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Failure of two commercially pure titanium dental implants was analysed. The
implants fractured at the abutments after only three years use. One abutment failed at the
junction of the threaded and unthreaded areas, the other failed within the threaded area. Both
failures were by reversed bending fatigue, whereby fatigue cracks began from relatively
coarse machining marks on the abutments. The final fracture areas were less than 10 % of the
total fracture surfaces, indicating that the abutments had not been abnormally loaded.
However, bone resorption would have increased the abutment bending stresses by causing an
increased moment arm of the acting forces and misalignment of the abutments in the maxilla.
The effect of misalignment was investigated by finite element modelling, which showed that
even a slight misalignment could double the bending stresses. This unanticipated large effect,
combined with the coarse machining marks, explains the premature failure of the implants.
Keywords: dental implant; fatigue; finite element simulation; metallography; titanium. |
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