title: [An in vitro study of the fracture strength of tooth preparations for Empress 2 veneers and crowns and mandibular incisors restored with Empress 2 veneers and crowns].
abstract: OBJECTIVE
  To compare the fracture resistance of mandibular incisors' preparations for veneers and crowns, mandibular incisors restored with Empress 2 veneers and crowns.
  
  
  METHODS
  50 human mandibular incisors were randomly divided into five groups. Each group consisted of ten teeth and the treatment obtained as follows: A, tooth preparations for veneers; B, tooth preparations for crowns; C, teeth restored with veneers; D, teeth restored with crowns; E, untreated group. The teeth received standardized preparation and the restorations were manufactured with Empress 2 system and cemented with resin luting agent. The fracture resistances of teeth were measured by Instron universal testing machine and statistically analyzed with one-way ANOVA.
  
  
  RESULTS
  The fracture resistances of A, B, C, D, E were (576.11 +/- 91.53), (204.13 +/- 85.88), (451.50 +/- 116.81), (386.16 +/- 117.75) and (566.05 +/- 121.37) N, respectively. The statistical analysis demonstrated significant differences between five groups. There were no significant differences between group A and E, group C and D.
  
  
  CONCLUSIONS
  Tooth preparations for veneers did not significantly reduce the fracture resistance of mandibular incisor. The fracture resistance of teeth restored with Empress 2 veneers and crowns did not significantly differ from each other.
authors.affiliation: Dept. of Prosthodontics, Stomatology Hospital Affiliated to Medical School of Nanjing University, Nanjing 210008, China.
authors.forename: Xue
authors.initials: X
authors.lastname: Wei
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
mesh_terms: D003442:Crowns; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D007180:Incisor; D018020:Lithium Compounds; D008334:Mandible; D019279:Resin Cements; D019246:Tooth Preparation
chemical_list: C118557:Empress 2; D018020:Lithium Compounds; D019279:Resin Cements; D003776:Dental Porcelain