Influence of cast surface finishing process on metal-ceramic bond ...

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Medicinski Glasnik, Volumen 6, Number 2, August 2009
INTRODUCTION
Ceramics are being used increasingly as a
restorative material in a variety <strong>of</strong> dental restorations,
including metal-ceramic crowns, all-ceramic
restorations, and fixed partial dentures, mainly
as a result <strong>of</strong> their excellent aesthetic properties,
durability, biocompatibility and resistance to wear
(1). Ceramic for dental reconstructive work are
multiphase silicate ceramics, glass ceramics or
monophased glasses with varying compositions
(2,3). Structure composed <strong>of</strong> ceramic layers on
a metal frame combined the strength <strong>of</strong> a metal
substrate (dental alloy) with aesthetic <strong>of</strong> a ceramic.
Currently, these ceramic fused to metal appliances
are widespread in use in prosthodontics. Because
<strong>of</strong> their inherently brittle nature susceptibility to
their failure was identified at localized areas <strong>of</strong> high
stress concentration on the ceramic <strong>surface</strong>, metalceramic
interface or within the microstructure (4).
In any laminate composite system the strength <strong>of</strong>
the interfacial bond between the individual laminates
is a major factor in determining the overall
resistance <strong>of</strong> the system to deformation and failure
(5,6). A strong interface should provide sufficient
stress transfer between the individual laminates to
allow the applied loads to be transferred and accommodated.
Conversely, a weak interface will
frequently result in failure by a <strong>process</strong> <strong>of</strong> delaminating
under an applied load possibly arising
from crack initiation and propagation within and
along the layer (7). These bilayered composites
have attracted considerable attention from laboratory
researchers seeking to understand the failure
characteristics <strong>of</strong> ceramic fused to metal systems.
Alterations to the interfacial region between bilayered
structures are <strong>of</strong> considerable interest and
authors have reported the effects <strong>of</strong> variations in
the interfacial <strong>surface</strong> roughness on the mechanical
properties <strong>of</strong> metal-ceramics specimens (8).
By improving a final <strong>surface</strong> treatment <strong>of</strong> metal
substructure could be significantly improved functional
durability <strong>of</strong> metal-ceramic appliances.
Oxidation heat treatment <strong>of</strong> the metal is used
to remove the entrapped gas, eliminate <strong>surface</strong>
contaminants, and form the metal oxide layer.
An alloy is deliberately given an oxidation treat-
ment prior to ceramic application, or whether it
oxidizes during the portion <strong>of</strong> the firing cycle
before flow <strong>of</strong> the ceramics begins, the fusing ceramics
comes into immediate contact with oxide
rather than with metal <strong>surface</strong> (9,10). Different
opinions exist as to how this oxide interacts with
ceramic during the firing cycle. It is widely believed,
that the fusing ceramic dissolves away the
oxide originally formed and produces an interaction
zone responsible for the formation <strong>of</strong> a bond
(11). King rejected the oxide layer theories extend
at that time (Kauzt 1936.) which postulated
that a layer <strong>of</strong> oxide adherent to the metal is wetted
by the ceramics and becomes the transition
zone between the metal and glassy matrices (12).
Pask (13) otherwise suggest a direct chemical
bonding between the ceramic and metal. According
to Mackert (11) the chromium-containing alloys
all contain oxygen-active elements: beryl,
aluminium, vanadium, titanium, and/or yttrium.
Boron oxide makes these alloys self-fluxing during
melting and gives them unique melting and
<strong>cast</strong>ing behaviour. The addition <strong>of</strong> aluminium to
these alloys adversely affects this behaviour because
<strong>of</strong> its tendency to produce slag (14). Because
<strong>of</strong> the close correspondence between oxide
adherence and ceramic bonding, it can only be
concluded that the adherence <strong>of</strong> the oxide plays a
dominant role in ceramic bonding (11).
The aim <strong>of</strong> this study was to investigate the
influence <strong>of</strong> different <strong>cast</strong> <strong>surface</strong> <strong>finishing</strong> <strong>process</strong>
on metal-ceramics bond strength.
Table 1. Procedures <strong>of</strong> metal <strong>surface</strong> treatment for each
group <strong>of</strong> samples
Specimen Metals <strong>surface</strong> treatment
1 Sand blasting with 110 μm Al2O3 particles
2
3
4
Sand blasting with 110 μm Al2O3 particles
Oxidation
Sand blasting with 110 μm Al2O3 particles
Sand blasting with 250 μm Al2O3 particles
Oxidation
Sand blasting with 250 μm Al2O3 particles
Sand blasting with 110 μm Al2O3 particles
Extended oxidation
Sand blasting with 110 μm Al2O3 particles
Sand blasting with 110 μm Al2O3 particles
Oxidation
5
Sand blasting with 110 μm Al2O3 particles
Bonding agent
6 Etching in acid mixture