Objectives

Chemical and mechanical degradation play a key role on the lifetime of dental restorative materials. Therefore, prediction of their long-term performance in the oral environment should base on fatigue, rather than inert strength data, as commonly observed in the dental material’s field. The objective of the present study was to provide mechanistic fatigue parameters of current dental CAD/CAM materials under cyclic biaxial flexure and assess their suitability in predicting clinical fracture behaviors.

Methods

Eight CAD/CAM materials, including polycrystalline zirconia (IPS e.max ZirCAD), reinforced glasses (Vitablocs Mark II, IPS Empress CAD), glass-ceramics (IPS e.max CAD, Suprinity PC, Celtra Duo), as well as hybrid materials (Enamic, Lava Ultimate) were evaluated. Rectangular plates (12 × 12 × 1.2 mm³) with highly polished surfaces were prepared and tested in biaxial cyclic fatigue in water until fracture using the Ball-on-Three-Balls (B3B) test. Cyclic fatigue parameters n and A* were obtained from the lifetime data for each material and further used to build SPT diagrams. The latter were used to compare in-vitro with in-vivo fracture distributions for IPS e.max CAD and IPS Empress CAD.

Results

Susceptibility to subcritical crack growth under cyclic loading was observed for all materials, being more severe (n ≤ 20) in lithium-based glass-ceramics and Vitablocs Mark II. Strength degradations of 40% up to 60% were predicted after only 1 year of service. Threshold stress intensity factors (K_th) representing the onset of subcritical crack growth (SCG), were estimated to lie in the range of 0.37–0.44 of K_Ic for the lithium-based glass-ceramics and Vitablocs Mark II and between 0.51–0.59 of K_Ic for the other materials. Failure distributions associated with mechanistic estimations of strength degradation in-vitro showed to be useful in interpreting failure behavior in-vivo. The parameter K_th stood out as a better predictor of clinical performance in detriment to the SCG n parameter.

Significance

Fatigue parameters obtained from cyclic loading experiments are more reliable predictors of the mechanical performance of contemporary dental CAD/CAM restoratives than quasi-static mechanical properties.

中文翻译：

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椅子旁的CAD / CAM材料。第3部分：循环疲劳参数和寿命预测

目标

化学和机械降解在牙科修复材料的寿命中起着关键作用。因此，对它们在口腔环境中的长期性能的预测应该基于疲劳，而不是牙科材料领域通常观察到的惰性强度数据。本研究的目的是提供当前的牙科CAD / CAM材料在周期性双轴挠曲下的机械疲劳参数，并评估其在预测临床骨折行为中的适用性。

方法

八种CAD / CAM材料，包括多晶氧化锆（IPS e.max ZirCAD），强化玻璃（Vitablocs Mark II，IPS Empress CAD），玻璃陶瓷（IPS e.max CAD，Suprinity PC，Celtra Duo）以及混合材料对材料（Enamic，Lava Ultimate）进行了评估。制备了具有高度抛光表面的矩形板（12×12×1.2 mm ³），并使用三对球（B3B）试验在水中进行了双轴循环疲劳试验直至断裂。从每种材料的寿命数据中获得循环疲劳参数n和A *，并将其进一步用于构建SPT图。后者用于比较IPS e.max CAD和IPS Empress CAD的体外和体内骨折分布。

结果

观察到所有材料易感性亚临界裂纹扩展循环荷载下，是更严重（Ñ 在基于锂的玻璃-陶瓷和VITABLOCS标记II≤20）。服役一年后，强度会下降40％至60％。代表亚临界裂纹增长（SCG）的阈值应力强度因子（K _th）估计在锂基玻璃陶瓷和Vitablocs Mark II的K _Ic的范围为0.37-0.44，在Vitablocs Mark II的范围为0.51-0.59。其他材料的K _Ic值。与体外强度退化的机械估计相关的失效分布在解释失效行为方面非常有用体内。参数K _th可以作为对SCG n参数不利的临床表现的更好的预测指标。

意义

与准静态机械性能相比，从循环加载实验获得的疲劳参数是当代牙科CAD / CAM修复剂机械性能的更可靠预测指标。