MEDICINSKI GLASNIK

creating a higher bond (17). It is difficult to quantify
the real bond strength because in vitro testing
is not usually in correlation with ceramic breakdown
in function. The shear strength of the metalceramic
bond was evaluated by the Shell-Nielsen
test described by Dent (18) method similar to that
used by Anthony (19), Moffa (20), Diaz (21),
Anusavice (22), Warpeha (23), Miller (24), Riley
(25). The authors suggested that the differences
in oxide composition and amount, influenced by
different surface finishing procedures. Sandblasting
the finished surface is though to remove furrows,
overlaps, and flakes of metal created by the
grinding process. A sandblasted surface may have
higher surface energy that alloys increased wetting
of the metal during ceramic application. Evidence
suggested that this roughened surface could also
provide mechanical interlocking and increase the
surface area for metal-ceramic bonding (26). According
to Brantley (27), oxide layer is different
before and after sandblasting. Graham (28) suggested
final finishing process in the order: sandblasting,
grinding, sandblasting and oxidation.
Smoother surface achieved the lowest values of
bond strength and bonding agent did not improve
bond strength because of hermetical sealing of cast
surface (29). It created alumina layer on cast surface
and thus change oxide ratio on it (30). The gold
rich bonding agent reduced the interfacial stress by
improving the compatibility between ceramic and
metal (31). Basic elements oxidised selective; and
created Fe 2 O 3 , In 2 O 3 i SnO 2 on cast surface (32).
The amount of oxides is not always in proportions
with elements, which were added. Rake (33) suggested
opaque in two layers on unutilised surfaces.
In Ni-Cr alloy (34) and alloy with Pd (35) ceramic
fired in vacuum produced excessive amount of oxides,
and argon reduced their appearance.
REFERENCES
1.
2.
3.
Mehulić K, Čvrljak Tomić I, Schauperl Z, Komar
D. Wear Characteristics of Esthetical Prosthetic
Materials. Acta Stom Croat 2006; 40:56-64
Mehulić K. Glassceramics. Acta Stom Croat
2005; 39:477-81.
Musić S, Živko-Babić J, Mehulić K, Ristić M,
Popović S, Furić K. Microstructure of leucite
glass-ceramics for dental use. Materials Letters
1996; 27:195-9.
Mehulić et al Surface finishing and bond strength
The most reliable evaluation of metal-ceramic
bond strengths should be based on minimal experimental
variables and least residual stresses
at metal-ceramic interfaces. Evaluation for types
of metal-ceramic failures is critical even though
cohesive failures within ceramic have been an indication
of clinically acceptable metal-ceramics
bond. Although laboratory studies offer predictable
guidance to comprehensive selection of materials,
clinical longitudinal studies should also
be encouraged to complement laboratory results
and enhance clinical standards (17).
It can be concluded that the analysis of all the
parameters used in assessing the strength of the
bond between metal and ceramics has confirmed
that the bond is the strongest in the surface treatment
procedure sandblasting with 250 µm Al 2 O 3 ,
oxidation, and sandblasting again with 250 µm,
and significantly weaker in the etched sample. It
should be noted that, in spite of the recommendations
of the producer of materials and the usual
practice, the application of the bonding medium
has not shown any influence on the bonding
strength of the tested metal-ceramic system. The
metal samples revealed an adhesive mode of failures
on the most part of surface, and adhesivecohesive
on the edges.
ACKNOWLEDGEMENT
Grant No. 065-0650446-0435, and No. 120-
1201767-1762 from the Ministry of Science,
Education and Sports of the Republic of Croatia
supported this work.
4.
5.
Competing interests: none declared.
Fleming GJ, Nolan L, Harris JJ. The in-vitro
clinical failure of all-ceramic crowns and the connector
area of fixed partial dentures: the influence
of interfacial surface roughness. J Dent 2005;
30:405-12.
Thomson GA. Influence of relative layer height
and testing method on the failure mode and origin
in a bilayered dental ceramic composite. Dent
Mater 2000;16:235-43.
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