title: Implant-abutment connection designs for anterior crowns: reliability and failure modes.
abstract: OBJECTIVE
  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.
authors.affiliation: *PhD Candidate, Department of Biomaterials and Biomimetics, College of Dentistry, New York University, New York, NY. †Assistant Professor, Department of Prosthodontics, University of Sao Paulo - Bauru College of Dentistry, Bauru, SP, Brazil. ‡Postdoctoral Researcher, Department of Biomaterials and Biomimetics, College of Dentistry, New York University, New York, NY; Assistant Professor, Department of Biomaterials Science, Osaka University Graduate School of Dentistry, Osaka, Japan. §Assistant Professor, Department of Biomaterials and Biomimetics, College of Dentistry, New York University, New York, NY; Director for Research, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, NY.
authors.forename: Lucas S
authors.initials: LS
authors.lastname: Machado
authors.forename: Estevam A
authors.initials: EA
authors.lastname: Bonfante
authors.forename: Rodolfo B
authors.initials: RB
authors.lastname: Anchieta
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
mesh_terms: D003442:Crowns / Q000009:adverse effects; D059605:Dental Implant-Abutment Design / Q000009:adverse effects / Q000379:methods; D019250:Dental Implants, Single-Tooth / Q000009:adverse effects; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D007180:Incisor; D008437:Maxilla