Abstract
In this study the marginal fit changes that occurred during the porcelain firing cycles of palladium–silver alloy (Pd–Ag) and nickel–chromium alloy (Ni–Cr) coping both with shoulder and heavy chamfer facial finishing lines were investigated with light microscope. Forty copings were fabricated which were divided into four groups according to alloy type and facial finishing line, each group consisted of ten copings: Group I (Pd–Ag) alloy copings with shoulder finishing line; group II (Pd–Ag) alloy copings with heavy chamfer finishing line; group III (Ni–Cr) alloy copings with shoulder finishing line; and group IV (Ni– Cr) alloy copings with heavy chamfer finishing line. Five control metal copings (non veneered) from each group were subjected to exactly the same firing cycles without the application of porcelain. Measurements were made during five stages of crown fabrication: (1) Before degassing, (2) after degassing, (3) after opaque application, (4) after body porcelain application, and (5) after glazing. Changes in the marginal fit of the coping after the various firing stages were calculated for each coping. The statistical analysis of the results showed that the mean marginal fit changes during porcelain firing cycles of the base metal alloy copings (Ni–Cr) were significantly greater than those of noble metal alloy copings (Pd–Ag). The copings with heavy chamferfinishing line showed significantly greatermarginal fit changes during porcelain firingcycles than those with shoulder finishingline.The greatest amount of marginal fitchanges occurred during the degassing stageof porcelain firing cycle followed by bodystage of porcelain firing cycles while therewere no significant marginal fit changes inthe other stages of porcelain firing cycles.
Highlights
The porcelain–fused–to–metal (PFM) restoration have been one of the most common restorations used in fixed prosthodontics because of their casting accuracy, high strength properties of the metal, and the cosmetic appearance of porcelain.(1) In spite of the variables that exist in the fabrication and function of these restorations, the PFM restorations still form the backbone of modern restorative dentistry despite many new systems.(2) It has been widely observed that the ascast fit of PFM restoration deteriorated during the high temperature firing cycles used for porcelain veneer application.(3) Studies on marginal fit changes have identified many factors, such as the mismatch of the porcelain–metal thermal contraction, alloy type, and preparation design, as contributing to the distortion
The mean of marginal fit changes and standard deviations for the non–veneered copings and veneered copings of group I (Pd–Ag alloy with shoulder margin), group II (Pd–Ag alloy with heavy chamfer margin), group III (Ni–Cr alloy with shoulder margin), and group IV (Ni–Cr alloy with heavy chamfer margin) during different firing cycles with the total marginal fit changes of each group with standard deviation are presented in Table (1)
The highest mean scores for marginal fit change for the tested groups happened in the degassing stage with group IV showing the highest mean (34.05 μm) followed by group II (28.84 μm)
Summary
The porcelain–fused–to–metal (PFM) restoration have been one of the most common restorations used in fixed prosthodontics because of their casting accuracy, high strength properties of the metal, and the cosmetic appearance of porcelain.(1) In spite of the variables that exist in the fabrication and function of these restorations, the PFM restorations still form the backbone of modern restorative dentistry despite many new systems.(2) It has been widely observed that the ascast fit of PFM restoration deteriorated during the high temperature firing cycles used for porcelain veneer application.(3) Studies on marginal fit changes have identified many factors, such as the mismatch of the porcelain–metal thermal contraction, alloy type, and preparation design, as contributing to the distortion. The aim of this study was to evaluate the effects of porcelain firing cycles on veneered and non–veneered PFM crowns constructed utilizing two different finishing lines and two different alloys
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
