Speaker: Dr. Keren Shemtov-Yona, Faculty of Mechanical Engineering, Technion, Haifa, Israel
Dental implants are a widely accepted solution for edentulous people to whom masticatory functions must be restored. To date, most of the emphasis has been put on clinical issues related to the implant and the implantation process, while the mechanical reliability of those bio-structures has been most often overlooked or taken for granted.
Time has come for a rigorous engineering evaluation of this issue so that not only the implant design, but also its performance can be known and specified.
The first issue is to identify beyond any doubt the operation of a fatigue failure mechanism in those structures, by means of carefully controlled tests, to be compared to failure analyses of retrieved broken implants.
Next, it will be shown that the scanning electron examination of biologically failed explanted metallic implants reveals a wealth of information on their structural health state. It will be shown that an unusually high fraction of those implants contain significant levels of structural damage at various stages of evolution.
Since fatigue performance is the main mechanical issue, we will introduce the random spectrum fatigue testing approach, in which randomly selected loads are applied at random frequencies to somewhat mimic mastication, thus providing readily an evaluation of the functional performance of the group of implants under investigation.
As an example, we will report a systematic evaluation of the fatigue functional performance of dental implants made of partially stabilized zirconia (Y-TZP), using random spectrum fatigue testing in both air and 0.9% saline solution.
This study reveals that saline solution reduces the static fracture strength of the zirconia implants. It also causes a marked degradation of their spectrum fatigue longevity, but does not affect their spectrum fatigue fracture strength.
The mechanical results will be presented along with a detailed electron fractographic analysis, thereby providing some guidelines for performing future failure analyses of in-vivo fractures of ceramic implants.
It is expected that the approach presented here will motivate further re-assessment of dental implant design, manufacturing and ultimately usage.