Home Subscription Services
 
   

 
The International Journal of Prosthodontics
IJP Home Page
About the Editor
Editorial Board
Accepted Manuscripts
Submit
Author Guidelines
Submission Form
Reprints / Articles
Permissions
Advertising
MEDLINE Search
 
 
 
 
 
FacebookTwitterYouTube
Quintessence Publishing: Journals: IJP
The International Journal of Prosthodontics

Edited by George A. Zarb, BChD, DDS, MS, MS, FRCD(C)

ISSN 0893-2174

Publication:
July/August 1998
Volume 11 , Issue 4

Back
Share Abstract:

Marginal Distortion of Thermally Incompatible Metal Ceramic Crowns with Overextended Margins

Nakamura/Anusavice

Pages: 325-332
PMID: 9758996

Purpose: The present study tested the hypothesis that metal ceramic crowns with a varying axial height are moer susceptible to marginal distortion during mechanical and thermal processing treatments than crowns with a uniform axial height. Materials and Methods: Copings of Pd-Cu-Ga alloy with buccal margin extensions of 0, 1.5, and 3.0 mm were prepared. Oxidized copings were veneered with experimental opaque porcelain with a mean thermal contraction coefficient (25 degrees C to 500 degrees C) that was either 2.1 ppm/degrees C below (a = + 2.1 ppm/degrees C) or 0. 1 ppm/degrees C above (a = - 0.1 ppm/degrees C) that of the alloy. Nine groups of six specimens each were prepared for analysis. Eighteen copings from these 54 specimens were used as porcelain-free controls. All specimens were subjected to a 10-step procedure including grinding, oxidation, firing of four opaque porcelain layers (O1: 0.15 mm; O2: 0.15 mm; O3: 0.5 mm; O4: 0.5 mm), glazing, abrasive blasting for 15 seconds, removal of ceramic by dissolution in hydrogen fluoride, and a postannealing treatment. The control specimens were also subjected to this procedure with the exception of the firing of four layers of porcelain, which were not applied. Marginal gap width was determined using a measuring microscope at a magnification of 30X. Results: Analysis of variance revealed a significant difference in mean gap width as a function of axial length. Th e largest gap change was associated with a 3.0-mm buccal extension and the negative mismatch condition (a < 0). Conclusion: Marginal distortion of crowns decreases as the axial length becomes more uniform. Analysis of crown distortion based on differences in the mean contraction coefficients of metal and porcelain alone is not recommended because it ignores the effects of metal grinding, metal sandblasting, and transient stress.

Full Text PDF File | Order Article

 

 
Get Adobe Reader
Adobe Acrobat Reader is required to view PDF files. This is a free program available from the Adobe web site.
Follow the download directions on the Adobe web site to get your copy of Adobe Acrobat Reader.
  © 2014 Quintessence Publishing Co Inc
 

Home | Subscription Services | Books | Journals | Multimedia | Events | Blog
Terms of Use | Privacy Policy | About Us | Contact Us | Advertising | Help | Sitemap | Catalog