Fatigue Failure of External Hexagon Connections on Cemented Implant-Supported Crowns

Purpose: To evaluate the probability of survival and failure modes of different external hexagon connection systems restored with anterior cement-retained single-unit crowns. The postulated null hypothesis was that there would be no differences under accelerated life testing. Materials and Methods: Fifty-four external hexagon dental implants (;4 mm diameter) were used for single cement-retained crown replacement and divided into 3 groups: (3i) Full OSSEOTITE, Biomet 3i (n ¼ 18); (OL) OEX P4, Osseolife Implants (n ¼ 18); and (IL) Unihex, Intra-Lock International (n ¼ 18). Abutments were torqued to the implants, and maxillary central incisor crowns were cemented and subjected to step-stress–accelerated life testing in water. Use-level probability Weibull curves and probability of survival for a mission of 100,000 cycles at 200 N (95% 2-sided confidence intervals) were calculated. Stereo and scanning electron microscopes were used for failure inspection. Results: The beta values for 3i, OL, and IL (1.60, 1.69, and 1.23, respectively) indicated that fatigue accelerated the failure of the 3 groups. Reliability for the 3i and OL (41% and 68%, respectively) was not different between each other, but both were significantly lower than IL group (98%). Abutment screw fracture was the failure mode consistently observed in all groups. Conclusion: Because the reliability was significantly different between the 3 groups, our postulated null hypothesis was rejected.