Confocal Raman Microscopy investigations: interface zirconia core and veneering porcelain

Objectives: The interface is the weakest component of core veneered all-ceramic restorations and it is the origin of failure. The purpose of this study is to investigate a transitional layer between a zirconia core and veneer porcelain, due mainly by interpenetration of components and crystalline phases diffusion. Methods: The samples were manufactured according dental laboratory's procedure. Y-TZP was used as a framework material suitable for CAD/CAM machines. An optional thin layer of liner was applied prior to layering veneer porcelain. To investigate the interface, the samples were cut (Isomet 2000) and polished (ESCIL). Raman spectra (MCR WITEC® Alpha 300R) and Raman imaging (K-Means Cluster Analysis, WITEC® Project 2) were carried out cross-sections of the interface area. Results: Raman spectra of Y-TZP or veneer porcelain are clearly distinguished. The line scan crossing the interface shows a unique spectrum characterized by the presence of components of both materials. The Raman maps allow phase contribution assignation selecting specific spectral regions. Greater interdiffusion zone seems to have occurred when a liner is present. Conclusion: With the limitations of this study, Raman microscopy is able to investigate the interface between zirconia core and veneering porcelain. Chemical modification are visible on 2d images and allow to clearly describe the interface by highlighting chemical differences due to different manufacturing methods.