Vertical fracture and marginal bone loss of internal-connection implants: a finite element analysis

Purpose: Marginal bone loss around implants is of great concern, and its cause may be multifactorial. Recently, clinical cases presenting marginal bone loss, in most cases accompanied by vertical fracture of internal connection implants in the bucco-lingual direction, have been reported, in which unfavorable stress distribution is one possible factor for marginal bone resorption. The purpose of the current study was to characterize this type of marginal bone loss and implant fracture by applying finite element analysis. Materials and Methods: From clinical and radiographic evaluation, the prostheses of all reported cases had implant-level setups and were directly screwed to the internal implants. Intriguingly, the vertical fractures reported were all in the bucco-lingual direction. Therefore, to characteristic the specific implant fracture, finite element analysis (FEA) was conducted with misfit models created for 2 different setups; abutment-level and implant-level, both with screw-retained prostheses. The 2 models were subjected to initial misfits of 0 µm (representing perfect fit), 50 µm, 100 µm, 150 µm or 200 µm, and vertical load was then applied to the models. Results: FEA revealed that for the implant-level setup, excessive stress at the neck of the implant gradually increased in the bucco-lingual direction as the misfit increased, which was not seen for the abutment-level setup. A broad maximum stress distribution was evident for the implant-level setup but not observed with the abutment-level setup. Conclusion: Broad distribution of excessive stress observed in the FEA correlated to the clinical cases, and marginal bone loss in these cases may be associated with the mechanical alterations. To avoid unnecessary complications, selection of an abutment-level setup is strongly suggested.

http://ift.tt/2spv5zk