Geometrical implant design can also be a contributing factor for ceramic implants failures.
Considering the brittle nature of ceramics, all areas of excessive stress concentration should be
avoided. This includes, but is not limited to, the configuration of the thread design. Sharp, deep and
thin threads as well as sharp internal line angles represent areas of stress concentration that can
enhance the likelihood of crack propagation and implant failure [78] (Figure 4). A reduced implant
diameter of 3.25 mm, associated with a higher bending moment, has also been reported by Gahlert et al.
to be a contributing factor for implant fracture during functional loading [80]. During surgical
procedures, difficulties can be encountered when inserting the implants in dense hard-type bone. If
hand torqueing is needed for final insertion of the implant and the applied forces are not purely
rotational in nature, bending forces may be generated, resulting in implant failure [78]. LTD can
account for the failure of zirconia implants through a process similar to “subcritical” or “slow-crack”