Studart André R, Filser Frank, Kocher Peter, Lüthy Heinz, Gauckler Ludwig J
Department of Materials, Nonmetallic Inorganic Materials, Wolfgang-Pauli-Strasse 10, ETH Hönggerberg, HCI G 539, 8093 Zürich, Switzerland.
Dent Mater. 2007 Jan;23(1):115-23. doi: 10.1016/j.dental.2005.12.009. Epub 2006 Feb 13.
High-strength ceramics are required in dental posterior restorations in order to withstand the excessive tensile stresses that occur during mastication. The aim of this study was to investigate the fracture behavior and the fast-fracture mechanical strength of three veneer-framework composites (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) for all-ceramic dental bridges.
The load bearing capacity of the veneer-framework composites were evaluated using a bending mechanical apparatus. The stress distribution through the rectangular-shaped layered samples was assessed using simple beam calculations and used to estimate the fracture strength of the veneer layer. Optical microscopy of fractured specimens was employed to determine the origin of cracks and the fracture mode.
Under fast fracture conditions, cracks were observed to initiate on, or close to, the veneer outer surface and propagate towards the inner framework material. Crack deflection occurred at the veneer-framework interface of composites containing a tough framework material (TZP/Cercon S and Inceram-Zirconia/Vita VM7), as opposed to the straight propagation observed in the case of weaker frameworks (Empress 2/IPS Eris).
The mechanical strength of dental composites containing a weak framework (K(IC)<3 MPam(1/2)) is ultimately determined by the low fracture strength of the veneer layer, since no crack arresting occurs at the veneer-framework interface. Therefore, high-toughness ceramics (K(IC)>5 MPam(1/2)) should be used as framework materials of posterior all-ceramic bridges, so that cracks propagating from the veneer layer do not lead to a premature failure of the prosthesis.
牙科后牙修复需要高强度陶瓷，以承受咀嚼过程中产生的过大拉应力。本研究的目的是调查三种用于全瓷牙桥的贴面 - 框架复合材料（Empress 2/IPS Eris、TZP/Cercon S和Inceram - 氧化锆/Vita VM7）的断裂行为和快速断裂机械强度。
使用弯曲力学装置评估贴面 - 框架复合材料的承载能力。通过简单梁计算评估矩形分层样品中的应力分布，并用于估计贴面层的断裂强度。采用断裂试样的光学显微镜来确定裂纹的起源和断裂模式。
在快速断裂条件下，观察到裂纹在贴面外表面上或其附近开始，并向内部框架材料扩展。在含有韧性框架材料的复合材料（TZP/Cercon S和Inceram - 氧化锆/Vita VM7）的贴面 - 框架界面处发生裂纹偏转，这与较弱框架（Empress 2/IPS Eris）情况下观察到的直线扩展相反。
含有弱框架（K(IC)<3 MPam(1/2)）的牙科复合材料的机械强度最终由贴面层的低断裂强度决定，因为在贴面 - 框架界面处不会发生裂纹止裂。因此，高韧性陶瓷（K(IC)>5 MPam(1/2)）应用作后牙全瓷桥的框架材料，以使从贴面层扩展的裂纹不会导致假体过早失效。
