title: Effect of fiber orientation and type of restorative material on fracture strength of the tooth.
abstract: OBJECTIVE
  To determine the effect of fiber and its orientation on the fracture resistance of composite restorations in root-filled premolars.
  
  
  METHODS
  50 sound human premolars were collected and assigned to five groups of ten specimens each. In group 1 (control), specimens were not root-filled. In the other four groups, MOD cavities were prepared and the cusps were reduced to 1.5 mm. In groups 2 and 3, the samples were filled with Z-250 and spectrum composites respectively without fiber reinforcement. Groups 4 and 5 were reinforced with Fiber-Ribbon-(Angelus) and restored with spectrum composite. Fibers were placed in the U-shaped design in group 4 while they were placed in the cross-shape in occlusal region in group 5. The fracture resistance was tested using a mechanical testing machine at crosshead speed of 1mm/min.
  
  
  RESULTS
  The fracture strength of control group was 1271.16±722.04 N while it was 952.05±330.16 N for group 2, 918.52±256.6 N for group 3, 857.13±184.58 N for group 4 and 1138.81±406.64 N for group 5. Fracture strength of group 5 was more than other groups except for group 1, there was no statistically significant differences.
  
  
  CONCLUSIONS
  The reinforcement of composite with fiber does not increase fracture resistance of root-filled premolars significantly.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Shaheed Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Moezizadeh
authors.forename: Mohadeseh
authors.initials: M
authors.lastname: Shokripour