title: Effect of cyclic loading on fracture strength of endodontically treated teeth restored with conventional and esthetic posts.
abstract: BACKGROUND
  Esthetic post and core systems were recently introduced. There are few reports regarding their behavior under cyclic loading.
  
  
  OBJECTIVE
  This study compared the effect of cyclic loading on survival rate, residual strength and mode of fracture of endodontically treated teeth restored with esthetic and direct metallic post systems subjected to mechanical cyclic loading.
  
  
  METHODS
  Thirty canines were endodontically treated, decoronated and prepared for metal free ceramic crowns, leaving 1.5 mm of dentin for ferrule effect. They were distributed in 3 groups and restored as follows: group 1 with zirconia posts (Cosmopost) and glass-ceramic cores (IPS Empress Cosmopost); group 2 with fiber reinforced composite posts (FibreKor) and group 3 with titanium posts (AZthec Anchor). Direct resin composite (Build It FR Resin Composite) was used as core in groups 2 and 3. All specimens were restored with all ceramic crowns (IPS Empress 2). A resin cement/adhesive system (Cement It/Bond It Primer A+B) was used to lute the posts to root canals and metal free porcelain crowns to the teeth preparation. Specimens were subjected to mechanical load of 250 N for 500,000x at a frequency of 1.7 Hz and then to static load until failure in a universal testing machine. Data were analyzed using One-way ANOVA and Fischer Exact tests alpha=0.05.
  
  
  RESULTS
  All groups had 100% survival rate after cyclic loading; fracture strength values (SD) in N were: group 1 = 886.5(170.6), group 2 = 762.2(113.6) and group 3 = 768.9(72.9); there was no difference among groups (p=0.08); the percentage of mode of favorable fracture found was: group 1 = 60%, group 2 = 90% and group 3 = 50%; there was no correlation between the mode of failure and post and core system used (P=0.142).
  
  
  CONCLUSIONS
  Esthetic post and core systems showed statistically equivalent fracture strength values, mode of failure and survival rate compared to conventional direct metallic post and resin composite core system after cyclic loading.
authors.affiliation: Department of Prosthodontics, Dental School, Espírito Santo Federal University, Brazil.
authors.forename: Anuar Antônio
authors.initials: AA
authors.lastname: Xible
authors.forename: Rudys Rodolfo
authors.initials: RR
authors.lastname: de Jesus Tavarez
authors.forename: Carlos Dos Reis Pereira
authors.initials: Cdos R
authors.lastname: de Araujo
authors.forename: Paulo César Rodrigues
authors.initials: PC
authors.lastname: Conti
authors.forename: Wellington Cardoso
authors.initials: WC
authors.lastname: Bonachella