title: Influence of coping design on the cervical color of ceramic crowns.
abstract: BACKGROUND
  The replication of natural teeth, especially with single-tooth restorations, represents a challenge. Similar to metal ceramic crowns, different designs of zirconia substructures have been suggested to improve the esthetic results of zirconia ceramic crowns.
  
  
  OBJECTIVE
  The purpose of the study was to analyze the color of the cervical portion of single zirconia ceramic crowns fabricated with different zirconia coping designs.
  
  
  METHODS
  The color, measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with zirconia coping (Lava) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a spectrophotometer. Conventional zirconia crowns with zirconia facial margins were compared with ceramic crowns with porcelain facial margins and either a horizontal reduction of the zirconia coping (1.0 mm reduction) or an additional vertical reduction (1.0 mm additional reduction). The 3 groups, each with a different coping extension, were examined with a 1-way ANOVA and the Fisher exact test, and the differences of the groups were evaluated by applying ΔE thresholds (α=.05).
  
  
  RESULTS
  The mean color difference among all the groups was not clinically significant (ΔE<3.7). Reduced color differences were present between the 2 porcelain butt margin groups of crowns (ΔE=1.06, between group H and V). Increased differences were present between the zirconia margin group and the porcelain butt margin group (ΔE=2.54 between group C and H; ΔE=2.41 between group C and V). Lab* values were examined in all the groups of crowns to determine the clinical implications.
  
  
  CONCLUSIONS
  Within the limitation of the study, no significant differences were present among the tested groups of crowns. Nevertheless, although some differences were present between the zirconia margin group and the porcelain butt margin group, reduced differences were present between the 2 different cutback designs.
authors.affiliation: Adjunct Assistant Professor, Graduate and Postgraduate Prosthodontics, Department of Prosthodontics and Operative Dentistry, Tufts University, Boston, Mass; and Visiting Professor, Department of Prosthodontics, University of Padova, Dental School, Padova, Italy. Electronic address: panizg@hotmail.com.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Paniz
authors.forename: Ki-Ho
authors.initials: KH
authors.lastname: Kang
authors.forename: Yongjeong
authors.initials: Y
authors.lastname: Kim
authors.forename: Naota
authors.initials: N
authors.lastname: Kumagai
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hirayama
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D003116:Color; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D004955:Esthetics, Dental; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D008422:Materials Testing; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods; D013499:Surface Properties; D019237:Tooth Cervix / Q000033:anatomy & histology; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; D017680:Potassium Compounds; D019279:Resin Cements; D003776:Dental Porcelain; C016447:feldspar; C103502:Variolink; D015040:Zirconium; C028541:zirconium oxide