface caused by mechanical finishing or chemical action. The fact that the strength of Flexo Ceram Dentine was not affected by the different surface treatments is probably due to the size of the leucite particles, which apparently induce more stress concentration than the surface flaws and the roughness of the surface.
It was concluded that surface roughness determines the strength of a porcelain material, except where the inner structure of the material causes greater stress concentration than that caused by the combination of surface roughness and surface flaws.
为了调整咬合，瓷修复体的功能面常常需要研磨，甚至机械加工是这些修复体CAD-CAM工艺的一个重要组成部分。本研究的目的是调查精加工工艺对四种商用瓷双轴弯曲强度的影响。
本研究使用了四种商用瓷，其中两种用于金属烤瓷修复体（Flexo Ceram Dentine和Vita VM K68），另外两种用于贴面和嵌体（Duceram LFC Dentine和Cerinate BODY）。对于每种瓷，使用十二种不同的精加工工艺制作六十个圆盘（直径 = 22毫米，高度 = 正负2.0毫米）。二十个圆盘不做处理，二十个圆盘使用高速金刚石圆盘进行研磨，二十个圆盘在高速研磨/抛光设备中加工。一半的样品进行上釉。在这六组中的每组中，一半的样品在80摄氏度的4%醋酸溶液中储存16小时。使用球环法测定双轴弯曲强度。在每组中测定表面粗糙度并通过扫描电子显微镜进行检查。
除了Flexo Ceram Dentine之外，在表面粗糙度和双轴强度之间发现了显著的相关性：表面越光滑，样品越强。双轴强度的差异可能归因于由于机械精加工或化学作用导致的表面粗糙度所引起的外加负荷的应力集中。Flexo Ceram Dentine的强度不受不同表面处理影响这一事实可能是由于白榴石颗粒的大小，其显然比表面缺陷和表面粗糙度引起更多的应力集中。
得出的结论是，表面粗糙度决定了瓷材料的强度，除非材料的内部结构导致比表面粗糙度和表面缺陷共同作用所引起的更大的应力集中。
