Objective

The effect of cusp angle on the load-carrying capacity and failure behaviour of BionZ Diamond zirconia crowns is carried out using experimental and numerical investigations.

Methods

The experimental program using monolithic crowns were divided into three groups (n = 14) for three cusp angles, 60, 80 and 120 degrees and were tested to failure under the static load. A 2-channel acoustic emission (AE) system was used to monitor the failure process while the piezo sensors were attached to the rigid stainless-steel jig for recoding the AE events. Load-displacement and AE response were simultaneously monitored until failure of specimens. Parametric AE analysis was conducted for the factors such as amplitude, energy released, signal duration and cumulative counts, for each AE signal. Fast Fourier transform (FFT) was conducted to assess the frequency at failure. Linear finite element analysis (FEA) was carried out using commercial software Ansys Workbench 19.1 to present the stress distribution and failure modes. Post-failure surface morphology study was carried out using scanning electron microscopy (SEM) and statistical analysis was performed using Weibull analysis.

Results

All the samples in three different groups have failed at the mid-line, splitting the zirconia crowns into two equal pieces. The load to failure was directly proportional to the cusp angle in crowns; 120° group had the highest load-carrying capacity of 2.93 ± 0.26 kN while 60 and 80° groups had a failure load of 2.46 ± 0.53 and 2.52 ± 0.16 kN, respectively. Parametric AE analysis revealed that the failure was instantaneous and 60-degree samples had higher AE signature. FE analysis showed the crack initiation at the occlusal surface of the crown which is in agreement with the SEM images. A close agreement of results for the load and stress distribution from FEA complemented with the experimental study.

Significance

Optimisation of cusp-angle could help clinicians to accurately design the monolithic zirconia crown focussing on maximum load-carrying capacity, increasing the restoration life.

中文翻译：

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尖锐角对氧化锆牙冠影响的声发射和有限元研究

目的

通过实验和数值研究，确定了尖角对BionZ Diamond氧化锆冠的承载能力和破坏行为的影响。

方法

使用整体式牙冠的实验程序针对三个尖角60、80和120度分为三组（n = 14），并测试了在静载荷下的破坏。当压电传感器连接到刚性不锈钢夹具上以记录AE事件时，使用2通道声发射（AE）系统监视故障过程。同时监测载荷-位移和AE响应，直到样品失效。对每个AE信号进行参数AE分析，以分析诸如幅度，释放的能量，信号持续时间和累积计数等因素。进行了快速傅立叶变换（FFT）来评估失效频率。使用商业软件Ansys Workbench 19.1进行了线性有限元分析（FEA），以显示应力分布和破坏模式。

结果

三个不同组中的所有样品在中线都失败了，将氧化锆冠切成两等份。破坏载荷与冠的尖角成正比。120°组的最大承载能力为2.93±0.26 kN，而60°和80°组的最大破坏承载力分别为2.46±0.53和2.52±0.16 kN。参数AE分析显示故障是瞬时的，并且60度样品具有较高的AE签名。有限元分析表明，在牙冠咬合面的裂纹萌生与SEM图像一致。FEA的载荷和应力分布结果与实验研究相吻合。

意义

牙尖角度的优化可以帮助临床医生准确地设计单片氧化锆冠，着重于最大承载能力，从而延长修复体的寿命。