title: Fracture resistance of crowns cemented on titanium and zirconia implant abutments: a comparison of monolithic versus manually veneered all-ceramic systems.
abstract: OBJECTIVE
  To evaluate the fracture resistance of all-ceramic crowns cemented on titanium and zirconia implant abutments.
  
  
  METHODS
  Customized implant abutments for maxillary right central incisors made of titanium (Ti) and zirconia (Zr) (n=60, n=30 per group) were fabricated for an internal connection implant system. All-ceramic crowns were fabricated for their corresponding implant abutments using the following systems (n=10 per group): (1) monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate (MLD); (2) pressed lithium disilicate (PLD); (3) yttrium stabilized tetragonal zirconia polycrystal (YTZP). The frameworks of both PLD and YTZP systems were manually veneered with a fluorapatite-based ceramic. The crowns were adhesively cemented to their implant abutments and loaded to fracture in a universal testing machine (0.5 mm/minute). Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test (α=0.05).
  
  
  RESULTS
  Both the abutment material (P=.0001) and the ceramic crown system (P=.028) significantly affected the results. Interaction terms were not significant (P=.598). Ti-MLD (558.5±35 N) showed the highest mean fracture resistance among all abutment-crown combinations (340.3±62-495.9±53 N) (P<.05). Both MLD and veneered ceramic systems in combination with Ti abutments (558.5±35-495.9±53 N) presented significantly higher values than with Zr abutments (392.9±55-340.3±62 N) (P<.05). MLD crown system showed significantly higher mean fracture resistance compared to manually veneered ones on both Ti and Zr abutments (P<.05). While Ti-MLD and Ti-PLD abutment-crown combinations failed only in the crowns without abutment fractures, Zr-YTZP combination failed exclusively in the abutment without crown fracture. Zr-MLD and Zr-PLD failed predominantly in both the abutment and the crown. Ti-YTZP showed only implant neck distortion.
  
  
  CONCLUSIONS
  The highest fracture resistance was obtained with titanium abutments restored with MLD crowns, but the failure type was more favorable with Ti-YTZP combination.
authors.affiliation: Department of Buccofacial Prosthesis, Faculty of Odontology, University Complutense of Madrid, Madrid, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Martínez-Rus
authors.forename: Alberto
authors.initials: A
authors.lastname: Ferreiroa
authors.forename: Mutlu
authors.initials: M
authors.lastname: Özcan
authors.forename: José F
authors.initials: JF
authors.lastname: Bartolomé
authors.forename: Guillermo
authors.initials: G
authors.lastname: Pradíes
mesh_terms: D000704:Analysis of Variance; D002516:Ceramics; D017076:Computer-Aided Design; D003442:Crowns; D059605:Dental Implant-Abutment Design / Q000379:methods / Q000592:standards; D003776:Dental Porcelain / Q000737:chemistry; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D007180:Incisor; D008437:Maxilla; D014025:Titanium / Q000737:chemistry; D015019:Yttrium; D015040:Zirconium
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide