A finite element study of short dental implants in the posterior maxilla.

PURPOSE: Elevated bite forces and reduced bone densities and dimensions associated with posterior regions of the maxilla cause relatively high failure rates when short dental implants are placed to substitute missing teeth. This study uses the finite element method to evaluate four distinctly different short implant designs (Bicon, Neodent, Nobel Biocare, and Straumann) for their influences on the von Mises stress characteristics within the posterior maxilla. MATERIALS AND METHODS: Finite element models of the supporting bone and tooth crowns are developed based on computed tomography data, and implant geometries are obtained from manufacturers' catalogs. The finite element models are meshed using three-dimensional hexahedral and wedge-shaped brick elements. Assumptions made in the analyses are: linear elastic material properties for bone, 50% osseointegration between bone and implant, and crown height-implant length ratio of 2:1. RESULTS: Bicon's neck indentation produced reduced stress in the cortical bone when compared with the Nobel Biocare and Straumann systems. The increased taper of the Neodent design decreased the stress level in cancellous bone. Nobel Biocare's rounded thread crest and reduced thread pitch produced a smoother stress profile. Straumann's increased thread pitch produced elevated stress in the cancellous bone. Generally, stresses were concentrated in the crestal bone region around the implant neck, attributable to the inclined nature of the masticatory force. CONCLUSION: Nobel Biocare and Bicon systems are recommended for use in type 4 cancellous and cortical bone, respectively.