title: The Influence of Composite Thickness with or without Fibers on Fracture Resistance of Direct Restorations in Endodontically Treated Teeth.
abstract: BACKGROUND
  This in vitro study evaluated the influence of composite thickness (with or without fiber reinforcement) on fracture resistance of direct restorations in endodontically treated teeth.
  
  
  METHODS
  Fifty-six intact human premolars were chosen and randomly divided into four groups (n=14). After preparation of a mesio-occluso-distal (MOD) cavities and cusp reduction, the teeth were endodontically treated. Subsequently, the samples were restored with composite resin using the following protocols: group 1; composite onlay with cusp coverage of 1.5 mm, group 2; composite onlay with cusp coverage of 2.5 mm, group 3; composite onlay (including resin-impregnated fiber) with cusp coverage of 1.5 mm and group 4; composite onlay (including resin-impregnated fiber) with cusp coverage of 2.5 mm. The fracture resistance of teeth in all test groups was calculated by subjecting them to a progressively increasing compressive axial force in the universal testing machine with the cross-head speed of 1 mm/min to the point of fracture. The data were analyzed using the Kruskal-Wallis test.
  
  
  RESULTS
  The mean fracture strengths and obtained standard error were 1263.85±74.03 N, 1330.26±128.01 N, 1344.92±64.40 N and 1312.54±75.63 N for groups 1 to 4, respectively. Statistical analysis revealed no significant difference between groups.
  
  
  CONCLUSIONS
  Cusp coverage of 1.5 and 2.5 mm in MOD access cavities with or without insertion of resin impregnated fiber had similar fracture rates in the endodontically treated teeth.
authors.affiliation: Iranian Center for Endodontic Research, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Torabzadeh
authors.affiliation: Dental Research Center, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Amir
authors.initials: A
authors.lastname: Ghassemi
authors.affiliation: Department of restorative Dentistry, Dental School, Shahed University, Tehran, Iran.
authors.forename: Masoud
authors.initials: M
authors.lastname: Sanei
authors.affiliation: Iranian Center for Endodontic Research, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Sara
authors.initials: S
authors.lastname: Razmavar
authors.affiliation: Dental faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Seyedeh Mahsa
authors.initials: SM
authors.lastname: Sheikh-Al-Eslamian
keywords: Composite Resins; Cusp Coverage; Cusp Reduction; Dental Restoration; Direct Restoration; Endodontically-Treated Teeth; Fiber; Resin Composite; Stress Fractures