Confocal Raman microscopic analysis of the zirconia/feldspathic ceramic interface

Esthetic demands and biocompatibility have prompted the development of all-ceramic dental crowns. Yttria tetragonal zirconia polycrystalline (Y-TZP) framework material has the best mechanical properties compared to other all-ceramic systems, but the interface is the weakest component of core veneered restorations. Confocal Raman microscopy possibilities are used to ensure the understanding of the zirconia-feldspathic ceramic relationship, which is not well known.

Bilayered zirconia (Vita In-Ceram(®) YZ) veneer (Vita VM(®)9) blocks were manufactured. Raman analyses were performed using two protocols: (1) single spectra, line scans and images on a sectioned and polished specimen and (2) in depth line scans on unprepared specimen. Single spectra, images and line scans provide information about the crystalline phases, their distribution and the existence of a possible diffusion at the Y-TZP/VM(®)9 interface, respectively. The elemental distribution of zirconium (Zr) and silicon (Si) around this interface were investigated using energy dispersive X-ray spectroscopy (EDS).

Raman single spectra embodied a unique spectrum (crystalline) on Y-TZP and two spectra (crystalline and amorphous) on VM(®)9; these spectra were clearly distinguished. Raman line scans showed a series of transition spectra across the interface from VM(®)9 to Y-TZP. It emphasized an interdiffusion zone, which was estimated at a maximum of 2 microns, found on 2d Raman images and confirmed by EDS. The elemental distribution with EDS showed a mutual diffusion of Zr and Si and was mainly dominated by Si diffusion in Y-TZP.

Confocal Raman microscopy highlights an interdiffusion zone at the zirconia-feldspathic ceramic interface. The elemental transition layer is estimated and is supported by EDS analysis as a coupling technique.