Three-dimensional finite element analysis of internal conical joint implant-supported fixed prostheses in the posterior maxilla

Background

There are various implant placement options, such as using a short implant or changing the direction of the implant placement to use more residual bone. Currently, the connection design between implant fixture and the abutment is in two forms- external hex type and internal conical type. The biomechanical information on the various implant systems and various implant placement option is not sufficient to determine reliable treatment plans and implant choices.

Aim/Hypothesis

This study aimed to compare the functional stresses generated in the internal conical joint implant, prosthesis and supporting bone in the posterior maxilla, using finite element method.

Material and Methods

Two internal joint type implant (Ø5 X 7 mm, Ø5 X 13 mm) with TS2 SA fixture design of Osstem (Seoul, Korea) were modeled by computer-aided design software (Solidwork 2018). The posterior maxillary bone and 3-unit all zirconia crowns were also simulated. Three different scenarios were modeled with various implant alignment (SI3+ 3 unit fixed prosthesis on 3 short implant abutments, SI2+ 3 unit fixed prosthesis on 2 short (7 mm) implant abutments, AI2+ 3 unit fixed prosthesis on 1 short implant abutment and 1 long (13 mm) implant with an angled abutment). A load of 30 N was applied vertically and obliquely, respectively to each of 12 occlusal contact points of the crown.

Results

The maximum Mises stresses produced by oblique loading was observed near the connection interfaces of the abutment. The peak value was 430 MPa for SI3, 568 MPa for SI2 and 656 MPa for AI2 respectively. There was no significant difference in peak von Mises stress between models due to vertical loading. The maximum compressive stresses due to oblique load on the supporting bone adjacent to the implant were 145 MPa for SI3, 204 MPa for SI2 and 200 MPa for AI2, respectively.

Conclusion and Clinical Implications

Internal joint type design of implant concentrated the stresses to the conical interface between fixture and abutment interface, demonstrating the wedge effect between them. Increasing the number of implants was the most effective contributing factor to reduce the stresses in the internal conical joint implant and supporting bone in our study models.