RESISTENCIA AL CIZALLAMIENTO EN LA UNION METAL CERAMICA
Enviado por MAGALIYQP • 23 de Julio de 2012 • 2.162 Palabras (9 Páginas) • 520 Visitas
Comparative Study of Ceramic-to-Metal Bonding
Juliano Milczewsky SCOLARO1
Jefferson Ricardo PEREIRA2
Accácio Lins do VALLE3
Gerson BONFANTE3
Luiz Fernando PEGORARO3
1Department of Prosthodontics, Paulista University, UNIP, Goiânia, GO, Brazil
2Department of Prosthodontics, School of Dentistry of Passo Fundo, University of Passo Fundo, Passo Fundo, RS, Brazil
3Department of Prosthodontics, School of Dentistry of Bauru, University of São Paulo, Bauru, SP, Brazil
Dentists and technicians have used dental ceramics associated with different types of alloys without taking into account the
characteristics of compatibility of these materials. Knowing the properties of the alloy and ceramic used in metal/ceramic restorations
is a key factor for treatment success. The purpose of this study was to evaluate the bond strength of a palladium-silver alloy (Pors-on
4) to 3 ceramics (Ceramco, Noritake and Vita VMK-68) using shear forces at the metal-ceramic interface. A stainless steel cylindrical
matrix was used for preparation of the metal dies, application of ceramic and shear strength testing. Thirty palladium-silver alloy
cylinders received two layers of opaque and two layers of body porcelain, and shear tests were performed in a universal testing machine
at a cross-head speed of 0.5 mm/min. Shear bond strength means (in MPa) were: 28.21(Ceramco), 28.96 (Noritake) and 24.11 (Vita
VMK-68). One-way ANOVA did not show statistically significant differences (p>0.05) among the materials. The results of this study
indicate that the three evaluated ceramic systems are suitable to be used in combination with the tested palladium-silver alloy.
Key Words: Metaloceramic restorations, alloys, ceramics, compressive strength.
INTRODUCTION
Since its introduction in the 1950’s, porcelainfused-
to-metal restorations have played an important
role in restorative dentistry because they are able to
combine a great color stability with resistance provided
by the metal framework. Over the past years, several
authors have emphasized the importance of evaluating
different alloys and ceramics using physical tests (1-7),
which have been designed (4-8) to reproduce the
complex set of forces that act on the metal-ceramic
interface (8-12). In view of this, there has been an
increased interest on the assessment of metaloceramic
bond strength, seeking the test that is closest to the ideal
and can simulate oral conditions as reliably as possible.
Several tests have been used to evaluate properties such
as color stability (4), shear (7), tensile (6), flexural (10)
and torsional strength (13).
According to Anusavice (3), a test must fulfill
two primary requirements to provide accurate results:
firstly, stresses concentration must take place only
along the interface because if stresses are concentrated
outside the interface (e.g., at the end of the ceramic
layer), the results will be lower than the actual metalceramic
bond strength; secondly, the amount of tension
should be zero because if this type of force exists, it is
likely that the ceramic fractures and the test results
become “contaminated”.
The circular-planar surface shear test proposed
by Chong et al. (7) provides easy specimen fabrication
and standardization. Furthermore, the matrix used for
specimen preparation is specific for shear testing.
According to the requirements described by these
authors (6-8,11,12), this test is highly reliable because
the metal-ceramic interface bonding is the only type of
adhesion present.
Braz Dent J (2007) 18(3): 240-243
Braz Dent J 18(3) 2007
Ceramic-to-metal bonding 241
Palladium alloys were introduced in the 1980’s
and proved suitable for dental purposes (9,12,14-16).
This type of alloy has particularities that, in spite of not
interfering with porcelain-metal union, should not be
overlooked. The main path for bonding with these alloys
is mechanical and such condition has not produced
significant clinical failures (3). However, there are other
elements in the alloy composition such as silver and tin,
which are susceptible to oxidation. Therefore, previous
oxidation is an important procedure that may increase
the bond strength at metal-ceramic interface (9,12,15-
18). Previous oxidation has been shown to result in
emergence of silver nodules that can undergo volatilization
(9,12,16-18), On the other hand, the presence of
silver
...