Heintze S D, Cavalleri A, Zellweger G, Büchler A, Zappini G
R&D, Ivoclar Vivadent AG, Bendererstrasse 2, FL-9494 Schaan, Liechtenstein.
Dent Mater. 2008 Oct;24(10):1352-61. doi: 10.1016/j.dental.2008.02.019. Epub 2008 Apr 22.
The purpose of this laboratory study was to compare the frequency of failures (complete fractures or partial cracks) of molar crowns made of two different all-ceramic materials during dynamic loading in a chewing simulator, as well as the fracture load when subjected to static loading, in relation to different dynamic loading and luting protocols.
One hundred and forty-four molar crowns fabricated with IPS Empress or an experimental e.max Press material with high translucency (e.max Press Exp) were luted on CAD/CAM milled PMMA abutments (first lower molar, circular chamfer) either with Variolink or glass-ionomer cement (GIC). All crowns were loaded according to three different loading protocols (n=12 per group) and two force profiles (sinusoidal, rectangular) in a pneumatically driven chewing simulator with a steel stylus (Ø 8 mm) and they underwent simultaneous thermocycling (5 degrees C/55 degrees C). After each phase the crowns were evaluated with regard to fractures or cracks. After dynamic testing, the crowns that did not fail were subjected to compression loading until complete fracture in a universal testing machine (UTM). As control groups, unloaded crowns were also subjected to a UTM. Survival statistics with log-rank tests were applied for the results of the dynamic loading, while ANOVA with post hoc Tukey B was used for the fracture load results and two-way ANOVA was carried out for logarithmically transformed data. Weibull statistics were calculated for pooled fracture load data of the dynamically loaded and control groups.
In the 144 IPS Empress crowns, complete fractures were observed in 9 crowns and partial cracks in another 3 crowns. When the data was pooled, a statistically significant increase in fractures occurred when the sinusoidal force profile was applied compared to a rectangular force profile (log-rank, p<0.05). No fractures occurred in the e.max Press Exp crowns. The two-way ANOVA showed that the type of luting protocol used had the most significant effect on the fracture load of both materials. In conjunction with Empress, however, the luting material influenced the variability twice as much as in e.max Press Exp. There was no statistically significant difference in the fracture load of GIC-luted e.max Press Exp crowns and that of the Variolink luted Empress crowns. The force profile had a significant effect on the fracture load only of the Empress crowns but not of the e.max Press Exp crowns. Weibull statistics revealed a higher scattering of the data of dynamically loaded crowns compared to that of the control groups.
For testing all-ceramic materials, dynamic loading is indispensable to draw valid conclusions on clinical performance of all-ceramic molar crowns. A sinusoidal profile is advisable, while a gradual increase of the force amplitude does not significantly affect the results.
本实验室研究旨在比较两种不同全瓷材料制成的磨牙冠在咀嚼模拟器动态加载过程中的失败频率（完全骨折或部分裂纹），以及在静态加载下的断裂载荷，同时考虑不同的动态加载和粘接方案。
用IPS Empress或具有高透明度的实验性e.max Press材料（e.max Press Exp）制作的144个磨牙冠，用Variolink或玻璃离子水门汀（GIC）粘接在CAD/CAM铣削的PMMA基台上（第一下颌磨牙，圆形肩台）。所有牙冠根据三种不同的加载方案（每组n = 12）和两种力型（正弦型、矩形），在气动驱动的咀嚼模拟器中用钢探针（Ø 8 mm）加载，并同时进行热循环（5℃/55℃）。每个阶段后，对牙冠的骨折或裂纹情况进行评估。动态测试后，未失败的牙冠在万能试验机（UTM）中进行压缩加载直至完全骨折。作为对照组，未加载的牙冠也进行UTM测试。动态加载结果采用对数秩检验进行生存统计，断裂载荷结果采用方差分析（ANOVA）和事后Tukey B检验，对对数转换数据进行双向方差分析。对动态加载组和对照组的合并断裂载荷数据计算威布尔统计量。
在144个IPS Empress牙冠中，观察到9个牙冠完全骨折，另外3个牙冠有部分裂纹。合并数据后，与矩形力型相比，应用正弦力型时骨折发生率有统计学意义的增加（对数秩检验，p < 0.05）。e.max Press Exp牙冠未发生骨折。双向方差分析表明，所用的粘接方案类型对两种材料的断裂载荷影响最为显著。然而，与Empress结合时，粘接材料对变异性的影响是e.max Press Exp的两倍。GIC粘接的e.max Press Exp牙冠和Variolink粘接的Empress牙冠的断裂载荷没有统计学显著差异。力型仅对Empress牙冠的断裂载荷有显著影响，而对e.max Press Exp牙冠没有影响。威布尔统计显示，与对照组相比，动态加载牙冠的数据离散度更高。
对于测试全瓷材料，动态加载对于得出全瓷磨牙冠临床性能的有效结论是必不可少的。建议采用正弦型，而力幅的逐渐增加对结果没有显著影响。
