title: The influence of substance loss and ferrule height on the fracture resistance of endodontically treated premolars. An in vitro study.
abstract: OBJECTIVE
  This study evaluated the effect of different ferrule heights and varying degrees of substance loss on the fracture resistance of endodontically treated premolars.
  
  
  METHODS
  Eighty extracted and endodontically treated lower premolars were used and divided into 5 test groups (n=16) depending on the ferrule height: A (0.0mm), B (0.5mm), C (1.0mm), D (1.5mm) and E (2.0mm) respectively. Teeth in subgroups were either with 1 or 2 residual coronal dentin walls which were 3mm in height and 1mm in thickness. Teeth were restored with glass fiber posts and cast crowns. All specimens were then subjected to dynamic loading in a masticatory simulator for 1,200,000 loading cycles with a nominal load of 5 kg at 1.2 Hz combined with thermal cycling (5-55 °C, dwell time 30s). Then specimens were quasi-statically loaded at 30 ° in a universal testing machine until fractured. Data were analyzed with 2-way ANOVA, followed by multiple comparisons using Tukey HSD test (α=.05).
  
  
  RESULTS
  Mean (SD) failure loads for groups ranged from 679.5 ± 164.9 N to 1084.5 ± 269.9 N. Two-way ANOVA revealed that both the ferrule height and the number of residual coronal walls had a significant influence on the fracture resistance (P<.001 and P=.006, respectively). Significant increases were produced in the final fracture resistance, when the ferrule height was increased, which was reduced to approximately 37% when teeth with 2mm ferrule height were compared with teeth without a ferrule.
  
  
  CONCLUSIONS
  Under the conditions of this in vitro study, increasing the number of residual coronal walls and ferrule height had a significant effect on the fracture resistance of endodontically treated premolars restored with prefabricated posts.
authors.affiliation: Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Kiel, Germany; Department of Fixed Prosthodontics, School of Dentistry, Ibb University, Ibb, Yemen; Al-Farabi Dental College, Riyadh, Saudi Arabia. Electronic address: asamran@proth.uni-kiel.de.
authors.forename: Abdulaziz
authors.initials: A
authors.lastname: Samran
authors.forename: Shadi
authors.initials: S
authors.lastname: El Bahra
authors.forename: Matthias
authors.initials: M
authors.lastname: Kern
mesh_terms: D001641:Bicuspid; D003442:Crowns; D004708:Endodontics; D066298:In Vitro Techniques; D014082:Tooth Fractures
keywords: Ferrule height; Glass fiber post; Residual coronal wall; Resin cement