title: Influence of internal-gap width and cement type on the retentive force of zirconia copings in pullout testing.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the influence of internal-gap width and cement type on the retentive force of zirconia copings.
  
  
  METHODS
  A CAD/CAM system was used to mill 48 identical abutments on extracted human molars and fabricate 48 zirconia copings. The internal-gap width for cement was set to 40 μm or 160 μm (n=24 each). Three cement types (Panavia F, RelyX Unicem, and RelyX Luting) were used with each internal-gap width (n=8/cement type). The intaglio surfaces of the copings were airborne-particle abraded, and each coping was cemented onto the corresponding abutment using the indicated luting agent. After 10,000 cycles of thermocycling, the retentive force was evaluated by pullout tests. Kruskal-Wallis and Wilcoxon Rank Sum tests were used for data analysis (α=0.05).
  
  
  RESULTS
  In the 40-μm gap groups, Panavia F had the highest mean retentive force compared to RelyX Unicem and RelyX Luting (P<0.000). In 160-μm gap groups, RelyX Unicem had the highest mean retentive force compared to Panavia F and RelyX Luting (P<0.000).
  
  
  CONCLUSIONS
  With the increase in internal gap width, a resin cement with self-etching agents as a co-initiator for autopolymerization resulted in significantly decreased retentive force, whereas a resin-modified glass ionomer cement or a self-adhesive resin cement did not. Use of resin cements rather than resin-modified glass ionomer cements improved the retentive force of zirconia copings regardless of the amount of internal gap width.
authors: Department of Prosthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, South Korea.
authors: Yong-Ha
authors: YH
authors: Son
authors: Chong-Hyun
authors: CH
authors: Han
authors: Sunjai
authors: S
authors: Kim
mesh_terms: D002484:Cementation / Q000379:methods; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D003738:Dental Cements / Q000737:chemistry*; D045662:Dental Etching / Q000379:methods; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D003799:Dental Stress Analysis / Q000295:instrumentation; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D019246:Tooth Preparation / Q000379:methods; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D003764:Dental Materials; D005899:Glass Ionomer Cements; C438843:Panavia-Fluoro; C483701:Rely X Unicem; D019279:Resin Cements; C084550:Vitremer; D015040:Zirconium; C028541:zirconium oxide