title: Fatigue stipulation of bulk-fill composites: An in vitro appraisal.
abstract: OBJECTIVE
  The aim of this study was to determine the Weibull and slow crack growth (SCG) parameters of bulk-fill resin based composites. The strength degradation over time of the materials was also assessed by strength-probability-time (SPT) analysis.
  
  
  METHODS
  Three bulk-fill [Tetric EvoCeram Bulk Fill (TBF); X-tra fil (XTR); Filtek Bulk-fill flowable (BFL)] and a conventional one [Filtek Z250 (Z250)] were studied. Seventy five disk-shaped specimens (12mm in diameter and 1mm thick) were prepared by inserting the uncured composites in a stainless steel split mold followed by photoactivation (1200mW/cm(2)/20s) and storage in distilled water (37°C/24h). Degree of conversion was evaluated in five specimens by analysis of FT-IR spectra obtained in the mid-IR region. The SCG parameters n (stress corrosion susceptibility coefficient) and σf0 (scaling parameter) were obtained by testing ten specimens in each of the five stress rates: 10(-2), 10(-1), 10(0), 10(1) and 10(2)MPa/s using a piston-on-three-balls device. Weibull parameter m (Weibull modulus) and σf0 (characteristic strength) were obtained by testing additional 20 specimens at 1MPa/s. Strength-probability-time (SPT) diagrams were constructed by merging SCG and Weibull parameters.
  
  
  RESULTS
  BFL and TBF presented higher n values, respectively (40.1 and 25.5). Z250 showed the highest (157.02MPa) and TBF the lowest (110.90MPa) σf0 value. Weibull analysis showed m (Weibull modulus) of 9.7, 8.6, 9.7 and 8.9 for TBF, BFL, XTR and Z250, respectively. SPT diagram for 5% probability of failure showed strength decrease of 18% for BFL, 25% for TBF, 32% for XTR and 36% for Z250, respectively, after 5 years as compared to 1 year.
  
  
  CONCLUSIONS
  The reliability and decadence of strength over time for bulk-fill resin composites studied are, at least, comparable to conventional composites. BFL shows the highest fatigue resistance under all simulations followed by TBF, while XTR was at par with Z250.
authors.affiliation: Faculty of Dentistry, National University of Singapore, Singapore, Singapore.
authors.forename: Shruti A
authors.initials: SA
authors.lastname: Vidhawan
authors.affiliation: Department of Dentistry, JurongHealth Services, Singapore, Singapore.
authors.forename: Adrian U
authors.initials: AU
authors.lastname: Yap
authors.affiliation: School of Dentistry, Positivo University, Curitiba, Brazil.
authors.forename: Barbara P
authors.initials: BP
authors.lastname: Ornaghi
authors.affiliation: Singapore Synchrotron Light Source, National University of Singapore, Singapore, Singapore.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Banas
authors.affiliation: Singapore Synchrotron Light Source, National University of Singapore, Singapore, Singapore.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Banas
authors.affiliation: Faculty of Dentistry, National University of Singapore, Singapore, Singapore.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Neo
authors.affiliation: Biomaterials and Biomechanics, Oregon Health and Science University, OR, United States.
authors.forename: Carmem S
authors.initials: CS
authors.lastname: Pfeifer
authors.affiliation: Faculty of Dentistry, National University of Singapore, Singapore, Singapore. Electronic address: denvr@nus.edu.sg.
authors.forename: Vinicius
authors.initials: V
authors.lastname: Rosa
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000627:therapeutic use; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D015203:Reproducibility of Results; D012117:Resins, Synthetic / Q000737:chemistry* / Q000627:therapeutic use; D017550:Spectroscopy, Fourier Transform Infrared; D013718:Tensile Strength
chemical_list: D003188:Composite Resins; C444701:Filtek Z250; D012117:Resins, Synthetic; C501891:Tetric EvoCeram
keywords: Dynamic fatigue; Resin composites; Strength degradation; Strength–probability–time diagram; Subcritical crack growth; Weibull analysis