title: Changes in retention force with electroplated copings on conical crowns: a comparison of gold and zirconia primary crowns.
abstract: OBJECTIVE
  The aim of this study was to examine the wear behavior of conical crowns with electroplated gold copings that are used to connect implants and teeth to a removable denture. Gold alloy and zirconium dioxide ceramic crowns were compared.
  
  
  METHODS
  Fifteen crowns each were milled for two groups: gold alloy and zirconium dioxide. Each specimen had a 2-degree taper. The electroplated coping was established by direct electroforming. The retentive forces and the correlating distance during insertion and separation were measured after 10,000 wear cycles were applied. The wear testing was separated into a start phase, an initial wear phase, and the long-term wear period. The retention force value and the force-distance integral of the first 0.3 mm of each cycle were calculated.
  
  
  RESULTS
  The changes in retention force and integral did not differ significantly between both groups in the start and the initial wear phase. No differences were seen in force development during the long-term wear period. Only the force-distance integral showed a significant difference: the median values of the gold crowns increased slightly, and they decreased slightly for the zirconia crowns. The median force values never fell below 6 N for gold and 4 N for zirconia.
  
  
  CONCLUSIONS
  Within the limitations of this study, the tested conical crowns showed clinically acceptable retentive properties. As with other retentive elements for dentures, the specimens tested showed the greatest amount of change in retentive forces during the first 2,000 cycles. The development of retention force in both groups was not significantly different. However, the zirconia specimens showed reduced variability, which is preferable in clinical practice.
authors.affiliation: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany. sbayer@uni-bonn.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Bayer
authors.forename: Dominik
authors.initials: D
authors.lastname: Kraus
authors.forename: Ludger
authors.initials: L
authors.lastname: Keilig
authors.forename: Lina
authors.initials: L
authors.lastname: Gölz
authors.forename: Helmut
authors.initials: H
authors.lastname: Stark
authors.forename: Norbert
authors.initials: N
authors.lastname: Enkling
mesh_terms: D003442:Crowns; D003776:Dental Porcelain; D017268:Dental Prosthesis Retention; D003799:Dental Stress Analysis; D004595:Electroplating; D006047:Gold Alloys; D015040:Zirconium
chemical_list: D006047:Gold Alloys; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide