Kaarela A Proos1, Michael V Swain, Jim Ironside, Grant P Steven. 1. School of Aerospace, Mechanical and Mechatronic Engineering and Faculty of Dentistry, University of Sydney, Biomaterials Science Research Unit, National Innovation Centre, Eveleigh, New South Wales, Australia. kpro2901@mail.usyd.edu.au
Abstract
PURPOSE: This study examined the stresses developed during loading in a first premolar metal-ceramic crown made of different metal cores, and used them to anticipate the locations and form of the most likely failure modes. The maximum principal stresses in the porcelain are indicators of fracture, and the von Mises stresses in the metal core are indicators of the location of yielding. MATERIALS AND METHODS: Two-dimensional axisymmetric models with different core metals were analyzed using finite element analyses. An axial load of 600 N was applied vertically downward, over a circular area around the crown's fissure. RESULTS: The peak maximum principal tensile stress in the porcelain existed on the surface of the crown, partially outside the cusp, with the greatest peak in the gold-porcelain system (15.8 MPa). An inverse relationship between the peak maximum principal tensile stress of each system and the elastic modulus of each core material was found. According to evaluation of the critical flaw size for each system, even a crack completely through the thickness of the porcelain was not critical. The maximum von Mises stress existed in the metal coping, on the radial edge at the axial/occlusal line angle, with the highest maximum in the nickel-chromium system (143.9 MPa). There existed a proportional relationship between the maximum von Mises stress in each metal and their respective elastic moduli. All maximums were well below the yield strength of the metal alloys used. CONCLUSION: A greater understanding of the influence of an axial load on the resulting stresses has been achieved, showing that the phenomena of fracture and yielding are unlikely for the crown experiencing this axial load.
PURPOSE: This study examined the stresses developed during loading in a first premolar metal-ceramic crown made of different metal cores, and used them to anticipate the locations and form of the most likely failure modes. The maximum principal stresses in the porcelain are indicators of fracture, and the von Mises stresses in the metal core are indicators of the location of yielding. MATERIALS AND METHODS: Two-dimensional axisymmetric models with different core metals were analyzed using finite element analyses. An axial load of 600 N was applied vertically downward, over a circular area around the crown's fissure. RESULTS: The peak maximum principal tensile stress in the porcelain existed on the surface of the crown, partially outside the cusp, with the greatest peak in the gold-porcelain system (15.8 MPa). An inverse relationship between the peak maximum principal tensile stress of each system and the elastic modulus of each core material was found. According to evaluation of the critical flaw size for each system, even a crack completely through the thickness of the porcelain was not critical. The maximum von Mises stress existed in the metal coping, on the radial edge at the axial/occlusal line angle, with the highest maximum in the nickel-chromium system (143.9 MPa). There existed a proportional relationship between the maximum von Mises stress in each metal and their respective elastic moduli. All maximums were well below the yield strength of the metal alloys used. CONCLUSION: A greater understanding of the influence of an axial load on the resulting stresses has been achieved, showing that the phenomena of fracture and yielding are unlikely for the crown experiencing this axial load.