Influence of Thread Geometry and Bone Density on Stress Distribution in Dental Implants: A Finite Element Study

Dental implant success relies on optimal stress distribution at the implant-bone interface, which may be influenced by thread design and bone density. While V-shaped and buttress threads have been extensively studied, square and trapezoidal designs remain underexplored, particularly in varying bone densities. This study aimed to compare the stress distribution patterns of square and trapezoidal thread designs using three-dimensional (3D) finite element analysis (FEA).

Eight 3D finite element models were constructed by combining two thread designs (square and trapezoidal) with four bone densities. A mandibular first molar implant (12 mm length and 4.5 mm diameter) was modeled in SolidWorks (Dassault Systèmes SolidWorks Corp., Waltham, MA), and mesh convergence was validated. The material properties were assigned assuming linear elasticity and isotropy. A 100 Newtons (N) axial load was applied to the crown, and von Mises stresses were analyzed in the implant, cortical bone, and cancellous bone in megapascals (MPa) using Ansys software (Ansys, Inc., Canonsburg, PA).

Trapezoidal threads generated higher implant stresses (7.16-18.83 MPa) than square threads (5.21-15.08 MPa), particularly in low-density bone. Square threads transferred more stress to the cortical bone (3.69-9.60 MPa vs. trapezoidal: 2.73-7.98 MPa) across all densities. In the cancellous bone, the trapezoidal threads induced higher stresses in the dense bone but converged with the square threads in the low-density bone. Stress concentrations were localized at the thread crests in dense bone but were dispersed diffusely in low-density bone.

The thread design significantly affected stress distribution, with square threads reducing implant stress but increasing cortical bone load, whereas trapezoidal threads minimized cortical stress at the cost of higher implant stress. Square threads may be preferable for dense bones, whereas trapezoidal designs may enhance stability in low-density bones. Preoperative bone density assessment is critical for optimizing thread selection and ensuring long-term implant success.