title: The influence of different convergence angles and resin cements on the retention of zirconia copings.
abstract: OBJECTIVE
  This in vitro study aimed to determine the ability of three resin cements to retain zirconia copings under two clinically simulated conditions.
  
  
  METHODS
  Extracted human molars (72) were collected, cleaned, and divided into two groups. All teeth were prepared with a 15° total convergence angle for group 1 and a 30° total convergence angle for group 2, a flat occlusal surface, and approximately 4-mm axial length. Each group was divided by surface area into three subgroups (n = 12). All zirconia copings were abraded with 50-μm Al(2)O(3), then cemented using Panavia F 2.0 (PAN-1) (PAN-2) Rely X Unicem (RXU-1) (RXU-2), and Clearfil SA (CSA-1) (CSA-2). After cementation, the copings were thermocycled for 5000 cycles between 5°C and 55°C with a 15-second dwell time. Then the copings were subjected to dislodgment force in a universal testing machine at 0.5 mm/min. The force of removal was recorded, and the dislodgement stress was calculated. A Kruskal-Wallis test (nonparametric ANOVA) was used to analyze the data (α= 0.05), and the nature of failure was also recorded.
  
  
  RESULTS
  The mean (SD) coping removal stresses (MPa) were as follows: PAN-1: 6.0 (1.3), CSA-1: 4.8 (1.4), RXU-1: 5.5 (2.3), PAN-2: 2.8 (1.1), CSA-2: 3.0 (1.25), and RXU-2: 2.6 (1.2). The Kruskal-Wallis test was significant. Mann-Whitney pairwise comparisons of the subgroups were significant (p < 0.05) for the comparisons between subgroups of group 1 and group 2. Mode of failure was mixed, with cement remaining principally on the tooth for PAN. For CSA and RXU, mode of failure was mixed with cement remaining principally on the zirconia copings.
  
  
  CONCLUSIONS
  Retention values of zirconia copings with three different resin cements were not significantly different. Retention of zirconia copings cemented on the teeth with adequate resistance and retention form was higher than that cemented on teeth lacking these forms. The cement remained mostly on the tooth with the adhesive resin cement with a dentin bonding system. The cement remained mostly on the coping with the self-adhesive resin cement.
authors: Department of Prosthodontics and Operative Dentistry, Tufts University School of Dental Medicine, Boston, MA, USA. Ala.Ali@tufts.edu
authors: Ala O
authors: AO
authors: Ali
authors: J Robert
authors: JR
authors: Kelly
authors: Roya
authors: R
authors: Zandparsa
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002484:Cementation / Q000379:methods; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D045662:Dental Etching / Q000379:methods; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D015040:Zirconium / Q000737:chemistry*
chemical_list: C581302:Clearfil SA; D003764:Dental Materials; C438843:Panavia-Fluoro; C483701:Rely X Unicem; D019279:Resin Cements; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide