Commercial 3y-tzp and nanostructured zirconia for ceramic veneering: a sem study

Bull Group Int Rech Sci Stomatol Odontol. 51(2): 1-2 (2012)

SHORT COMMUNICATION

OC1- COMMERCIAL 3Y-TZP AND NANOSTRUCTURED ZIRCONIA FOR CERAMIC VENEERING: A SEM STUDY T.L Castello1, G. Merlati1, P. Menghini1 University of Pavia: Section of Odontostomatology, Dental Materials Unit, Pavia, Italia

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Key words Dental Materials, Y-TZP, Ceramic, Interfaces

for a sintering cycle of 5 min. In a FEI Helios NanoLabTM 600 (FEI CompanyTM, Eindhoven, Netherlands), a thin layer of platinum (1μm) was deposited on samples (a) surface crossing the interfaces after a tilting of the column (52°). Then, increasingly deeper trenches were milled by a focused ion beam, first using a relatively higher and later using a lower ion current (from 9 nA to 0.28 nA, 30KV). The sections were used to acquire high-resolution FEG-SEM (5KV) micrographs (1000–50,000X) using both the electron and the ion guns for imaging. In a scanning electron microscopy (SEM, FEI XL30 model, LaB6) the analysis of samples (b) was performed by 13KV secondary and backscattered electrons signals. Microstructural characterization was made using a high-resolution scanning electron microscope (TESCAN Mira 3 SEM) operated at 25 kV.

Introduction 3Y-TZP based dental devices are processed either by soft machining of pre-sintered blanks or by hard machining of fully sintered blocks; then a ceramic layer has to be applied in the dental lab by direct firing or by heat-pressing technique. Consequently, the sintering conditions have a strong impact on mechanical properties of the final product regarding both the materials involved [1,2,3,4]. Recently, a new sintering technique, known as high-pressure field-assisted sintering (HP-FAST), was proved to be successful in the preparation of fully dense nanocrystalline materials with minimal grain growth, thanks to its rapid sintering cycles (5 min) at high pressures (up to 1 GPa) [5,6,7]. Aim of this study was the application of this technique to the preparation of 3Y-TZP bulk samples and the comparative analysis with commercial products by SEM.

Results In (a) samples, the FIB/SEM analysis showed the presence of a lot of voids in the ceramic layers at the interface, but it was possible to observe (in the frameworks) the grain structures of the zirconia and the roughness of the two different zirconia cores and their interactions with the ceramic interface. In (b) samples the SEM micrographs showed the remarkable nanostructure and the absence of residual porosity of the experimental zirconia with uniform rounded shaped nanograins with sizes ranging between 20 and 30 nm.

Materials and Methods Dental fibroblasts were obtained from the Samples (a) of fully-sintered commercial zirconia (Will-Ceram ZTM “K” Blocks - Provident Dental Products, Somerset, NJ, USA) and pre-sintered commercial zirconia (IPS e.max ZirCAD, Ivoclar-Vivadent AG, Schaan, Liechtenstein) were veneered by the related ceramics (Avanté ZTM, Pentron Ceramics Inc., Somerset, NJ, USA and IPS e.max ZirPress, Ivoclar-Vivadent AG, Schaan, Liechtenstein). Samples (b) of 3Y-TZP nanopowders were prepared by a hydrothermal method and successively densified using a custom made HP-FAST apparatus, at 900°C, under a uniaxial pressure of 700 MPa,

Discussion In a partial agreement with our previous study, a lot of voids were reported in all the ceramic layers probably due to the dental laboratory production procedures, even if the operators e1

Bull Group Int Rech Sci Stomatol Odontol. 51(2): 1-2 (2012)

strictly followed the manufacturer instructions. It is also worth noting the presence of a strong interfacial roughness, resulting from the previous blasting process or to mechanical processing of the zirconia. The preparation of fully dense 3Y-TZP samples was achieved through application of HP-FAST technique starting from nanopowders (prepared by a simple hydrothermal method); and samples could be obtained at temperatures as low as 900°C and for sintering times of only 5 min at 700 MPa. At the comparative SEM/EDS analysis, a limited grain growth was observed, with final grain sizes around 25 nm and a remarkable fine microstructure.

nia- ceramic interfaces. Dent Mater (2010) 26(S1):(e59)126 4. Massimi F, Merlati G, Sebastiani M, Battaini P, Menghini P, Bemporad E. FIB/SEM and SEM/EDS microstructural analysis of metal-ceramic and zirconia-ceramic interfaces. Bull Group Int Rech Sci Stomatol Odontol. 2011;50:1-10 5. Tredici IG, Maglia F, Dapiaggi M, Spinolo G, Anselmi-Tamburini U. Synthesis of bulk tetragonal zirconia without stabilizer: The role of precursor nanopowders. J Eur Ceram Soc 32 (2012) 343–352

References

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1. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater 24 (2008) 299–307 2. Merlati G, Salvi R, Sebastiani M, Massimi F, Battaini P, Menghini P, Bemporad E. Fracture toughness of different zirconia cores and veneered or heat-pressed ceramic layers. Dent Mater (2011) 27(S1):(e67)155

7. Tredici IG, Lucco Castello T, Merlati G, Menghini P, Anselmi-Tamburini U, Maglia F. Synthesis of nanostructured fully dense 3Y-TZP for dental applications by a new HP-Fast system. Poster presentation at the XIX Congresso Nazionale del Collegio dei Docenti di Odontoiatria, Torino 12-14 Aprile 2012

3. Salvi R, Merlati G, Battaini P, Sebastiani M, Massimi F, Menghini P, Bemporad E. FIB/SEM analysis of metal- and zirco-

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