Abstract
We investigated a cause of a fractured abutment screw made of a Ti alloy, a physical and environmental factor. We observed the fracture surface of the abutment screw with a scanning electron microscope (SEM) and conducted stress analysis by three dimensional finite element method, and corrosion reaction experiment in a pseudo-oral environment. A pitting corrosion and fatigue destruction were discovered in the fracture surface of the abutment screw and accretion such as S was detected by the surface. A stress concentration was found in the same place as the broken part of abutment screw when stress was vertically loaded to marginal ridge region of implant superstructure in a three-dimensional finite element. In a corrosion test, stress was loaded to Ti alloy (Ti-6Al-4V) boards and dipped in Na2SO4 solution and isotonic sodium chloride solution at 37 degrees Celsius, and likewise dipped non-stressed Ti alloy boards in Na2SO4 solution. The dipping periods were 1week, 2weeks, 3weeks and 4weeks. Then, SEM images were examined and the element assay was conducted using an energy dispersive x-ray spectroscopy (EDS), but indication of corrosion such as pits was not found in any test pieces. Fatigue destruction stemmed from a pitting corrosion is believed to be the cause of the abutment screw fracture, but cause of pit initiation could not be identified.
