Three-dimensional finite-element analysis of functional stresses in different bone locations produced by implants placed in the maxillary posterior region of the sinus floor

Statement of problem. Implants placed in the posterior maxilla have lower success rates compared to implants placed in other oral regions. Inadequate bone levels have been suggested as a reason for this differential success rate. Purpose. The purpose of this study was to determine the amount and localization of functional stresses in implants and adjacent bone locations when the implants were placed in the posterior maxilla in proximity to the sinus using finite element analysis (FEA). Material and methods. A 3-dimensional finite element model of a maxillary posterior section of bone (Type 3) was used in this study. Different bony dimensions were generated to perform nonlinear calculations. A singlepiece 4.1 x 10-mm screw-shaped dental implant system (ITI solid implant) was modeled and inserted into atrophic maxillary models with crestal bone heights of 4, 5, 7, 10, or 13 rum. In some models the implant penetrated the sinus floor. Cobalt-Chromium (Wiron 99) was used as the crown framework material placed onto the implant, and porcelain was used for occlusal surface of the crown. A total average occlusal force (vertical load) of 300 N was applied at the palatal Cusp (150 N) and mesial fossa (150 N) of the crown. The implant and superstructure were simulated in finite element software (Pro/Engineer 2000i program). Results. For the porcelain Superstructure for bone levels, maximum von Mises stress values were observed on the mesial fossae and palatal cusp. For the bone structure, the maximum von Mises stress values were observed in the palatal cortical bone adjacent to the implant neck. There was no stress within the spongy bone. High stresses occurred within the implants for all bone levels. Conclusion. The maximum von Mises stresses in the implants were localized in the neck of implants for 4- and 5-mm bone levels, but for 7-, 10-, and 13-mm bone levels more even stresses occurred within the implants.