Short Dental Implants: Finite Element Analysis of Stress Characteristics in Posterior Maxilla

Abstract

Objectives: Reduced bone height, elevated masticatory force and increased crown height-implant length ratio are all associated with dental implants of short length placed in the posterior mandible or maxilla. Consequently, dental practitioners generally aim to increase the bone to implant surface area contact by choosing wider diameters for short implants. With implant designs being driven at times by market demands rather than basic scientific research, the influence of different designs on the stress characteristics in the surrounding bone becomes an important issue. This research uses the Finite Element Method to evaluate the stress characteristics within the posterior maxilla for four distinctly different short implant designs (Bicon, Neodent, Nobel Biocare and Straumann) subject to unfavourable crown height-implant length ratio and masticatory forces. Material and Methods: The four bone-implant systems are modelled using three-dimensional hexahedral and wedge shaped brick elements. Assumptions made in the analyses are: temperature sensitive elements are used to replicate the torque within the abutment screw; crown height-implant length ratio is 2:1; 50% osseointegration between bone and implant; and, linear elastic material properties of bone. Results and Conclusion: Bicon's thread design causes larger stress variances from minimum to maximum when compared to all other systems. The combination of a decreased diameter and increased taperage of the Neodent design increases the stress level when compared to the Bicon implant. Nobel Biocare's rounded implant thread crest design and reduced thread pitch produces a preferred smoothed out stress profile. Straumann's increased thread pitch gives elevated stress in cancellous bone. Generally, stresses are concentrated in the crestal bone region next to the implant neck, attributable to the combination of crown height-implant length ratio and the inclined nature of the masticatory force.