MEDICINSKI GLASNIK

phadent N.V., Antwerpen, Belgium) is applied to
the samples in group 5. The samples of group 6
are kept in the solution obtained by mixing 50 ml
of distilled water and 50 ml of 32% hydrochloric
acid for 30 minutes. After etching these samples
are first of all washed in distilled water, and then
in the compound of ethyl alcohol and acetone in
ratio 1:1. Figure 1 shows the characteristic surface
of the sample prepared in this way recorded
by a scanning electronic microscope (Tescan
Vega TS5136LS, Tescan, Brno, Czech R) with
the secondary electron detector (SE).
Along the middle of thus prepared metal
plates the ceramics (Duceram Kiss, DeguDent,
Hanau-Wolfgang, Germany) is fired (ceramic
furnace Focus 2006, Shenpaz, Tel Aviv, Israel) in
the length of 8 mm, width of 3 mm, and thickness
of 1 mm. The ceramics corresponds to the manufacturer’s
instructions and belongs to the group
of ceramics with the fired temperature of up to
980°C, suitable for coating of the mentioned alloy.
The samples are tested by bending in three points
on the tester machine (LRX Lloyd Instruments,
Fareham, Great Britain) with installed Nexygen
programme for the processing of results. The
samples are set so that the surface with ceramics
is turned opposite to the pin, and the metal part
resting on the supports at a distance of 20 mm,
and the diameter of pin that loads the sample is 1
mm. The shift of pin is constant during testing at
a speed of 1.5 mm/min, and the testing continues
Figure 3. Typical areas during three-point bending test
Mehulić et al Surface finishing and bond strength
until the fracture, i.e. to full separation of the ceramics
from the metal.
Testing procedure has been carried out according
to the guidelines given in ISO 9693
(15).
After testing the samples type of fracture surfaces
(cohesive, adhesive or cohesive-adhesive)
were examined by scanning electronic microscope
(Tescan Vega TS5136LS, Tescan, Brno, Czech R).
The same person has performed all the tests.
The multiple range tests, Fischer’s LSD test
and ANOVA have been used for statistic analysis.
RESULTS
The results of 3-point bending test performed
on 6 groups of specimens, (each group has three
specimens) are presented in Figure 2.
The diagrams obtained by testing on the tester
and presented in Figure 2 show the same trend,
i.e. the behaviour of all samples during testing is
inter-compatible. Therefore, Figure 3 can generally
explain the behaviour of all metal-ceramic
systems in a three-point flexure bond test.
According to Figure 3 it is possible to define
three characteristic areas during testing. The
beginning of testing where the force-deflection
diagram is a horizontal line, i.e. the pin is lowered
without increase of force, represents the first
area. Such behaviour is caused by preparation of
testing and represents the period from beginning
of testing to the moment of achieving the predefined
pre-load.
Point A (Figure 3), where a sudden increase
in force is noticed, represents the moment of
contact between the pin and the sample and the
actual beginning of the testing area 2. The linear
part of the diagram that follows from this point
represents common resistance to flexing of the
metal-ceramic sample, since in this area the bond
between metal and ceramics is still strong.
Point B (Figure 3) represents the start of the
third area, i.e. the moment of loosening of the bond
between metal and ceramics and the moment at
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