MEtallographic aspEcts of wEldings bEtwEEn orthodontic rings and ...

a
g
h
i
Figure 3. Metallographic structures of ring, welding area and wire: a.
Martensite and fine carbids - Osteofix Wipla; b. Solid solution of CoCr; c.
Orthodontic ring; d,e. Details - welded joint zones: BM,HAZ,WM; f. Ring
with Wipla wire welded zone; g. Ring with Finolloy CoCr wire (Fino, Bad
Bocklet, Germany) welded zone; h. Mixed zone of ring-wipla alloys; i.
Mixed zone of ring-CoCr alloys.
Microhardness (HV) was measured on the polished
surface of the samples at room temperature using a
Zwick 3212 (Zwick, Ulm, Germany) microhardness
unit.
Individual tests with a peak load of 9.8 N (HV1)
or 49 N (HV5), depending on probe thickness, and a
loading time of 20 seconds were performed for each
determination.
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202 TMJ 2008, Vol. 58, No. 3 - 4
rEsUlts
Accomplishment of welded joints and analysis of
the results prove that the great majority of the samples
point out the existence of a joint with austenitic and/
or martensitic structure, with ferrite and carbides
complex. This is the way the characteristic structures
of the melted alloys are noted. 18
Some metallographic aspects of alloys structures
resulted after analysis are shown in Figure 3 (those of
wipla wire, CoCr wire and orthodontic ring, those of
welded joints and those where the alloys miscibility
can be observed).
The VICKERS hardness tests were realized with
1kg load [HV1] (CoCr wire and rings) and 5kg [HV5]
(wipla wire). Table 1 presents the results of the
hardness tests performed on the samples.
It has been noted that the hardness of wipla wire
(with approximately 100 HV units) is twice as that of
the orthodontic ring, which imposes some welding
precaution.
Certainly, there were also joining failures, which
resulted especially from the lack of experience in
welding and from the inadequate welding parameters,
like those presented in Figure 4. These failures can
be visible: deterioration/melting of the orthodontic
ring, the welding itself being resistant at tearing.
More failures can be noticed in case of wipla wire
welding, which has a bigger microhardness.
Figure 4. Failures in the welding of orthodontic rings arches
discUssion
The laser and microplasma welding are performed
using through rapid, economic and highly accurate
techniques. 12,13 Time is saved, because the frameworks
are welded directly on the working cast. Distortions,
which are caused by the transfer from the working cast,
disappear; the welding can be done very close to the acrylic
resins or the ceramics, without any damage or chromatic
modification. Theoretically, all metals can suffer joining
processes. 16,17,19,20 Sometimes, when the cooling is to fast,
we observe cracks in the base material. 14,15