Finite Element Analysis of an Osseointegrated Stepped Screw Dental Implant
An osseointegrated stepped screw dental implant was evaluated using 2-dimensional finite element analysis (FEA). The implant was modeled in a cross section of the posterior human mandible digitized from a computed tomography (CT) generated patient data set. A 15-mm regular platform (RP) Branemark implant with equivalent length and neck diameter was used as a control. The study was performed under a number of clinically relevant parameters: loading at the top of the transmucosal abutment in vertical, horizontal, and 45° oblique 3 orientations. Elastic moduli of the mandible varied from a normal cortical bone level (13.4 GPa) to a trabecular bone level (1.37 GPa). The study indicated that an oblique load and elastic moduli of the cortical bone are important parameters to the implant design optimization. Compared with the cylindrical screw implant, the maximum von Mises stress of the stepped screw implant model was 17.9% lower in the trabecular bone-implant area. The study also showed that the stepped screw implant is suitable for the cortical bone modulus from 10 to 13.4 GPa, which is not necessarily as strict as the Branemark implant, for which a minimum 13.4 GPa cortical bone modulus is recommended.Abstract
The 2 implant-bone systems: the cylindrical screw osseointegrated dental implant (left) and the stepped screw osseointegrated dental implant (right)
The finite element analysis (FEA) load and boundary conditions
The maximum von Mises stress in the cortical bone adjacent to the implant neck under 3 different loads (condition A, vertical load, 100 N; condition B, horizontal load, 100 N; and condition C, oblique load, 141 N at 45° inclination)
Corresponding L1 to B10 locations between the stepped screw and cylindrical screw implant along the trabecular bone-implant interface. L indicates lingual; A, apex; B, buccal
The maximum von Mises stress along the path L1 to B10 in the trabecular bone adjacent to the implant under a vertical load of 100 N, a horizontal load of 100 N, and an oblique load of 141 N at 45° inclination
The location of the maximum stress adjacent to the bone implant interface: cylindrical screw implant (a) and the stepped screw implant (b). MSC(Sup) and MSC(Inf) indicates the maximum von Mises stress in the cortical bone adjacent to the implant neck at the superior (Sup) and inferior (Inf) notches, respectively; MST, the maximum von Mises stress in the trabecular bone adjacent to the implant, which is at the section L1 (left) or the interpoint between L1 and L2 (right)
(a, b). Stress distribution in the cylindrical screw implant and in the stepped screw implant under an oblique load of 141 N in condition 1 (cortical bone E = 13.4 GPa, Poisson ratio = 0.30)
The von Mises stress of (a) MSC(sup), (b) MSC(inf), and (c) MST under an oblique load of 141 N at 45° and different cortical bone properties (conditions 1–5)
(a, b) Stress distribution in cylindrical screw implant and in stepped screw implant under oblique load of 141 N in condition 3 (cortical bone E = 7.5 GPa, Poisson ratio = 0.30)
(a, b) Stress distribution in cylindrical screw implant and in stepped screw implant under oblique load of 141 N in condition 5 (cortical bone E = 1.37 GPa, Poisson ratio = 0.30; similar with trabecular bone)
Contributor Notes
J. P. Geng, BDS, DrPH, MScD, is with the Department of Dentistry, China Medical University Huayu Hospital, Shaoxing, 312030, ZJ, P. R. China
W. Xu, BEng, PhD is with the Centre for Biomedical Engineering, School of Engineering, University of Surrey GU2 7XH, United Kingdom. Address correspondence to Dr Xu.
K. B. C. Tan, BDS, PhD,andG. R. Liu, PhD are with the National University of Singapore.