Fatigue Failure of External Hexagon Connections on Cemented Implant-Supported Crowns João Malta Barbosa, DDS, MSc,* Daniel Navarro da Rocha, DDS, MS, PhD,† Ronaldo Hirata, DDS, MS, PhD,‡ Gileade Freitas, DDS, MS, PhD,§ Estevam A. Bonfante, DDS, MS, PhD,¶ and Paulo G. Coelho, DDS, BS, MS, MSMtE, PhDk A ccording to the presently avail- able scientific evidence, single tooth replacement supported by an osseointegrated implant is a treat- ment modality that presents a 10-year estimated survival rate of 89.4%. 1 Sev- eral clinical studies corroborate the successful use of single-unit implant- supported restorations. 2–6 However, biological complications such as peri- implantitis have shown to affect the long-term success of the implant, 7 whereas mechanical complications have been reported as the most fre- quent reason for failures. 8 Among these, loosening and/or fracture of the abutment or prosthetic screws are the most common, 9–12 with a cumulative incidence of 12.7% after 5 years in both internal and external connec- tions. 13 The external hexagon implant- abutment connection has the longest history of service because it was the first to be used. It was originally developed to allow the engagement of the implant during its surgical placement and was later used to provide an antirotational mechanism in single-unit restorations. However, the implant-abutment assembly is mainly held together by a connecting screw, which bears most of bending moments and hinders micromovements that may result in screw joint opening and loosening. 14,15 The clinical impact has been reported in a comprehensive com- parison between internal and external connections, which showed a significantly higher rate of mechanical complications, including abutment screw loosening or fracture, in the latter. 16 *Resident, Department of Prosthodontics, New York University, New York, NY; Volunteer Researcher, Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY. †PhD Candidate, Department of Materials Science, Military Institute of Engineering, Rio de Janeiro, RJ, Brazil. ‡Assistant Professor, Department of Biomaterials and Biomimetics, New York University, New York, NY, USA. §PhD Candidate, Department of Oral and Maxillofacial Surgery, University of São Paulo–Ribeirão Preto Dental School, Ribeirão Preto, SP, Brazil. ¶Assistant Professor, Department of Prosthodontics and Peri- odontology, University of São Paulo–Bauru School of Dentistry, Bauru, SP, Brazil. kProfessor, Department of Biomaterials and Biomimetics, New York University/Hansjörg Wyss Department of Plastic Surgery, NYU, Langone Medical Center/Mechanical and Aerospace Engineering, NYU, Tandon School of Engineering, New York, NY. Reprint requests and correspondence to: João Malta Barbosa, DDS, MSc, New York University College of Dentistry, Department of Biomaterials and Biomimetics, 433 1st Avenue, room 844, New York, NY 10010, Phone: 212-998-9368, Fax: 212-995-4244, E-mail: jmbarbosa@ nyu.edu ISSN 1056-6163/18/02701-001 Implant Dentistry Volume 27  Number 1 Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000725 Purpose: To evaluate the proba- bility 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 im- plants (;4 mm diameter) were used for single cement-retained crown replacement and divided into 3 groups: (3i) Full OSSEOTITE, Bio- met 3i (n ¼ 18); (OL) OEX P4, Os- seolife 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 prob- ability Weibull curves and probabil- ity 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 frac- ture was the failure mode consis- tently observed in all groups. Conclusion: Because the reli- ability was significantly different between the 3 groups, our postulated null hypothesis was rejected. (Implant Dent 2018;27:1–6) Key Words: dental implants, frac- tography, step-stress–accelerated life testing MALTA BARBOSA ET AL IMPLANT DENTISTRY /VOLUME 27, NUMBER 1 2018 1 Copyright Ó 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.