In Vitro Reliability and Stress Distribution of Wide Diameter Extra-Short Implants as Support for Single Crowns and Fixed Partial Dentures

Abstract

This study evaluated the reliability, failure mode, and stress distribution of wide-diameter extra-short dental implants (ESDI) as support for single crowns (SC) and fixed partial dentures (FPD) (3:1 crown-to-implant ratio [C:I]) for rehabilitation in the posterior atrophic mandible. For that, 126 ESDI (of 5 mm length) were allocated in four groups based on diameter (Ø4 and Ø6 mm) and prostheses (SC and FPD): SC4, SC6, FPD4, and FPD6. The fatigue test was performed by step-stress accelerated life testing (n = 21/group), failure mode by fractographic analysis, and stress distribution by finite element analysis: von Mises stress (σ_vM), maximum shear stress (τ_max), and minimum principal stress (σ_min). Reliability at 200 N was higher than 84% in both SC4 and SC6, with SC6 showing significantly higher reliability at 300 N. Failure mode involved the abutment (SC4 and SC6). The missions were suspended for the FPD groups due to 100% survival at the maximum load. The σ_vM showed a stress reduction of about 40% at the SC6 implant when compared to SC4 and FPD6 compared to FPD4. For the abutment, a minor decrease of at least 6.72% was observed comparing SC6 to SC4 and 2.78% for the FPD6 compared to FPD4. The τ_max and σ_min in the cortical bone demonstrated a stress reduction of at least 38.85% for the SC6 compared to SC4 and at least 3.78% in FPD6 compared to FPD4. The σ_min in the cancellous bone showed an overall reduction of at least 8.46% for SC6 compared to SC4 and for FPD6 compared to FPD4. But, for τ_max, in the cancellous bone, a 19.42% higher stress was found in SC6 compared to SC4 and 27.21% in FPD6 compared to FPD4. Finally, when splinting was used, a general stress reduction was found, about 50% in both diameters in the implant and abutment. According to the limitations of this in vitro study, it is possible to conclude that both groups (SC4 and SC6) showed high reliability in clinically relevant loads for the posterior atrophic mandible, SC6 having the lowest probability of failure at 300 N, with failure restricted to the abutment. Meanwhile, FPD6 has better stress distribution.