Can an increase in abutment screw length enable biomechanical advantages for implants with increased crown height space?

Purpose: The purpose of this finite element analysis (FEA) study was to investigate how screw length and crown height affect the stresses generated in the implant-abutment complex and alveolar bone for anterior single implants and whether the use of longer abutment screw would compensate for increased stresses originated from increased crown height space (CHS).

Materials and methods: A maxillary anterior segment was modeled, and one implant (Straumann bone level implants, 4.1 mm × 12 mm) was placed at the central incisor site. Three different crown heights (11, 13, and 15 mm) with two different abutment screw lengths (regular [R] 7.9 and long [L] 9.9 mm) were modeled, and coded as M 11-R, M 13-R, M 15-R, M 11-L, M 13-L, and M 15-L depending on the height and length, respectively. Horizontal (25.5 N) and 30-degree oblique forces (178 N) were applied to the crown. The stress magnitude and distribution were evaluated.

Results: M 15-L showed the highest von Mises stress value (869.72 MPa) at the abutment under oblique loads. For both screw lengths, von Mises stress values in the abutment, abutment screw, and inside and outside of the implant walls around the implant platform increased with increased crown height. With the increase in length of the abutment screw, the von Mises stresses decreased in the inside and outside walls of the implant, while the stresses in the abutment increased.

Conclusions: Abutment screw length and crown height affected the amount of stress generated on implant components. Increasing the screw length may reduce the stresses on the implant and bone without increasing the stresses in the screw, potentially mitigating the risk of implant platform fractures and bone resorption, both of which are critical failures. Screw related issues may decrease as the area stresses effect has a tendency to reduce when longer screw is used in increased CHS situation (tall crowns).