Statement of problem
When performing an adjustment on metal-ceramic restorations, opaque porcelain may
become exposed, particularly on the lingual surface of maxillary anterior teeth. It
is generally believed that exposed opaque porcelain can be more abrasive and destructive
to an opposing dentition than body porcelain, and that these teeth may require restoration
as a consequence.
Purpose
This study compared the debonding strengths of 2 types of porcelain, with and without
opaque porcelain, to 2 types of dental casting alloys.
Material and methods
Two porcelain systems, Ceramco3 and Vita 900, and 2 metal alloys, a high noble (Encore)
and a base metal (Duceranium U), were used to fabricate and test 56 flexure bars in
accordance with ISO 9693:1999(E): Metal-Ceramic Dental Restorative Systems. Half of
the bars received opaque porcelain prior to body porcelain additions, and the other
half did not. The metal-ceramic debonding strength was determined by using a 3-point
flexure apparatus and a mechanical testing device (Instron). A center load was applied
at a crosshead speed of 1.5 mm/min−1 until debonding occurred. In addition to the load-versus-displacement curve, a precision
measurement microphone was used to assist in ascertaining the point in time when debonding
occurred. Since the sound analysis and the mechanical test were started simultaneously,
the debonding load could be more accurately determined. Data were statistically analyzed
using 3-way analysis of variance, and all pairwise multiple comparisons were made
with the Tukey HSD test (α=.05).
Results
The difference in mean debonding strength values for opaqued and non-opaqued flexure
bars were statistically significant (P=.028). The mean debonding strength values (MPa) for each metal-ceramic system were
as follows: Encore-Opaque-Ceramco3 (EOC), 31.43 ± 6.92a; Encore-Opaque-Vita 900 (EOV), 30.37 ± 3.25a; Duceranium U-No Opaque-Ceramco3 (DNC), 29.20 ± 6.97a; Duceranium U-Opaque-Ceramco3 (DOC), 26.61 ± 4.98a; Duceranium U-Opaque-Vita 900 (DOV), 26.15 ± 4.29a; Encore-No Opaque-Vita 900 (ENV), 25.45 ± 4.04a; Encore-No Opaque-Ceramco3 (ENC), 23.96 ± 4.14a; Duceranium U-No Opaque-Vita 900 (DNV), 22.88 ± 6.15a. Identical superscript letters denote no significant difference among groups. The
precision measurement microphone resulted in selection of a debonding strength/crack
initiation load that was lower than the peak load recorded during strength testing.
Conclusion
Initial debonding during crack initiation strength testing may not always correspond
to the peak load recorded, but rather to the point on the load-versus-displacement
curve beyond which the relationship is no longer a straight line. Presence of opaque
porcelain generally increased the debonding strength for metal-ceramic systems; however,
opaque porcelain may not be necessary for a clinically acceptable metal-ceramic bond
for some metal-ceramic systems.
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Article info
Publication history
University of Connecticut, Farmington, Conn; US Army Dental and Trauma Research Detachment, Great Lakes, Ill
Footnotes
This investigation was supported by Graduate Prosthodontics, Department of Prosthodontics and Operative Dentistry University of Connecticut Health Center and the 2004 American Academy of Fixed Prosthodontics Tylman Research Grant Program.
The views expressed in the article are those of the author and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the US Government (Para 4-3, AR 360-5).
Identification
Copyright
© 2007 The Editorial Council of The Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
