Xu H H, Liao H, Eichmiller F C
Paffenbarger Research Center, American Dental Association Health Foundation, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Dent Res. 1998 Dec;77(12):1991-8. doi: 10.1177/00220345980770120701.
Amalgam creep has been identified as a key parameter associated with marginal breakdown and corrosion. The aim of this study was to evaluate the time-dependent deformation (creep) of a novel silver filling material as an alternative to amalgam. We made the silver specimens by pressing a precipitated powder at room temperature to a density that can be achieved in clinical hand consolidation. The surface of the silver was either polished or burnished. To examine local contact creep and the effect of surface finishing, we used an indentation creep method in which a Vickers indenter was loaded on the specimen surface at a load of 10 N with dwell times of 5 sec to 6x10(4) sec. We used a bonded-interface technique to examine subsurface creep mechanisms. The flexural strength (mean+/-SD; n = 10) was 86+/-20 MPa for amalgam, 180+/-21 MPa for polished silver, and 209+/-19 MPa for burnished silver-values which are significantly different from each other (family confidence coefficient = 0.95; Tukey's multiple-comparison test). Indentation creep manifested as hardness number decreasing with increased dwell time. With dwell time increasing from 5 sec to 6x10(4) sec, the hardness number of amalgam was reduced by approximately 80%; that of the polished silver and the burnished silver was reduced by only 40%. Subsurface creep in amalgam consisted of the shape change of the alloy particles from spherical to elongated shapes, and the separation of matrix grains from each other, possibly due to grain-boundary sliding. Creep of the polished silver occurred by densification reducing porosity and increasing hardness; that of the burnished silver occurred by the displacement of the burnished layer. These results suggest that, due to creep-induced subsurface work-hardening and densification, the consolidated silver exhibits a higher resistance to indentation creep than does amalgam. The hardness number of silver approaches that of amalgam after prolonged indentation loading.
汞合金蠕变已被确认为与边缘破裂和腐蚀相关的关键参数。本研究的目的是评估一种新型银填充材料随时间的变形（蠕变）情况，以替代汞合金。我们通过在室温下压制沉淀粉末来制备银试样，使其达到临床手工压实所能达到的密度。银的表面要么进行抛光，要么进行打磨。为了研究局部接触蠕变和表面处理的效果，我们采用了压痕蠕变方法，其中维氏压头以10 N的载荷加载在试样表面，保载时间为5秒至6×10⁴秒。我们使用粘结界面技术来研究亚表面蠕变机制。汞合金的抗弯强度（平均值±标准差；n = 10）为86±20 MPa，抛光银为180±21 MPa，打磨银为209±19 MPa，这些数值彼此之间有显著差异（家族置信系数 = 0.95；Tukey多重比较检验）。压痕蠕变表现为硬度值随保载时间增加而降低。随着保载时间从5秒增加到6×10⁴秒，汞合金的硬度值降低了约80%；抛光银和打磨银的硬度值仅降低了40%。汞合金的亚表面蠕变包括合金颗粒从球形变为细长形，以及基体晶粒彼此分离，这可能是由于晶界滑动所致。抛光银的蠕变是通过致密化减少孔隙率并增加硬度而发生的；打磨银的蠕变是通过打磨层的位移而发生的。这些结果表明，由于蠕变引起的亚表面加工硬化和致密化，压实后的银比汞合金表现出更高的抗压痕蠕变能力。长时间压痕加载后，银的硬度值接近汞合金的硬度值。
