title: Wear behavior of different double-crown systems.
abstract: OBJECTIVE
  The aim of this study was to evaluate aging effects on the retentive forces (RFs) of different double-crown systems. The effects of abutment height, inner- and outer-crown-material, taper angle, and artificial aging were analyzed.
  
  
  METHODS
  Inner (IC) and outer crowns (OC) (240), divided into four groups, 60 specimens each, were manufactured: A: IC = zirconia, OC = electroformed; B: IC = non-precious alloy, OC = electroformed; C: IC = precious alloy, OC = electroformed; D: IC = precious alloy, OC = conventionally cast (control group). Ten specimens each with three different abutment heights and two different tapers were used. Ten thousand separation cycles were performed for each specimen, and the RFs were measured at baseline, 5,000, and 10,000 cycles in the presence of artificial saliva. Data were imported into a statistical software (SPSS, V18) and analyzed by a multivariate ANOVA test. Significance level was set at 5 %.
  
  
  RESULTS
  Group D showed highest RFs (baseline: 4.0 N; 5,000 cycles: 3.9 N; 10,000 cycles: 3.9 N) compared to A, B, and C (baseline: 2.6/3.5/2.6 N; 5,000 cycles: 2.5/3.4/2.5 N, 10,000: 2.5/3.3/2.5 N). RF was dependent on material (p < 0.001). The RF of groups A, B, and C were dependent on abutment height (p < 0.001), taper angle (p < 0.001), and artificial aging (p < 0.001). Group D showed no correlation between retentive force and abutment height (p = 0.550).
  
  
  CONCLUSIONS
  Wear caused loss of RF in all evaluated groups. However, the material used exhibited significant influence. Conventionally, cast DCs can provide higher RFs, and electroformed DCs can provide more predictable results.
  
  
  CONCLUSIONS
  In clinical cases with few and short abutment teeth, conventionally cast DCs can rather provide the necessary RF than electroformed DCs.
authors.affiliation: Department of Prosthodontics, Ludwig-Maximilians University, Goethestr. 70, 80336 Munich, Germany. Joerg.engels@med.uni-muenchen.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Engels
authors.forename: Oliver
authors.initials: O
authors.lastname: Schubert
authors.forename: Jan-Frederik
authors.initials: JF
authors.lastname: Güth
authors.forename: Matthias
authors.initials: M
authors.lastname: Hoffmann
authors.forename: Christian
authors.initials: C
authors.lastname: Jauernig
authors.forename: Kurt
authors.initials: K
authors.lastname: Erdelt
authors.forename: Michael
authors.initials: M
authors.lastname: Stimmelmayr
authors.forename: Florian
authors.initials: F
authors.lastname: Beuer
mesh_terms: D001732:Bite Force; D002484:Cementation / Q000379:methods; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D003735:Dental Casting Technique; D003760:Dental Impression Materials / Q000737:chemistry; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D019554:Dental Restoration Wear; D055664:Electrochemical Techniques; D005899:Glass Ionomer Cements / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008277:Magnesium Oxide / Q000737:chemistry; D008768:Methylmethacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D003765:Models, Dental; D008963:Molar; D011076:Polycarboxylate Cement / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D015034:Zinc Oxide / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; D003760:Dental Impression Materials; D003764:Dental Materials; C082318:GC Pattern Resin; D005899:Glass Ionomer Cements; D006047:Gold Alloys; C022821:Impregum; D008768:Methylmethacrylates; D011076:Polycarboxylate Cement; D012117:Resins, Synthetic; D012464:Saliva, Artificial; D008277:Magnesium Oxide; C040235:Ketac-cem; D015040:Zirconium; C028541:zirconium oxide; D015034:Zinc Oxide