title: Comparison of the marginal adaptation of zirconium dioxide crowns in preparations with two different finish lines.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the marginal adaptation of zirconium dioxide crowns in preparations with two different finish line configurations before and after porcelain firing cycles, after a glaze cycle, and after cementation.
  
  
  METHODS
  Twenty human molar teeth were prepared to receive full crowns; ten were prepared with a 90° round shoulder and another ten with a 45° chamfer finish line. Zirconium dioxide copings were fabricated using CAD/CAM technology (Lava™ system). They were then veneered with a low-fusing glass-ceramic (IPS e.max® Ceram). Finally, they were glazed and cemented with a resin-composite cement (RelyX™ Unicem, Aplicap™). Measurements for marginal adaptation using stereomicroscopy (40×) were performed at four stages: copings (S1), after porcelain firing cycles (S2), after glazing (S3), and after cementation (S4). One-way ANOVA was used to assess the influence of the finish line design on the marginal adaptation in each stage. Two-way ANOVA with repeated measurements was performed to assess the influence on the marginal adaptation of the porcelain firing cycles, glaze firing cycle, and cementation.
  
  
  RESULTS
  The measured marginal gap mean values for the shoulder group (μm) were: 50.13 (S1), 54.32 (S2), 55.12 (S3), and 59.83 (S4). The values for the chamfer group were: 63.56 (S1), 71.85 (S2), 74.12 (S3), and 76.97 (S4). When comparing marginal gaps between specimens with two different finish lines, differences were noticed at the four studied stages (p = 0.0165, p = 0.0027, p = 0.0009, and p = 0.0009, respectively). No differences were manifested in the marginal gap measurements of the shoulder group at the different stages of fabrication (p = 0.4335); however, in the chamfer group, differences were noticed between S1 and S3 (p = 0.0042).
  
  
  CONCLUSIONS
  Marginal adaptation was influenced by the finish line design. The firing cycles significantly affected the chamfer group; nevertheless, the marginal gap was within the range of clinical acceptability.
authors.affiliation: Department of Prosthodontics, University of Catalunya, Barcelona, Spain. r_euan@hotmail.com
authors.forename: Raúl
authors.initials: R
authors.lastname: Euán
authors.forename: Oscar
authors.initials: O
authors.lastname: Figueras-Álvarez
authors.forename: Josep
authors.initials: J
authors.lastname: Cabratosa-Termes
authors.forename: Magí
authors.initials: M
authors.lastname: Brufau-de Barberà
authors.forename: Susana
authors.initials: S
authors.lastname: Gomes-Azevedo
mesh_terms: D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing / Q000295:instrumentation / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D003801:Dental Veneers; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008963:Molar; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000145:classification / Q000379:methods; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C483701:Rely X Unicem; D019279:Resin Cements; D003776:Dental Porcelain; C023506:Glass ceramics; D015040:Zirconium; C028541:zirconium oxide