title: Retention of zirconium oxide ceramic crowns with three types of cement.
abstract: BACKGROUND
  Information about the retentive strength of luting agents for zirconium oxide-based crowns is limited. It is unknown if this type of high-strength ceramic restoration requires adhesive cementation to enhance retention.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to determine the ability of selected luting agents to retain a representative zirconium oxide ceramic crown under clinically simulated conditions.
  
  
  METHODS
  Recently extracted human molars were prepared with a flat occlusal surface, 20-degree taper, and approximately 4-mm axial length. The axial and occlusal surface areas were determined, and specimens were distributed equally by total surface area into 3 cementation groups (n=12). Zirconium oxide ceramic copings (Procera AllZirkon) with an occlusal bar to facilitate removal were fabricated using computer-aided design/computer-assisted manufacturing (CAD/CAM) technology. All copings were airborne-particle abraded with 50-mum Al(2)O(3) and then cleaned in an ultrasonic bath with isopropyl alcohol. Provisional cement was removed from the prepared teeth, followed by a pumice prophy. After trial insertion, the copings were cleaned with phosphoric acid, rinsed, dried, and dehydrated with isopropyl alcohol. They were then cemented with a seating force of 10 kg per tooth, using either a composite resin cement with adhesive agent (Panavia F 2.0 and ED Primer A & B [PAN]), a resin-modified glass ionomer cement (Rely X Luting [RXL]), or a self-adhesive modified composite resin (Rely X Unicem [RXU]). The cemented copings were thermal cycled at 5 degrees C and 55 degrees C for 5000 cycles with a 15 second dwell time, and then removed along the path of insertion using a universal testing machine at 0.5 mm/min. The removal force was recorded, and the stress of dislodgement was calculated using the surface area of each preparation. A 1-way analysis of variance was used to analyze the data (alpha=.05). The nature of failure was also recorded.
  
  
  RESULTS
  Mean dislodgement stresses were 5.1, 6.1, and 5.0 MPa for PAN, RXL, and RXU, respectively. The 1-way analysis of variance revealed no differences in mean crown removal stress among the 3 cementation groups. The predominant mode of failure was cement remaining principally on the zirconium oxide copings in 46% of the specimens, followed by cement found on the tooth in 25.7% of the specimens.
  
  
  CONCLUSIONS
  Within the limitations of this study, the 3 luting agents, with mean removal stresses ranging from 5.0 to 6.1 MPa were not significantly different. The use of a composite resin cement with a bonding agent did not yield higher coping retention compared to the other 2 cements tested.
authors.affiliation: Department of Restorative Dentistry, University of Washington, Seattle 98195-7456, USA. rpp4@u.washington.edu
authors.forename: Rosario P
authors.initials: RP
authors.lastname: Palacios
authors.forename: Glen H
authors.initials: GH
authors.lastname: Johnson
authors.forename: Keith M
authors.initials: KM
authors.lastname: Phillips
authors.forename: Ariel J
authors.initials: AJ
authors.lastname: Raigrodski
mesh_terms: D000268:Adhesiveness; D020906:Air Abrasion, Dental; D000537:Aluminum Oxide / Q000737:chemistry; D002484:Cementation / Q000379:methods; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D003764:Dental Materials; C500742:ED Primer II; D005899:Glass Ionomer Cements; D008689:Methacrylates; C438843:Panavia-Fluoro; C483701:Rely X Unicem; D019279:Resin Cements; C084550:Vitremer; D003776:Dental Porcelain; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide