Abstract
Background: The influence of typical manufacturing regimes for producing fixed dental prostheses (FDPs) from yttria partly-stabilized zirconia polycrystals (3Y/4Y/5Y-TZP) on the phase composition is quantified. Methods: Fixed dental prostheses (FDPs) were designed using a CAD process and machined from different Y-TZP blanks from two manufacturers differing in yttria contents. Subsequent to sintering, the FDPs were glaze fired and air-blasted using alumina particles. Phase composition was determined with X-ray diffraction and quantified with Rietveld refinement. Results: The blanks from VITA Zahnfabrik (VITA YZ HT, VITA YZ ST, VITA YZ XT) and Dental Direct (DD Bio ZX2, DD cube ONE, DD cube X2) featured a rhombohedral portion with rather small crystallites and a small monoclinic portion for 3Y/4Y-TZPs, which increased after machining and disappeared after sintering. Glaze firing and air-blasting with alumina particles had no significant influence on the phase composition. Conclusion: The phase history of dental zirconia is revealed, which may have implications on further processing and aging of the FDP (e.g. low temperature degradation) in mouth.
Highlights
Yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics were introduced in dentistry in 1998 as a material that is processed by CAD/CAM techniques [1]
Because of its outstanding mechanical as well as favorable physical [4,5,6,7] and aesthetic properties it is widely used for the fabrication of fixed-dental prostheses (FDPs)
Zirconia is used in many dental applications such as fixed partial dentures (FPD), primary telescopic crowns, citations for Figure 1 in Section 1 dental implants, and suprastructures [8]
Summary
Yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics were introduced in dentistry in 1998 as a material that is processed by CAD/CAM techniques [1]. For the fabrication of esthetic restorations, a high translucency [9] of Y-TZP is necessary This is most commonly achieved by inducing the isotropic cubic phase through an increased content of stabilizing Yttria (Y2O3), where less light scattering at the grain boundaries occurs. While in the tetragonal and the cubic phases each zirconium ion is bonded to eight oxygen atoms, the zirconium atoms in the monoclinic and rhombohedral phases are only bonded to seven and six oxygen atoms [12,14] This leads to a distortion of the elementary cell, which may result, e.g., in micro cracks and a degradation of the mechanical properties [14,20].
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