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238 Medicinski Glasnik, Volumen 6, Number 2, August 2009 ics is applied are treated by different procedures and combinations of procedures (Table 1). Sandblasting was achieved with 110 and 250 μm Al2O3 particles (Shera, Lemförde, Germany). The used bonding agent (3C-Bond, Al- Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Figure 2. Results of 3-point bending test performed on six groups of specimens
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 239
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