Residual stress plays a critical role in failure of all ceramic crowns. The magnitude and distribution of residual stress in the crown system are largely unknown. Determining the residual stress quantitatively is challenging since the crown has such complex contours and shapes. This work explored the feasibility and validity of measuring residual stress of zirconia and porcelain in ceramic crowns by nanoindentation. Nanoindentation tests were performed on the cross section of a crown along both porcelain and zirconia. Here, one critical location of the crown was selected. It has the thickest section of porcelain and curvature at the crown surface. A half crown annealed at 400 °C was used as a reference sample. The residual stress was determined by comparing the measured apparent hardness of the stressed sample with that of the reference sample. The nanoindentation impression images were acquired through Scanning Probe Microscope (SPM) equipped with a Hysitron Triboindenter. The derived normal contact area value was corrected using the measured real area. Residual stress is determined along the thickness of crowns at the chosen location for both porcelain and zirconia. Results show residual stress across the thickness for both porcelain and zirconia is significantly different. Porcelain showed more tensile stress closer to the crown surface, while zirconia showed more tensile stress closer to the zirconia-porcelain interface.
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