title: Marginal and internal discrepancies of zirconia copings: effects of milling system and finish line design.
abstract: BACKGROUND
  Discrepancies at the abutment/crown interface can affect the longevity of zirconia restorations.
  
  
  OBJECTIVE
  The aim was to evaluate the marginal and internal discrepancies (MD and ID) of zirconia copings manufactured by two milling systems with different finish lines.
  
  
  METHODS
  Three aluminum-master-dies (h = 5.5 mm; Ψ =7.5 mm; 6΀), with different finish lines (large chamfer [LC]; tilted chamfer [TC]; rounded shoulder [RS]) were fabricated. Twenty impressions were made from each master die and poured. Sixty zirconia copings were manufactured and divided according to the factors "finish line" and "milling system" (n = 10): CAD LC = Computer-aided design/computer-aided manufacturing (CAD/CAM) + LC; CAD TC = CAD/CAM + TC; CAD RS = CAD/CAM + RS; MAD LC = manually aided design/manually aided manufacturing (MAD/MAM) + LC; MAD TC = MAD/MAM + TC; and MAD RS = MAD/MAM + RS. For MD analysis, each coping was fixed, and the distance between the external edges of the coping and the edge of the cervical preparation was measured (50 points). Using the same copings, the ID of each coping was evaluated, by the replica technique, at 12 points equally distributed among the regions (n = 10): Ray (R), axial (A), and occlusal (Occl). The measurements were performed by optical microscopy (Χ250). The data (μm) were subjected to parametric and non-parametric statistical analyses.
  
  
  RESULTS
  For the MAD/MAM system, the "finish line" (P = 0.0001) affected significantly the MD median values (μm): LC = 251.80 a , RS = 68.40 a and TC = 8.10 b (Dunn's test). For the CAD/CAM system, the median MD values (μm) were not affected by the factor "finish line" (P = 0.4037): LC = 0.82 a , RS = 0.52 a , and TC = 0.89 a . For the ID, it was observed interaction between the finish line types and the region (P = 0.0001) and between region and milling system (P = 0.0031) (RM-ANOVA).
  
  
  CONCLUSIONS
  The CAD/CAM system presented lower MD values, regardless the finish line. However, the MAD/MAM system showed ID values smaller than those of CAD/CAM.
authors.forename: Isabella Lima Arrais
authors.initials: IL
authors.lastname: Ribeiro
authors.forename: Fernanda
authors.initials: F
authors.lastname: Campos
authors.forename: Rafael Santiago
authors.initials: RS
authors.lastname: Sousa
authors.forename: Maria Luiza Lima
authors.initials: ML
authors.lastname: Alves
authors.forename: Dalton Matos
authors.initials: DM
authors.lastname: Rodrigues
authors.affiliation: Department of Dentistry, Federal University of Rio Grande do Norte (UFRN), Natal/RN, Brazil.
authors.forename: Rodrigo Othavio Assuncão
authors.initials: RO
authors.lastname: Souza
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design; D016628:Replica Techniques; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015040:Zirconium; C028541:zirconium oxide