title: In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations.
abstract: BACKGROUND
  The in vitro effectiveness of a uniform circumferential ferrule has been established in the literature; however, the effect of a nonuniform circumferential ferrule height on fracture resistance is unknown.
  
  
  OBJECTIVE
  This in vitro study investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations.
  
  
  METHODS
  Fifty extracted intact maxillary human central incisors were randomly assigned to 1 of 5 groups: CRN, no root canal treatment (RCT), restored with a crown; RCT/CRN, no dowel/core, restored with a crown; 2 FRL, 2-mm ferrule, cast dowel/core and crown; 0.5/2 FRL, nonuniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast dowel/core and crown; and 0 FRL, no ferrule, cast dowel/core and crown. The teeth were prepared to standardized specifications and stored for 72 hours in 100% humidity prior to testing. Testing was conducted with a universal testing machine with the application of a static load, and the load (N) at failure was recorded. Statistical analysis was performed with a 1-way analysis of variance and the Tukey Honestly Significant Difference test (alpha=.05). The mode of fracture was noted by visual inspection for all specimens.
  
  
  RESULTS
  There was strong evidence of group differences in mean fracture strength ( P <.0001). Following adjustment for all pairwise group comparisons, it was found that the lack of a ferrule resulted in a significantly lower mean fracture strength (0 FRL: 264.93 +/- 78.33 N) relative to all other groups. The presence of a nonuniform (0.5 to 2-mm vertical height) ferrule (0.5/2 FRL: 426.64 +/- 88.33 N) resulted in a significant decrease ( P =.0001) in mean fracture strength when compared with the uniform 2-mm vertical ferrule (2 FRL: 587.23 +/- 110.25 N), the group without RCT (CRN: 583.67 +/- 86.09 N), and the RCT-treated tooth with a crown alone (CRN/RCT: 571.04 +/- 154.86 N). The predominant mode of failure was an oblique fracture extending from the lingual margin to the facial surface just below the insertion of the tooth into the acrylic resin.
  
  
  CONCLUSIONS
  The results demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.
authors.affiliation: Department of Family Dentistry, College of Dentistry, University of Iowa City, IA 52242-1001, USA. philip-l-tan@uiowa.edu
authors.forename: Philip L B
authors.initials: PL
authors.lastname: Tan
authors.forename: Steven A
authors.initials: SA
authors.lastname: Aquilino
authors.forename: David G
authors.initials: DG
authors.lastname: Gratton
authors.forename: Clark M
authors.initials: CM
authors.lastname: Stanford
authors.forename: Swee Chian
authors.initials: SC
authors.lastname: Tan
authors.forename: William T
authors.initials: WT
authors.lastname: Johnson
authors.forename: Deborah
authors.initials: D
authors.lastname: Dawson
mesh_terms: D003442:Crowns; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D006801:Humans; D007180:Incisor / Q000503:physiopathology*; D008422:Materials Testing; D011176:Post and Core Technique; D012390:Root Canal Therapy; D013314:Stress, Mechanical; D014082:Tooth Fractures / Q000145:classification / Q000503:physiopathology*; D019231:Tooth Preparation, Prosthodontic; D019553:Tooth, Nonvital / Q000503:physiopathology*