Yttria-partially stabilized zirconia: using the transformed layer as a permeable membrane for the infiltration of materials

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Three-mol% Yttria-tetragonal zirconia polycrystal (3Y-TZP) is a unique ceramic for dental application, due to the transformability of the crystallographic structures (from tetragonal to monoclinic – t-m), which is responsible for the transformation-toughening mechanism. However, conditions such as body temperature, cyclic loading and humidity cause the tetragonal-to-monoclinic (t-m) phase transformation to happen at a faster pace, changing the 3Y-TZP's characteristics in the original processed state. This 3Y-TZP transformed zone runs from the surface down to the bulk of the material. Furthermore, 3Y-TZP is considered biologically inert, which restricts its application as a dental implant due to the lack of osseointegration. 3Y-TZP is also chemically inert, resulting in lack of chemical interaction with active monomers for bonding to the tooth structure and to other ceramic materials. To improve the bonding between 3Y-TZP and other substrates, most of the studies done so far attempted to increase surface roughness through surface alumina blasting. However, this procedure compromises the mechanical performance of 3Y-TZP and bond strength results are inconclusive. 3Y-TZP aging results in the combination of surface m spots and grain pull-out, and a microcracked layer underneath as a consequence of the dislodgement of the martensitic plates. Our preliminary data indicate that the 3Y-TZP t-m transformed layer is porous and may be used for the infiltration of thin films. Therefore, the long-term objective of my research program is to develop a ceramic-based material that presents reliable biomechanical performance for dental application. In the short-term, my goal is to develop a hybrid interface between 3Y-TZP t-m transformed layer and silicon/titanium oxides using RT-ALD. Therefore, the 3 main objectives of this research program are: 1: to define the ideal thickness of the 3Y-TZP t-m transformed layer as a function of porosity and mechanical properties; 2: to develop a method to produce a hybrid interface between 3Y-TZP transformed layer and silica-based nanofilm to enable better bonding between 3Y-TZP and other materials; 3: To develop a method to produce a hybrid interface between 3Y-TZP transformed layer and titania-based nanofilm to enable better osseointegration. The characterization of the 3Y-TZP transformed layer is of interest to a large scientific community, in the continuous search for more stable and more receptive zirconia-based substrates. It will also impact the training of high-qualified personnel, by proposing a multidisciplinary approach in a well-equipped environment.