MEtallographic aspEcts of wEldings bEtwEEn orthodontic rings and ...

a
b
c
Figure 1. Orthodontic device of type Quad Helix: a. situated on the cast;
b. detached from the cast; c. ring-arch welding detail
The coming out of a new series of devices like
MIA (Mobile Intraoral Arch) satisfies the patients
not only orthodontic but also esthetically. We
insisted on the Quad Helix, an orthodontic device
with orthodontic rings, on which an oral arch is
attached. 5,9 The orthodontic rings are placed on the
molars and the palatal or lingual arch is welded on
these rings.
The arch, which is orally placed, moves
symmetrically or asymmetrically various groups of
teeth and can solve complicated anomalies (maxillary
disjunction, open bite, posterior cross bite), without
being noticed by the entourage. From this group of
devices, we present a QUAD HELIX/CRIB variant,
created at the Orthodontic Department in Timisoara
and which was tested. (Fig. 1)
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200 TMJ 2008, Vol. 58, No. 3 - 4
Generally, Orthodontics uses voltaic arch point
soldering which often is followed by failures and/or
the deterioration of the orthodontic ring. The concept
of joints welded using microimpulses or laser welding
was tested in Prosthodontics, (but not frequently) and
only rarely for the orthodontic devices. 3,4,10-17 For this
reason, we tested the system in order to indicate the
right solution: no matter the welding procedures or
the material precipitate, always structures (rings and
arches) modification takes place, especially in the
heat-affected zone (HAZ), namely near the welded
zone. Here, due to the overheating, precipitates of
some compounds can appear and hardens the zone.
MatErial and MEthods:
We studied 15 joint samples, welded with material
addition, on worn out orthodontic rings (Ormco,
Ormco Corporation, West Collins USA). For these
joints, two types of wire were used, Wipla Osteofix
(FeCrNi) (Zelezarny Chomutov, Chomutov, Cehia)
wire and CoCr Finoloy (Fino, Bad Bocklet, Germany)
wire. The welding was performed with a microimpulse
device (Schütz Dental, Rosbach, Germany). (Fig. 2)
The welding were point-like when the wire position
was vertically (perpendicular on the ring) and linear, in
case of an oblique position of the welded joints.
The welding parameters were those indicated (for
these types of stainless steels) by the company that
produces microplasma welder (Schütz Dental): Power
3; time/ welding point 40msec.; time between impulses
1 sec.; time for Argon running before pointing 1 sec.
We used the following sequence of the experimental
program, in order to evaluate the welded joint:
- Evaluation of the chemical composition of the
alloys, through metallographic analysis (structure,
defects) and hardness tests.
- Evaluation of the welded joints, probes loading,
metallographic analysis (structure, defects), and
hardness attempts on specific zones: base material,
heat affected zone, welding zone.
- Establishment of optimal possibilities for
welding and loading, followed by analysis and tests.
Microscopic observations were made using an inverted
metallographic microscope Reichert MeF 2 (Reichert, NY,
USA). Therefore the samples were incorporated into an
acrylic resin, cut perpendicularly to the weld axis, grinded
using silicon carbide abrasive paper and polished with a
series of abrasives rubbers. The surfaces to be analyzed
were chemically attacked using acid solution of ferric
chloride for 2-3 seconds at room temperature. The images
magnification was 100x on polarized light.