title: Three- to nine-year survival estimates and fracture mechanisms of zirconia- and alumina-based restorations using standardized criteria to distinguish the severity of ceramic fractures.
abstract: OBJECTIVE
  The aims of this study were set as follows: 1. To provide verifiable criteria to categorize the ceramic fractures into non-critical (i.e., amenable to polishing) or critical (i.e., in need of replacement) 2. To establish the corresponding survival rates for alumina and zirconia restorations 3. To establish the mechanism of fracture using fractography
  
  
  METHODS
  Fifty-eight patients restored with 115 alumina-/zirconia-based crowns and 26 zirconia-based fixed dental prostheses (FDPs) were included. Ceramic fractures were classified into four types and further subclassified into "critical" or "non-critical." Kaplan-Meier survival estimates were calculated for "critical fractures only" and "all fractures." Intra-oral replicas were taken for fractographic analyses.
  
  
  RESULTS
  Kaplan-Meier survival estimates for "critical fractures only" and "all fractures" were respectively: Alumina single crowns: 90.9 and 68.3 % after 9.5 years (mean 5.71 ± 2.6 years). Zirconia single crowns: 89.4 and 80.9 % after 6.3 years (mean 3.88 ± 1.2 years). Zirconia FDPs: 68.6 % (critical fractures) and 24.6 % (all fractures) after 7.2 and 4.6 years respectively (FDP mean observation time 3.02 ± 1.4 years). No core/framework fractures were detected.
  
  
  CONCLUSIONS
  Survival estimates varied significantly depending on whether "all" fractures were considered as failures or only those deemed as "critical". For all restorations, fractographic analyses of failed veneering ceramics systematically demonstrated heavy occlusal wear at the failure origin. Therefore, the relief of local contact pressures on unsupported ceramic is recommended. Occlusal contacts on mesial or distal ridges should systematically be eliminated.
  
  
  CONCLUSIONS
  A classification standard for ceramic fractures into four categories with subtypes "critical" and "non-critical" provides a differentiated view of the survival of ceramic restorations.
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, School of Dental Medicine, University of Geneva, Rue Barthélemy-Menn 19, 1205, Geneva, Switzerland. Osvaldo.Moraguez@unige.ch.
authors.forename: Osvaldo D
authors.initials: OD
authors.lastname: Moráguez
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, School of Dental Medicine, University of Geneva, Rue Barthélemy-Menn 19, 1205, Geneva, Switzerland. Anselm.Wiskott@unige.com.
authors.forename: H W Anselm
authors.initials: HW
authors.lastname: Wiskott
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, School of Dental Medicine, University of Geneva, Rue Barthélemy-Menn 19, 1205, Geneva, Switzerland. Susanne.Scherrer@unige.ch.
authors.forename: Susanne S
authors.initials: SS
authors.lastname: Scherrer
mesh_terms: D000328:Adult; D000368:Aged; D000537:Aluminum Oxide / Q000737:chemistry*; D002516:Ceramics / Q000737:chemistry*; D003442:Crowns; D017266:Dental Prosthesis; D019232:Dental Restoration Failure / Q000145:classification*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012189:Retrospective Studies; D015996:Survival Rate; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide
keywords: All-ceramic restoration; Alumina; Chipping; Fractography; Fracture; Survival; Zirconia