Biomechanical Analysis of Craniofacial Implants: Effects of Loading Conditions

Objectives: Some clinical studies showed that the survival rates of craniofacial osseointegrated implants (COIs) were lower than those of dental implants. This may be caused by biomechanical reasons, as the length of the implants for facial prosthesis are smaller than almost of all dental implants. The purpose of this study was to investigate the adequate conditions for COIs from the biomechanical point of view. Methods: A three-dimensional finite element model of two COIs (diameter=3.75mm, height=4.0mm) with abutments (diameter & height=4.0mm) inserted in the bone portion was created. The abutments were connected to each other by the superstructure, and an extension beam (length=5mm) was added to one of the two COIs on the opposite side of another COI. The static load (10N) was applied on the top surface of the superstructure or the extension beam in the direction of 0°, 30°, 60° or 90° to the long axis of COIs. Results: The maximum von Mieses stress in the bone portion was smallest when the vertical load was applied at the midpoint between the two COIs. In case that load was applied at the end of the extended beam, obvious increase of von Mieses stress was observed by the lateral inclination of the load. Conclusions: These results showed that the load should be applied between the connected COIs. And it was suggested the direction of the load by facial prosthesis should be considered, if free-end extension of the superstructure was needed.