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avai lab le at www.sc iencedi rec t .com

journa l homepage: www.e lsev ier .com/ locate /e tap

Exposure to metals from orthodontic appliances by hairmineral analysis

Marcin Mikulewicza,∗, Katarzyna Chojnackab, Agnieszka Zielinskab, Izabela Michalakb

a Department of Dentofacial Orthopeadics and Orthodontics, Medical University of Wrocław, ul. Krakowska 26, 50-425 Wrocław, Polandb Institute of Inorganic Technology and Mineral Fertilizers, Wrocław University of Technology, Wrocław, Poland

a r t i c l e i n f o

Article history:

Received 7 December 2010

Received in revised form

4 February 2011

Accepted 24 February 2011

Available online 22 March 2011

Keywords:

Exposure to metals

Orthodontic treatment

Hair mineral analysis

Nickel

a b s t r a c t

The aim of the present work was to investigate the exposure of patients to metals released

from orthodontic appliances in situ. The paper reports the results of biocompatibility studies

of orthodontic appliances by an in vivo method using hair sampled from the group of patients

(N = 28) and a control group (N = 18). The mean content of metals (Ni, Cr, Mn, Fe) in hair

that were hypothesized to be systemically absorbed from stainless steel, was provided. The

highest difference between the groups was found for Ni (39% higher level in hair of patients),

Mn (18%), Fe (4.1%), Cr (2.5%), as calculated by a new dimensionless metal release coefficient

(˛). The second coefficient defined in the present work (ˇ) corresponded to the difference in

the mean content of elements between the groups. The coefficient was the highest for Fe,

subsequently Ni, Mn and Cr. None of the differences was statistically significant. For each

group and a given element, ranges between 10th and 90th percentile were determined. The

upper value of the range differed the mostly between the groups for Ni (82.5%) showing that

stainless steel of orthodontic appliance can be the source of exposure to this element. The

difference was also identified for Mn (26.5%). For Cr and Fe, the lower value of the range was

elevated. It was noted that 22% of patients undergoing orthodontic treatment had elevated

levels of Ni in hair.

A correlation matrix between the content of the elements in hair was calculated. Statis-

tically significant correlations were found between Cr and Fe, showing similar sources of

exposure. Multiple regression analysis showed the dependence of Ni content (dependent

variable) on the level of Co and Mg (synergism) and V (antagonism).

(Bencko, 1995; Kim and Song, 2002; Miekeley et al., 1998). Due

1. Introduction

Orthodontic treatment of different types of malocclusionincorporates the use of wide range of appliances (removable

and fixed). Elements of fixed appliances are mostly manu-factured from stainless steel/nickel–titanium alloys. Becauseorthodontic therapy lasts around 1.5–2 years, a question arises

∗ Corresponding author.E-mail addresses: mmikulewicz@poczta.onet.pl, mikulewicz.marcin

1382-6689/$ – see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.etap.2011.02.009

© 2011 Elsevier B.V. All rights reserved.

about potential accumulation and influence on an organism ofcorrosion products (Mikulewicz and Chojnacka, 2010, 2011a).

Hair mineral analysis is the technique of the assessmentof human chronic exposure to toxic and non-toxic metals

@gmail.com (M. Mikulewicz).

to the difficulties in sampling of invasive matrices, such asblood or tissues of internal organs, non-invasive markers ofexposure (urine, saliva, hair, nails) seem to be good indicators

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Table 1 – The content of elements in human scalp hair (N1 = 28, N0 = 18), control group (0), experimental group (1), and�g/g d.h.m. (dry hair mass).

Element Control Experimental p U Mann–Whitney

Mean – 0 SD – 0 Mean – 1 SD – 1

Ni 0.3642 0.2485 0.5073 0.3729 0.166200

12

o2taeirEsHirtaln

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Cr 0.1298 0.1316Mn 0.4850 0.4912Fe 11.74 8.0698

f determination of potentially toxic doses of metals (Bencko,005). The technique has found an application in environmen-al biomonitoring (Maloney et al., 1998; Lee et al., 2000; Saadnd Hassanien, 2001; Klevay et al., 2002; Bencko, 2005; Benckot al., 2009; Zhang et al., 2007). The content of bioelementsn hair for healthy population is recommended by U.S. Envi-onmental Protection Agency (U.S. EPA), International Atomicnergy Agency (IAEA) as significant biomarker of human expo-ure to metals (Bencko, 2005; Moreda-Pineiro et al., 2007).air is highly mineralized (compared to blood and urine); for

nstance, the content of Pb is 10–50 and 100–500 times higher,espectively (Lekouch et al., 1999). Although it is required thathe sample is purified from organic components before thenalytical process, the concentrations of trace elements are atevels detectable by e.g. ICP-MS or ICP-OES with an ultrasonicebulizer (Bencko et al., 2009).

The aim of the present study was to investigate the expo-ure to metals of patients undergoing orthodontic treatmenty using hair mineral analysis.

. Materials and methods

.1. Sampling

he material was sampled from 46 individuals (28 orthodonticatients, 18 subjects in the control group). The average dura-ion of the orthodontic treatment was 1.5–2 years. The averagege of individuals was 20 ± 2 in the whole group. Among sub-ects there were 31 females and 15 males. Age and sex profile ofoth groups (patients and control) was similar. All the individ-als were healthy. Hair was sampled from the back of the heady stainless steel surgical scissors by hairdresser. Hair samplesere stored in paper envelopes. Hair was washed with a pro-rietary baby shampoo under laboratory conditions and thenith water. Shampoo selection was based on its compositionamong the metal cations, only sodium was present. After

he washing procedure, hair samples underwent purificationrom organic components.

.2. Analytical methods

sample (0.5 g) was purified from organic matter with concen-rated nitric acid – 69% m/m (5 ml), spectrally pure (Suprapur,erck) in Teflon bombs in microwave oven Milestone Start

(USA). The selected parameters of the process assured the

omplete digestion of samples. After mineralization, samplesere diluted with re-demineralized water (Millipore Simplic-

ty) to 50 g.

.1331 0.0883 0.5813

.5739 0.6200 0.6445

.22 9.9111 0.7957

Mineralized samples underwent multielemental analysis.The concentration of the following elements was deter-mined: Ni, Cr, Mn, Fe. ICP-OES Varian-Vista MPX (Australia),equipped with ultrasonic nebulizer CETAC U5000AT+ wasused. Also, determinations of additional elements wereundertaken.

The analyses were carried out in quality management sys-tem according to PN-EN ISO/IEC 17025:2005. Quality assuranceof the test results was achieved by using certified referencematerial – Human Hair NCS ZC81002 from the China NationalAnalysis Centre. The samples were analyzed in three repeats(the reported results of analysis were arithmetic mean, therelative standard deviation was <5%).

2.3. Statistical methods

Statistical analysis of the results was performed by the soft-ware Statistica ver. 9.0. Descriptive statistics (means, standarddeviations) were reported. Normality of distribution of exper-imental results was assessed by Shapiro–Wilk test. On thisbasis, statistical test was selected, which was used to inves-tigate the significance of differences between the groups.For normally distributed results, the parametric Student’st-test was used. In the case of non-parametric data, theMann–Whitney U test was applied. Statistical significancebetween the groups was accepted at the ˛ < 0.05 level. Analysisof correlation was carried out by determination of the Pearsoncoefficient. Correlation was considered statistically significantat ˛ < 0.05. Also, multiple regression analysis was undertakenby the use of the Statistica ver. 9.0 programme.

3. Results

Fig. 1 and Table 1 describe the contents of elements in hair ofthe control group (0) and patients (1). The differences in themean values were markedly larger for Ni and Mn in the testgroup of patients (39 and 18%, respectively). The content of Fewas also slightly higher (4%), although Cr was lower (2.5%) inthe patient group with respect to control. The Shapiro–Wilktest showed the lack of normal distribution of the results.Therefore, a non-parametric U Mann–Whitney test was usedto assess the significance of differences between the groups.The differences between all the groups were not statisticallysignificant. For the control and experimental group, ranges

were elaborated between 10 and 90% of observations (Table 2).The upper value of the range for the group of patients vs. con-trol differed; this was mostly (was higher) for Ni (82%), Mn(26%), Cr (16%), and was lower for Fe (8%).

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Table 2 – Ranges of values between 10th and 90th percentile for elements in hair for the control group (0) andexperimental (1), �g/g d.h.m. (dry hair mass).

Element Control Experimental

Percentile – 10 (0) Percentile – 90 (0) Percentile – 10 (1) Percentile – 90 (1)

Ni 0.1910 0.7415 0.1848 1.3530Cr 0.0000 0.3195 0.0402 0.2692Mn 0.0913 1.3304 0.1123 1.6831Fe 4.6357 22.053 5.5839 20.404

wee

Fig. 2 – Matrix of figures presenting correlations bet

Interactions between the contents of the studied ele-ments in hair were analyzed and presented as correlationplot matrices (Fig. 2). Statistically significant correlations wereencountered only between Fe and Cr (synergism) (Table 3).Also, interpretation by multiple regression analysis wasundertaken, with the additional consideration of other ele-ments, as reported previously (Mikulewicz and Chojnacka,2011b). The following equation was derived:

CNi = 1.76 × CCo + 0.00851 × CMg − 1.21 × CV + 0.144 (1)

Table 3 – Correlation matrix between the content ofelements in hair in all individuals.

Cr Fe Mn Ni

1.0000 0.4463 0.2029 0.0998 Crp = 0.001 p = 0.167 p = 0.5001.0000 0.2445 0.2171 Fe

p = 0.094 p = 0.1381.0000 0.1309 Mn

p = 0.3751.0000 Ni

n the content of elements in hair of all individuals.

Fig. 2 reports correlation matrix between the content ofsingle elements. Multiple regression enabled the derivation ofinformation on the effect of several independent variables on asingle independent variable – a level of Ni in hair. It was foundthat this was related additionally to hair levels of Co and Mg.The above equation was analogous to the formula determinedpreviously for the solutions of artificial saliva (Mikulewiczand Chojnacka, 2011b). Statistically significant dependencebetween the content of Co and Ni was determined. In patienthair, the additional influence of the following independentvariables was found: Mg (synergism) and V (antagonism) onthe dependent variable – the content of Ni in human hair.

The following coefficients were defined – ˛hair and ˇhair

in the assessment of bioavailability of released metal ionsinto the organism of a patient, as the quotient (dimensionlessvalue):

˛Hair = CWith apply

CWithout apply(2)

and the difference (expressed as mg/kg):

ˇHair = CWith apply − CWithout apply (3)

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Median Upper-lower quartile Min-Max10

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

aN

i, m

g/k

g

Median Upper-lower quartile Min-Max10

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Cr, m

g/k

g

Median Upper-lower quartile Min-Max10

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Mn, m

g/k

g

Median Upper-lower quartile Min-Max10

0

5

10

15

20

25

30

35

40

45

50

55

Fe, m

g/k

g

b

c

d

Fig. 1 – The content of Ni (a), Cr (b), Mn (c) and Fe (d) incontrol (0) and experimental group (1).

Table 4 – Coefficients ˛ and ˇ in hair of patients.

˛Hair ˇHair, �g/g

Cr 1.025 0.0033

Fe 1.041 0.4896Mn 1.183 0.0889Ni 1.393 0.1431

The values of these coefficients are presented in Table 4.The coefficient ˛hair was a measure of concentration factor,ˇhair was the difference between the content of elements inpatients vs. control.

4. Discussion

In toxicology and environmental sciences, markers of expo-sure to toxic metals usually concern the sites of eliminationor accumulation, although measurement in these sites ofaccumulation (internal organs – liver, kidneys, bones) is notpossible by non-invasive means (Fairbrother et al., 2007). Themain route of elimination of metal ions is urine, because oftheir hydrophilic nature and small ionic radii. As metal cationsmay bind to cysteinyl thiol groups in proteins, keratinoussubstances such as hair and act as both additional routes ofelimination as well as indices of intermediate to longer termbioaccumulation (Fairbrother et al., 2007).

In the majority of in vivo studies aimed at the assessmentof the concentrations of released metal ions from orthodon-tic appliances, the biomarkers of exposure chosen includesaliva (Amini et al., 2008; Eliades et al., 2003; Kerosuo et al.,1997; Kocadereli et al., 2000; Matos de Souza and Macedo deMenezes, 2008; Petoumeno et al., 2008), serum (Agaoglu et al.,2001), mucosa cells (Amini et al., 2008; Faccioni et al., 2003)and urine (Menezes et al., 2007). However, such biomarkersare more suited to acute, rather than chronic monitoring ofexposure to trace elements and do not provide evidence ofaccumulation (Eliades et al., 2003).

Mineral analysis of hair is accepted as a meaningful indi-cator of chronic exposure to metals and the content ofnickel in hair, nails correlates with that of blood (Bencko,1995; Gammelgaard, 1990; Shamberger, 2002; Unkiewicz-Winiarczyk et al., 2009; Fairbrother et al., 2007). Indeed, hairmineral analysis is recommended by the US EnvironmentalProtection Agency (U.S. EPA) and International Atomic EnergyAgency (IAEA) as one of the most credible biomarkers ofhuman exposure to metals (Bencko, 2005). In the present work,hair mineral analysis was selected as a biomarker to assessexposure to toxic metals of patients undergoing orthodontictreatment. This report is in agreement with previous stud-ies, where nickel ions were shown to be bioavailable aftersampling in various matrices, such as urine, saliva and blood(Gammelgaard, 1990; Fairbrother et al., 2007). In the avail-able literature there is lack of long-term in vivo studies thathave assessed chronic exposure during orthodontic treatment(Mikulewicz and Chojnacka, 2010, 2011a).

In Table 5 reference ranges are reported for the contentof elements in hair of commercial laboratories in US and

Australia which specialize in mineral analysis of hair, aswell as literature data (Korea, Brazil, Sweden, Italy, Poland).Reference ranges present a wide spectrum of data, which

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Table 5 – Reference ranges and mean (for Sweden) for the content of Cr, Fe, Ni and Mn in human hair, �g/g.

Element Commerciallaboratories

Scientificdata

Doctor’sDataa

TraceelementsInc.b

HairAnalysisLabc

Koreanreferencerangesd

Koreanreferenceranges –kindergartenchildrene

Brazil,Rio deJaneirof

Swedeng Schoolchildren(boys)h

Poland,Wrocławi

Cr 0.23–0.50 0.20–0.80 0.04–0.35 0.80–0.90 0.20–0.90 0.78–1 0.167 0.08–4.56 0.91–1.53Fe 6–17 5–16 0.9–3 11–13 7–21 6–15 9.6 5.9–36.8 16.9–29.6Ni <0.4 <0.1 10–32 n.a. n.a. <1.6 0.430 0.07–3.40 0.508–1.534Mn 0.18–0.60 0.10–1.30 0.04–0.35 0.23–0.32 0.10–0.60 5 0.560 0.04–0.77 0.459–1.046

a http://www.doctorsdata.com – entry date 01.02.2010.b http://www.traceelements.com – entry date 01.02.2010.c http://www.hairanalysiskit.com – entry date 01.02.2010.d Kim and Song (2002).e Park et al. (2007).f Miekeley et al. (1998).g Rodushkin and Axelssom (2000).

h Senofonte et al. (2000).i Chojnacka et al. (2010).

is the result of the application of various methodologicalapproaches towards analysis and assessment of various pop-ulations (ethnical and age groups). So far, internationallyaccepted reference ranges for the content of Ni, Cr, Fe andMn have not been established and so we have referred tothe ranges reported by other authors. Additionally, in thepresent work, new ranges were determined for the groupof patients before treatment (Table 2). In this work, the fol-lowing results for the mean content of elements in hair inexperimental and control group were found: Cr 0.133/0.130, Fe12.2/11.7, Ni 0.507/0.364 mg/kg, respectively. Referring to theranges determined for non-exposed populations, the contentof Ni exceeded the upper normal value in 22% of the patients.This shows that release of Ni from orthodontic appliances canconstitute a significant source of exposure to this element.

Nickel is a toxic metal, widely used in various industrialprocesses (mining, steel or electroplating) and the level ofexposure is frequently related to the degree of urbanizationof the assayed population (Jergovic et al., 2010). Aside fromoccupational sources of exposure, nickel can also be encoun-tered in cigarette smoke or in asphalt (road dust) (Sturaroet al., 1994). Ni accumulates with age and it is hypothe-sized that excessive exposure causes cardiovascular disease,contact dermatitis, immune dysfunction and cancer (Jergovicet al., 2010; Olmedo et al., 2010; Sturaro et al., 1994). Themechanisms of toxicological activity include impairment ofenzymatic function, hormonal metabolism and the stabilityof various biomolecules (Sturaro et al., 1994). Since Ni reducesthe number of sulfhydryl groups in proteins, reactive oxygenspecies are produced and consequently oxygen stress occurs(Baig, 2009; Kandhro et al., 2010). Liver and kidney are amongthe sites of toxicological action of Ni (Sturaro et al., 1994).

There are few published reports on exposure to Ni by hairmineral analysis (HMA). In these studies, the content of Ni

and other elements in hair in an exposed population wascompared with that of non-exposed individuals. Attempts tocompare the results with reference ranges reported by otherresearchers were also made. However, the authors concluded

that relating to the results of the control groups was betterjustified. A probable explanation can be methodological differ-ences (sample preparation procedures, analytical techniques,etc.) and characteristics of a given population (geographicallocation, dietary habits, the composition of drinking water,ethnicity, etc.), which strongly influence the composition ofhair. Similarly in the present work, the results in the exposedgroup were related to the control group.

Sturaro et al. (1994) investigated the exposure to Ni of steelmill workers by analysis of the composition of scalp hair, incomparison with blood and urine. Statistically significantlyhigher levels of Ni in all the matrices were found in com-parison with control populations. The content of Ni in hairin the control group was 5.25 mg/kg and increased 72 and62% (9.02, 13.76 mg/kg) in hair of workers of steel mill (qual-ity and production department, respectively) and the contentof Ni increased with the time of employment. These resultswere well correlated with the composition of the remainingmatrices. This confirmed that the analysis of Ni in hair wasa good indicator of long-term exposure. Among 6 employeesof production department, three had abnormal liver function,one proteinuria and two exhibited allergic dermatitis. Similarresults were obtained for Cr (Sturaro et al., 1994).

In another study (Jergovic et al., 2010) the authors comparedNi and other toxic elements in hair from citizens living in theproximity of battlefields. The content of Ni in areas whereheavy fighting had taken place was evaluated as 0.36 mg/kgvs. 0.28 mg/kg in areas of moderate fighting. The differenceswere statistically significant. The reference ranges reported inthis study were 0.2–1.0 and 0.08–0.90 mg/kg. Grabeklis et al.(2010) investigated the content of Ni in hair of chemical plantworkers. In the results, the authors underlined that the Nilevel increased from 0.360 in the control to 0.459 mg/kg in theexposed population (28%). Also, the content of Cr, Mn and Fe

increased in the hair of employees. The differences betweenthe groups were statistically significant.

In the study undertaken by Kandhro et al. (2010), smokingand non-smoking hypertensive patients were investigated vs.

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ontrol for the content of metals (e.g. Ni) in hair. Hair of hyper-ensive patients contained twice as much Ni as non-smokers.he content of Ni increased with level of smoking (ca. 30%).

t was hypothesized that Ni was accumulated from cigarettemoke by the inhalation route, which consequently increasedhe risk of hypertension. It was also suggested that the mecha-ism of toxic action was the replacement of Zn with Ni, which

ed to physiological disorders (Kandhro et al., 2010).

. Conclusions

ineral analysis of hair enabled long-term assessment ofxposure to metals released during orthodontic treatment.iomarkers of exposure such as hair metal content enable notnly the assessment of the degree of release of metal ionsrom orthodontic appliances, but also facilitate the evalua-ion of toxic metal bioavailability. This is possible through thessessment of the quantity in which the excess of elements isliminated from an organism and deposited in hair tissue.

Differences in the content of metals in hair betweenxposed and non-exposed groups were not significant statis-ically in this report, because this was a preliminary work inhich a small number of participants was included. The valuef HMA, in particular in the context of investigation of chronic

ong-term exposure to Ni, has found confirmation elsewhereJergovic et al., 2010; Sturaro et al., 1994). Hence, our futuretudies in orthodontic patients, will involve additional patientumbers and consideration of confounding factors such asetal exposure from other sources.In this report, patient hair analysis revealed that orthodon-

ic treatment with stainless steel appliances is the source ofxposure to nickel. This was the first attempt to use humanair to investigate exposure of human to metals from fixedrthodontic appliances. Aside from Ni, hair contents of Cr ande were also higher in orthodontic patients than in the con-rol. These findings showed that determination of metals inair is a useful biomarker of exposure to metals of orthodonticatients.

onflict of interest

one.

cknowledgments

his research was financially supported by Ministry of Sciencend Higher Education (no. N N204 019135) and The Nationalentre for Research and Development in Poland (no. N R13006 10).

e f e r e n c e s

gaoglu, G., Arun, T., Izgi, B., Yarat, A., 2001. Nickel andchromium levels in the saliva and serum of patients with

fixed orthodontic appliances. Angle Orthod. 71,375–379.

mini, F., Borzabadi, F.A., Jafari, A., Rabbani, M., 2008. In vivostudy of metal content of oral mucosa cells in patients with

a r m a c o l o g y 3 2 ( 2 0 1 1 ) 10–16 15

and without fixed orthodontic appliances. Orthod. Craniofac.Res. 11, 51–56.

Baig, J.A., 2009. Evaluation of arsenic, cobalt, copper andmanganese in biological samples of steel mill workers byelectrothermal atomic absorption spectrometry. Toxicol. Ind.Health 25, 59–69.

Bencko, V., 1995. Use of human hair as a biomarker in theassessment of exposure to pollutants in occupational andenvironmental settings. Toxicology 101, 29–39.

Bencko, V., 2005. In: Tobin, J. (Ed.), Hair and Exposure toEnvironmental Pollutants. Hair in Toxicology. An ImportantBio-monitor, vol. 7. RSC Publishing Cambridge, pp. 159–172.

Bencko, V., Rames, J., Fabianowa, E., Pesek, J., Kakubis, M., 2009.Ecological and human health risk aspects of burningarsenic-rich coal. Environ. Geochem. Health 31, 239–243.

Chojnacka, K., Zielinska, A., Górecka, H., Dobrzanski, Z., Górecki,H., 2010. Reference values for hair minerals of Polish students.Environ. Toxicol. Pharmacol. 29, 314–319.

Eliades, T., Trapalis, C., Eliades, G., Katsavrias, E., 2003. Salivarymetal levels of orthodontic patients: a novel methodologicaland analytical approach. Eur. J. Orthod. 25, 103–106.

Faccioni, F., Franceschetti, P., Cerpelloni, M., Fracasso, M.E., 2003.In vivo study on metal release from fixed orthodonticappliances and DNA damage in oral mucosa cells. Am. J.Orthod. Dentofacial Orthop. 124, 687–694.

Fairbrother, A., Wenstel, R., Sappington, K., Wood, W., 2007.Framework for metals risk assessment. Ecotoxicol. Environ.Saf. 68, 145–227.

Gammelgaard, N.K.V., 1990. Nickel in nails, hair and plasma fromnickel-hypersensitive women. Derm. Venerol. (Stock.) 70,417–420.

Grabeklis, A.R., Skalny, A.V., Nechiporenko, S.P., Lakarov, E.V.,2010. Indicator ability of biosubstances in monitoring themoderate occupational exposure to toxic metals. J. TraceElements Med. Biol., doi:10. 1016/j. jtemb. 2010. 10. 014,http://www.doctorsdata.com – entry date 01. 02. 2010.http://www.hairanalysiskit.com – entry date 01. 02. 2010.http://www.traceelements.com – entry date 01.02.2010.

Jergovic, M., Miskulin, M., Puntaric, D., Gmajnic, R., Milas, J.,Sipos, L., 2010. Cross-sectional biomonitoring of metals inadult populations in post-war eastern Croatia: differencesbetween areas of moderate and heavy combat. Public Health,doi:10.3325/cmj.2010.51.451.

Kandhro, G.A., Wadhwa, S.K., Shah, A.Q., 2010. Evaluation ofcadmium, lead, nickel and zinc status in biological samples ofsmokers and nonsmokers hypertensive patients. J. Hum.Hypertens. 24, 34–43.

Kerosuo, H., Moe, G., Hensten-Pettersen, A., 1997. Salivary nickeland chromium in subjects with different types of fixedorthodontic appliances. Am. J. Orthod. Dentofacial Orthop.111, 595–598.

Kim, G.N., Song, H.J., 2002. Hair mineral analysis of normalKorean children. Korean J. Dermatol. 40, 1518–1526.

Klevay, L.M., Christopherson, D.M., Shuler, T.R., 2002. Lead in hairand gasoline. Environ. Toxicol. Pharmacol. 11,141–142.

Kocadereli, L., Atac, P.A., Kale, P.S., Ozer, D., 2000. Salivary nickeland chromium in patients with fixed orthodontic appliances.Angle Orthod. 70, 431–434.

Lee, W.-C., Lee, M.-J., Lee, S.-M., Kim, J.-S., Bae, C.-S., Park, T.-K.,2000. An observation on the mercury contents of scalp hair inthe urban residents of South Korea. Environ. Toxicol.Pharmacol. 8, 275–278.

Lekouch, N., Sedki, A., Bouhouch, S., Nejmeddine, A., Pineaus, A.,Pihanc, J., 1999. Trace elements in children’s hair as related toexposure in wastewater spreading field of Marrakesh,

Morocco. Sci. Total Environ. 243, 323–328.

Maloney, S.R., Phillips, C.A., Mills, A., 1998. Mercury in the hair ofcrematoria workers. Lancet 352, 1602–11602.

Journal Identification = ENVTOX Article Identification = 1406 Date: May 26, 2011 Time: 10:7 am

n d p

16 e n v i r o n m e n t a l t o x i c o l o g y a

Matos de Souza, R., Macedo de Menezes, L., 2008. Nickel,chromium and iron levels in the saliva of patients withsimulated fixed orthodontic appliances. Angle Orthod. 78,345–350.

Menezes, L.M., Quintão, C.A., Bolognese, A.M., 2007. Urinaryexcretion levels of nickel in orthodontic patients. Am. J.Orthod. Dentofacial Orthop. 131, 635–638.

Miekeley, N., Dias Carneiro, M.T.W., Porto da Silveira, C.L., 1998.How reliable are human hair reference intervals for traceelements? Sci. Total Environ. 218, 9–17.

Mikulewicz, M., Chojnacka, K., 2010. Trace metal release fromorthodontic appliances by in vivo studies: a systematicliterature review. Biol. Trace Elem. Res. 137, 127–138.

Mikulewicz, M., Chojnacka, K., 2011a. Release of metal ions fromorthodontic appliances by in vitro studies: a systematicliterature review. Biol. Trace Elem. Res. 139, 241–256.

Mikulewicz, M., Chojnacka, K., 2011b. Trace metal ions releasefrom orthodontic appliances by in vitro study. Sent to theeditorial office of Biol. Trace Elem. Res.

Moreda-Pineiro, J., Alonso-Rodrigues, E., Lopez-Mahia, P.,Muniategui-Lorenzo, S., Prada-Rodriguez, D., Moreda-Pineiro,A., Bermejo-Barrera, P., 2007. Determination of major andtrace elements in human scalp hair by pressurized-liquidextraction with acetic acid and inductively coupledplasma-optical emission spectrometry. Anal. Bioanal. Chem.388, 441–449.

Olmedo, P., Pla, A., Hernández, A.F., López-Guarnido, O., Rodrigo,

L., Gil, F., 2010. Validation of a method to quantify chromium,cadmium, manganese, nickel and lead in human whole blood,urine, saliva and hair samples by electrothermal atomicabsorption spectrometry. Anal. Chim. Acta 659, 60–67.

h a r m a c o l o g y 3 2 ( 2 0 1 1 ) 10–16

Park, H., Shin, K., Kim, J., 2007. Assessment of reference valuesfor hair minerals of Korean preschool children. Biol. TraceElem. Res. 116, 119–130.

Petoumeno, E., Kislyuk, M., Hoederath, H., Keilig, L., Bourauel, C.,Jäger, A., 2008. Corrosion susceptibility and nickel release ofnickel titanium wires during clinical application. J. Orofac.Orthop. 69, 411–423.

Rodushkin, I., Axelssom, M.D., 2000. Application of doublefocusing sector field ICP-MS for multielementalcharacterization of human hair and nails. Part II. A study ofthe inhabitants of northern Sweden. Sci. Total Environ. 262,21–36.

Saad, A., Hassanien, M.A., 2001. Assessment of arsenic level inthe hair of the nonoccupational Egyptian population: pilotstudy. Environ. Int. 27, 471–478.

Senofonte, O., Violante, N., Caroli, S., 2000. Assessment ofreference values for elements in human hair of urbanschoolboys. J. Trace Elem. Med. Biol. 14, 6–13.

Shamberger, R.J., 2002. Validity of hair mineral testing. Biol. TraceElem. Res. 87, 1–25.

Sturaro, A., Parvoli, G., Doretti, L., Allegri, G., Costa, C., 1994. Theinfluence of color, age and sex on the content of zinc, copper,nickel, manganese and lead in human hair. Biol. Trace Elem.Res. 40, 1–8.

Unkiewicz-Winiarczyk, A., Bagniuk, A., Gromysz-Kałkowska, K.,Szaubartowska, E., 2009. Calcium, magnesium, iron, zinc andcopper concentration in the hair of tobacco smokers. Biol.

Trace Elem. Res. 128, 152–160.

Zhang, H., Chai, Z., Sun, H., 2007. Human hair as a potentialbiomonitor for assessing persistent organic pollutants.Environ. Int. 33, 685–693.