title: Fracture strength after dynamic loading of endodontically treated teeth restored with different post-and-core systems.
abstract: BACKGROUND
  Prefabricated metal and ceramic posts can be used with direct or indirect cores as an alternative to the conventional cast post and core. It is unclear how the fracture strength of zirconia posts with composite or ceramic cores and titanium posts with composite cores compares to the fracture strength of gold posts and cores after dynamic loading.
  
  
  OBJECTIVE
  This study compared the fracture strength of endodontically treated, crowned maxillary incisors with limited ferrule length and different post-and-core systems after fatigue loading.
  
  
  METHODS
  Sixty-four caries-free, human maxillary central incisors were divided into 4 groups. After root canal treatment, Group 1 was restored with titanium posts and composite cores, Group 2 with zirconia posts and composite cores, and Group 3 with zirconia posts and heat-pressed ceramic cores. Teeth restored with cast-on gold posts and cores served as the controls (Group 4). Teeth were prepared with a circumferential shoulder including a 1 to 2 mm ferrule; all posts were cemented with an adhesive resin cement, restored with complete-coverage crowns, and exposed to 1.2 million load cycles (30 N) in a computer-controlled chewing simulator. Simultaneous thermocycling between 5 degrees C and 55 degrees C was applied for 60 seconds with an intermediate pause of 12 seconds. All specimens that did not fracture during dynamic loading were loaded until fracture in a universal testing machine at a crosshead speed of 1.5 mm/min; loads were applied at an angle of 130 degrees at the incisal edge. Fracture loads (N) and modes (repairable or catastrophic) were recorded. The Kruskal-Wallis test was used to compare fracture loads among the 4 test groups. Analyses were conducted both with and without the specimens that failed during the chewing simulation. A Fisher exact test was performed to detect group differences in fracture modes. A significance level of P<.05 was used for all comparisons.
  
  
  RESULTS
  The following survival rates were recorded after the chewing simulation: 93.8% (Group 1), 93.8% (Group 2), 100% (Group 3), and 87.5% (Group 4). The median fracture strengths for Groups 1 to 4 were 450 N, 503 N, 521 N, and 408 N, respectively. No significant differences were detected among the groups. The use of zirconia posts resulted in a nonsignificant lower number of catastrophic root fractures.
  
  
  CONCLUSIONS
  Within the limitations of this study, the results suggest that zirconia posts with ceramic cores can be recommended as an alternative to cast posts and cores. If a chairside procedure is preferred, zirconia or titanium posts with composite cores can be used. Clinical trials are required to verify these in vitro results.
authors.affiliation: Department of Biological and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, USA. heydecke@umich.edu
authors.forename: Guido
authors.initials: G
authors.lastname: Heydecke
authors.forename: Frank
authors.initials: F
authors.lastname: Butz
authors.forename: Amr
authors.initials: A
authors.lastname: Hussein
authors.forename: Jörg R
authors.initials: JR
authors.lastname: Strub
mesh_terms: D002516:Ceramics; D003188:Composite Resins; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006047:Gold Alloys; D006801:Humans; D007180:Incisor; D008409:Mastication; D008422:Materials Testing; D011176:Post and Core Technique; D011897:Random Allocation; D018709:Statistics, Nonparametric; D014025:Titanium; D014082:Tooth Fractures / Q000517:prevention & control*; D019553:Tooth, Nonvital / Q000503:physiopathology*; D015040:Zirconium
chemical_list: D003188:Composite Resins; D006047:Gold Alloys; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide