title: Wear of double crown systems: electroplated vs. casted female part.
abstract: OBJECTIVE
  The wear of telescopic crowns is a common problem often reducing the patient's satisfaction with the denture and resulting in a renewal of the denture. The study aims to compare the wear behavior of conical crowns using electroplated copings (group E ) with standard telescopic crowns with cast female parts (group C).
  
  
  METHODS
  10 conical crowns were milled for each group of a cast gold alloy. The specimen of group E had a conicity of 2º. The cast secondary crowns of group C had a 0º design. The electroplated coping was established by direct electroforming. An apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in 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 0.33 mm of each cycle were calculated.
  
  
  RESULTS
  The retentive forces were significantly higher for group E and the integrals were significantly lower for this group except the integral at cycle 10,000. The changes of retention force and integral did not differ significantly between both groups in all phases. The change of the integrals as well as the integral at the particular cycles showed higher interquartile distances for group C.
  
  
  CONCLUSIONS
  Within the limitations of this study the tested conical crowns showed clinically acceptable retentive properties. The values reached a range comparable to retentive elements tested in recent literature. The values of group C showed higher ranges. The force measured for group E was significantly higher than for group C but the integrals showed an opposite tendency. The results indicate that an exclusive analysis of the force is not sufficient as the integral is not equivalent to the force although it describes the retentive property of the system in a better way than the force over a distance is described. Both systems seem to be suitable for clinical practice.
authors.affiliation: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of 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; D003735:Dental Casting Technique; D017267:Dental Prosthesis Design / Q000379:methods*; D019554:Dental Restoration Wear; D003781:Denture Retention / Q000379:methods; D004595:Electroplating; D006801:Humans; D008422:Materials Testing; D018709:Statistics, Nonparametric; D013499:Surface Properties; D013997:Time Factors