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.