title: Comparison of incidence of complications and aesthetic performance for posterior metal-free polymer crowns and metal-ceramic crowns: results from a randomized clinical trial.
abstract: OBJECTIVE
  The purpose of this randomized clinical study was to evaluate the clinical performance of posterior, metal-free polymer crowns after follow-up for up to six years, and to compare it with the performance of metal-ceramic crowns.
  
  
  METHODS
  Eighty single crowns, manufactured from a polymer composite resin, were set on posterior teeth. Half of these received a glass-fibre framework (group 1) whereas half were prepared without framework stabilization (group 2). As the control group, 40 conventional metal-ceramic crowns were inserted. Primary endpoints were incidence of complications, investigated on a time-to-event basis, plaque status, and aesthetic performance.
  
  
  RESULTS
  Thirty clinically relevant complications occurred after a median time of 2.3 years. Median follow-up time was four years. The most frequent complications were delamination (n=24) and root-canal treatment (n=4) of the crowns; the incidence of complications was not significantly different among crown materials (p=0.60). Twenty crowns had to be replaced (six polymer crowns in group 1, nine polymer crowns in group 2, four crowns in the control group, and one tooth (in group 1) had to be extracted). Mean plaque and gingival indexes for the test groups did not differ from those for the control group.
  
  
  CONCLUSIONS
  Within a median follow-up period of four years, the clinical performance of posterior polymer crowns with and without a glass-fibre framework was not significantly different from that of metal-ceramic crowns, although the number of catastrophic failures of composite crowns was higher than that of the metal-ceramic crowns.
  
  
  CONCLUSIONS
  On the basis of the study results, posterior polymer crowns may be an alternative to metal-ceramic crowns, although additional research is needed before they can be recommended, without reservation, as permanent restorations.
authors.affiliation: Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany. Electronic address: Brigitte_Ohlmann@med.uni-heidelberg.de.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Ohlmann
authors.affiliation: Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany.
authors.forename: Justo Lorenzo
authors.initials: JL
authors.lastname: Bermejo
authors.affiliation: Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Rammelsberg
authors.affiliation: Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Schmitter
authors.affiliation: Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Zenthöfer
authors.affiliation: Department of Prosthodontics, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stober
mesh_terms: D000328:Adult; D000368:Aged; D001031:Apatites / Q000737:chemistry; D002484:Cementation / Q000379:methods; D003188:Composite Resins / Q000737:chemistry*; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry*; D003774:Dental Plaque Index; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D019554:Dental Restoration Wear; D004955:Esthetics, Dental; D005260:Female; D005500:Follow-Up Studies; D005898:Glass / Q000737:chemistry; D006801:Humans; D008297:Male; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008875:Middle Aged; D010512:Periodontal Index; D019279:Resin Cements / Q000737:chemistry; D012390:Root Canal Therapy; D055815:Young Adult
chemical_list: D001031:Apatites; D003188:Composite Resins; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D019279:Resin Cements; C516054:Trend HP; C506670:d.SIGN ceramic; C009753:fiberglass; C103502:Variolink
keywords: Clinical; Crowns; Polymer; Posterior; Randomized