Augmentation of the atrophic maxillary sinus floor: graft stiffness, implant shape and length

This study investigates the characteristics of load transmission to bone of alternative treatments for posterior maxilla edentulism with relatively limited available bone volume. Implant shape (conical and cylindrical), augmentation technique and the effect of bone-graft stiffness were taken into consideration. The finite element models of the atrophic sinus implanted with short implant were compared to two grafted-sinus models implanted with longer implants, engaged bicortically. Bone-graft stiffness was varied to describe different stages of graft-maturation (from short-term to long-term). Stress and load distributions due to axial and bending loads were compared on the bony structures. In the short-term, axial force is supported almost equally by the cortical layers and the trabecular core, while a bending load is mainly supported by the crestal cortical layer and secondarily by the cortical floor, the bone-graft supported a negligible load. Bicortical engagement produces higher load transfer to the cortical floor under axial load. In the long-term, as the stiffness of the bone-graft increases, the load is transferred progressively towards the grafted region, progressively unloading other structures, particularly the internal cortical layer.