title: Fracture resistance of endodontically treated teeth: three walls versus four walls of remaining coronal tooth structure.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the fracture resistance of endodontically treated teeth between those with four walls and those with three walls of remaining coronal tooth structure and the effect of the site of the missing coronal wall.
  
  
  METHODS
  Thirty-two endodontically treated second mandibular premolars were decoronated, leaving 3 mm above the cementoenamel junction (CEJ). A 0.5-mm-wide chamfer was prepared 1 mm above the CEJ. The teeth were randomly divided into four groups. Group 1 had four walls of coronal tooth structure, whereas groups 2, 3, and 4 had only three walls, missing the buccal, lingual, and mesial wall, respectively. The cast dowel and cores and crowns (Ni-Cr alloy) were cemented with zinc phosphate cement. A compressive load was applied 45 degrees to the long axis, 2 mm below the buccal cusp, with an Instron machine until failure at a crosshead speed of 5 mm/min. Failure load (kg) and mode of failure were recorded. Data were analyzed with one-way ANOVA and Scheffé tests (p < 0.05).
  
  
  RESULTS
  Group 1 had the highest fracture resistance (1190.3 +/- 110.5 kg), significantly different from the other groups (p < 0.05) (group 2: 578.5 +/- 197.4 kg; group 3: 786.6 +/- 132.8 kg; group 4: 785.4 +/- 289.9 kg). There were no significant differences among the test groups. The mode of failure in group 1 was a horizontal root fracture, whereas that of the other groups was either vertical or oblique fracture.
  
  
  CONCLUSIONS
  Teeth with four walls of remaining coronal dentine had significantly higher fracture resistance than teeth with only three walls. The site of the missing coronal wall did not affect the fracture resistance of endodontically treated teeth.
authors.affiliation: Department of Conservative Dentistry and Prosthodontics, Faculty of Dentistry, Srinakharinwirot University, Bangkok, Thailand. siriporr@hotmail.com
authors.forename: Siriporn
authors.initials: S
authors.lastname: Arunpraditkul
authors.forename: Siranee
authors.initials: S
authors.lastname: Saengsanon
authors.forename: Wilasinee
authors.initials: W
authors.lastname: Pakviwat
mesh_terms: D001641:Bicuspid; D002484:Cementation; D002858:Chromium Alloys; D003735:Dental Casting Technique; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D008334:Mandible; D011176:Post and Core Technique; D019228:Tooth Crown / Q000503:physiopathology*; D014082:Tooth Fractures / Q000517:prevention & control*; D019231:Tooth Preparation, Prosthodontic; D019553:Tooth, Nonvital / Q000503:physiopathology*; D015036:Zinc Phosphate Cement
chemical_list: D002858:Chromium Alloys; D015036:Zinc Phosphate Cement