Implant-abutment connection designs for anterior crowns: Reliability and failure modes

OBJECTIVES: To investigate the effect of implant-abutment connection types on reliability and failure modes of anterior single-unit crowns. METHODS: Fifty-four implants were divided in 3 groups (n = 18 each): external hexagon (EH), internal hexagon (IH), and Morse taper (MT) connection. Abutments were screwed to the implants, and maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing. RESULTS: The beta values derived from use-level probability Weibull calculations for groups IH (2.52), EH (1.67), and MT (0.88) indicated that fatigue influenced the failure only of IH and EH groups. The reliability for a mission of 100,000 cycles at 175 N was 0.99 (0.98-1.00), 0.84 (0.62-0.94) and 0.97 (0.87-0.99) for the EH, IH, and MT, respectively. The characteristic strength was not significantly different between EH (290 N) and IH (251 N) but significantly higher for MT (357 N). For IH and EH groups, failure involved screw fracture, and the MT implants primary failure mode was abutment fracture. CONCLUSIONS: Reliability was higher for the EH and MT relative to IH groups, whereas the characteristic strength was significantly higher for implants with MT connection.