title: Effect of crown lengthening and ferrule placement on static load failure of cemented cast post-cores and crowns.
abstract: BACKGROUND
  Restoration of mandibular second premolars with completely missing clinical crowns in the Kennedy Class I and II arches is costly and the risk of failure is high. Should the dentist choose crown-lengthening to allow the addition of a ferrule, despite incurring the disadvantage of an increased crown/root ratio?
  
  
  OBJECTIVE
  This in vitro study determined the combined effect of crown lengthening and placement of a ferrule on the failure resistance to static load of decoronated and restored mandibular second premolar analog teeth.
  
  
  METHODS
  An extracted mandibular second premolar of average dimensions was selected to form molded composite root analogs and metal crowns. Ten specimens prepared with no-ferrule root and negligible axial wall lengths and 10 specimens with ferrule root, apically repositioned finish lines, were made. Cast gold alloy post and cores and complete crowns were made and cemented. Each root was placed in bone-simulating resin located 3 mm from the finish line. Crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were equally subdivided, whereby 5 crowns were compressively loaded on the buccal cusp tip and 5 were compressively loaded on the mesial marginal ridge. A testing machine applied force until failure occurred. Failure loads were examined with 2-way ANOVA. Significant differences were accepted at P </=.05.
  
  
  RESULTS
  Mean failure loads for the crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were as follows: buccal load, 0.61 kN (SD +/- 0.11) and 0.83 kN (SD +/- 0.08); mesial load, 0.70 kN (SD +/- 0.08) and 1.00 kN (SD +/- 0.15), respectively. Crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were significantly different (P <.001).
  
  
  CONCLUSIONS
  The combination of simulated surgical crown-lengthening and more apical crown margin placement to provide a 2-mm crown ferrule on a decoronated mandibular second premolar analog resulted in a reduction of static load failure for the restored analog tooth.
authors.affiliation: The Ohio State University College of Dentistry, Columbus, Ohio 43210, USA. gegauff.1@osu.edu
authors.forename: A G
authors.initials: AG
authors.lastname: Gegauff
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid; D001732:Bite Force; D002484:Cementation; D003188:Composite Resins; D019245:Compressive Strength; D016556:Crown Lengthening / Q000295:instrumentation*; D003442:Crowns; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D008334:Mandible; D011176:Post and Core Technique / Q000295:instrumentation*; D014082:Tooth Fractures / Q000517:prevention & control; D019231:Tooth Preparation, Prosthodontic / Q000295:instrumentation*
chemical_list: D003188:Composite Resins