title: Effect of incomplete crown ferrules on load capacity of endodontically treated maxillary incisors restored with fiber posts, composite build-ups, and all-ceramic crowns: an in vitro evaluation after chewing simulation.
abstract: OBJECTIVE
  The aim of this study was to compare the fracture resistance of endodontically treated maxillary central incisors with incomplete crown ferrules after chewing simulation.
  
  
  METHODS
  Forty caries-free maxillary central incisors were divided into 4 groups (n = 10). Endodontic treatment was performed. Teeth were decoronated 2 mm above the cemento-enamel junction (CEJ). Group I (control) provided a 360 degrees circumferential 2-mm ferrule. In group II, a 2-mm ferrule was present on the palatal aspect (status after occlusal overload), and in group III on the facial aspect (status after traumatic injury). In group IV, the ferrule was interrupted by bi-proximal cavitations (simulating caries treatment). The teeth received glass fiber reinforced posts and composite core restorations. All-ceramic crowns were adhesively cemented. Specimens were simultaneously exposed to thermal cycling and mechanical loading (1.2 million cycles; 6,000 cycles 5 degrees/55 degrees C) and finally statically loaded until failure in a universal testing machine (crosshead speed = 1 mm/min). For statistical analysis, the Kruskal-Wallis test was applied followed by the Mann-Whitney U-test as post hoc testing.
  
  
  RESULTS
  The median fracture load values (min./max.) were: group I = 502 (326/561), group II = 658 (280/827), group III = 899 (396/1176), and group IV = 360 (279/646). Analysis revealed statistically significant differences between test groups, except between groups I and IV and groups II and IV.
  
  
  CONCLUSIONS
  The fracture resistance of endodontically and post/core restored teeth is dependent on the degree of tooth conservation. An incomplete crown ferrule is associated with greater variation in load capacity and, despite high fracture values, inclines to fracture.
authors.affiliation: Department of Prosthodontics and Geriatric Dentistry, Charité, Humboldt University, Berlin, Germany. michael.naumann@charite.de
authors.forename: Michael
authors.initials: M
authors.lastname: Naumann
authors.forename: Anja
authors.initials: A
authors.lastname: Preuss
authors.forename: Martin
authors.initials: M
authors.lastname: Rosentritt
mesh_terms: D003188:Composite Resins; D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design / Q000295:instrumentation*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D005898:Glass; D006801:Humans; D007180:Incisor; D008409:Mastication; D008437:Maxilla; D011176:Post and Core Technique; D018709:Statistics, Nonparametric
chemical_list: D003188:Composite Resins; C009753:fiberglass; D003776:Dental Porcelain