title: Fracture Resistance of Straight and Angulated Zirconia Implant Abutments Supporting Anterior Three-Unit Lithium Disilicate Fixed Dental Prostheses.
abstract: OBJECTIVE
  The purpose of this study was to evaluate fracture resistance of straight and angulated zirconia implant abutments supporting anterior three-unit lithium disilicate fixed dental prostheses (FDPs).
  
  
  METHODS
  Four different test groups (n = 8) representing anterior three-unit implant-supported all-ceramic FDPs were fabricated to fit an in vitro model with two implants. Groups 1 and 2 simulated a clinical situation with an ideal implant position for maxillary left central and right lateral incisors from a prosthetic point of view, which allowed for the use of a straight, prefabricated zirconia and titanium abutment. Groups 3 and 4 simulated a situation with a compromised implant position that required an angulated (15-degree) abutment. Tapered internal-connection implants (Direct's Legacy, 13-mm length, 3.7-mm diameter, Implant Direct) mounted in epoxy resin models were used in this study. Lithium disilicate (IPS e.max press, Ivoclar Vivadent) three-unit FDPs were fabricated and cemented using self-adhesive resin cement. The samples were subjected to thermocycling (2 × 3,000 × 5°C/55°C) and mechanical loading (TCML; 50 N × 600,000 cycles). Fracture resistances were determined for all the samples that survived aging. Kruskal-Wallis analysis of variance and Mann-Whitney U tests were performed to test for differences in fracture strength values at a 5% significance level.
  
  
  RESULTS
  All samples subjected to TCML survived without mechanical failure. The highest fracture loads were associated with FDPs supported by implants with 0-degree abutment angulations compared with those FDPs supported by 15-degree abutment angulations (group 1: 538.7 ± 24.77 N; group 2: 542.17 ± 21.64 N; group 3: 523.57 ± 19.71 N; group 4: 528.37 ± 24.57 N). This difference in load-bearing capacity was not statistically significant (P > .05).
  
  
  CONCLUSIONS
  The use of angulated zirconia abutments for compensation of nonideal implant locations is possible without reducing the load-bearing capacity of implant-supported anterior three-unit lithium disilicate FDPs.
authors.forename: Samah
authors.initials: S
authors.lastname: Saker
authors.forename: Sameh
authors.initials: S
authors.lastname: El-Shahat
authors.forename: Mohamed
authors.initials: M
authors.lastname: Ghazy
mesh_terms: D002516:Ceramics; D000044:Dental Abutments; D015921:Dental Implants; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported / Q000379:methods*; D019232:Dental Restoration Failure / Q000706:statistics & numerical data; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D016474:Weight-Bearing; D015040:Zirconium
chemical_list: D015921:Dental Implants; C493120:lithia disilicate; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide