Abstract
Statement of problem
Milling is a well-established method for manufacturing prosthetic frameworks. However,
information about the influence of ceramic veneer and spark erosion on the accuracy
of the all-on-six complete-arch fixed frameworks manufactured from different materials
is lacking.
Purpose
The purpose of this in vitro study was to compare the accuracy of milled complete-arch
fixed frameworks with zirconia, cobalt-chromium, and titanium at different steps of
their manufacturing process and the influence of mechanical cycling.
Material and methods
Fifteen milled complete-arch fixed frameworks, supported by 6 implants, were made
in zirconia, cobalt-chromium, and titanium (n=5). The fit was measured by the single-screw
test protocol. Stress was measured by photoelastic analysis. The loosening torque was
evaluated by tightening the screws, retightening them after 10 minutes, and then evaluating
the loosening torque 24 hours later. Thereafter, all frameworks received ceramic veneer,
and the previous tests were repeated. Cobalt-chromium and titanium frameworks received
spark erosion after ceramic veneer, and all analyses were repeated. Before and after
mechanical cycling, loosening torque was evaluated. The results were subjected to
2-way repeated-measures ANOVA and the Bonferroni test (α=.05).
Results
Titanium presented higher fit values than zirconia (P=.037) and similar to cobalt-chromium frameworks (P>.05) at baseline. After ceramic veneer, higher fit levels were observed for zirconia
(P=.001) and cobalt-chromium (P=.008). Titanium showed higher stress values (P<.05) regardless of time. Baseline for all materials presented lower stress values
(P<.05). Higher loosening torque values were found for the titanium group at baseline
(P<.001) and after ceramic veneer (P<.001). Spark erosion improved fit and loosening torque values only for cobalt-chromium
(P<.05). Mechanical cycling did not influence the loosening torque (P>.05).
Conclusions
Titanium milled complete-arch fixed frameworks presented poorer fit values than zirconia,
although the loosening torque at baseline was higher. Ceramic veneer increased the
fit levels for zirconia and cobalt-chromium, decreased the loosening torque values
for cobalt-chromium, and enhanced stress levels. Spark erosion can be a reliable technique
to improve fit and loosening torque for cobalt-chromium frameworks. Mechanical cycling
did not decrease loosening torque.
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Article info
Publication history
Published online: October 18, 2020
Footnotes
Supported by grant #2017/16303-3 from the São Paulo Research Foundation (FAPESP), by the National Council for Scientific and Technological Development (CNPq) Brazil, grants #170040/2018-6 and #306373/2015-7, and by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES) (Finance Code 001).
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© 2020 by the Editorial Council for the Journal of Prosthetic Dentistry.
