Implant-abutment interface: biomechanical study of flat top versus conical.

BACKGROUND: Overloading has been identified as a primary factor behind dental implant failure. The peak bone stresses normally appear in the marginal bone. The anchorage strength is maximized if the implant is given a design that minimizes the peak bone stress caused by a standardized load. Clinical studies have shown that it is possible to obtain a marginal bone level close to the crest of the implant. Different implant systems make use of different designs of the implant-abutment interface. Different implant-abutment interfaces imply that the functional load is distributed in different ways upon the implant. According to Saint-Venant's principle, this will result in different stress patterns in the marginal bone when this reaches levels close to the implant crest.
PURPOSE: One aim of the study was to theoretically investigate if a conical implant-abutment interface gives rise to a changed stress pattern in the marginal bone, as compared to a flat top interface, for an axially loaded mandibular titanium implant, the neck of which is provided with retention elements giving effective interlocking with the bone. Further aims were to investigate if the way in which the axial load is distributed on the flat top and on the inner conus respectively affects the stress pattern in the marginal bone. The pertinent stress was considered to be the bone-implant interfacial shear stress. It was assumed that the marginal bone reached the level of the implant-abutment interface.
METHOD: The investigation was performed by means of axisymmetric finite element analysis.
RESULTS: The conical implant-abutment interface of the type studied brought about a decrease in the peak bone-implant interfacial shear stress as compared to the flat top interface of the type studied. This peak interfacial shear stress was located at the top marginal bone for the flat top implant-abutment interface whereas it was located more apically in the bone for the conical implant-abutment interface. The way in which the axial load was distributed on the flat top and on the inner conus respectively affected the peak interfacial shear stress level.
CONCLUSION: The design of the implant-abutment interface has a profound effect upon the stress state in the marginal bone when this reaches the level of this interface. The implant with the conical interface can theoretically resist a larger axial load than the implant with the flat top interface.