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Conclusions: The silane heat treatment media decreased the bond strength between ceramic and resin cement when the etching with 10% HF was not done. Hypothesis was rejected. doi:10.1016/j.dental.2010.08.123 116 Influence of veneer thickness on residual stresses in zirconia prostheses A.K. Mainjot 1 , G.S. Schajer 2 , A.J. Vanheusden 1 , M.J. Sadoun 3 1 University Hospital of Liège, Belgium 2 University of British Columbia, Canada 3 University Paris Descartes, France Objectives: Mismatch in physical, especially thermal properties between veneering ceramics and high-strength ceramic cores can induce residual stresses and lead to crack initiation when combined with functional stresses. Stresses distribution within the veneering ceramic in function of depth, is a key factor influencing failure by chipping, which is a well-known problem with Y-TZP (Yttria Tetragonal Zirconia Polycrystal) based fixed partial dentures. The objective of this study was to investigate thickness dependence of the stress profile in veneering ceramic layered on zirconia frameworks. Materials and methods: The hole-drilling method, often used for engineering measurements, was adapted for use with veneering ceramic. The stress profile was measured in 10 bilayered disc samples of 20 mm diameter, with a 1 mm thick Y-TZP framework. Different veneering ceramic (Vita VM9) thicknesses were performed: 1 mm, 1.5 mm, 2 mm and 2.5 mm. Results: All samples exhibited the same type of stress vs. depth profile, starting with compressive at the ceramic surface, decreasing with depth, getting close to the tensile area. The magnitude of the stress and its decreasing rate vs. depth profile were found to increase with veneering ceramic thickness. Calculated residual stresses were lower than 20 MPa. Conclusions: Veneering ceramic thickness increases magnitude of residual stresses and then influences mechanical behaviour of zirconia-based bilayered systems. doi:10.1016/j.dental.2010.08.124 dental materials 26S (2010) e1–e84 e55 117 Identifying subsurface fatigue cracks in resin bonded ceramics subjected to cyclic compression L.H. Mair 1 , P. Padipatvuthikul 2 1 University of Central Lancashire, Preston, UK 2 Srinakharinwirot University, Bangkok, Thailand Objectives: To identify fatigue cracks in ceramics using silver nitrate staining. Materials and methods: 45 Disks of ceramic 1 (˚ 5mm× 4 mm) were fabricated by sintering and randomly divided into 3 groups. They were etched with 9.5% HF for 15 min and sandblasted with 50 �m alumina; then bonded onto enamel using three bonding systems 2,3,4 following the manufacturer’s instructions. The bonded specimens were subjected to a Staircase Fatigue Limit test using 5000 cycles with a load/unload increment of 4 kg. The “survivors” were sectioned using a diamond disk saw, ground flat with wet SiC papers (240, 400, 600, 1200 Grit) and polished with 1 �m Al2O3. They were immersed in AgNO3 (3 mole/l) for 48 h. The specimens were examined by incident light microscopy using crossed polars to filter directly reflected light and reveal the colour of silver. The specimens were subsequently sputter coated with gold and examined by SEM. Results: In a number of “survivors” there was a network of cracks extending from the point of load application into the subsurface. These cracks were not visible on the SEM because they were obscured by filler particles. This corresponded with the “failures” where the crack started in the specimen rather than at the bonding interface. Conclusions: Silver nitrate staining is a useful technique to indentify forming fatigue cracks in ceramics. The cracks started under the point of load application rather than at the interface with the bonding resin. doi:10.1016/j.dental.2010.08.125 1 Vitadur Alpha; VITA Zahnfabrik, Germany. 2 Prime and bond + Calibra, Dentsply, USA. 3 Clearfil SE Bond + Panavia, Kuraray, Japan. 4 Optibond Solo Plus + Nexus, Kerr, USA.
e56 dental materials 26S (2010) e1–e84 118 Withdrawn doi:10.1016/j.dental.2010.08.126 119 Adhesion mechanisms at the interface between Y-TZP and veneering ceramics C. Monaco 1 , P. Cardelli 1 , A. Tucci 2 , L. Esposito 2 , R. Scotti 1 1 University of Bologna, Italy 2 Centro Ceramico Bologna, Italy Objectives: Zirconium oxide based ceramics, in particular Y-TZP, present positive characteristics as high flexural strength and fracture toughness (Studart et al. Dental Materials 2006;23:106). Since poor information is available about the interfaces of Y-TZP and veneering ceramics, the aim of this study was to analyse this interface regarding phase composition and microstructure. Materials and methods: Sixteen specimens of Y-TZP 1 were sintered following manufacturer’s instructions and divided into 4 groups (n = 4). The specimens of group A were veneered with a pressable ceramic 2 without a ceramic liner; group B were liner coated 3 and fired before the final veneering; group C were sandblasted with 30 �m SiO2 4 and then veneered without application of liner; group D were both sandblasted and liner layered before veneering. The microstructure of the surface and the interfaces between the two ceramics were analyzed by a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analyzer (EDS). Results: The SEM analysis of the samples showed that sandblasting zirconia surfaces, before applying the veneering ceramic, drastically changed their surface microstructure. For samples of groups C and D, several fine silica particles, from CoJet abrasive, were smeared on the zirconia surface. Different punctual microanalysis, conducted in the contact area of zirconia-veneering ceramic of group D, presented a reaction area at the interface of the different materials. The EDS spectrum corresponding to the interface area presented a large amount of zirconia and characteristic elements of the veneering layer. It is to underline as the sandblasting, after the sintering step, as in groups C and D, not only caused a widespread silica particles smearing the surface, but it was also responsible for a partial zirconia phase transformation from tetragonal to monoclinic Conclusions: Sandblast the zirconia before veneering, could be able to give a higher reactivity to the zirconia surfaces with the veneering ceramic, increasing, in this way, the bonding and the mechanical performance of the component. doi:10.1016/j.dental.2010.08.127 1 e.max ZirCAD, Ivoclar Vivadent. 2 ZirPress, ivoclar Vivadent. 3 ZirLiner, Ivoclar Vivadent. 4 CoJet, 3M ESPE. 120 Fit and fracture behaviour of metal laser sintered posterior bridges W.-D. Mueller, U.W. Stecher, R.I. Hmaidouch “Charité” Universitaetsmedizin Berlin, CC3 Dental School, Berlin, Germany Objectives: The purpose of this study was to evaluate the marginal fit and fracture strength of four-unit fixed partial dentures (FDPS) constructed using direct laser sintering. Materials and methods: A steel model with two abutments, a first premolar and a second molar was scanned and a framework designed. 25 Frameworks were produced by metal laser sintering using CoCrMo-alloy. Cross sections of 5 samples were produced to illustrate the microstructure. 10 frameworks were cemented using zinc phosphate cement, embedded, and then sectioned buccolingually and mesiodistally. Widths of the marginal and internal gap were measured using a light microscope at magnification 40×, 82 measurements for each framework. 5 samples were positioned on the steel model as delivered after machining without cementation and then loaded in a universal testing machine; the fracture strength was determined; 5 samples were cemented on the metal model using zinc phosphate cement, sorted in distilled water at 37 ◦ C for 24 h before testing to failure (CHS = 1 mm/min). The maximum force was registered. Results: Cementation significantly (P < 0.05) affected the fracture resistance (1677.48 N before and 2210.44 N after). Mean values of marginal fit (87.87 ± 17.27) and internal fit (126.84 ± 15.37). Conclusions: The fit of tested frameworks was clinically acceptable, the fracture strength increased considerably after cementation, based on the accepted minimum initial strength of 1000 N for posterior FDPS. The results of this study show that the laser sintering core material tested can be used for the construction of the four-unit posterior FDPS. doi:10.1016/j.dental.2010.08.128 121 Different protocol for silane application on ceramic: A FTIR analyses J.R.C. Queiroz, H.C. Garcia, L.F.C. Oliveira, C.E. Silva, M.P.C. Neto Universidade Federal de Juiz de Fora, Brazil Objectives: To characterize by attenuated total reflection infrared Fourier transform analysis (ATR-FTIR) the ceramic surface after silane application with different dry protocols. Materials and methods: Sixteen ceramic bars (2 mm × 4mm× 10 mm) of VM7 (VITA-Zahnfabrik, Germany) were prepared and finished to 1 �m alumina paste. Before silane application, the specimens were cleaned in a distilled water sonic bath for 10 min. Four groups (n =4) were treated with different silane dry protocols. The silane 3M ESPE SIL (3M/ESPE) was applied to all specimens using a microbrush and left to dry at 20 ◦ C for 2 min (G20). After first drying, the specimens were submitted to heating at
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