Interfacial modulus mapping of layered dental ceramics using nanoindentation

Layered dental ceramics are widely used in restorative dentistry, but their performance depends on interfacial properties. Prior research has shown that mechanical behavior at interfaces can differ from bulk properties. However, no prior work had resolved how specific layers affect modulus of elasticity in multilayer systems. This gap motivated the need to evaluate interfacial properties using advanced techniques. Established methods like X-ray diffraction and SEM provide structural insights but lack spatial resolution for modulus mapping. Nanoindentation offers a way to assess mechanical properties at microscale interfaces. The study of yttria-stabilized zirconia as a core material is well documented. Yet, the role of liners in veneered ceramics remains unclear. This paper's contribution lies in directly measuring modulus variations across interfaces in dental ceramics.

The objective was to evaluate the modulus of elasticity across interfaces in layered dental ceramics. The specific problem addressed is the lack of detailed mechanical data at microscale interfaces. The motivation stems from the need to understand how liners affect interface performance. This paper aims to test whether the liner introduces a weak point in the multilayer system. The study compares two specimen types: one with a liner and one without. The goal is to determine if the liner significantly alters the modulus. The method involves nanoindentation with spherical tips and partial unloading. The study also seeks to validate nanoindentation as a reliable tool for interface analysis.

The study used spherical indentation with a 5 µm tip on a UMIS CSIRO 2000 system. Two specimen types were prepared: one with a liner and one without. The specimens were made from yttria-stabilized zirconia and veneered with a glass-ceramic. A multiple point load - partial unload method was applied to measure modulus. Scanning Electron Microscopy and X-ray powder diffraction were used for material characterization. The interfaces were polished and exposed for indentation testing. Data from indentation were used to create modulus maps of the tested areas. The study focused on the veneer material at a 40 µm distance from the interface.

Modulus values showed a significant difference at 40 µm in the veneer material between the two specimen types. The presence of the liner was associated with a lower modulus in that region. The difference was statistically significant with a p-value less than 0.05. X-ray diffraction confirmed a tetragonal phase in the zirconia core material. Scanning electron microscopy showed fine-grained structure in the core material. The liner and veneer materials were characterized as amorphous. The liner was identified as a potential weak link in the multilayer system. Nanoindentation using spherical tips and partial unloading was found to be a reliable method for modulus mapping.

The study found that the liner significantly affects modulus in the veneer material at 40 µm distance. The lower modulus suggests the liner may act as a weak link in the dental multilayer. The results support the use of nanoindentation for interface analysis in layered ceramics. The method proved reliable for modulus mapping and evaluation of interfacial properties. The findings are specific to the materials and conditions tested in this study. No generalizations beyond the tested materials are proposed. The study does not suggest that all liners behave similarly in dental ceramics. The results align with the authors' hypothesis that interface properties can differ from bulk properties.