Abstract
Statement of problem
How multiple firing cycles may affect the oxide layer and, consequently, the shear
bond strength of metal-ceramic restorations is unclear.
Purpose
The purpose of this in vitro study was to determine the effect of multiple firings
on the shear bond strength of porcelain to cobalt-chromium (Co-Cr) alloy.
Material and methods
Forty cylinders (Ø6.8×9 mm) of a representative presintered Co-Cr alloy (Ceramill
Sintron) were prepared with computer-aided design and computer-aided manufacturing
(CAD-CAM) technology. After airborne-particle abrasion and polishing, the specimens
were ultrasonically cleaned of surface contaminants. A circular surface (Ø4×2 mm)
was veneered on each specimen with porcelain (VM13) after 3 firings (wash opaque,
opaque, and dentin). The specimens were then randomly divided into 4 groups (n=10).
The normal group underwent 3 firings. The other groups underwent an additional porcelain
firing: the one-plus firing group underwent 4 firings, the two-plus firing group underwent
5 firings, and the three-plus firing group underwent 6 firings. Next, the specimens
were mounted in autopolymerized acrylic resin and tested in a universal testing machine
and loaded at a crosshead speed of 0.5 mm/min at the metal-ceramic interface until
fracture occurred. The average shear bond strength (MPa) was calculated by dividing
the maximum fracture force (N) by the bonded surface of the specimens (mm2). The fracture patterns were observed microscopically and classified as adhesive,
cohesive, or mixed. One-way ANOVA was used to determine differences between groups
(α=.05).
Results
No significant differences were found among the shear bond strengths of specimens
after 3, 4, 5, and 6 porcelain firings (P>.05). The mean bond strength of all groups ranged from 30 to 34 MPa. The fracture
pattern of all specimens was mixed, indicating that multiple firings had no significant
effect on the failure pattern.
Conclusions
Multiple porcelain firings under controlled conditions had no significant effect on
the fracture pattern or shear bond strength of porcelain to a presintered Co-Cr alloy.
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Article info
Publication history
Published online: October 26, 2021
Identification
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© 2021 by the Editorial Council for the Journal of Prosthetic Dentistry.
