Fatigue lifetime prediction of a reduced-diameter dental implant system: Numerical and experimental study

Abstract

Objective: To validate the fatigue lifetime of a reduced-diameter dental implant system predicted by three-dimensional finite element analysis (FEA) by testing physical implant specimens using an accelerated lifetime testing (ALT) strategy with the apparatus specified by ISO 14801.

Methods: A commercially-available reduced-diameter titanium dental implant system (Straumann Standard Plus NN) was digitized using a micro-CT scanner. Axial slices were processed using an interactive medical image processing software (Mimics) to create 3D models. FEA analysis was performed in ABAQUS, and fatigue lifetime was predicted using fe-safe^® software. The same implant specimens (n=15) were tested at a frequency of 2Hz on load frames using apparatus specified by ISO 14801 and ALT. Multiple step-stress load profiles with various aggressiveness were used to improve testing efficiency. Fatigue lifetime statistics of physical specimens were estimated in a reliability analysis software (ALTA PRO). Fractured specimens were examined using SEM with fractographic technique to determine the failure mode.

Results: FEA predicted lifetime was within the 95% confidence interval of lifetime estimated by experimental results, which suggested that FEA prediction was accurate for this implant system. The highest probability of failure was located at the root of the implant body screw thread adjacent to the simulated bone level, which also agreed with the failure origin in physical specimens.

Significance: Fatigue lifetime predictions based on finite element modeling could yield similar results in lieu of physical testing, allowing the use of virtual testing in the early stages of future research projects on implant fatigue.

Keywords: Accelerated lifetime testing; Brown-Miller criteria; Cyclic fatigue; Dental implants; Finite element modeling; Fractography; Plastic strain; Simulated bone; Titanium.

Fig. 1.

(a) Projection image of dental implant by micro-CT (before reconstruction); (b) Transverse view of CT scanning (after reconstruction).

Fig. 2.

FE model of dental implant system. (a) Separate parts and final assembly; (b) Whole model with contour of FE elements.

Fig. 3.

(a) The test apparatus of dental implant; (b) The experimental test on hydraulic machine.

Fig. 4.

Load profiles for fatigue test.

Fig. 5.

Stress distributions and lifetime contour plot of FE analysis for a load of 100 N. (a) von Mises stress; (b) maximum principal stress; (c) maximum principal strain; (d) log lifetime.

Fig. 6.

Life-stress contour for the physical specimens.

Fig. 7.

Optical photos of fractured specimen (a) and fracture surface (b-d).

Fig. 8.

SEM images of fractured surface. (a) Gross view of the fracture surface; (b) area of fracture origin; (c) fatigue striations; (d) ductile dimples.