Implant Diameter: Effect on Stress in Bone: Finite Element Analysis

Dental implants that are 2.0mm in diameter, or smaller (mini-implant, small diameter implant), have been advocated as an acceptable alternative to conventional diameter implants (3.0 – 5.0mm diameter) for definitive oral restoration.  Studies indicate that, under normal intra-oral loads, the pattern of force transmitted to supporting crestal bone increases in inverse proportion to the implant diameter.  For conventional diameter implants, these stresses were not predicted to exceed physiologic limits.  However, none of the available studies investigates implant diameters less than 3.0mm.  Extrapolation of the data suggests that further reduction of implant diameter would induce greater crestal bone stress, possibly beyond physiologic limits.  Objectives: A finite element analysis study was designed to ascertain if reduction of implant diameter to 1.8m would, 1) increase cervical bone stress, and 2) result in non-physiologic stress in the investing bone.  Methods: A finite element model of a 1.8mm X 12mm titanium implant was produced via micro CT scanner (Scanco, Switzerland, FEA elements = 144,194.  FEA nodes = 162,784).

 

Implant properties	Bone properties	Boundary load
Young's Modulus: 106 (GPa)	Yield stress, cortical bone: ~100 MPa (Tensile)	100 N vertical
Poisson's Ratio: 0.30	Yield stress, trabecular bone: ~33MPa (Tensile)	30 N @45 degrees with vertical (z-axis)

Results: Crestal bone stresses increased as predicted, and Von Mises stresses (an average of 300 MPa) exceed the trabecular and cortical bone yield stress of 100MPa and 33MPa respectively.  Conclusions: The results indicate that, for implants of 1.8mm diameter, normal occlusal forces  can induce stresses that are destructive to investing bone.