title: Evaluation of fracture resistance in aqueous environment under dynamic loading of lithium disilicate restorative systems for posterior applications. Part 2.
abstract: OBJECTIVE
  The goals of part 2 of the study presented here were 1) to assess whether there is a difference in failure mode of different thicknesses (2.0, 1.5, 1.0, and 0.5 mm) of anatomically standardized full contour monolithic lithium disilicate restorations for posterior teeth, and 2) to assess if there is a difference among various crown thicknesses when these restorations are subjected to dynamic load forces common for posterior teeth.
  
  
  METHODS
  Four groups (n = 10), each with a different thickness of anatomically appropriate all-ceramic crowns, were to be tested as established from the statistical analysis of the preliminary phase. Group 1: 2.0 mm; group 2: 1.5 mm; group 3: 1.0 mm; group 4: 0.5 mm. The specimens were adhesively luted to the corresponding die, and underwent dynamic cyclic loading (380 to 390 N) completely submerged in an aqueous environment until a failure was noted by graphic recording and continuous monitoring.
  
  
  RESULTS
  There was a statistically significant difference of the fatigue cycles to failure among four groups (p < 0.001; Kruskal-Wallis test). The mean number of cycles to fail for 2.0 mm specimens was 17 times more than the mean number of cycles to fail for 1.0 mm specimens and 1.5 times more than the mean number of cycles to fail for 1.5 mm specimens. The 0.5 mm specimens failed with one cycle of loading. A qualitative characteristic noted among the 2.0 mm specimens was wear of the area of indenter contact followed by shearing of the material and/or crack propagation.
  
  
  CONCLUSIONS
  Based on the findings of this study, it may be reasonable to consider a crown thickness of 1.5 mm or greater for clinical applications of milled monolithic lithium disilicate crowns for posterior single teeth.
authors.affiliation: Former Assistant Professor of Dentistry, Mayo Clinic College of Medicine, Chief Resident, Prosthodontics and Maxillofacial Prosthetics, Division of Prosthetic and Esthetic Dentistry, Department of Dental Specialties, Mayo Clinic, Rochester, MN Currently: Maxillofacial Prosthodontist, University of Pittsburgh School of Dental Medicine, Department of Prosthodontics, Pittsburgh, PA.
authors.forename: Matilda
authors.initials: M
authors.lastname: Dhima
authors.forename: Alan B
authors.initials: AB
authors.lastname: Carr
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Salinas
authors.forename: Christine
authors.initials: C
authors.lastname: Lohse
authors.forename: Lawrence
authors.initials: L
authors.lastname: Berglund
authors.forename: Kai-An
authors.initials: KA
authors.lastname: Nan
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D006858:Hydrofluoric Acid / Q000737:chemistry; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D014867:Water / Q000737:chemistry
chemical_list: C520133:IPS e.max CAD LT; C528569:Rely-X; D019279:Resin Cements; C493120:lithia disilicate; D014867:Water; D003776:Dental Porcelain; D006858:Hydrofluoric Acid
keywords: Lithium disilicate; aqueous; bonding; ceramic; crown; digital technology; dynamic testing; indenter; load; tooth