title: Fatigue resistance of ultrathin CAD/CAM complete crowns with a simplified cementation process.
abstract: BACKGROUND
  Traditional tooth preparation for complete crowns requires a substantial amount of hard tissue reduction. This is in contrast with the principles of minimally invasive dentistry. An ultrathin complete crown preparation is proposed instead.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to assess the fatigue resistance and failure mode of computer-aided design and computer-aided manufacturing (CAD/CAM) ultrathin complete molar crowns placed with self-adhesive cement. Different restorative materials (resin nanoceramic [RNC], feldspathic ceramic [FEL], and lithium disilicate [LD]) were compared.
  
  
  METHODS
  Forty-five extracted molars with a standardized crown preparation were restored with the Cerec 3 CAD/CAM system using FEL, LD, or RNC (n=15). FEL and LD restorations were etched with hydrofluoric acid and silanated. RNC restorations and all preparations were treated with airborne-particle abrasion. All restorations (thickness=0.7 mm) were cemented with RelyX Unicem II Automix cement and submitted to cyclic isometric loading, beginning with a load of 200 N (5000 cycles) and followed by stages of 400, 600, 800, 1000, 1200, and 1400 N at a maximum of 30 000 cycles each. The specimens were loaded until failure or for a maximum of 185 000 cycles. The failure mode was categorized as "catastrophic," "possibly reparable," or "reparable." The groups were compared using life table survival analysis (log rank test at α=.05). Previously published data from the same authors about traditional complete crowns (thickness 1.5 mm) using the same experimental design were included for comparison.
  
  
  RESULTS
  All specimens survived the fatigue test until the 600 N step. RNC, LD, and FEL failed at an average load of 1014 N (1 survival), 1123 N (2 survivals), and 987 N (no survivals), and no difference in survival rate was found. No catastrophic failures were reported after the fatigue test. Comparison with previously published data showed that 1.5-mm thick complete crowns demonstrated higher survival rates than the ultrathin restorations, independent of the material.
  
  
  CONCLUSIONS
  The fatigue resistance of ultrathin complete molar crowns (placed with a simplified cementation process) made of RNC, LD, and FEL was not significantly different. All materials survived the normal range of masticatory forces. All failures were re-restorable. Regular crowns of 1.5 to 2.0 mm thickness may present higher survival rates than ultrathin ones.
authors.affiliation: Don and Sybil Harrington Professor of Esthetic Dentistry, Restorative Sciences, Ostrow School of Dentistry, University of Southern California, Los Angeles, Calif.
authors.forename: Pascal
authors.initials: P
authors.lastname: Magne
authors.affiliation: Substitute Professor, Health Department, State University of Feira de Santana, Feira de Santana, Bahia, Brazil. Electronic address: aoc1981@hotmail.com.
authors.forename: Adriana O
authors.initials: AO
authors.lastname: Carvalho
authors.affiliation: PhD Student, Department of Operative Dentistry, Federal University of Santa Catarina, Florianópolis, Brazil.
authors.forename: Greciana
authors.initials: G
authors.lastname: Bruzi
authors.affiliation: Associate Professor, Department of Restorative Dentistry, Piracicaba School of Dentistry, Campinas State University, Piracicaba, Brazil.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Giannini
mesh_terms: D002484:Cementation / Q000379:methods*; D002516:Ceramics; D003188:Composite Resins / Q000737:chemistry*; D017076:Computer-Aided Design; D003442:Crowns; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D006801:Humans; D008422:Materials Testing; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D003764:Dental Materials