title: Evaluation of high-temperature distortion of high-palladium metal-ceramic crowns.
abstract: BACKGROUND
  Crown fit is a prerequisite for long-term clinical success; however, crown distortion may occur during porcelain firing. The dimensional stability of some high-palladium alloys at high temperatures has been questioned.
  
  
  OBJECTIVE
  The purpose of this study was to use a new method to measure the distortion of copings for metal-ceramic single units of selected high-palladium alloys with compositions representative of commercial alloys.
  
  
  METHODS
  Four high-palladium alloys containing copper and 3 containing no copper were tested. A palladium-silver alloy was included for comparison, and a gold-palladium alloy served as the control. By using reference points scribed on the margin, the mesiodistal and buccolingual margin diameters of identical copings were measured with a traveling microscope at 4 stages: as-cast, oxidized, after 2 simulated opaque porcelain firings, and after 2 simulated dentin porcelain firings. The margin distortions for the various specimen groups representing combinations of alloys, stages, and measurement diameters were compared with the use of 1-way analysis of variance and a multiple range test.
  
  
  RESULTS
  Most of the high-palladium alloys had high-temperature distortions that were not significantly different from those of the control alloy. The distortions occurred principally during the oxidation cycle. The effect of mesiodistal groove reinforcement on preventing distortion was not the same for all alloys.
  
  
  CONCLUSIONS
  The results suggest that small observed distortions of these alloys will not produce clinical problems. Several laboratory techniques are available to counteract the distortions.
authors.affiliation: Section of Restorative Dentistry, Prosthodontics, and Endodontics, College of Dentistry, The Ohio State University, Columbus, Ohio, USA. spapazog@otenet.gr
authors.forename: E
authors.initials: E
authors.lastname: Papazoglou
authors.forename: W A
authors.initials: WA
authors.lastname: Brantley
authors.forename: W M
authors.initials: WM
authors.lastname: Johnston
mesh_terms: D000704:Analysis of Variance; D003300:Copper / Q000737:chemistry; D003442:Crowns; D003735:Dental Casting Technique; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D005708:Gallium / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008853:Microscopy; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D012834:Silver / Q000737:chemistry; D013223:Statistics as Topic; D013499:Surface Properties
chemical_list: D006047:Gold Alloys; D016876:Metal Ceramic Alloys; D003776:Dental Porcelain; D012834:Silver; D010165:Palladium; D003300:Copper; D005708:Gallium