Department of Advanced Free Radical Science, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 980 8575, Japan.
Sweden Dental Sendai (private practice), 1-6-2 Tsutsujigaoka, Miyagino-ku, Sendai 983 0852, Japan.
J Mech Behav Biomed Mater. 2018 Nov;87:180-189. doi: 10.1016/j.jmbbm.2018.07.034. Epub 2018 Jul 25.
Application of monolithic zirconia crowns (MZCs) with reduced thickness to the molar region has been proposed, but potential complications have yet to be fully evaluated in laboratory tests. The present study aimed to develop a clinically relevant load-to-failure test in combination with fatigue treatments involving thermal and mechanical cycling (TC and MC) to evaluate the fracture resistance of molar MZCs. MZCs with a minimal thickness of 0.5 mm were bonded to dies made of resin-based composite (RBC), epoxy resin (EP), or polyoxymethylene-copolymer (POM-C). The samples were either untreated (UT) or subjected to TC (5-55 °C for 1 × 10 cycles) and MC (300 N for 2.4 × 10 cycles). The stress generated by TC and MC was simulated by finite element modeling. The load-to-failure test was performed using an inverse V-shaped two-plane indenter and was followed by fractographic analysis. The median values of fracture load for MZC/RBC and MZC/EP in the TC group were significantly lower than those in the UT group. MC also decreased the median value of fracture load for MZC/RBC significantly, but not that for MZC/EP and MZC/POM-C. Fractography revealed that the fracture started in the cervical area in all groups, which is similar to clinically failed crowns. The simulation confirmed stress concentration at the cervical area in both TC and MC groups. The present study suggests that the load-to-failure test using a two-plane indenter could induce clinically relevant fracture of MZCs, the vulnerability of the MZCs depends largely on the die material employed, and MZCs are more likely to be damaged by thermal fatigue than mechanical fatigue.
应用于磨牙区的薄型整体氧化锆全冠（MZCs）已被提出，但在实验室测试中尚未充分评估其潜在并发症。本研究旨在开发一种临床相关的负载失效试验，并结合热和机械循环（TC 和 MC）疲劳处理，以评估磨牙 MZCs 的抗断裂能力。最小厚度为 0.5mm 的 MZCs 粘接到由树脂基复合材料（RBC）、环氧树脂（EP）或聚甲醛共聚物（POM-C）制成的模具上。样本未经处理（UT）或经过 TC（5-55°C 1×10 循环）和 MC（300N 2.4×10 循环）处理。TC 和 MC 产生的应力通过有限元建模进行模拟。负载失效试验使用反向 V 形双平面压头进行，并进行断裂分析。TC 组中 MZC/RBC 和 MZC/EP 的断裂载荷中位数明显低于 UT 组。MC 也显著降低了 MZC/RBC 的断裂载荷中位数，但对 MZC/EP 和 MZC/POM-C 没有影响。断裂分析表明，所有组的断裂均始于颈部区域，这与临床上失败的牙冠相似。模拟证实了 TC 和 MC 组中颈部区域的应力集中。本研究表明，使用双平面压头的负载失效试验可以诱导 MZCs 的临床相关断裂，MZCs 的脆弱性在很大程度上取决于所使用的模具材料，并且 MZCs 更容易受到热疲劳而不是机械疲劳的损坏。
