compressive residual stress in zirconia due to the porcelain veneer, the behavior under cyclic fatigue would be expected to be entirely different. Such in-situ cyclic tests could suggest important clues in explaining the catastrophic failures seen in dental restorations. Conclusions An experimental procedure of measuring the residual stress state in zirconia dental restorations undergoing insitu cyclic impact fatigue has been developed. Over a large area on the surface of the monolithic zirconia, roughly 10 - 25 % of the grains were observed to have highly localized residual stresses in the range of 0.5 GPa to 1.5 GPa. Multiple sets of measurements of grain averaged residual stress at various impact fatigue steps have been conducted. The impact fatigue steps ranged from pristine state, one year's service life and a four year service life. The effects of fatigue over such long durations on monolithic zirconia showed no significant changes in the global residual stress state. However the understanding of the events at the grain level are yet to be investigated. Similar investigations on the veneered bilayered zirconia were conducted and the results of the analysis will be published elsewhere. Acknowledgements Martin Kunz, Advanced Light Source, Berkeley, CA; and Paulo Coelho, New York University, NY provided valuable collaboration. Use of the Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Research support provided by the Oklahoma Health Research award (project number HR07-134), from the Oklahoma Center for the Advancement of Science and Technology (OCAST). We gratefully acknowledge the assistance of Dr. V. Thompson, Dr. E. D. Rekow and M. Cabrera at NYU Dental College. References 1. Fradeani, M. and M. Redemagni, An 11-year clinical evaluation of leucite-reinforced glass-ceramic crowns: A retrospective study. Quintessence International, 2002. 33(7): p. 503-510. 2. Coelho, P.G., et al., Laboratory Simulation of Y-TZP All-ceramic Crown Clinical Failures. Journal of Dental Research, 2009. 88(4): p. 382-386. 3. Zhang, Y., A. Pajares, and B.R. Lawn, Fatigue and damage tolerance of Y-TZP ceramics in layered biomechanical systems. Journal of Biomedical Materials Research Part B-Applied Biomaterials, 2004. 71B(1): p. 166-171. 4. Zhang, Y. and B.R. Lawn, Fatigue sensitivity of Y-TZP to microscale sharp-contact flaws. Journal of Biomedical Materials Research Part B-Applied Biomaterials, 2005. 72B(2): p. 388-392. 5. Tamura, N., et al., Scanning X-ray microdiffraction with submicrometer white beam for strain/stress and orientation mapping in thin films. Journal of Synchrotron Radiation, 2003. 10: p. 137-143. 6. N. Phelps, Local and Global Deformation from Synchrotron Imaging of Closed Cell Foams in Compression. Master's Thesis,(Advisor) Jay Hanan, Oklahoma State University, OK, 2007. 7. Bale, H.A., J.C. Hanan, and N. Tamura, 4-D XRD for Strain in Many Grains Using Triangulation. Powder Diffraction, 2006. 21: p. 184. 8. Bale, H.A., N. Tamura, and J.C. Hanan. Triangulation method for grain depth measurement using polychromatic micro-beam radiation. in Syncrotron Radiation for Material Science - 5. 2006. Chicago. 9. Bale, H.A., et al., Interface Residual Stresses in Dental Zirconia Using Laue Micro-Diffraction. The Eighth International Conference on Residual Stresses, 2008. 10. Coelho P. G., et al., Laboratory Simulation of Y-TZP All-Ceramic Crown Clinical Failures. Journal of Dental Research, 2008. 11. Lawn, B.R., Y. Deng, and V.P. Thompson. Use of contact testing in the characterization and design of allceramic crownlike layer structures: A review. 2001. 406
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