title: Influence of zirconia abutment preparation on the fracture strength of single implant lithium disilicate crowns after chewing simulation.
abstract: OBJECTIVE
  The use of all-ceramic crowns over zirconia abutments is a well-established esthetic treatment option in implant dentistry; however, the effect of the mechanical processing due to abutment preparation has not been investigated under functional loading. The purpose of the study was to evaluate the influence of the zirconia abutment preparation depth and preparation mode on the fracture strength and fracture mode of lithium disilicate crowns after chewing simulation.
  
  
  METHODS
  Seventy single implant-supported lithium disilicate glass-ceramic crowns (IPS e.max Press, Ivoclar Vivadent) were adhesively cemented (Multilink Automix, Ivoclar Vivadent) onto zirconia abutments (ZirDesign, Astra Tech) using implants with a diameter of 4.5 mm and a length of 15.0 mm (Osseospeed, Astra Tech). Study design concerned the replacement of a maxillary central incisor (11.0 mm in height and 8.0 mm in width). Subgroups (n = 7) were subjected to dynamic loading (C) up to 1.2 × 10(6) loading cycles at 135° with 98N in a thermomechanical chewing simulator (Kausimulator, Willytech); followed by quasi-static loading at a cross-head speed of 0.5 mm/min until fracture in a universal testing machine (Z010/TN2S, Zwick). Additional subgroups were also subjected to quasi-static loading (S) at 135°. Lithium disilicate implant crowns were divided into five study groups (n = 14) according to the abutment preparation depth [A (control): 0.5 mm, B: 0.7 mm, C: 0.9 mm, and preparation mode [(No label): milling by the manufacturer, (P): copy-milling by the Celay System (Mikrona)].
  
  
  RESULTS
  All specimens survived dynamic loading and mean fracture strengths (N) after quasi-static loading were as follows: Group SA: 384 ± 84; Group CA: 403 ± 67; Group SB: 294 ± 95; Group CB: 374 ± 75; Group SC: 332 ± 52; Group CC: 373 ± 105; Group SPB: 332 ± 80; Group CPB: 499 ± 91; Group SPC: 380 ± 101; and Group CPC: 358 ± 54.
  
  
  CONCLUSIONS
  Statistical analysis using multiple linear regression showed that both the preparation depth and mode had no influence on the fracture strength of the implant crowns (P > 0.05); however, fracture strength increased statistically significantly after 5 years chewing simulation (P = 0.01).
authors.affiliation: Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry Christian-Albrechts University at Kiel, Kiel, Germany; Private Practice, Athens, Greece.
authors.forename: Miltiadis
authors.initials: M
authors.lastname: Mitsias
authors.forename: Spiridon-Oumvertos
authors.initials: SO
authors.lastname: Koutayas
authors.forename: Stefan
authors.initials: S
authors.lastname: Wolfart
authors.forename: Matthias
authors.initials: M
authors.lastname: Kern
mesh_terms: D002516:Ceramics; D003442:Crowns; D000044:Dental Abutments; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D007180:Incisor; D008409:Mastication; D008422:Materials Testing; D008437:Maxilla; D015040:Zirconium / Q000737:chemistry
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain; D015040:Zirconium
keywords: fracture mode; fracture strength; implant abutment; internal connection; lithium disilicate; preparation; zirconia