Title: Clinically Relevant Surface Treatments on the Strength of Ultra-translucent Zirconia
Lydia Nieto (Presenter)
New York University
Ling Mao, Guizhou Medical University
Hazem Shuaeib, New York University
Minglei Zhao, New York University
Marina Kaizer, New York University
Yu Zhang, New York University
Objectives: New ultra-translucent zirconia has been introduced, expanding the monolithic zirconia indications to the esthetic areas. However, it is not yet clear how these materials are affected by common surface treatments used clinically for bonding, esthetics, and function. Thus, the objective of this study is to compare the flexural strength of ultra translucent zirconia as-machined and after sandblasting, glazing, or polishing.
Methods: The ultra-translucent zirconia used was Zpex Smile (5Y-TZP) and 4 groups were prepared: Control, Sandblasted, Glazed, and Polished. Bar-shaped specimens were cut from CAD/CAM blocks and sintered at 1450oC for 2 h, to the final dimension of 2×3×25 mm3. In the pre-sintered state, all bars received CAD/CAM-like grinding (320-grit). The Control group was kept as-machined; Sand-blasted group was treated with 50 µm alumina sand at 2 bar pressure; Zenostar glaze was applied to the as-machined surface of the Glazed group and fired at 910oC for 1 min; finally, polishing was performed with diamond discs, down to 0.5 µm finish for the Polished group. Four-point-bending was used to compare the flexural strength among groups.
Results: For the Control group, ZPEX Smile flexural strength was 352 ± 47 MPa. Polishing to a mirror finish surface, thus removing surface defects originated during milling, significantly improved the material’s fracture resistance (452 ± 49 MPa). On the other hand, when the surface was treated with sandblasting, increasing the defect population, the flexural strength decreased (227 ± 24 MPa). Finally, the presence of a glaze layer on the tensile surface decreased fracture resistance (265 ± 50 MPa), similarly to sandblasting.
Conclusions: Despite the poorer flexural strength of the new ultra-translucent zirconia (5Y-TZP) compared to the traditional dental zirconia (3Y-TZP), common clinical surface treatments affect these materials in a similar way: increasing the strength when the surface becomes smoother, while decreasing when surface defects are introduced.