title: Stiffness, strength, and failure modes of implant-supported monolithic lithium disilicate crowns: influence of titanium and zirconia abutments.
abstract: OBJECTIVE
  The objective of this study was to evaluate stiffness, strength, and failure modes of monolithic crowns produced using computer-aided design/computer-assisted manufacture, which are connected to diverse titanium and zirconia abutments on an implant system with tapered, internal connections.
  
  
  METHODS
  Twenty monolithic lithium disilicate (LS2) crowns were constructed and loaded on bone level-type implants in a universal testing machine under quasistatic conditions according to DIN ISO 14801. Comparative analysis included a 2 × 2 format: prefabricated titanium abutments using proprietary bonding bases (group A) vs nonproprietary bonding bases (group B), and customized zirconia abutments using proprietary Straumann CARES (group C) vs nonproprietary Astra Atlantis (group D) material. Stiffness and strength were assessed and calculated statistically with the Wilcoxon rank sum test. Cross-sections of each tested group were inspected microscopically.
  
  
  RESULTS
  Loaded LS2 crowns, implants, and abutment screws in all tested specimens (groups A, B, C, and D) did not show any visible fractures. For an analysis of titanium abutments (groups A and B), stiffness and strength showed equally high stability. In contrast, proprietary and nonproprietary customized zirconia abutments exhibited statistically significant differences with a mean strength of 366 N (Astra) and 541 N (CARES) (P < .05); as well as a mean stiffness of 884 N/mm (Astra) and 1,751 N/mm (CARES) (P < .05), respectively. Microscopic cross-sections revealed cracks in all zirconia abutments (groups C and D) below the implant shoulder.
  
  
  CONCLUSIONS
  Depending on the abutment design, prefabricated titanium abutment and proprietary customized zirconia implant-abutment connections in conjunction with monolithic LS2 crowns had the best results in this laboratory investigation.
authors.forename: Tim
authors.initials: T
authors.lastname: Joda
authors.forename: Alexander
authors.initials: A
authors.lastname: Bürki
authors.forename: Stefan
authors.initials: S
authors.lastname: Bethge
authors.forename: Urs
authors.initials: U
authors.lastname: Brägger
authors.forename: Philippe
authors.initials: P
authors.lastname: Zysset
mesh_terms: D001696:Biomechanical Phenomena; D017076:Computer-Aided Design; D003442:Crowns / Q000592:standards*; D000044:Dental Abutments / Q000592:standards*; D059605:Dental Implant-Abutment Design / Q000592:standards*; D015921:Dental Implants / Q000592:standards*; D003776:Dental Porcelain; D019232:Dental Restoration Failure / Q000706:statistics & numerical data; D003799:Dental Stress Analysis / Q000379:methods; D006801:Humans; D008422:Materials Testing; D014025:Titanium; D015040:Zirconium
chemical_list: D015921:Dental Implants; C493120:lithia disilicate; D003776:Dental Porcelain; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide