title: Effect of a crown ferrule on the fracture resistance of endodontically treated teeth restored with prefabricated posts.
abstract: BACKGROUND
  Root fracture is one of the most serious complications following restoration of endodontically treated teeth.
  
  
  OBJECTIVE
  The purpose of this study was to compare the fracture strengths of endodontically treated teeth using posts and cores and variable quantities of coronal dentin located apical to core foundations with corresponding ferrule designs incorporated into cast restorations.
  
  
  METHODS
  Fifty freshly extracted canines were endodontically treated. The teeth were randomly divided into groups of 10 and prepared according to 5 experimental protocols.
  
  
  METHODS
  teeth with custom cast post and core; 0-mm group: teeth without coronal structure (no ferrule); 1-mm, 2-mm, and 3-mm groups: teeth with 1 mm, 2 mm, and 3 mm of remaining coronal tooth structure (1-, 2-, and 3-mm ferrule), respectively. All specimens in 0-mm through 3-mm (noncontrol) groups were restored with a prefabricated post (Screw-Post) and composite resin (Z100) core located superior to the different tooth structure heights. All teeth were restored with complete metal crowns. The fracture resistance (N) was measured in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed by 1-way analysis of variance and Tukey test (alpha=.05).
  
  
  RESULTS
  Significant differences (P<.001) were found among the mean fracture forces of the test groups (control group: 818.2 N; 0-mm, 1-mm, 2-mm, and 3-mm groups: 561.0 N, 627.6 N, 745.3 N, and 907.1 N, respectively). When the mode of failure was evaluated, all failures in the control group occurred due to root fracture, and all failures in the 0-mm group occurred due to core fracture. The majority of failures in the other groups occurred due to crown cementation failure.
  
  
  CONCLUSIONS
  The results of this study showed that an increased amount of coronal dentin significantly increases the fracture resistance of endodontically treated teeth.
authors.affiliation: Oral Rehabilitation, Department of Prosthodontics, Bauru Dental School, University of Sao Paulo, Brazil. jeffripe@rocketmail.com
authors.forename: Jefferson Ricardo
authors.initials: JR
authors.lastname: Pereira
authors.forename: Fabio
authors.initials: F
authors.lastname: de Ornelas
authors.forename: Paulo Cesar Rodrigues
authors.initials: PC
authors.lastname: Conti
authors.forename: Accacio Lins
authors.initials: AL
authors.lastname: do Valle
mesh_terms: D000704:Analysis of Variance; D002484:Cementation; D003188:Composite Resins; D003442:Crowns; D003481:Cuspid; D017267:Dental Prosthesis Design / Q000295:instrumentation*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D011176:Post and Core Technique / Q000009:adverse effects; D012822:Silicon Dioxide; D014082:Tooth Fractures / Q000209:etiology*; D014092:Tooth Root / Q000293:injuries; D015040:Zirconium
chemical_list: D003188:Composite Resins; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium