The Failure Envelope Concept Applied To The Bone-Dental Implant System

Abstract

Dental implants interact with the jawbone through their common interface. While the implant is an inert structure, the jawbone is a living one that reacts to mechanical stimuli. Setting aside mechanical failure considerations of the implant, the bone is the main component to be addressed. With most failure criteria being expressed in terms of stress or strain values, their fulfillment can mean structural flow or fracture. However, in addition to those effects, the bony structure is likely to react biologically to the applied loads by dissolution or remodeling, so that additional (strain-based) criteria must be taken into account. While the literature abounds in studies of particular loading configurations, e.g. angle and value of the applied load to the implant, a general study of the admissible implant loads is still missing. This paper introduces the concept of failure envelopes for the dental implant-jawbone system, thereby defining admissible combinations of vertical and lateral loads for various failure criteria of the jawbone. Those envelopes are compared in terms of conservatism, thereby providing a systematic comparison of the various failure criteria and their determination of the admissible loads.

Figure 1

Graphs of lateral vs. vertical load causing cortical bone yielding. (A,B) Isotropic and anisotropic cortical bone respectively, for Tresca stress yield criterion. (C,D) Isotropic and anisotropic cortical bone respectively, for maximum compression stress yield criterion. (E,F) Isotropic and anisotropic cortical bone respectively, for maximum compression strain yield criterion. The coefficient of friction is marked as COF.

Figure 2

Lateral crestal bone displacement vs. COF for the different loading cases. (A,B) Isotropic and anisotropic cortical bone respectively, for Tresca stress yield criterion. (C,D) Isotropic and anisotropic cortical bone respectively, for maximum compression stress yield criterion. (E,F) Isotropic and anisotropic cortical bone respectively, for maximum compression strain yield criterion.

Figure 3

Graphs of lateral load vs. vertical load, causing cortical bone octahedral strain of magnitude 1000 µε (solid curves) and 3000 µε (dashed curves), for 3 levels of COF and isotropic bone model.

Figure 4

The implant system: (A) Implant (B) Abutment (C) Connecting screw (D) Exploded view of the implant system used in the model.

Figure 5

(A) Full model of the scanned mandible. (B) Cut section of the mandible between the left first and third molars. (C) Sectioning the cut bone into cortical and cancellous bone. (D) The mandible bone section after implant insertion.

Figure 6

Mandible containing samples (9 × 2) of interest for mechanical properties, the blue rectangle indicates the bone section used in the model. Reprinted with permission from ref. .

Figure 7

Meshed model of the bone-implant system, showing the refined peri-implant mesh, boundary conditions and loading region in the model.

Figure 8

The critical region (marked in red) where the yield criteria were fulfilled. The arrows indicate the loading directions.