| dc.description.abstract | The aim of this study was to evaluate the flexural strength, elastic modulus,
mass changes and surface roughness of two cobalt-chromium alloys, before and
after immersions in four cleaning solutions and distilled water (as control). Co-Cr
alloys (Co-Cr®, Dentsply-DeguDent Industria e Comércio, São Paulo, Brasil; and GM
800+®, Dentaurum GmbH & Co KG, Ispringen, Alemanha) were investigated. Fifty
bar specimens (25 x 3 x 0,5 mm) for the flexural test, 50 quadrangular specimens
(10 x 10 x 1 mm) for mass changes evaluation and 35 cylindrical specimens (10 x 1
mm) for surface roughness measurements were obtained by casting. They were
polished by abrasive paper (#240 to #2500) and diamond polishing paste (3μm).
Specimens were randomly divided into 5 groups according the following cleaning,
solutions: pure white vinegar, 0.2% peracetic acid, sodium perborate - Corega
Tabs®, 0.37% sodium hypochlorite and the control, distilled water. Surface
roughness (Ra parameter) was analyzed using a profilometer (Mitutoyo SJ 410,
Mitutoyo Corp, Kanagawa, Japan) before and after 5, 20 e 90 immersions (10 min
each). Ra changes (ΔRa5, ΔRa20 e ΔRa90) were calculated for the different
intervals. Qualitative surface analyses were performed by Scanning Electron
Microscope (JSM 6360 SEM, JEOL). Both alloys, immersed in pure white vinegar,
0.2% peracetic acid, sodium perborate - Corega Tabs®, 0.37% sodium hypochlorite
had similar roughness changes after 90 immersions (ΔRa from -0,012 to 0,022 μm).
There was a significant surface roughening in hypochlorite (ΔRa90= 0,064 μm for
CoCr®; and ΔRa90 = 0,592 μm for GM 800+). The number of immersions influenced
on the roughness changes only in hypochlorite and there were greater changes in
the GM 800+ alloy. After 90 immersions, GM 800+ alloy showed mass lost in the
hypochlorite solution (-0,3%). This alloy presented higher flexural strength after 90
immersions in SH (σF= 1516 MPa in hypochlorite; 1366 MPa in control). However,
there were no elastic modulus changes. CoCr® alloy did not present differences in
the σF or in elastic modulus in any solution. The only solution that damaged the alloy
surface was 0.37% sodium hypochlorite. | |
