title: An in vitro study to investigate the load at fracture of Procera AllCeram crowns with various thickness of occlusal veneer porcelain.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of occlusal veneer porcelain thickness on the load at fracture of Procera AllCeram crowns.
  
  
  METHODS
  Fifty resin dies were manufactured to incorporate the features of an all-ceramic crown preparation on a premolar tooth. Fifty corresponding crowns were constructed and divided into five groups. Groups 1, 2, 3, and 4 were crowns with 0.6-mm-thick Procera cores and 0.4-mm-thick axial veneer porcelain and occlusal veneer porcelain thicknesses of 0.0 mm, 0.4 mm, 0.9 mm, and 1.4 mm, respectively. Group 5 specimens consisted of 0.6-mm-thick In-Ceram cores with 0.4 mm of axial porcelain and 0.4 mm of occlusal porcelain. The crowns were cemented onto their respective dies with a resin luting agent. Specimens were stored in distilled water at 37 degrees C for 24 hours prior to placing them in a universal testing machine and applying a controlled compressive load at a cross-head speed of 0.1 mm/min until fracture occurred.
  
  
  RESULTS
  The mean loads at fracture were 419 N (group 1), 702 N (group 2), 1,142 N (group 3), 1,297 N (group 4), and 732 N (group 5). Statistical analysis revealed significant differences (P < .05) in the load at fracture between the groups, except for between groups 2 and 5.
  
  
  CONCLUSIONS
  Increasing the thickness of the occlusal veneer porcelain increased the load at fracture for Procera AllCeram crowns. There was no significant difference in load at fracture between the Procera and In-Ceram crowns.
authors.affiliation: Department of Conservative Dentistry, Eastman Dental Institute, University College London, United Kingdom.
authors.forename: Zoe
authors.initials: Z
authors.lastname: Harrington
authors.forename: Ailbhe
authors.initials: A
authors.lastname: McDonald
authors.forename: Jonathan
authors.initials: J
authors.lastname: Knowles
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D000704:Analysis of Variance; D002484:Cementation; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003801:Dental Veneers; D006801:Humans; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D016474:Weight-Bearing
chemical_list: C105314:AllCeram; D019279:Resin Cements; D012821:Silanes; D003776:Dental Porcelain; C070870:In-Ceram; D000537:Aluminum Oxide