title: Fatigue loading and R-curve behavior of a dental glass-ceramic with multiple flaw distributions.
abstract: OBJECTIVE
  To determine the effects of surface finish and mechanical loading on the rising toughness curve (R-curve) behavior of a fluorapatite glass-ceramic (IPS e.max ZirPress) and to determine a statistical model for fitting fatigue lifetime data with multiple flaw distributions.
  
  
  METHODS
  Rectangular beam specimens were fabricated by pressing. Two groups of specimens (n=30) with polished (15 μm) or air abraded surface were tested under rapid monotonic loading in oil. Additional polished specimens were subjected to cyclic loading at 2 Hz (n=44) and 10 Hz (n=36). All fatigue tests were performed using a fully articulated four-point flexure fixture in 37°C water. Fractography was used to determine the critical flaw size and estimate fracture toughness. To prove the presence of R-curve behavior, non-linear regression was used. Forward stepwise regression was performed to determine the effects on fracture toughness of different variables, such as initial flaw type, critical flaw size, critical flaw eccentricity, cycling frequency, peak load, and number of cycles. Fatigue lifetime data were fit to an exclusive flaw model.
  
  
  RESULTS
  There was an increase in fracture toughness values with increasing critical flaw size for both loading methods (rapid monotonic loading and fatigue). The values for the fracture toughness ranged from 0.75 to 1.1 MPam(1/2) reaching a plateau at different critical flaw sizes based on loading method.
  
  
  CONCLUSIONS
  Cyclic loading had a significant effect on the R-curve behavior. The fatigue lifetime distribution was dependent on the flaw distribution, and it fit well to an exclusive flaw model.
authors.affiliation: Department of Biomedical Materials Science, School of Dentistry, University of Mississippi Medical Center, Jackson, MS, United States.
authors.forename: Gaurav V
authors.initials: GV
authors.lastname: Joshi
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Duan
authors.forename: Alvaro
authors.initials: A
authors.lastname: Della Bona
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Hill
authors.forename: Kenneth
authors.initials: K
authors.lastname: St John
authors.forename: Jason A
authors.initials: JA
authors.lastname: Griggs
mesh_terms: D002516:Ceramics; D003764:Dental Materials; D005898:Glass; D008422:Materials Testing; D008962:Models, Theoretical
chemical_list: D003764:Dental Materials
keywords: Dental ceramic; Exclusive flaw model; Fractography; Pressable ceramic
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