title: Fracture strength and fracture patterns of root-filled teeth restored with direct resin composite restorations under static and fatigue loading.
abstract: OBJECTIVE
  To assess fracture strength and fracture patterns of root-filled teeth with direct resin composite restorations under static and fatigue loading.
  
  
  METHODS
  MOD cavities plus endodontic access were prepared in 48 premolars. Teeth were root filled and divided into three restorative groups, as follows 1) resin composite; 2) glass ionomer cement (GIC) core and resin composite; and 3) open laminate technique with GIC and resin composite. Teeth were loaded in a servohydraulic material test system. Eight samples in each group were subjected to stepped fatigue loading: a preconditioning load of 100 N (5000 cycles) followed by 30,000 cycles each at 200 N and higher loads in 50-N increments until fracture. Noncycled teeth were subjected to a ramped load. Fracture load, number of cycles, and fracture patterns were recorded. Data were analyzed using two-way analysis of variance and Bonferroni tests.
  
  
  RESULTS
  Fatigue cycling reduced fracture strength significantly (p<0.001). Teeth restored with a GIC core and a laminate technique were significantly weaker than the composite group (379±56 N, 352±67 N vs 490±78 N, p=0.001). Initial debonding occurred before the tooth underwent fracture. All failures were predominantly adhesive, with subcrestal fracture of the buccal cusp.
  
  
  CONCLUSIONS
  Resin composite restorations had significantly higher fracture strength than did other restorations. Fatigue cycled teeth failed at lower load than did noncycled teeth.
authors.forename: N A
authors.initials: NA
authors.lastname: Taha
authors.forename: J E
authors.initials: JE
authors.lastname: Palamara
authors.forename: H H
authors.initials: HH
authors.lastname: Messer
mesh_terms: D001641:Bicuspid / Q000601:surgery; D003188:Composite Resins / Q000627:therapeutic use*; D003793:Dental Restoration, Permanent / Q000009:adverse effects / Q000379:methods; D003799:Dental Stress Analysis; D006801:Humans; D012389:Root Canal Obturation / Q000009:adverse effects / Q000379:methods; D014082:Tooth Fractures / Q000209:etiology*
chemical_list: D003188:Composite Resins