Release of nickel and chromium ions from orthodontic wires following the use of teeth whitening mouthwashes
Mirhashemi et al. Progress in Orthodontics
Release of nickel and chromium ions from orthodontic wires following the use of teeth whitening mouthwashes
AmirHossein Mirhashemi 2
Sahar Jahangiri 0
MohammadJavad Kharrazifard 1
0 School of Dentistry, Tehran University of Medical Sciences , Tehran , Iran
1 Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences , Tehran , Iran
2 Orthodontic Department, School of Dentistry, Tehran University of Medical Sciences, International Campus, Laser Research Center of Dentistry , Tehran , Iran
Background: Corrosion resistance is an important requirement for orthodontic appliances. Nickel and chromium may be released from orthodontic wires and can cause allergic reactions and cytotoxicity when patients use various mouthwashes to whiten their teeth. Our study aimed to assess the release of nickel and chromium ions from nickel titanium (NiTi) and stainless steel (SS) orthodontic wires following the use of four common mouthwashes available on the market. Methods: This in vitro, experimental study was conducted on 120 orthodontic appliances for one maxillary quadrant including five brackets, one band and half of the required length of SS, and NiTi wires. The samples were immersed in Oral B, Oral B 3D White Luxe, Listerine, and Listerine Advance White for 1, 6, 24, and 168 h. The samples immersed in distilled water served as the control group. Atomic absorption spectroscopy served to quantify the amount of released ions. Results: Nickel ions were released from both wires at all time-points; the highest amount was in Listerine and the lowest in Oral B mouthwashes. The remaining two solutions were in-between this range. The process of release of chromium from the SS wire was the same as that of nickel. However, the release trend in NiTi wires was not uniform. Conclusions: Listerine caused the highest release of ions. Listerine Advance White, Oral B 3D White Luxe, and distilled water were the same in terms of ion release. Oral B showed the lowest amount of ion release.
Ions; Nickel; Chromium; Mouthwash; Wire
Fixed orthodontic wires and brackets are made of stainless
steel (SS) and nickel titanium (NiTi) which consists of
chromium, cobalt, nickel, and titanium [
]. All metal
components undergo corrosion in the oral environment
due to chemical, mechanical, thermal, microbiological,
and enzymatic changes leading to release of ions .
Electrochemical processes play an important role in corrosion
when two alloys and one medium as the electrolyte are
present. The alloy with lower resistance against corrosion
acts as the anode and dissolves into the electrolyte, and
ions are then released.
Release of ions can cause discoloration of the adjacent
soft tissues, allergic reactions, or pain. The released ions
can also cause toxic and biological side effects [
Nickel can cause allergic reactions . Allergic reactions
to chromium released from orthodontic components
have also been reported [
]. Aside from the allergic
reactions, release of ions may even cause cytotoxic effects,
mutagenesis, and carcinogenesis [
Tooth color and appearance of the teeth significantly
affect the self-esteem and social self-image [
]. Thus, many
patients seek tooth bleaching which can be performed in
the office or at home [
]. Several over-the-counter
bleaching products are available on the market. These
products contain lower percentage of bleaching agents compared
to in-office bleaching agents. These products, available in
the form of mouthwashes, do not require a prescription and
are usually used daily over a period of 2 weeks .
Several studies have assessed the release of ions from
orthodontic wires and brackets in contact with the saliva
of 120 wires were obtained (60 NiTi and 60 SS wires).
The wires were cleaned using acetone, rinsed with
distilled water, and dried. Orthodontic components for
one maxillary quadrant including five brackets, one
band and wire were placed in a screw-top vial (10 mm
volume and a total of 120 samples). Since sample size
was 3 in each group [
] and the assessments were
made at four time-points, a total of 60 wires were used.
The vials were divided into five groups each with 24
samples. In each group, 10 mL of the respective
solutions were poured (12 containers containing SS and 12
containing NiTi wires).
The samples were incubated at 37 °C for 1, 6, and 12 h
and 1 week. At each time-point, 15 vials of each type of
wire were randomly chosen and removed from the
incubator. The wires were removed from the solution, and
then, one drop of 65% nitric acid was added to stabilize
the released ions. Calibration was done by measuring
the amount of nickel released using atomic absorption
spectroscopy. Univariate ANOVA served to assess the
effect of mouthwashes on release of nickel and chromium
ions from the orthodontic wires. Since the interaction
of the variables was significant, one-way ANOVA and
Tukey’s HSD test were used to assess the effect of each
The results showed an increase in release of nickel and
chromium ions in all mouthwashes and at all time-points
from both types of wires (Tables 2, 3, 4, 5, 6, and 7). The
release of nickel ions from both types of wires at all
time-points was the highest in Listerine and the lowest in Oral
B. The other two solutions were somewhere between this
range. Also, the release of chromium from SS wires was
similar to that of nickel from NiTi with the difference that
chromium release did not follow a uniform trend as in
Our results showed the release of nickel and chromium
ions from orthodontic wires in mouthwashes but not in
distilled water. This release from SS wires was less than
that from NiTi wires. At all time-points, release of both
ions in Listerine was the highest from both wires.
However, the rate of release of nickel from SS wire at 24 h
and fluoridated mouthwashes. A previous study stated
that orthodontists must be careful when prescribing
mouthwashes for orthodontic patients with orthodontic
]. Release of ions increases with increase
in the pH [
]. It has been reported that the amount of
ions released from NiTi wires is higher than that released
from SS wires [
Our study aimed to assess the release of nickel and
chromium ions during immersion in Listerine, Oral B,
Oral B 3D White Luxe, and Listerine Advance White.
In this in vitro, experimental study, release of nickel and
chromium ions from a complex of one 0.016-in wire
(NiTi or SS), five brackets, and one band (American
Orthodontics, Sheboygan USA) immersed in different
mouthwashes was evaluated. Four different
mouthwashes (Listerine, Oral B, Oral B 3D White Luxe, and
Listerine Advanced White) and distilled water as the
control group were used in this study (Table 1). A total
and 1 week in Listerine was similar to that in Oral B 3D
White Luxe. The amount of released chromium ions at
1 week from SS wire in Oral B 3D White Luxe was
higher than that in Listerine. It seems that Oral B 3D
White Luxe caused greater release of ions at 1 week.
Also, our results showed that the lowest release of ions
occurred in Oral B, although the release of chromium
ions from NiTi wire did not completely follow this
Since it has been reported that nickel and chromium
ions may have toxic or carcinogenic effects [
many orthodontists became concerned. Barret et al. in
1993 assessed the release of chromium and nickel ions
from NiTi and SS wires at 1, 7, 14, 21, and 28 days and
reported that release of nickel ions after 1 week and
chromium after 2 weeks reached the maximum level .
Thus, 1 week was considered as the longest time of
immersion in our study. Also, the release of nickel ions
from both wires was 37 times greater than that of
]. Gursoy et al. in 2005 compared the
release of ions from NiTi wires during 45 days, and the
results indicated significant increase in concentration
of these ions especially nickel and chromium released
from the wires [
]. Thus, new wires were used for
various immersion periods in our study.
Matos de Souza et al. in 2008 assessed the release of
nickel, chromium, and iron ions from three types of
brackets in the saliva in vivo and showed an abrupt
increase in concentration of nickel and chromium after
immersion of orthodontic components in all three
groups. They found no significant difference in release
of these ions among the three types of brackets [
our study, this value reached maximum at 1 week, and a
significant difference was found between the two types
of wires in this respect.
Kuhta et al. in 2009 assessed the release of ions from
three types of wires namely Thermo NiTi, SS, and NiTi
immersed in artificial saliva with a pH of 3.5 and 6.75
for 1, 7, 14, and 28 days. In their study, the highest
release of nickel from SS wires occurred at a pH of 6.75,
but at a pH of 3.5, the release rate was almost the same
in the three types of wires and was significantly higher
than that at a pH of 6.75 [
]. It seems that the
difference in the pH of Listerine (4 ± 0.5) and other solutions
(7 ± 0.5) was responsible for the difference in release of
ions. They also found that in the first 7 days of immersion,
ion release occurred more intensely compared to other
time-points; therefore, we studied 1 week duration of
immersion. Momeni Danai et al. in 2011 assessed the
release of nickel and chromium ions from SS brackets in
chlorhexidine, Persica, and Oral B; they noticed that this
rate, being close to the threshold, was higher in
chlorhexidine compared to that in other mouthwashes. Moreover,
this rate was higher in distilled water [
]. In our study,
nickel release was noticeable from SS wires in Oral B at
24 h and 1 week, and in Listerine and Advance White at
1 week. Chromium release was noted in Oral B at all
timepoints and in Oral B 3D White Luxe at 1 h. Mikulewicz et
al. in 2012 assessed the release of ions from SS wires in
artificial saliva and found that this value reached the
maximum safe threshold for nickel ions at 30 days, but
the release of chromium was lower than this rate [
In our study, the amount of nickel released in Listerine
at all time-points was close to the threshold, but the
release of chromium was not concerning.
Senkutvan et al. in 2014 assessed the release of nickel
ions from all four types of SS, NiTi, CuNiTi, and implanted
NiTi wires in artificial saliva and found that ion release in
the first 7 days was more severe compared to that in other
time-points. Also, they found that this value was the
highest for NiTi and the lowest for SS wires [
results confirmed their findings.
Jamilian et al. in 2014 evaluated ion release from NiTi
and SS wires in Oral B and Orthokin mouthwashes and
noticed that this value was lower than the safe threshold.
Also, NiTi wires released more ions than did SS wires
]. This finding was also confirmed in our study.
Tahmasebi et al. in 2015 evaluated the release of ions
from wires and brackets in Oral B fluoride mouth rinse
and found that NiTi wires had the highest release of
nickel ions and SS wires had the highest release of
]. In our study, the release of both ions
from NiTi wires was higher than that from SS wires,
although some differences were observed at different
time-points. The results of our study showed that the
release of ions from both wires in Oral B 3D White
Luxe, Listerine Advance White, and Oral B was within
the safe threshold [
14, 26, 27
], but the release of nickel
from NiTi wires in Listerine was higher than this threshold
probably due to the low pH of this solution. Thus, it seems
that more attention must be paid when prescribing this
rinse for patients with NiTi wires. Due to differences in
physiological conditions of the oral cavity [
] and in
vitro conditions, in vivo studies on this subject and use of
artificial saliva are recommended to obtain more accurate
results. Also, due to the variability in rinses available over
the counter, future studies using other mouthwashes are
It seems that Listerine causes the highest release of ions,
and Listerine Advance White, Oral B 3D White Luxe,
and distilled water were similar in terms of ion release.
Oral B caused the lowest release of ions.
This study was based on a thesis for a doctoral degree in dentistry.
This study is provided by Tehran University of Medical Sciences, International
Campus, grant number 32007.
AM owns the main idea, designed the study, and helped in data
interpretation. HE also designed the study. SJ performed the study and
searched the literature, helped in preparing the manuscript, and helped in
data interpretation. AM and SJ performed the study and interpreted the data
and prepared the final manuscript. MK performed the statistics and helped
in data interpretation. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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