title: Effects of mechanical cycling on the bonding of zirconia and fiber posts to human root dentin.
abstract: OBJECTIVE
  To evaluate the effect of cyclical mechanical loading on the bond strength of a fiber and a zirconia post bonded to root dentin.
  
  
  METHODS
  Forty single-rooted human teeth (maxillary incisors and canines) were sectioned, and the root canals were prepared at 12 mm. Twenty randomly seleced specimens received a quartz fiber post (FRC) (D.T. Light-Post) and 20 others received a zirconia post (ZR) (Cosmopost). The posts were resin luted (All Bond 2 + resin cement Duo-link) and each specimen was embedded in epoxy resin inside a PVC cylinder. Ten specimens with FRC post and 10 specimens with ZR post were submitted to fatigue testing (2,000,000 cycles; load: 50 N; angle of 45 degrees; frequency: 8 Hz), while the other 20 specimens were not fatigued. Thus, 4 groups were formed: G1: FRC+O cycles; G2: FRC+2,000,000 cycles; G3: ZR+O cycles; G4: ZR+2,000,000 cycles. Later, the specimens were cut perpendicular to their long axis to form 2-mm-thick disk-shaped samples (4 sections/specimen), which were submitted to the push-out test (1 mm/min). The mean bond strength values (MPa) were calculated for each tooth (n = 10) and data were submitted to statistical analysis (alpha = 0.05).
  
  
  RESULTS
  Two-way ANOVA revealed that the bond strength was significantly affected by mechanical cycling (p = 0.0014) and root post (p = 0.0325). The interaction was also statistically significant (p = 0.0010). Tukey's test showed that the mechanical cycling did not affect the bonding of FRC to root dentin, while fatigue impaired the bonding of zirconium to root dentin.
  
  
  CONCLUSIONS
  (1) The bond strength of the FRC postto root dentin was not reduced after fatigue testing, whereas the bonding of the zirconia post was significantly affected by the fatigue. (2) Cyclical mechanical loading appears to damage the bond strength of the rigid post only.
authors.affiliation: Department of Dental Materials and Prosthodontics, São José dos Campos Dental School, São Paulo State University (UNESP), Brazil.
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
authors.forename: Paolo
authors.initials: P
authors.lastname: Baldissara
authors.forename: Luiz Felipe
authors.initials: LF
authors.lastname: Valandro
authors.forename: Graziela Avila
authors.initials: GA
authors.lastname: Galhano
authors.forename: Roberto
authors.initials: R
authors.lastname: Scotti
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins; D001840:Dental Bonding; D003799:Dental Stress Analysis; D003804:Dentin; D017220:Dentin-Bonding Agents; D004548:Elasticity; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates; D011176:Post and Core Technique; D011791:Quartz; D019279:Resin Cements; D015040:Zirconium
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C431350:Duo-Link; D008689:Methacrylates; D019279:Resin Cements; D011791:Quartz; C100742:All-Bond 2; D015040:Zirconium; C028541:zirconium oxide