Objectives

A competing risk (CR) model distinguishing adhesive, cohesive and mixed failures as competing events was used for the analysis of micro-tensile bond strength (μTBS) data and compared with a conventional failure mode non-distinguishing survival model.

Methods

Fifty human molars were bonded using five universal adhesives (n = 10) and subdivided according to aging conditions (24-h water storage, thermocycling). After μTBS to dentin was tested, a fractographic analysis was performed using scanning electron microscopy. Survival analyses of the μTBS data were performed using both a failure mode distinguishing Weibull CR model, and a conventional failure mode non-distinguishing Weibull model. Weibull shape (m) and scale (σ_θ) parameters were calculated for both models using the maximum likelihood estimation method, and strength at 10 % probability of failure, σ_0.10, was estimated. Groups were compared using 95 % confidence intervals.

Results

CR-model estimates of σ_θ and σ_0.10 for adhesive failures were higher than those of the conventional model, more markedly in groups with lower percentages of adhesive failures. CR-model strength estimates for cohesive failures were similar in all groups regardless of their bond strengths and failure mode distributions.

Significance

Merging all bond-strength data into one dataset irrespective of the failure mode may result in a severe underestimation of bond strength, especially in groups with low incidence of adhesive failures. Bond-strength data analysis using a CR model could provide more accurate estimates of bond strength, and strength estimates for cohesive failures which were apparently independent of bond strength could serve as an internal validity indicator of the CR model.

中文翻译：

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用于债券强度数据分析的竞争性风险模型。

目标

使用竞争风险（CR）模型将粘合，内聚和混合失效作为竞争事件进行区分，该模型用于分析微拉伸粘合强度（μTBS）数据，并与常规失效模式无区别生存模型进行比较。

方法

用五种通用粘合剂（n = 10）粘合五十个人类臼齿，并根据老化条件（24小时储水，热循环）进行细分。测试了对牙本质的μTBS后，使用扫描电子显微镜进行了分形分析。使用区分故障模式的Weibull CR模型和传统的故障模式非区别Weibull模型对μTBS数据进行生存分析。威布尔形状（米）和标度（σ _θ计算）参数为使用最大似然估计法两种模型中，与失败的强度在10％的概率，σ _0.10，估计。使用95％置信区间比较各组。

结果

的σCR-模型估计值_θ和σ _0.10对粘接失败均较常规模式，更显着地在与粘接失败的百分比较低组更高。内聚破坏的CR模型强度估计在所有组中都是相似的，无论其粘结强度和破坏模式分布如何。

意义

不管失效模式如何，将所有粘结强度数据合并到一个数据集中可能会导致严重低估粘结强度，尤其是在粘结故障发生率较低的组中。使用CR模型的粘结强度数据分析可以提供对粘结强度的更准确的估计，而明显与粘结强度无关的内聚破坏的强度估计可以用作CR模型的内部有效性指标。