Fatigue Failure of Narrow Implants with Different Implant-Abutment Connection Designs

To evaluate the reliability of narrow diameter dental implants (NDIs) with similar macrogeometry and 3 implant-abutment connection designs.

Eighty-four NDIs (3.5 × 10 mm) were selected and divided into 4 groups (n = 21/group) according to implant-abutment connection design, as follows: EH - external hexagon, IH - internal hexagon, IC - internal conical, and IC-M - internal conical connected to a monolithic titanium abutment. 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. Use of level probability Weibull curves, and reliability for a mission of 50,000 cycles at 75 N and 200 N were calculated.

The beta (β) values were: 1.48 for IC, 1.40 for IC-M, 8.54 for EH, and 1.98 for IH, indicating that damage accumulation was an acceleration factor for failure of all groups. At 75 N the probability of survival was not significantly different between groups. A decrease in reliability was observed for all groups at 200 N with no significant differences between IC (81.71%) and IC-M (94.28%), or between EH and IH (0%) which presented the lowest values. EH failures were primarily restricted to the screw, while IH involved screw and implant fracture. IC and IC-M were restricted to prosthetic failures (fracture and bending).

Narrow implants with external or internal hexagon connections presented the lowest reliability at high loads compared to internal conical connections. Failure modes differed among connections.