title: Influence of preparation mode and depth on the fracture strength of zirconia ceramic abutments restored with lithium disilicate crowns.
abstract: OBJECTIVE
  Zirconia implant abutments offer enhanced esthetics and promote biologic sealing; however, the effect of laboratory or intraoral preparation on the mechanical stability of zirconia has not been investigated. The purpose of the study was to evaluate the influence of the preparation mode and depth on the fracture strength of zirconia abutments restored with lithium disilicate crowns.
  
  
  METHODS
  To replace a maxillary central incisor (11.0 mm in height and 8.0 mm in width), 35 lithium disilicate crowns were cemented onto zirconia abutments on 4.5- ° - 15-mm titanium implants. Lithium disilicate implant crowns were divided into five study groups (n = 7) according to the abutment preparation mode (milling by the manufacturer or milling by the Celay System [Mikrona] [P]) and preparation depth (0.5 mm [A], 0.7 mm [B], or 0.9 mm [C]). All groups were subjected to quasi-static loading (S) at 135 degrees to the implant axis in a universal testing machine.
  
  
  RESULTS
  Mean fracture strengths were: group SA, 384 ± 84 N (control); group SB, 294 ± 95 N; group SPB, 332 ± 80 N; group SC, 332 ± 52; group SPC, 381 ± 101 N. All specimens presented a typical fracture mode within the implant/abutment internal connection. Multiple regression analysis revealed that preparation depth up to 0.7 mm statistically influenced the fracture strength (P = .034), whereas the preparation mode did not seem to play an important role (P = .175).
  
  
  CONCLUSIONS
  Regardless of preparation mode, circumferential preparation of zirconia abutments might negatively affect the fracture strength of adhesively cemented single implant lithium disilicate crowns.
authors: Department of Prosthodontics, School of Dentistry, Albert-Ludwig University, Freiburg, Germany. koutayas@otenet.gr
authors: Spiridon-Oumvertos
authors: SO
authors: Koutayas
authors: Miltiadis
authors: M
authors: Mitsias
authors: Stefan
authors: S
authors: Wolfart
authors: Matthias
authors: M
authors: Kern
mesh_terms: D002516:Ceramics; D003442:Crowns; D000044:Dental Abutments; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D008422:Materials Testing; D008437:Maxilla; D014025:Titanium; D015040:Zirconium / Q000737:chemistry*
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide