Fracture strength and probability of survival of narrow and extra-narrow dental implants after fatigue testing: In vitro and in silico analysis

Purpose To assess the probability of survival (reliability) and failure modes of narrow implants with different diameters. Materials and methods For fatigue testing, 42 implants with the same macrogeometry and internal conical connection were divided, according to diameter, as follows: narrow (Ø3.3×10 mm) and extra-narrow (Ø2.9×10 mm) (21 per group). Identical abutments were torqued to the implants and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. The use-level probability Weibull curves, and reliability for a mission of 50,000 and 100,000 cycles at 50 N, 100, 150 and 180 N were calculated. For the finite element analysis (FEA), two virtual models, simulating the samples tested in fatigue, were constructed. Loading at 50 N and 100 N were applied 30° off-axis at the crown. The von-Mises stress was calculated for implant and abutment. Results The beta (β) values were: 0.67 for narrow and 1.32 for extra-narrow implants, indicating that failure rates did not increase with fatigue in the former, but more likely were associated with damage accumulation and wear-out failures in the latter. Both groups showed high reliability (up to 97.5%) at 50 and 100 N. A decreased reliability was observed for both groups at 150 and 180 N (ranging from 0 to 82.3%), but no significant difference was observed between groups. Failure predominantly involved abutment fracture for both groups. FEA at 50 N-load, Ø3.3 mm showed higher von-Mises stress for abutment (7.75%) and implant (2%) when compared to the Ø2.9 mm. Conclusions There was no significant difference between narrow and extra-narrow implants regarding probability of survival. The failure mode was similar for both groups, restricted to abutment fracture.