Supervisors info:
Κ. Σπυρόπουλος (Επικ. Καθηγητής), Τρ. Παπαδόπουλος (Αναπλ. Καθηγητής), Α. Π. Τριποδάκης (Αναπλ. Καθηγητής)
Summary:
INTRODUCTION
The use of the Direct Metal Laser Sintering technique (DMLS) in the
construction of dental restorations is a new and promising technique, because
its advantages as ability to manufacture up to 90 units in a single operation,
ease of use, improved physic-mechanical properties, reduced porosity etc are
favoring the use in the manufacture of metal-ceramic restorations. The lack of
sufficient evidence for the efficacy of this technique to the strength of
metal-ceramic bond, led to the completion of this research.
PURPOSE
This research is intended to contribute to the investigation of the strength of
the metal-ceramic bond between the dental alloy Co-Cr and dental porcelain,
when for the metal substrate manufacturing has been used the DMLS technique and
compared to the corresponding, when for the construction of the metal
substrate has been used the casting technique.
MATERIALS AND METHODS
In order to control the metal ceramic bond are constructed 20 metal substrate,
according to the specifications ISO 9693, which are divided into two groups:
the control group, in which the metal substrates were constructed with casting
technique by base metal alloy Co-Cr (Wirobond C) and the test group, in which
the metal substrates were constructed using the DMLS technique by base metal
alloy Co-Cr (EOS-Cobalt-Chrome SP2). Moreover, based on the same specification,
of any construction technique, we made three metal substrates in order to check
their module of elasticity. The ceramic mass which was placed on metal
substrates according to ISO 9693, was Vita, VMK-Master. After the radiographic
examination of metallic substrates of each group so as to establish the
internal porosity, the three-point bending test was used both to control the
elastic modulus of the metal substrate and for the control of the metal-ceramic
bond, using apparatus engineering assays (Tensometer10, Monsanto, Akron, Ohio,
USA). After completion of the three-point bending test, for determining the
failure mode of the metal-ceramic specimen, the crushed pieces were tested in
an optical microscope (Eclipse ME600 Nickon, Japan) at a magnification x5. For
the qualitative determination of the type of fracture, took control, of
fractured surfaces of specimens in the middle and at the edges in a scanning
electron microscope SEM (FEI Company, SEM Quanta 200) with EDAX system. In this
study, in the concept of cohesive failure mode, we include the staying cracked
on the surfaces of the adhesive agent and ceramic mass, while in the concept of
adhesive failure mode we include the retention of data of the metal substrate.
For the statistical analysis was used t-test method.
RESULTS
The metal substrates prepared by the technique DMLS do not show internal
porosity as compared to them produced by the casting technique. Regarding to
the results of the three-point bending test for determine the metal-ceramic
bond strength no statistically significant difference was recorded between the
mean values of the two groups. The values for the control group was 54,60±6.20
MPa and 51,87±7.50 MPa for the test group. Regarding the determination of the
failure type, of control specimens in optical and electron microscopes revealed
that all specimens exhibited cohesive failure type.
CONCLUSIONS
The results showed that, the two techniques of construction of the metallic
substrate on the one hand covering the lower allowable stress limits of the
metal-ceramic bond of 25 MPa specified in ISO 9693, and on the other hand
display any statistically significant difference (p=0,39) bond strength. The
failure type for both techniques was cohesive type.
