title: Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic.
abstract: OBJECTIVE
  The objective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth.
  
  
  METHODS
  Rectangular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N=30/group) with polished (15μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2Hz (N=44) and 10Hz (N=36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37°C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software.
  
  
  RESULTS
  SCG parameters determined were n=21.7 and A=4.99×10(-5) for 2Hz, and n=19.1 and A=7.39×10(-6) for 10Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α1), the stress term (α2), and the interaction term (α3) had estimates and 95% confidence intervals of α1=-3.16 (-15.1, 6.30), α2=-21.2 (-34.9, -9.73), and α3=0.820 (-1.59, 4.02). Only α2 was significantly different from zero.
  
  
  CONCLUSIONS
  (1) Cyclic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material.
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.affiliation: Department of Biomedical Materials Science, School of Dentistry, University of Mississippi Medical Center, Jackson, MS, United States.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Duan
authors.affiliation: Post-graduate Program in Dentistry, University of Passo Fundo, Passo Fundo, Brazil.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Della Bona
authors.affiliation: Ivoclar-Vivadent, Inc., Amherst, NY, United States.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Hill
authors.affiliation: Department of Biomedical Materials Science, School of Dentistry, University of Mississippi Medical Center, Jackson, MS, United States.
authors.forename: Kenneth
authors.initials: K
authors.lastname: St John
authors.affiliation: Department of Biomedical Materials Science, School of Dentistry, University of Mississippi Medical Center, Jackson, MS, United States. Electronic address: JGriggs@umc.edu.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Griggs
mesh_terms: D002516:Ceramics; D003343:Corrosion; D003799:Dental Stress Analysis; D008422:Materials Testing
chemical_list: C023506:Glass ceramics
keywords: Air abrasion; Cyclic fatigue; Dental ceramic; Pressable ceramic; Stress corrosion