|M.Sc Student||Shemtov-Yona Keren )Rima(|
|Subject||Effect of Dental Implants' Diameter on their Fatigue|
|Department||Department of Medicine||Supervisors||Professor Eli Machtei|
|Dr. Liran Levin|
|Professor Daniel Rittel|
|Full Thesis text|
The purpose of this study was to evaluate the mechanical function and load-fatigue performance of dental implants using different implant diameters and different implants’ environments.
Materials and methods: In the first part of the work, three groups of implants with different diameters (3.3 mm, 3.75 mm and 5 mm) joint with a standard abutment were tested under static and cyclic compressive loading. In the cyclic test, the machine ceased operating when the structure fractured or when it reached 5x106 cycles without apparent failure. A total of 112 implants were tested. The load versus the number of cycles was plotted (S-N curve) for each implant diameter.
In the second part of the work, thirty-two 3.75mm diameter implants were tested under cyclic compressive loading in artificial saliva substitute containing 250ppm of fluoride. A new S-N curve was than plotted. The S-N curve obtained was compared to the curve obtained previously for the same implants tested in a dry room-air environment.
A microscopic failure analysis, comprising a detailed scanning electron (SEM) fractographic analysis was carried out. The analysis characterized the fatigue related typical failure micromechanics.
Results: The S -N curve plotted for the 5 mm implants showed a classic fatigue behavior with a finite life region starting from 620N. The same was observed for the 3.75 mm diameter implants, with a finite life region starting below 620N. By contrast, the 3.3 mm diameter implants failed to show a predictable fatigue behavior and a fatigue limit could not be defined.
Four distinct fracture loci were identified whose relative occurrence was characterized for each implant diameter and load range. The implant’s metallographic sections revealed that the different fracture loci were located in the immediate vicinity of sharp stress concentrators (e.g. sharp notches and fillets) in sections of reduced implant wall thickness.
A comparison of the S-N curves obtained in artificial saliva and in room-air showed a significant reduction of fatigue life with respect to that reported for dry laboratory-air conditions. For the same load magnitude, the number of cycles to reach failure in artificial saliva is markedly reduced compared with that obtained in room-air.
Conclusions: This research demonstrated that narrow diameter implants had a profound effect on implants fatigue performance. Thus, proper implants’ design is crucial to ensure long-term fatigue performance for dental implants. The combination of sharp notches (thread) and narrow metal cross-section derived from the implant's diameter, affect the implants fatigue performance.