Impact of abutment rotation and angulation on marginal fit: theoretical considerations.

Purpose: Rotational freedom of various implant positional index designs has been previously calculated. To investigate its clinical relevance, a three-dimensional simulation was performed to demonstrate the influence of rotational displacements of the abutment on the marginal fit of prosthetic superstructures. Materials and Methods: Idealized abutments with different angulations (0, 5, 10, 15, and 20 degrees) were virtually constructed (SolidWorks Office Premium 2007). Then, rotational displacement was simulated with various degrees of rotational freedom (0.7, 0.95, 1.5, 1.65, and 1.85 degrees). The resulting horizontal displacement of the abutment from the original position was quantified in microns, followed by a simulated pressure-less positioning of superstructures with defined internal gaps (5 Mum, 60 Mum, and 100 Mum). The resulting marginal gap between the abutment and the superstructure was measured vertically with the SolidWorks measurement tool. Results: Rotation resulted in a displacement of the abutment of up to 157 Mum at maximum rotation and angulation. Interference of a superstructure with a defined internal gap of 5 Mum placed on the abutment resulted in marginal gaps up to 2.33 mm at maximum rotation and angulation; with a 60-Mum internal gap, the marginal gaps reached a maximum of 802 Mum. Simulation using a superstructure with an internal gap of 100 Mum revealed a marginal gap of 162 Mum at abutment angulation of 20 degrees and rotation of 1.85?degrees. The marginal gaps increased with the degree of abutment angulation and the extent of rotational freedom. Conclusions: Rotational displacement of the abutment influenced prosthesis misfit. The marginal gaps between the abutment and the superstructure increased with the rotational freedom of the index and the angulation of the abutment.