Fractographic analysis of a dental zirconia framework: A case study on design issues

Fractographic analysis of clinically failed dental ceramics can provide insights as to the failure origin and related mechanisms. One anterior 6-unit all-ceramic zirconia fixed partial denture (FPD) (Cercon®) has been clinically recovered and examined using qualitative fractography. The purpose was to identify the fracture origin and to state the reasons for failure. The recovered parts of the zirconia FPD were microscopically examined to identify classic fractographic patterns such as arrest lines, hackle, twist hackle and wake hackle. The direction of crack propagation was mapped and interpreted back to the origin of failure at the interface of the occlusal–palatal tip of the core and the veneering ceramic. An inappropriate core drop design favoring localized stress concentration combined with a pore cluster in the veneering ceramic at the core tip interface were the reasons for this premature through-the-core thickness failure.

Research highlights
► Failure occurred due to an inappropriate framework connector design.
► Framework adjustment by the lab technician was the major failure reason.
► Fracture started from the incisal tip of the zirconia framework.
► Pore clusters were found at the incisal tip of the framework.
► A large pore in the veneering ceramic did not influence the fracture event.