Comparing loosening between cement retained and screw retained implant supported crowns: a dynamic non-linear finite element analysis

Titanium root form implants are widely accepted because of the advantages of their mechanical properties. This study compared the screw loosening between two types of implant supported crowns (cement retained and screw retained) at the location of left lower first molar, using finite element method in a nonlinear analysis. The Dentis system was used for modeling of the implant, abutment and suprastructure. The amount of preload displacement was almost the same for both types of abutments. Applying force in any direction reduced the amount of downward preload displacement and decreased abutment implant stability. In the cement retained crown, the amount of inner abutment displacement was always less than the screw head displacement by applying vertical, oblique and vertical horizontal loads, so the stability of the abutment-implant complex was maintained. In the screw retained crowns under vertical-horizontal load the amount of displacement at the screw head and inner side of abutment was close to each other and this put the screw on the verge of loosening. However, under oblique pressure of 100 N, the inner abutment displacement exceeded the screw head displacement and the screw was loosened. Under vertical loading of 100 and 150 N, the stability of implant abutment was maintained. Screw loosening is less likely to occur under vertical load compared with oblique load. The cemented retained crowns have a higher biomechanical stability than screw retained crowns.