טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShemtov-Yona Keren )Rima(
SubjectMechanical Durability of Dental Implants
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Daniel Rittel
Full Thesis textFull thesis text - English Version


Abstract

With the growing use of dental implants, so grows the incidence of implants’ failures. Late treatment complications, after reaching full osseointegration and functionality, include mechanical failures, such as fracture of the implant and its components. Those complications are deemed severe in dentistry, albeit usually considered as rare, and therefore seldom addressed in the clinical literature.

The introduction of dental implants into clinical practice has fostered a wealth of research on their biological aspects. By contrast, mechanical strength and reliability issues were seldom investigated in the open literature, so that most of the information to date remains essentially with the manufacturers.

Over the years, dental implants have gone through major changes regarding the material, the design, and the surface characteristics aimed at improving osseointegration. Did those changes improve the implants’ mechanical performance?

This research presents results on various aspects of the mechanical integrity and failure of dental implants.

We first identify beyond any doubt metal fatigue as the main failure mechanism by means of careful and systematic failure analysis of both laboratory tested and clinically retrieved broken dental implants.

Next, we show that the grit-blasting surface roughening treatment, besides its beneficial aspects, can also have deleterious effects in the sense that the small ceramic particles can embed in the implant’s surface and generate microcracks that will later grow by fatigue to full maturity. This point is further strengthened by further systematic surface scanning of 100 retrieved dental implants, none of which fractured, with the observation that 60% of the implants contain cracks and flaws having reached different levels of maturity. Such flaws are the precursors to future catastrophic fracture.

A novel in-vitro approach to fatigue functional performance of dental implants is then presented, that relies on random spectrum loading, as an alternative to conventional fatigue testing of limited applicability in design. This approach, that is readily implemented in aeronautical and earthquake engineering,  is further developed and implemented to test the influence of various intraoral media on the performance of dental implants. The premise here is that we seek to identify the longevity of the loaded implant until its fracture, instead of the determination of a fatigue limit, often assimilated to an “infinite life” duration.

The main outcomes of this work are then discussed from a general perspective.