MEtallographic aspEcts of wEldings bEtwEEn orthodontic rings and ...

ORIGINAL ARTICLES
MEtallographic aspEcts of wEldings bEtwEEn
orthodontic rings and wirEs
Cristina Bortun, Florica Glavan, Sorin Porojan, Liliana Sandu, Otilia Gombos
rEZUMat
Introducere: Aparatele ortodontice fixe sunt frecvent utilizate n practica medicinei dentare. Quad Helix/Crib Therapy este unul din aparatele tip MIA (Mobile
Intraoral Arch) cu arcuri aplicabile palatinal sau lingual, sudate de inele ortodontice aplicabile pe molari, ce este utilizat n anomalii dentomaxilare, cum
ar fi: endogna]ia maxilar\, ocluzia deschis\. Obiective: Obiectivul principal al studiului este cel de a determina parametrii optimi de imbinare sudat\ cu
microimpulsuri a componentelor aparatului ortodontic. Material [i metode: S-au utilizat inele ortodontice (Ormco, Ormco Corporation, West Collins USA)
uzate, srma de CoCr Finolloy (Fino, Bad Bocklet, Germany) sau de Wipla Osteofix (Zelezarny, Chomutov, Cehia) pentru sudarea arcurilor la inele. A fost folosit
aparatul de sudur\ cu microimpulsuri Welder (Schutz Dental). Sudurile au fost analizate metalografic [i li s-au evaluat microdurit\]ile, pentru a defini parametrii
optimi de sudur\ (putere 3; timp /punct sudur\ 40msec.; interval de timp ntre impulsuri 1 sec.; timp de curgere a argonului nainte de sudare 1 sec.). Rezultate
[i discu]ii: Analizele microscopice ale sudurilor arcurilor linguale la inele ortodontice au relevat structurile caracteristice ale aliajelor metalice din zona de baz\,
zona sudat\ [i zona de influen]\ termic\. S-a constatat c\ duritatea srmei de wipla este dubl\ fa]\ de cea a inelului ortodontic, ceea ce impune anumite condi]ii
de sudur\. Dac\ nu este luat n calcul acest fapt [i experien]a profesional\, la mbin\rile sudate se deterioreaz\ inelul ortodontic. Concluzii: 1. Se indic\ s\ se
sudeze inelele ortodontice cu srm\ de wipla. 2. Sudura tangen]ial\ este mult mai confortabil\ dect cea punctiform\ [i d\ rezultate mai bune.
Cuvinte cheie: inele ortodontice, sudura cu microimpulsuri, srm\ de CoCr, srm\ de wipla
abstract
Introduction: Fixed orthodontic devices are frequently used in Dental Medicine. Quad Helix/Crib Therapy is an MIA (Mobile Intraoral Arch) with palatal or
lingual appliance, used for Dento-skeletal anomalies like: constricted maxillary, open bite. It uses orthodontics rings that can be fixed on molars. Objectives:
The main objective of the study is to determine the optimal parameters of microplasma-welded joints, for the compounds of the orthodontic devices. Material
and methods: We used worn-out orthodontic rings and Wipla and CoCr wires, in order to weld the arches to the rings. Microplasma Welding Device (Schutz
Dental- Rosbach, Germany) was used for welding. In order to define the optimal welding parameters (Power 3; time/ welding point 40msec.; time between
impulses 1 sec.; time for Argon running before pointing 1 sec.), the weldings underwent a metallographic analysis and a microhardness evaluation. Results:
The structural analyses of welding zone between lingual arches and orthodontic rings revealed typical alloys structure from the base material, welding material
and heat affected zone. The microhardness of Wipla wire is twice as that of the orthodontic ring, which imposes some special welding conditions. If this fact is
not considered, the orthodontic rings can be destroyed. Conclusions: 1. It is recommended to weld the orthodontic rings using Wipla wire. 2. The tangential
welding is much more comfortable compared with the point-like one and has better results.
Key Words: orthodontic rings, microplasma welding, CoCr wire, wipla wire, metallographic analysis, hardness
introdUction
The alloys used in Orthodontics and in the Denture
Technology are metallic structures, obtained through
the melting of many chemical metallic compounds
(Co, Cr, Mo, Ni, Ti, etc). 1-8 Generally, the alloys used in
dentistry have to fulfill specific conditions, in order to
be used in the oral cavity:
Department of Removable Partial Dentures Technology, Faculty of Dentistry,
Dental Technology Specialization, Victor Babes University of Medicine and
Pharmacy Timisoara
Correspondence to:
Prof. Cristina Bortun, 9 Revolutiei din 1989 Blvd., Timisoara, Romania
Email: cristinabortun@yahoo.com
Received for publication: Jul. 10, 2007. Revised: Dec. 12., 2007.
a. To have corrosion strength, no matter the
processing types; the alloy compounds to be chemically
stable, without any influence of various factors or the
pH-alteration in the mouth.
b. The mechanical characteristics of the devices or
dentures to be optimal for the stress developed during
the functions of dento-maxillar apparatus (elasticity,
tearing strength, wear, etc)
The fixed orthodontic devices appeared due to
the necessity of solving complicated cases of dentalmaxillary
anomalies, as fast as possible and with a
permanent control of dental movements. These devices
are helpful both for the coronal or radicular movement
and the entire dento-parodontal units movement.
Lately, a new era was opened in the Orthodontic
appliance, which is in connection with the placement
of the orthodontic device depending on the minimum
visibility.
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Cristina Bortun et al 199

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.

a
b
c
Figure 2. Welder Schűtz Dental - a. welding equipment; b. Ormco
orthodontic ring (Ormco Corporation, West Collins USA); c. Welded joining
on an orthodontic ring with two types of wire (wipla- thick wire and CoCr-
thin wire)
a
b
c
d
e
f
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Cristina Bortun et al 201

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

Table 1. Microhardness of some welding areas
Track no Material
The modern lasers, like Girrbach Dental System
(Neolaser L 126500), Vision Industry (LWI 4 th
Generation), Interdent Laser System (Herculea),
Manfredi, can be electronically programmed; they have
a microscopic visualization system and the parameters
can be set depending on the welded alloy. The welding
has a maximum stability, gives a biocompatible zone,
which is mechanically resistant and can be realized
rapidly and with maximum precision, also at room
temperature.
Experimentally, some alloys used in Dental
Technology have been welded using laser techniques.
Their quality can be estimated through destructive and
nondestructive methods. 5,14,21-23 The metallographic
analysis and microhardness evaluation belong to
the destructive methods, while Spectrographic and
Radiologic analyses are nondestructive. Our studies
regarding laser Nd:Yag welding were made with help
of Welding Department from Politehnica University
Timisoara and researchers from ISIM/ WMTI
Timisoara (Welding and Materials Testing Institute);
they demonstrated a good compactness of the
studied samples and the lack of defects in the joining
area. 14
Orthodontic ring CoCr wire Wipla wire
Vickers HV1 HV5
BM HAZ WM BM HAZ WM BM HAZ WM
0 1 2 3 4 5 6 7 8 9 10
1
193 229 210 368 - - 454 - -
2 RING 1
210 228 210 378 - - 466 - -
3 214 229 210 389 - - 480 - -
1
239 - 224 368 - - 460 - -
2 RING 2
219 - 229 378 - - 460 - -
3 214 - 234 358 - - 454 - -
1
205 219 197 358 - - 473 - -
2 RING 3
201 218 201 378 - - 488 - -
3 202 210 224 348 - - 473 - -
1
201 215 225 360 476
2 RING 4
209 224 226 354 484
3 198 213 236 367 463
1
204 220 235 358 459
2 RING 5
189 211 232 362 469
3 207 210 227 369 456
The microhardness evaluation was realized with
loads of 100g; it pointed out a light increase of the
hardness in HAZ (heated affected zone). The hardness
values of the weld metal (WM) are situated between
those in the base material (BM) and heat affected zone
(HAZ). Regarding the chemical composition of the
joint, a small diminution of the main reactive elements
has been noticed. In the testing base material of over
1 mm thickness cracks appear, which can be observed
not only macroscopically but also by metallographic
study That is why, at 1 mm thickness, we recommend
welding without material addition, while, for the rest,
material addition being necessary and mandatory.
The microplasma welding offers good quality
at a reasonable price and rapidly. The (effective)
welding takes place also under the microscope, in a
way the spot overlapping should be optimal, namely
more than ½. Different types of welding on dental
alloys used in Removable Partial Denture Technology
were experimented before; this is the reason why we
considered interesting this experience in Orthodontics.
On this type of welding, the alloy’s lowest thickness is
0.4-0.5 mm, while in that of the orthodontic ring the
ring thickness is 0.3 mm. Therefore, there were some
_____________________________
Cristina Bortun et al 203

welding difficulties when the power degree was too
high, because the orthodontic ring effectively melted.
conclUsions
1. It is recommended to weld the orthodontic
rings using Wipla wire.
2. The tangential welding is much more
comfortable in comparison with the point-like one
and has better results.
acKnowlEdgEMEnt
This study was supported by the CNCSIS Grant
Type A, No. 744/2006
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