Chai Herzl, Lee James J-W, Mieleszko Adam J, Chu Stephen J, Zhang Yu
Tel Aviv University, School of Mechanical Engineering, Faculty of Engineering, Tel Aviv, Israel.
National Institute of Standards and Technology, Ceramics Division, Gaithersburg, MD 20899, USA.
Acta Biomater. 2014 Aug;10(8):3756-61. doi: 10.1016/j.actbio.2014.04.016. Epub 2014 Apr 24.
Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their susceptibility to fracture remains a practical problem. The failure of PFZ prostheses often involves crack initiation and growth in the porcelain, which may be followed by fracture along the porcelain/zirconia (P/Z) interface. In this work, we characterized the process of fracture in two PFZ systems, as well as a newly developed graded glass-zirconia structure with emphases placed on resistance to interfacial cracking. Thin porcelain layers were fused onto Y-TZP plates with or without the presence of a glass binder. The specimens were loaded in a four-point-bending fixture with the thin porcelain veneer in tension, simulating the lower portion of the connectors and marginal areas of a fixed dental prosthesis (FDP) during occlusal loading. The evolution of damage was observed by a video camera. The fracture was characterized by unstable growth of cracks perpendicular to the P/Z interface (channel cracks) in the porcelain layer, which was followed by stable cracking along the P/Z interface. The interfacial fracture energy GC was determined by a finite-element analysis taking into account stress-shielding effects due to the presence of adjacent channel cracks. The resulting GC was considerably less than commonly reported values for similar systems. Fracture in the graded Y-TZP samples occurred via a single channel crack at a much greater stress than for PFZ. No delamination between the residual glass layer and graded zirconia occurred in any of the tests. Combined with its enhanced resistance to edge chipping and good esthetic quality, graded Y-TZP emerges as a viable material concept for dental restorations.
氧化锆熔附烤瓷（PFZ）修复体在口腔修复学中被广泛应用。然而，其易发生断裂仍是一个实际问题。PFZ修复体的失效通常涉及烤瓷层中裂纹的萌生和扩展，随后可能沿着烤瓷/氧化锆（P/Z）界面发生断裂。在本研究中，我们对两种PFZ系统以及一种新开发的梯度玻璃-氧化锆结构的断裂过程进行了表征，重点关注其对界面裂纹的抗性。在有或没有玻璃粘结剂存在的情况下，将薄的烤瓷层熔附到Y-TZP板上。将试件置于四点弯曲夹具中加载，使薄的烤瓷贴面处于拉伸状态，模拟固定义齿（FDP）在咬合加载时连接体的下部和边缘区域。通过摄像机观察损伤的演变。断裂的特征是在烤瓷层中垂直于P/Z界面的裂纹（通道裂纹）不稳定扩展，随后沿着P/Z界面稳定开裂。通过有限元分析确定界面断裂能GC，该分析考虑了相邻通道裂纹存在时的应力屏蔽效应。得到的GC远小于类似系统通常报道的值。梯度Y-TZP样品中的断裂通过单个通道裂纹在比PFZ大得多的应力下发生。在任何测试中，残余玻璃层和梯度氧化锆之间均未发生分层。结合其增强的抗边缘崩裂性能和良好的美学质量，梯度Y-TZP成为一种可行的牙科修复材料概念。
