title: Resistance to fracture of mandibular premolars restored using post-and-core systems.
abstract: OBJECTIVE
  To assess the influence of post-and-core systems on the resistance to fracture of mandibular premolars restored with metal crowns and a 2.0-mm cervical ferrule.
  
  
  METHODS
  Forty extracted premolars were selected and divided into 4 groups of 10 teeth each. Samples were sectioned 2.0 mm coronal to the CEJ. Following canal preparation, four restorative treatments were performed: group 1, post and core cast in type IV gold alloy; group 2, prefabricated titanium post with composite resin core; group 3, prefabricated quartz-fiber post combined with composite resin core; and group 4, composite resin core without post. Posts (groups 1, 2, and 3) were cemented with resin cement. Metal crowns were fabricated using nickel-chromium alloy. Specimens were placed in acrylic resin blocks and filled up to 2.0 mm apical to the CEJ. Fracture resistance was assessed by applying a continuous compressive force on the buccal cusp of the crowns at a 45-degree angle until fracture. Results were analyzed using ANOVA and Tukey multiple comparison test at a significance level of 5%.
  
  
  RESULTS
  Mean loads at fracture were as follows: group 1 = 1,189.23 N, group 2 = 1,816.43 N, group 3 = 1,224.51 N, and group 4 = 2,010.63 N. Groups 2 and 4 presented statistically similar results; the same was observed in groups 1 and 3. However, groups 2 and 4 presented significantly better results than groups 1 and 3.
  
  
  CONCLUSIONS
  Restoration of mandibular premolars with composite resin core (without post) showed an increased resistance to fracture when compared with other post-and-core systems whenever a minimum of 2.0 mm of remaining tooth structure was covered with a full metal crown (ferrule effect). Preservation of tooth structure was the most important factor in tooth resistance.
authors.affiliation: massafernando@terra.com.br
authors.forename: Fernando
authors.initials: F
authors.lastname: Massa
authors.forename: Caroline
authors.initials: C
authors.lastname: Dias
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Blos
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid / Q000293:injuries; D002858:Chromium Alloys; D003188:Composite Resins; D019245:Compressive Strength; D003799:Dental Stress Analysis; D006047:Gold Alloys; D006801:Humans; D008334:Mandible; D011176:Post and Core Technique; D011791:Quartz; D018709:Statistics, Nonparametric; D014025:Titanium; D014082:Tooth Fractures / Q000517:prevention & control*; D019246:Tooth Preparation; D019553:Tooth, Nonvital
chemical_list: D002858:Chromium Alloys; D003188:Composite Resins; D006047:Gold Alloys; D011791:Quartz; D014025:Titanium