title: Fracture resistance of endodontically treated maxillary premolars restored by silorane-based composite with or without fiber or nano-ionomer.
abstract: OBJECTIVE
  This in vitro study investigated the fracture resistance of endodontically treated premolars restored using silorane- or methacrylate-based composite along with or without fiber or nano-ionomer base.
  
  
  METHODS
  Ninety-six intact maxillary premolars were randomly divided into eight groups (n = 12). G1 (negative control) was the intact teeth. In Groups 2-8, root canal treatment with mesio-occlusodistal preparation was performed. G2 (positive control) was kept unrestored. The other groups were restored using composite resin as follows: G3, methacrylate-based composite (Z250); G4, methacrylate composite (Z250) with polyethylene fiber; G5 and G6, silorane-based composite (Filtek P90) without and with the fiber, respectively; G7 and G8, methacrylate- and silorane-based composite with nano-ionomer base, respectively. After aging period and thermocycling for 1000 cycles, fracture strength was tested and fracture patterns were inspected. The results were analyzed using ANOVA and Tukey HSD tests (α=0.05).
  
  
  RESULTS
  Mean fracture resistance for the eight groups (in Newton) were G1: 1200 ± 169(a), G2: 360 ± 93(b), G3: 632 ± 196(c), G4: 692 ± 195(c), G5: 917 ± 159(d), G6: 1013 ± 125(ad), G7: 959 ± 148(d), G8: 947 ± 105(d) (different superscript letters revealed significant difference among groups). Most of the fractures in all the groups were restorable, except Group 3.
  
  
  CONCLUSIONS
  Silorane-based composite revealed significantly higher strength of the restored premolars compared to that of methacrylate one. Fiber insertion demonstrated no additional effect on the strength of both composite restorations; however, it increased the prevalence of restorable fracture of methacrylate-based composite restored teeth. Using nano-ionomer base under methacrylate-based composite had a positive effect on fracture resistance and pattern. Only fiber-reinforced silorane composite restoration resulted in a strength similar to that of the intact teeth.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Fereshteh
authors.initials: F
authors.lastname: Shafiei
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. ; Biomaterial Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Maryam Sadat
authors.initials: MS
authors.lastname: Tavangar
authors.affiliation: Department of Endodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Yasamin
authors.initials: Y
authors.lastname: Ghahramani
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Fattah
keywords: Endodontically treated premolar; Fracture resistance; Intracoronal direct restoration; Nano-ionomer; Polyethylene fiber; Silorane-based composite