RESISTENCIA AL CIZALLAMIENTO EN LA UNION METAL CERAMICA

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 vapors may cause ceramic spotting or darkening.

Another characteristic of palladium alloys is their

high sensitivity to the presence of carbon during the

casting procedures, which may generate problems like

ceramic porosities and carbon contamination in the alloy

(9,12,13,15). Carbon leads to formation of carbon

monoxide during ceramic baking, originating bubbles

and porosities that can cause cracks or fractures.

In view of the continuous development of dental

porcelains and the increasingly widespread use of palladium

alloys, the aim of this study was to evaluate the

shear bond strength of a palladium-silver alloy (Pors-on 4)

to 3 ceramics (Ceramco, Noritake and Vita VMK-68).

MATERIAL AND METHODS

A cylindrical stainless steel matrix (Fig. 1 A-D)

was used for specimen preparation. The same matrix

was used for ceramic layering and shear strength

testing. The matrix had a central hole with 6.5 mm in

depth and 6.0 mm in diameter, and an auxiliary 2.0-mm

diameter perforation across the matrix (Fig. 1-B) up to

the bottom of the central perforation, which was used

to remove the dies and specimens using a metallic pin

(Fig. 1-C). The set of matrix components also includes

a metallic base (Fig. 1-A) to which the matrix was

screwed to adapt to the testing machine and a disc (6.0

mm in diameter; 1.5-mm thick) used as a spacer to

standardize the ceramic layer thickness (Fig. 1-D).

The wax patterns were made with the disc

positioned inside the perforation. The wax (Green

Regular Wax; Kota Ind. Ltd., São Paulo, SP, Brazil) was

liquefied at 75ºC and flowed with the aid of a dropper

into the perforation. After wax cooling, the patterns

were removed by the introduction of the metallic

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