In Vivo Axial Forces on Implants: Theory vs. Experiment

Objectives: Theory is available to predict oral implant loading, but this theory has not yet been tested against data in vivo. This study assessed the level of agreement between theory and experiment for implant loading in humans. Methods: Two male patients each had 6 Branemark implants supporting a full-arch prosthesis. Case C had an implant-supported metal prosthesis in the maxilla with a natural opposing dentition. Case H had implant-supported prostheses in both jaws; data came only from the lower. The 6 implants in case C were located in tooth positions 1, 2, and 3 bilaterally, while the 6 implants in Case H were located in tooth positions 1, 3 and 5 bilaterally. Metal prostheses mated with 5.5 mm, strain-gauged abutments that sensed axial force and bending moment. Here only axial forces are discussed. Prostheses were connected to abutments using recommended gold screws and torque. Data were taken when each patient exerted 50 N on a bite fork located at each of six different locations on the prosthesis. Analyses of Cases C and H were made using the Skalak theory, assuming equal stiffness implants and an infinitely rigid prosthesis. Implant locations and prosthetic loading points were measured from study models of Cases C and H. Results: Good qualitative agreement existed between theory and data; theory and data from patients agreed about: (a) which implants were loaded in axial tension or compression; and (b) which implants were most heavily loaded. On the last point, theory and data tended toward higher loading on implants nearest the loading point on the prosthesis. There was only moderate quantitative agreement between theory and data; in some instances, theory disagreed from data by 25-100%. Conclusions: In two human patients, theory provided good qualitative agreement with in vivo data on axial implant loading.