title: Mechanical fatigue cycling on teeth restored with fiber posts: impact of coronal grooves and diameter of glass fiber post on fracture resistance.
abstract: OBJECTIVE
  The aim of this paper was to evaluate the effect of different diameters and surface characteristics of a glass fiber post on the fracture resistance of teeth restored with fiber posts.
  
  
  METHODS
  Eighty single-rooted bovine teeth were prepared, embedded in a PVC cylinder using acrylic resin, and allocated into 8 groups (N.=10) according to post diameter and shape: (smooth double-tapered fiber post) G1, G2, G3, and G4 with cervical diameters of 1.4 mm, 1.6 mm, 1.8 mm, and 2 mm, respectively; (double-tapered fiber posts with coronal grooves) G5, G6, G7, and G8 with cervical diameters of 1.4 mm, 1.6 mm, 1.8 mm, and 2 mm, respectively. A self-adhesive cement was used for post cementation, and the core build-up was standardized and made with composite resin. Specimens were stored for 7 days and then submitted to the mechanical fatigue testing (load=50 N., angle= 45°, frequency=1 Hz, temperature=37 ± 1 °C, number of cycles=1000000); the specimens that survived were submitted to static resistance testing (1 mm/min, 45°). The fracture loads and fracture modes was recorded. Data were submitted to 2-way ANOVA, post-hoc Tukey test and Pearson Correlation analysis.
  
  
  RESULTS
  The cervical diameter of the post (P<0.0001) and surface characteristics (P=0.01013) significantly affected the fracture resistance (2-way ANOVA). Grooves reduced the fracture resistance when post diameter was 1.4 mm (G1 and G5). A moderate positive correlation was found between the fracture resistance and the fiber post diameter (r2=0.4445; P<0.0001) (Pearson correlation test).
  
  
  CONCLUSIONS
  It appears that there is a direct relation between the diameter of the fiber post and the fracture strength of roots restored with fiber posts. But other factors may have influenced the fracture strength such as the reduction of intracanal dentin by the preparation for placement of wider fiber posts, since no difference was found for smooth fiber posts with different diameter. Otherwise, grooves at coronal part of the fiber post can damage the fracture resistance.
authors.affiliation: Federal University of Santa Maria, Santa Maria, Rio Grande do Sul State, Brazil.
authors.forename: M F
authors.initials: MF
authors.lastname: Santini
authors.forename: V
authors.initials: V
authors.lastname: Wandscher
authors.forename: M
authors.initials: M
authors.lastname: Amaral
authors.forename: P
authors.initials: P
authors.lastname: Baldissara
authors.forename: L F
authors.initials: LF
authors.lastname: Valandro
mesh_terms: D000818:Animals; D002417:Cattle; D003738:Dental Cements; D004867:Equipment Design; D005898:Glass; D066298:In Vitro Techniques; D007180:Incisor; D008422:Materials Testing; D011176:Post and Core Technique; D013314:Stress, Mechanical; D014082:Tooth Fractures / Q000517:prevention & control; D014092:Tooth Root / Q000293:injuries*; D016474:Weight-Bearing
chemical_list: D003738:Dental Cements; C009753:fiberglass