Fatigue behavior and estimated lifetime of implant/abutments of different diameters.

Objectives: Narrow-diameter (ND) implants may show distinct long-term mechanical behavior compared to standard-diameter (SD) implants when subjected to fatigue. This study evaluated the longevity of implant systems with different diameters by assessing structural damage and loosening after fatigue challenge.

Methods: This in vitro study used sixty internal conical connection implants/abutments that were divided into two groups (n = 30) based on their diameters (3.0mm-ND and 4.0mm-SD). The manufacturer recommended torque was achieved for each abutment using a digital torque wrench. In order to determine damage and permanent displacement of abutments, cone beam computed tomography (CBCT) scans were post-processed (software e-Vol DX). The boundary fatigue method was adapted to use 2 × 10⁶ cycles, with frequency of 2 Hz, and constant peak load of 80 N for the first experiment. Load was adjusted (17.8 %) according to the failure rate for the second and third experiments. In addition to the aforementioned CBCT scans, removal torque values were used to assess torque loss. The probability of failure over time and the Weibull modulus were calculated for each group.

Results: Loosening was observed in all ND specimens, regardless of the level of loading, and structural bending was observed in 6 abutments. In addition, 4 fractures occurred. No structural damage was observed for the SD specimens, and 6 of them did not suffer from loosening. The Weibull analysis showed a lower modulus (m) for SD (m=3.90; 95 %CI=2.75-5.54) than for ND (m=1.99; 95 %CI=1.50-2.64) resulting in lower probability of failure over time and slower decrease in removal torque for SD compared with ND specimens.

Significance: The shorter predicted lifetime and faster torque loss of narrow-diameter implant/abutment suggest for a more frequent clinical follow-up of this treatment option.