Mechanical and biomechanical guidelines for the use of Brånemark System--general principles

The understanding of biomechanical principles increases in importance as the number of potential indications for implant treatment increases. Recognising these principles as they relate to specific treatment indications helps to prevent conditions leading to overload. One consequence of recent findings shows that prosthetic loading conditions could significantly differ in the partially edentulous or single tooth cases as opposed to full arch bridges. It is reasonable to imagine that if you can make a full arch bridge on 4 to 6 fixtures, then two fixtures would be more than enough support for the traditional three-unit bridge. However, full arch restorations are based on multiple fixtures spread in an arch form which allows the masticatory forces to load the implants generally in an axial direction. Axial forces, whether compressive or tensile in nature, provide favourable loading throughout the entire cross-sectional area of the implants, and the forces are distributed through a maximum bone/implant interface. On the other hand, in partial restorations, the implants are placed more along a straight line. Any straight line arrangement increases the possibility for bending forces on the implants around an axis of rotation. Bending has much poorer stress distribution patterns on both the components and the supporting bone than axial load.