Dental Materials Science, Dept of Bioclinical Sciences, Faculty of Dentistry, Health Sciences Centre, Kuwait University, Jabriya, Kuwait.
Dent Mater. 2012 Oct;28(10):e207-17. doi: 10.1016/j.dental.2012.05.002. Epub 2012 Jun 5.
To characterize the development of strength during the setting process of dental silver amalgam in the context of 'early strength' measurements for standards compliance testing in relation to patient instructions, and demonstrate the applicability of the Hertzian 'ball on disc' method.
Sixteen dental silver amalgam products were tested using the 'ball on disc' protocol at 1, 2, 3, 4 and 24h after setting at 37°C in air. The mixed materials were packed into a tapered steel disc mold (10mm diameter, 3mm thick) resting on a glass surface, slightly overfilled and carved level with a sharp edge, then ejected at ∼10min and placed immediately into an incubator at 37°C. Testing was in Hertzian mode, using a 20mm steel ball, with the specimen resting on a disc of glass-filled polyamide (E=10GPa) at a cross-head speed of 0.2mm/min on a universal testing machine (E3000, Instron). The load at first crack was recorded, as was the number of radial cracks produced.
Radial cracking into 2-5 pieces, in a clinically-relevant (non-explosive) mode was observed in all cases. Considerable variation in setting rate between products, as indicated by the development of load at failure with time, was found. The distribution of normalized failure load values overall was lognormal (Weibull was excluded). The RMS coefficient of variation overall was 12.4%.
The ball-on-disc test provides a facile, relevant measure of the strength of dental silver amalgam, and is viable as a standards compliance test. Early strength testing at a minimum of 2h is suggested.
在与患者说明相关的标准符合性测试的“早期强度”测量中，描述牙科银汞合金在凝固过程中的强度发展，并展示赫兹“球压盘”方法的适用性。
将 16 种牙科银汞合金产品在 37°C 空气中凝固后 1、2、3、4 和 24 小时，使用“球压盘”方案进行测试。混合材料装入锥形钢盘模具（直径 10mm，厚 3mm）中，放置在玻璃表面上，稍微过量填充并用锋利的边缘刮平，然后在约 10 分钟后弹出，并立即放入 37°C 的培养箱中。测试采用赫兹模式，使用 20mm 钢球，在万能试验机（Instron E3000）上以 0.2mm/min 的十字头速度，将样品放置在填充玻璃的聚酰胺（E=10GPa）圆盘上。记录首次出现裂缝时的载荷，以及产生的径向裂缝数量。
在所有情况下，均观察到以临床相关（非爆炸）模式裂成 2-5 块的径向裂纹。发现产品之间的凝固速率存在很大差异，表现为破坏时的载荷随时间的发展。归一化失效载荷值的总体分布呈对数正态分布（排除了 Weibull）。总体 RMS 变异系数为 12.4%。
球压盘测试提供了一种简便、相关的牙科银汞合金强度测量方法，可作为标准符合性测试。建议至少在 2 小时后进行早期强度测试。
