Different bone loading patterns due to fixation of three-unit and five-unit implant prostheses.

Background: It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs).

Methods: Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress.

Results: The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load.

Conclusions: Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development.