Explain the biomechanics of cantilevers
The biomechanics of cantilevers need to be understood. It has been found that when a three unit prosthesis is supported by two implants and has a distal cantilevered pontic, the bending moments are twice those found in a prosthesis with two terminal implants. When the occlusal forces are applied on the cantilever the implant functions as a fulcrum and is subjected to axial, rotational and torsional forces. It is vital to understand the nature and effects of bending moments. Bending overload is a situation in which the occlusal forces on an implant supported prosthesis exerts a bending moment on the implant cross section at the crestal bone, leading to marginal bone loss and/or eventual implant fatigue. Overload is a well documented factor for bone resorption around implants. The factors associated with bending moments are:
- In line implant placement.
- Leverage- cantilever.
- Parafunction and heavy occlusal force.
These factors should be considered while planning. Placing implants in a triangular configuration, avoiding or reducing cantilevers, reducing the mesiodistal and buccolingual width of the final restoration and centering the occlusal contacts should be the objectives involved in the treatment.