Understanding the microstructural bonding mechanisms between Y-TZP and veneering ceramic

目前，牙科贴面氧化锆基牙核修复体的应用非常广泛。氧化锆核心与瓷饰面材料分层，以达到合适的美学效果。然而，基于氧化锆的修复会产生临床问题，如瓷贴面层的碎裂或断裂。先前的研究报告了单板失效的显著发生率，如分层、碎裂和开裂。这种断裂行为可归因于贴面/芯面界面结合强度差、芯材与贴面之间弹性模量不匹配、芯材与贴面之间热膨胀系数不匹配、瓷体强度弱以及热过程中由于冷却速率和/或高温烧结导致的残余应力。为了提高贴面与瓷芯界面的相容性，避免其过早失效，需要进一步了解氧化锆/瓷的界面。

Dental veneered zirconia-based core restorations have been used widely to date. The zirconia core is layered with a porcelain veneer material to achieve suitable esthetics. However, zirconia-based restorations can create clinical issues such as chipping or fracture of the porcelain veneered layer. Previous studies have reported a significant incidence of veneer failures such as delaminations, chipping and cracking. This fracture behavior could be attributed to the poor veneer/core interface bond strength, elastic modulus mismatch between the core material and the veneer, coefficient of thermal expansion mismatch between the core and the veneer, weak porcelain strength and thermal procedure which could introduce residual stress induced by cooling rate and/or sintering at high temperatures. To improve the compatibility at the interface between veneer and core, and to avoid premature failure, the interface zirconia/porcelain should be better understood. The proposed research will investigate the detailed mechanism for the adhesion at the interface zirconia/porcelain to develop a feasible solution to improve the bonding between these two materials, using both molding techniques (the layering technique and the press technique). The thermal stresses will be also evaluated. The main objectives of this study are to characterize the interaction between porcelain and zirconia then, materials or new designs will be developed based on the results. Therefore, better bonding stability between porcelain veneer and zirconia core of an all-ceramic restoration can be achieved. The adhesion of porcelain veneer to zirconia is fundamental for the success of the zirconia-based restorations. After determining the new protocol and/or design to fabricate zirconia-based restorations, mechanical tests will be performed. Different tests will be carefully conducted to describe the microstructural mechanisms of zirconia/porcelain bond. The tests are SEM, EDS, Electron Backscatter Diffraction (EBSD). Furthermore, microstructures, texture, defects, grain morphology and deformation will also be evaluated by EBSD. In addition, the Focused Ion Beam microscopy (FIB) will be used to prepare thin specimens for the TEM and for Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Auger Microprobe will contribute to the determination of 2D and 3D elemental distributions on surfaces with high spatial resolution. The bond formation of the zirconia to porcelain will also be examined by XPS. The outcome of the research is to provide the dental laboratories with a new protocol to fabricate dental veneered zirconia-based core restorations in order to improve the success rate of this type of dental restoration. The new protocol will be based on the detailed bond mechanisms at the zirconia/porcelain interface obtained from the results of this study. Over 5 years, I will train 3 graduate students.