title: Fracture strength and fracture patterns of root filled teeth restored with direct resin restorations.
abstract: OBJECTIVE
  To compare fracture characteristics of root-filled teeth with variable cavity design and resin composite restoration.
  
  
  METHODS
  80 extracted intact maxillary premolars were divided randomly into eight groups; (1) intact teeth; (2) unrestored MOD cavity; (3) unrestored MOD cavity plus endodontic access through the occlusal floor; (4) unrestored MOD plus endodontic access with axial walls removed; (5) MOD restored with resin composite; (6) MOD plus endodontic access, resin composite; (7) MOD plus extensive endodontic access, resin composite; (8) MOD plus extensive endodontic access, GIC core and resin composite. A ramped oblique load was applied to the buccal cusp in a servohydraulic testing machine. Fracture load and fracture patterns were recorded. Fracture loads were compared statistically using 1-way ANOVA, with Dunnett test for multiple comparisons.
  
  
  RESULTS
  Unrestored teeth became progressively weaker with more extensive preparations. Endodontic access confined within the occlusal floor did not significantly affect strength compared to an MOD cavity. Loss of axial walls weakened teeth considerably [292+80N vs 747+130N for intact teeth]. Restoration increased the strength of prepared teeth particularly in teeth without axial walls. Teeth with a GIC core were not significantly weaker than intact teeth [560+167N]. Failures were mostly adhesive at the buccal interface, with the fracture propagating from the buccal line angle of the occlusal floor (MOD and MOD plus access groups) or of the proximal box (axial wall removed).
  
  
  CONCLUSIONS
  Direct restorations increased fracture resistance of root filled teeth with extensive endodontic access. Both restored and unrestored teeth showed similar fracture patterns.
authors.affiliation: Melbourne Dental School, University of Melbourne, Melbourne, Australia. n.taha@just.edu.jo
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: D000134:Acid Etching, Dental / Q000379:methods; D000180:Acrylic Resins / Q000737:chemistry; D001641:Bicuspid / Q000033:anatomy & histology / Q000293:injuries; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000145:classification; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000033:anatomy & histology / Q000293:injuries; D017220:Dentin-Bonding Agents / Q000737:chemistry; D004853:Epoxy Resins / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006171:Gutta-Percha / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D011176:Post and Core Technique; D012387:Root Canal Filling Materials / Q000737:chemistry; D018915:Root Canal Preparation / Q000145:classification; D012390:Root Canal Therapy; D013314:Stress, Mechanical; D019237:Tooth Cervix / Q000033:anatomy & histology; D019228:Tooth Crown / Q000033:anatomy & histology / Q000293:injuries; D014082:Tooth Fractures / Q000503:physiopathology*
chemical_list: D000180:Acrylic Resins; D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; D004853:Epoxy Resins; C493186:Fuji VII; D005899:Glass Ionomer Cements; D012387:Root Canal Filling Materials; C534916:epoxy resin-based root canal sealer; C471182:glacier hybrid composite; C115612:single bond; D017438:Bisphenol A-Glycidyl Methacrylate; C006903:carbopol 940; D006171:Gutta-Percha