In the article “Effect of anchorage systems and extension base contact on load transfer with mandibular implant-retained overdentures” Drs. Sadowsky and Caputo (J Prosthet Dent 2000;84:327-334) used photoelastic models to compare the amount of stress to substructure designs utilizing a cantilevered bar, spark erosion framework, non cantilevered bar, and solitary anchors. Records were taken with and without a silicon spacer (representing soft tissue support for the cantilever)

The greatest stress was exhibited in the distal implant of the case with the cantilever bar, then the spark erosion case, bar without a cantilever, and finally the solitary anchor. The stress was greatly reduced with positive tissue contact in all cases. All anchorage systems, with or without intimate ridge contact to the extension, exhibited low stress to the contra-lateral side.

This reinforces the need for constant relines to reduce pressure on the distal abutment implant in overdenture cases. The results also bring into question whether cross arch stabilization in implant cases functions the same way it does in the dentate case.

Stresses produced at loaded side of spark erosion prosthesis under 30 lb in central fossa of first molar. A, WIthout spacer (No tissue support), B, with spacer (Soft tissue support)