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Do soft drinks affect metal ions release from orthodontic appliances?
Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
Contents lists available at ScienceDirect
Journal of Trace Elements in Medicine and Biology journal homepage: www.elsevier.com/locate/jtemb
Toxicology
Do soft drinks affect metal ions release from orthodontic appliances? Marcin Mikulewicz a,∗ , Paulina Wołowiec b , Bartłomiej W. Loster c , Katarzyna Chojnacka b a Department of Dentofacial Orthopeadics and Orthodontics, Division of Facial Abnormalities, Medical University of Wrocław, ul. Krakowska 25, 50-425 Wrocław, Poland b Department of Advanced Material Technologies, Faculty of Chemistry, Wrocław University of Technology, ul. Smoluchowskiego 25, 50-372 Wrocław, Poland c Department of Orthodontics, Dental Institute, Faculty of Medicine, Medical College, Jagiellonian University, Cracow, ul. Montelupich 4/108, 30-383 Kraków, Poland
a r t i c l e
i n f o
Article history: Received 28 November 2014 Accepted 27 March 2015 Keywords: Artificial saliva Coca Cola® Metal ions release Orthodontic appliance Stainless steel Orange juice
a b s t r a c t Objective: The effect of orange juice and Coca Cola® on the release of metal ions from fixed orthodontic appliances. Materials and methods: A continuous flow system designed for in vitro testing of orthodontic appliances was used. Orange juice/Coca Cola® was flowing through the system alternately with artificial saliva for 5.5 and 18.5 h, respectively. The collected samples underwent a multielemental ICP-OES analysis in order to determine the metal ions release pattern in time. Results: The total mass of ions released from the appliance into orange juice and Coca Cola® (respectively) during the experiment was calculated (g): Ni (15.33; 37.75), Cr (3.604; 1.052), Fe (48.42; ≥156.1), Cu (57.87, 32.91), Mn (9.164; 41.16), Mo (9.999; 30.12), and Cd (0.5967; 2.173). Conclusions: It was found that orange juice did not intensify the release of metal ions from orthodontic appliances, whereas Coca Cola® caused increased release of Ni ions. © 2015 Elsevier GmbH. All rights reserved.
Introduction Usually, scientific papers dealing with metal ions release from orthodontic appliances in in vitro conditions are performed in the environment of artificial saliva [1]. Saliva is known as one of the corrosion causing factors. All other factors present in the oral cavity, like temperature, microflora, saliva flow as well as the effect of the working parameters of the elements of the appliance, like to name just one can also be enhanced by the patient’s dietary habits [2]. Corrosion is an electrochemical process whereby in the presence of an electrolyte (saliva), the orthodontic appliance starts to act as an electric cell, in consequence of which metal ions are released. There is an observable in increase in the consumption of soft sugar-rich, acidic, drinks with some of them containing carbon dioxide, such as fruit juices or Coca Cola® especially among teenagers [3]. Orange juice has vitamins (e.g., vitamin C), phenolic compounds and flavonoids [4]. These compounds have antioxidative properties and consequently may reduce the formation of the passivation layer [5]. Although the disadvantageous effect of these
∗ Corresponding author at: ul. Krakowska 26, 50-425, Wrocław, Poland. Tel.: +48 71 784 02 99. E-mail address: [email protected] (M. Mikulewicz). http://dx.doi.org/10.1016/j.jtemb.2015.03.007 0946-672X/© 2015 Elsevier GmbH. All rights reserved.
dietary habits on teeth (caries and erosion) has been known for some time now, only a very few reports concerning the effect of soft drinks on solubilization of metal ions from orthodontic appliances have been published [6,7]. The elements that constitute the orthodontic fixed appliances are usually manufactured from stainless steel, which contains approximately 8–12% Ni and 7–22% Cr [8]. Ni in turn is known to trigger more allergic reactions than all other metals [9]. The aim of the present work is the evaluation of soft drink effect on metal ions release from orthodontic appliances under in vitro conditions, in a continuous flow system. Materials and methods Materials The evaluated material was a brand new orthodontic appliance consisting of 2 wires (0.017 × 0.025 in., Resilient OrthoformTM III Ovoid, 3M Unitek, Monrovia, CA), 4 bands (size 37+, Victory Series, 3M Unitek, Monrovia), 20 brackets (Victory Series Miniature Mesh Twin Bracket, 3M Unitek, Monrovia), and 20 elastic ligatures (Colored Unistick Ligatures, American Orthodontics). Wires, brackets, and bands were all made of stainless steel. The percentage of particular constituents of the chemical composition formed by the
M. Mikulewicz et al. / Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
Fig. 1. Experimental system for evaluation of metal ions release from orthodontic appliances.
manufacturer was: brackets (70 Fe, 17 Cr, 4 Ni, 4 Cu, 1 Mn, 1 Si, 0.3 Nb + Ta), bands (65 Fe, 17 Cr, 12 Ni, 2.5 Mo, 2 Mn, 1 Si, 0.045 P, 0.03 C, 0.03 S), and wires (68 Fe, 20 Cr, 9 Ni, 2 Mn, 1 Si, 0.10 N, 0.07 C, 0.045 P, 0.03 S). The experiments were carried out with the use of commercial orange juice (Hortex Holding, Poland) or Coca Cola® , and modified artificial saliva solution as the media flowing through the system. The composition of the modified artificial saliva was described in previous studies [10]. The pH of orange juice and artificial saliva was measured with a pH-meter (SevenMulti, Mettler Toledo, Schwerzenbach, Switzerland) at room temperature.
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nitric acid (69% m m−1 , Suprapur, Merck, Darmstadt, Germany) in a microwave oven (Milestone, USA). The solution was diluted with re-demineralized water (Simplicity UV, Millipore, Molsheim, France) to 25 mL. The artificial saliva (25 mL) was mineralized with nitric acid (2.5 mL) before the analysis. The Coca Cola® (25 mL) was degassed and partially evaporated, and then digested with concentrated HNO3 (10 mL). The digested mixture was boiled for 2 h in a covered flask, left to stand overnight, and diluted to 50 mL with re-demineralized water. The digestion procedure was performed in the following way: (1) artificial saliva: 200 ◦ C, 3 steps, 1000 W (8 min), 0 W (5 min), 1000 W (12 min), (2) orange juice: 200 ◦ C, 3 steps, 1000 W (8 min), 0 W (5 min), 1000 W (12 min), 3) Coca Cola® : microwave digestion was not possible due to the very high calorific value of the material; sand bath digestion in an open system was performed (50 mL was evaporated to the volume of 10 mL; HNO3 was added and the solution was boiled for 0.5 h and then diluted to 50 mL). The samples were then analyzed directly by inductively coupled plasma optical emission spectrometry (ICP-OES Vista MPX Varian, Brisbane, Australia) with an ultrasonic nebulizer (U5000AT+, CETAC, Omaha, USA) for the concentration of Cd, Cr, Cu, Fe, Mn, Mo, and Ni ions according to PN-EN ISO 17025 in a certified laboratory (No. AB 696 by Polish Centre for Accreditation, ILAC-MRA). In order to control the stability of the instrument, the check standard procedure was used. CRM was Combined Quality Control Standard UltraScientific with the concentrations: 0.1 and 1 g mL−1 . The detection limit for Cr was 0.00035 mg L−1 , and for Ni 0.0018 mg L−1 . The samples were analyzed in triplicates (the relative standard deviation of the measurements did not exceed 5%).
Release of metal ions into in the vitro system The in vitro system has been described in detail in previous studies [10]. The appliance was placed in a thermostated glass reactor (Fig. 1) with a cover and alternately orange juice/Coca Cola® and artificial saliva solution were made to flow through the system. Orange juice/Coca Cola® (330 mL) was flowing through the system at 37 ◦ C for 5.5 h (1.0 mL min−1 ) every day, and artificial saliva solution was flowing through the system with a flow rate reflecting the flow of saliva in the human mouth (0.5 mL min−1 ) at 37 ◦ C for the rest of the day (18.5 h). The experimental conditions of the in vitro test are reported in Table 1. The duration of the experiment was 28 days. The samples were collected at the following time intervals after days 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18, 21, and 28. As a control, orange juice and artificial saliva was made to flow through the system under the same conditions under which the experimental set was operating, but without the orthodontic appliance.
Results The results of the experiment on the release of metal ions from the orthodontic appliance in time are reported in Fig. 2 (Cr ions) and 3 (Ni ions). The total mass of the released ions (in g) is presented in Table 1. These data originate from the subtraction of the concentration obtained in the experimental samples (experimental setup with the orthodontic appliance) from the concentration present in the control samples (experimental setup without the orthodontic appliance). The quantity of released metal ions into the orange juice and Coca Cola® in the present study was compared with the outcomes of previous experiments on artificial saliva [10]. The comparison of various metal ions release kinetics is presented in Figs. 2 and 3. The total mass of solubilized ions is shown in Table 2.
Analytical methods The samples of artificial saliva and the samples of orange juice and Coca Cola® were mineralized prior to being subjected to an analysis. The orange juice (10 mL) was digested with 5 mL of Table 1 Experimental setup.
pH Density (g mL−1 ) Average flow rate (experimental) (mL min−1 ) Average flow rate (control) (mL min−1 ) Total volume (experimental) (L) Total volume (control) (L)
Orange juice
Coca Cola®
3.765 1.0402 1.01 ± 0.10
2.465 1.0384 1.01 ± 0.10
6.752 0.9966 0.51 ± 0.03
1.01 ± 0.10
0.985 ± 0.110
0.51 ± 0.02
9.37
9.40
15.8
9.35
9.38
16.0
Artificial saliva
Fig. 2. Kinetics of release of Cr ions from the orthodontic appliance.
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M. Mikulewicz et al. / Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
Fig. 3. Kinetics of release of Ni ions from the orthodontic appliance.
The pattern of kinetics of Cr ions released into orange juice is almost the same as that in artificial saliva. In the case of Coca Cola® , remarkably lower quantities of Cr ions were released. However, the rate at the initial step was similar during the first day of the experiment. Presumably, the passivation of stainless steel being dependent on Cr enrichment of the surface oxide prevented Cr ions from being further released. In both experiments with orange juice the passivation occurred after 20 days within the commencement of the experiment. The release of Ni was the most intense into the environment of Coca Cola® , with visible two distinctive rates of the release, suggesting a possible complex mechanism of the process. In the case of the orange juice, the rate was slightly higher than it was in the case of the artificial saliva. In the former, the equilibrium was reached after 15 days, whereas in the latter, after 28 days. The total amount of the released metal ions was similar in the orange juice environment (15.3 g) and in that of artificial saliva (15.5 g); it was higher (150%) after coming into contact with Coca Cola® (37.8 g). Discussion The initial, more intense release of metal ions finds the confirmation in in vivo experiments on humans [11] and animals [12], where also showed an intense initial release of metal ions only within the first month of placement of the appliance in the solution. Scientific literature reports that soft drinks consumption by youngsters has dramatically increased [3]. Over the past 20 years, the consumption of soft drinks by school children has increased 11 times [2]. It seems that soft drinks consumption patterns ought not to be recommended especially to orthodontic patients, since they increase the metal ions release but also cause a higher incidence caries. Tahmassebi et al. [13] elaborated dietary recommendations for soft drinks consumption for patients in order to reduce dental caries and corrosion of orthodontic appliance.
Shahabi et al. [6] studied the effect of dietary habits (lemon juice, vinegar, and Coca Cola® ) on the corrosion of stainless steel brackets under in vitro conditions. The thesis was that the low pH of the oral environment can contribute to the corrosion of stainless steel. Brackets were immersed in soft drinks at 37 ◦ C and in artificial saliva (control) for 6 weeks. The brackets were weighed before and after the experiment. On the basis of the differences in weights of the brackets obtained before and after the experiment, the authors concluded that the more intense corrosion occurred after exposure to Coca Cola® rather than vinegar or lemon juice. Finally, the authors recommended that orthodontic patients should minimize or eliminate the consumption of acidic drinks. This conclusion was only based on the differences of the weight between the brackets, without the author’s taking into account the actual release of metal ions and the forming of the layer of oxides [6]. The conclusions supports the point raised in this paper. Parenti et al. [7] investigated the effect of soft drinks (orange juice, Coca Cola® , and energy drink Gatorade® ) on physical and chemical properties of NiTi orthodontic wires. The wires were soaked in 10 mL of the drink for 60 min. No statistically significant differences in Young modulus, hardness, surface color change, topography, nor chemical composition (evaluated by SEM–EDS) were found. The authors concluded that the consumption of soft drinks did not lead to the degradation of NiTi wires [7]. Barcelos et al. immersed stainless steel and NiTi wires in the solution of artificial saliva and fluorides for 15 and 30 days after which they investigated the release of Ni(II) ions and the open circuit potential (OCP). The authors found that corrosion depended on a combination of the pH of saliva, contact time, and the concentration of F− ions, and they also found out that the critical pH for NiTi corrosion was 3 [14]. Danaei et al. investigated the effect of mouthwashes on the release of metal ions (Ni, Cr, Fe, Cu, and Mn) from stainless steel brackets under in vitro conditions. The brackets were incubated at 37 ◦ C for 45 days. The concentration of metal ions was determined by ICP-OES. The most intense dissolution of metal ions was found to occur in the control group (water). The lowest dissolution was observed in the chlorhexidine group as compared with Oral B and Persica (Iranian mouthwash) groups [15]. The magnitude of pH could provide another explanation of the results: orange juice (3.765), artificial saliva (6.752), and Coca Cola® (2.465). pH remained stable over the 28 days of the experiment. The difference could also be associated with the reduction of (antioxidative) properties of orange juice and oxidative properties of Coca Cola® as the medium. Coca Cola® is a carbonated soft drink, containing very high sugar levels and a low pH. Low pH intensifies the cathodic reaction of corrosion. The postulated mechanism is that at first the passivation layer of oxides is formed, which is further dissoluted by the action of protons in acidic pH, leading to the release of metal ions [16]. Theoretically, the acidic pH (ca. 3) of sugar-rich carbonated beverages can lead to the breakdown of the protective layer that is formed on the surface of stainless steel. Also Kao and Huang [17] stated that lower pH enhances corrosion of orthodontic stainless steel wires. In another study it was found that acidic
Table 2 The total mass of metal ions released during experiments (g). Metal ion
Ni Cr Fe Cu Mn Mo Cd
Artificial saliva [10]
15.54 4.435 8.923 53.45 0.8690 2.124 0.3870
Coca Cola® and artificial saliva
Orange juice and artificial saliva Orange juice
Artificial saliva
Total
Coca Cola®
Artificial saliva
Total
4.355 1.553 23.96 12.27 5.598 1.873 0.2385
10.97 2.051 24.46 45.60 3.566 8.126 0.3582
15.33 3.604 48.42 57.87 9.164 9.999 0.5967
22.51 0.9810 156.1 1.709 36.49 27.38 0.8917
15.24 0.0711
37.75 1.052 ≥156.1 32.91 41.16 30.12 2.173
M. Mikulewicz et al. / Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
pH strongly intensified the release of metal ions from orthodontic archwires. The majority of ions were released during the first week of the experiment [18]. The total quantity of the released Cr ions was higher in artificial saliva (4.44 g) than in orange juice (3.60 g), and the lowest in Coca Cola® (1.05 g). Coca Cola® intensified the release of Fe ions (a mass 18 times as large as that released in artificial saliva). In the environment of orange juice, more Fe solubilized (5 times). The release of Cu ions was similar in orange juice and slightly lower in Coca Cola® . Significantly more Mn was released in juice (10 times) and Coca Cola® (47 times), although the dose was low. Similarly to Mo: in orange juice (5 times) and Coca Cola® (15 times). In the case of Cd, also soft drinks increased the solubilization: orange juice (54%), and Coca Cola® (5.6 times). These doses were also at a very low level. The formulation of different brands of orange juice differs. This may have an impact on the dissolution process of stainless steel components. The juice in this study was exemplary, to show the effect of orange juice on solubilization of metal ions from the orthodontic appliance. The general outcome of the studies was that Coca Cola® environment facilitates solubilization of Ni(II) ions from alloys (in particular stainless steel), which was also observed in the present work. This is of particular concern, since Ni can pose toxic effects [19]. It must be admitted, though, that in vitro studies have limitations in simulation of real oral cavity conditions. The daily doses (RDD) recommended by WHO for Cr and Ni are as follows: Cr 50–200 g/day, and Ni 25–35 g/day [20]. In the present study, the mass of released Cr and Ni ions daily into different media was: Cr 0.159 (artificial saliva), 0.129 (orange juice), 0.0375 (Coca Cola® ) g/day, Ni: 0.554 (artificial saliva), 0.548 (orange juice), and 1.35 (Coca Cola® ) g/day. Conclusions The present in vitro study showed that acidic soft drinks contributed to more intense solubilization of stainless steel of which orthodontic appliances are manufactured only to a certain extent. Coca Cola® intensified the release of Ni ions, while orange juice did not seem to have a significant impact on the release of metal ions from orthodontic appliances. The ions released from orthodontic appliances were far below RDD, which means that the dissolution of stainless steel did not provide a substantial increase of released metal cations and as a result of which the daily dose of Cr and Ni did not remarkably increase in all tested media. Conflict of Interest The authors declare that there is no conflict of interest.
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Acknowledgment This research was financially supported by The National Centre for Research and Development in Poland (NR13000610).
References [1] Mikulewicz M, Chojnacka K. Release of metal ions from orthodontic appliances by in vitro studies: a systematic literature review. Biol Trace Elem Res 2011;139:241–56. [2] Yip HHY, Wong RWK, Hägg U. Complications of orthodontic treatment: are soft drinks a risk factor? World J Orthod 2009;10:33–40. [3] Shenkin JD, Heller KE, Warren JJ, Marshall TA. Soft drink consumption and caries risk in children and adolescents. Gen Dent 2003;51:30–6. [4] Aptekmann NP, Cesar TB. Long-term orange juice consumption is associated with low LDL–cholesterol and apolipoprotein B in normal and moderately hypercholesterolemic subjects. Lipids Health Dis 2013;12:119. [5] Foroudi S, Potter AS, Stamatikos A, Patil BS, Deyhim F. Drinking orange juice increases total antioxidant status and decreases lipid peroxidation in adults. J Med Food 2014;17:612–7. [6] Shahabi M, Jahanbin A, Esmaily H, Sharifi H, Salari S. Comparison of some dietary habits on corrosion behavior of stainless steel brackets: an in vitro study. J Clin Pediatr Dent 2011;35:429–32. [7] Parenti SI, Guicciardi S, Melandri C, Sprio S, Lafratta E, Tampieri A, et al. Effect of soft drinks on the physical and chemical features of nickel–titanium-based orthodontic wires. Acta Odontol Scand 2012;70:49–55. [8] Kusy RP. Orthodontic biomaterials: from the past to the present. Angle Orthod 2002;72:501–12. [9] Eliades T, Bourauel C. Intraoral aging of orthodontic materials: the picture we miss and its clinical relevance. Am J Orthod Dentofacial Orthop 2005;127:403–12. [10] Mikulewicz M, Chojnacka W, Wołowiec P. Release of metal ions from fixed orthodontic appliance: an in vitro study in continuous flow system. Angle Orthod 2014;84:140–8. [11] Amini F, Jafari A, Amini P, Sepasi S. Metal ion release from fixed orthodontic appliances – an in vivo study. Eur J Orthod 2012;34:126–30. [12] Mikulewicz M, Wołowiec P, Janeczek M, Gedrange T, Chojnacka K. The release of metal ions from orthodontic appliances: animal tests. Angle Orthod 2014;84:673–9. [13] Tahmassebi JF, Duggal MS, Malik-Kotru G, Curzon ME. Soft drinks and dental health: a review of the current literature. J Dent 2006;34:2–11. [14] Barcelos AM, Luna AS, Ferreira NA, Braga AVC, Lago DCP, Senna LF. Corrosion evaluation of orthodontic wires in artificial saliva solutions by using response surface methodology. Mater Res 2013;16:50–64. [15] Danaei SM, Safavi A, Roeinpeikar SM, Oshagh M, Iranpour S, Omidkhoda M. Ion release from orthodontic brackets in 3 mouthwashes: an in-vitro study. Am J Orthod Dentofacial Orthop 2011;139:730–4. [16] Huang HH, Chiu YH, Lee TH, Wu SC, Yang HW, Su KH, et al. Ion release from NiTi orthodontic wires in artificial saliva with various acidities. Biomaterials 2003;24(20):3585–92. [17] Kao CT, Huang TH. Variations in surface characteristics and corrosion behaviour of metal brackets and wires in different electrolyte solutions. Eur J Orthod 2010;32(5):555–60. [18] Kuhta M, Pavlin D, Slaj M, Varga S, Lapter-Varga M, Slaj M. Type of archwire and level of acidity: effects on the release of metal ions from orthodontic appliances. Angle Orthod 2009;79(1):102–10. [19] Schaumlöffel D. Nickel species: analysis and toxic effects. J Trace Elem Med Biol 2012;26(1):1–6. [20] Kabata-Pendias A, Pendias H. Biogeochemistry of trace elements. Warsaw: PWN; 1993. p. 53–66 (in Polish).
Contents lists available at ScienceDirect
Journal of Trace Elements in Medicine and Biology journal homepage: www.elsevier.com/locate/jtemb
Toxicology
Do soft drinks affect metal ions release from orthodontic appliances? Marcin Mikulewicz a,∗ , Paulina Wołowiec b , Bartłomiej W. Loster c , Katarzyna Chojnacka b a Department of Dentofacial Orthopeadics and Orthodontics, Division of Facial Abnormalities, Medical University of Wrocław, ul. Krakowska 25, 50-425 Wrocław, Poland b Department of Advanced Material Technologies, Faculty of Chemistry, Wrocław University of Technology, ul. Smoluchowskiego 25, 50-372 Wrocław, Poland c Department of Orthodontics, Dental Institute, Faculty of Medicine, Medical College, Jagiellonian University, Cracow, ul. Montelupich 4/108, 30-383 Kraków, Poland
a r t i c l e
i n f o
Article history: Received 28 November 2014 Accepted 27 March 2015 Keywords: Artificial saliva Coca Cola® Metal ions release Orthodontic appliance Stainless steel Orange juice
a b s t r a c t Objective: The effect of orange juice and Coca Cola® on the release of metal ions from fixed orthodontic appliances. Materials and methods: A continuous flow system designed for in vitro testing of orthodontic appliances was used. Orange juice/Coca Cola® was flowing through the system alternately with artificial saliva for 5.5 and 18.5 h, respectively. The collected samples underwent a multielemental ICP-OES analysis in order to determine the metal ions release pattern in time. Results: The total mass of ions released from the appliance into orange juice and Coca Cola® (respectively) during the experiment was calculated (g): Ni (15.33; 37.75), Cr (3.604; 1.052), Fe (48.42; ≥156.1), Cu (57.87, 32.91), Mn (9.164; 41.16), Mo (9.999; 30.12), and Cd (0.5967; 2.173). Conclusions: It was found that orange juice did not intensify the release of metal ions from orthodontic appliances, whereas Coca Cola® caused increased release of Ni ions. © 2015 Elsevier GmbH. All rights reserved.
Introduction Usually, scientific papers dealing with metal ions release from orthodontic appliances in in vitro conditions are performed in the environment of artificial saliva [1]. Saliva is known as one of the corrosion causing factors. All other factors present in the oral cavity, like temperature, microflora, saliva flow as well as the effect of the working parameters of the elements of the appliance, like to name just one can also be enhanced by the patient’s dietary habits [2]. Corrosion is an electrochemical process whereby in the presence of an electrolyte (saliva), the orthodontic appliance starts to act as an electric cell, in consequence of which metal ions are released. There is an observable in increase in the consumption of soft sugar-rich, acidic, drinks with some of them containing carbon dioxide, such as fruit juices or Coca Cola® especially among teenagers [3]. Orange juice has vitamins (e.g., vitamin C), phenolic compounds and flavonoids [4]. These compounds have antioxidative properties and consequently may reduce the formation of the passivation layer [5]. Although the disadvantageous effect of these
∗ Corresponding author at: ul. Krakowska 26, 50-425, Wrocław, Poland. Tel.: +48 71 784 02 99. E-mail address: [email protected] (M. Mikulewicz). http://dx.doi.org/10.1016/j.jtemb.2015.03.007 0946-672X/© 2015 Elsevier GmbH. All rights reserved.
dietary habits on teeth (caries and erosion) has been known for some time now, only a very few reports concerning the effect of soft drinks on solubilization of metal ions from orthodontic appliances have been published [6,7]. The elements that constitute the orthodontic fixed appliances are usually manufactured from stainless steel, which contains approximately 8–12% Ni and 7–22% Cr [8]. Ni in turn is known to trigger more allergic reactions than all other metals [9]. The aim of the present work is the evaluation of soft drink effect on metal ions release from orthodontic appliances under in vitro conditions, in a continuous flow system. Materials and methods Materials The evaluated material was a brand new orthodontic appliance consisting of 2 wires (0.017 × 0.025 in., Resilient OrthoformTM III Ovoid, 3M Unitek, Monrovia, CA), 4 bands (size 37+, Victory Series, 3M Unitek, Monrovia), 20 brackets (Victory Series Miniature Mesh Twin Bracket, 3M Unitek, Monrovia), and 20 elastic ligatures (Colored Unistick Ligatures, American Orthodontics). Wires, brackets, and bands were all made of stainless steel. The percentage of particular constituents of the chemical composition formed by the
M. Mikulewicz et al. / Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
Fig. 1. Experimental system for evaluation of metal ions release from orthodontic appliances.
manufacturer was: brackets (70 Fe, 17 Cr, 4 Ni, 4 Cu, 1 Mn, 1 Si, 0.3 Nb + Ta), bands (65 Fe, 17 Cr, 12 Ni, 2.5 Mo, 2 Mn, 1 Si, 0.045 P, 0.03 C, 0.03 S), and wires (68 Fe, 20 Cr, 9 Ni, 2 Mn, 1 Si, 0.10 N, 0.07 C, 0.045 P, 0.03 S). The experiments were carried out with the use of commercial orange juice (Hortex Holding, Poland) or Coca Cola® , and modified artificial saliva solution as the media flowing through the system. The composition of the modified artificial saliva was described in previous studies [10]. The pH of orange juice and artificial saliva was measured with a pH-meter (SevenMulti, Mettler Toledo, Schwerzenbach, Switzerland) at room temperature.
75
nitric acid (69% m m−1 , Suprapur, Merck, Darmstadt, Germany) in a microwave oven (Milestone, USA). The solution was diluted with re-demineralized water (Simplicity UV, Millipore, Molsheim, France) to 25 mL. The artificial saliva (25 mL) was mineralized with nitric acid (2.5 mL) before the analysis. The Coca Cola® (25 mL) was degassed and partially evaporated, and then digested with concentrated HNO3 (10 mL). The digested mixture was boiled for 2 h in a covered flask, left to stand overnight, and diluted to 50 mL with re-demineralized water. The digestion procedure was performed in the following way: (1) artificial saliva: 200 ◦ C, 3 steps, 1000 W (8 min), 0 W (5 min), 1000 W (12 min), (2) orange juice: 200 ◦ C, 3 steps, 1000 W (8 min), 0 W (5 min), 1000 W (12 min), 3) Coca Cola® : microwave digestion was not possible due to the very high calorific value of the material; sand bath digestion in an open system was performed (50 mL was evaporated to the volume of 10 mL; HNO3 was added and the solution was boiled for 0.5 h and then diluted to 50 mL). The samples were then analyzed directly by inductively coupled plasma optical emission spectrometry (ICP-OES Vista MPX Varian, Brisbane, Australia) with an ultrasonic nebulizer (U5000AT+, CETAC, Omaha, USA) for the concentration of Cd, Cr, Cu, Fe, Mn, Mo, and Ni ions according to PN-EN ISO 17025 in a certified laboratory (No. AB 696 by Polish Centre for Accreditation, ILAC-MRA). In order to control the stability of the instrument, the check standard procedure was used. CRM was Combined Quality Control Standard UltraScientific with the concentrations: 0.1 and 1 g mL−1 . The detection limit for Cr was 0.00035 mg L−1 , and for Ni 0.0018 mg L−1 . The samples were analyzed in triplicates (the relative standard deviation of the measurements did not exceed 5%).
Release of metal ions into in the vitro system The in vitro system has been described in detail in previous studies [10]. The appliance was placed in a thermostated glass reactor (Fig. 1) with a cover and alternately orange juice/Coca Cola® and artificial saliva solution were made to flow through the system. Orange juice/Coca Cola® (330 mL) was flowing through the system at 37 ◦ C for 5.5 h (1.0 mL min−1 ) every day, and artificial saliva solution was flowing through the system with a flow rate reflecting the flow of saliva in the human mouth (0.5 mL min−1 ) at 37 ◦ C for the rest of the day (18.5 h). The experimental conditions of the in vitro test are reported in Table 1. The duration of the experiment was 28 days. The samples were collected at the following time intervals after days 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18, 21, and 28. As a control, orange juice and artificial saliva was made to flow through the system under the same conditions under which the experimental set was operating, but without the orthodontic appliance.
Results The results of the experiment on the release of metal ions from the orthodontic appliance in time are reported in Fig. 2 (Cr ions) and 3 (Ni ions). The total mass of the released ions (in g) is presented in Table 1. These data originate from the subtraction of the concentration obtained in the experimental samples (experimental setup with the orthodontic appliance) from the concentration present in the control samples (experimental setup without the orthodontic appliance). The quantity of released metal ions into the orange juice and Coca Cola® in the present study was compared with the outcomes of previous experiments on artificial saliva [10]. The comparison of various metal ions release kinetics is presented in Figs. 2 and 3. The total mass of solubilized ions is shown in Table 2.
Analytical methods The samples of artificial saliva and the samples of orange juice and Coca Cola® were mineralized prior to being subjected to an analysis. The orange juice (10 mL) was digested with 5 mL of Table 1 Experimental setup.
pH Density (g mL−1 ) Average flow rate (experimental) (mL min−1 ) Average flow rate (control) (mL min−1 ) Total volume (experimental) (L) Total volume (control) (L)
Orange juice
Coca Cola®
3.765 1.0402 1.01 ± 0.10
2.465 1.0384 1.01 ± 0.10
6.752 0.9966 0.51 ± 0.03
1.01 ± 0.10
0.985 ± 0.110
0.51 ± 0.02
9.37
9.40
15.8
9.35
9.38
16.0
Artificial saliva
Fig. 2. Kinetics of release of Cr ions from the orthodontic appliance.
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M. Mikulewicz et al. / Journal of Trace Elements in Medicine and Biology 31 (2015) 74–77
Fig. 3. Kinetics of release of Ni ions from the orthodontic appliance.
The pattern of kinetics of Cr ions released into orange juice is almost the same as that in artificial saliva. In the case of Coca Cola® , remarkably lower quantities of Cr ions were released. However, the rate at the initial step was similar during the first day of the experiment. Presumably, the passivation of stainless steel being dependent on Cr enrichment of the surface oxide prevented Cr ions from being further released. In both experiments with orange juice the passivation occurred after 20 days within the commencement of the experiment. The release of Ni was the most intense into the environment of Coca Cola® , with visible two distinctive rates of the release, suggesting a possible complex mechanism of the process. In the case of the orange juice, the rate was slightly higher than it was in the case of the artificial saliva. In the former, the equilibrium was reached after 15 days, whereas in the latter, after 28 days. The total amount of the released metal ions was similar in the orange juice environment (15.3 g) and in that of artificial saliva (15.5 g); it was higher (150%) after coming into contact with Coca Cola® (37.8 g). Discussion The initial, more intense release of metal ions finds the confirmation in in vivo experiments on humans [11] and animals [12], where also showed an intense initial release of metal ions only within the first month of placement of the appliance in the solution. Scientific literature reports that soft drinks consumption by youngsters has dramatically increased [3]. Over the past 20 years, the consumption of soft drinks by school children has increased 11 times [2]. It seems that soft drinks consumption patterns ought not to be recommended especially to orthodontic patients, since they increase the metal ions release but also cause a higher incidence caries. Tahmassebi et al. [13] elaborated dietary recommendations for soft drinks consumption for patients in order to reduce dental caries and corrosion of orthodontic appliance.
Shahabi et al. [6] studied the effect of dietary habits (lemon juice, vinegar, and Coca Cola® ) on the corrosion of stainless steel brackets under in vitro conditions. The thesis was that the low pH of the oral environment can contribute to the corrosion of stainless steel. Brackets were immersed in soft drinks at 37 ◦ C and in artificial saliva (control) for 6 weeks. The brackets were weighed before and after the experiment. On the basis of the differences in weights of the brackets obtained before and after the experiment, the authors concluded that the more intense corrosion occurred after exposure to Coca Cola® rather than vinegar or lemon juice. Finally, the authors recommended that orthodontic patients should minimize or eliminate the consumption of acidic drinks. This conclusion was only based on the differences of the weight between the brackets, without the author’s taking into account the actual release of metal ions and the forming of the layer of oxides [6]. The conclusions supports the point raised in this paper. Parenti et al. [7] investigated the effect of soft drinks (orange juice, Coca Cola® , and energy drink Gatorade® ) on physical and chemical properties of NiTi orthodontic wires. The wires were soaked in 10 mL of the drink for 60 min. No statistically significant differences in Young modulus, hardness, surface color change, topography, nor chemical composition (evaluated by SEM–EDS) were found. The authors concluded that the consumption of soft drinks did not lead to the degradation of NiTi wires [7]. Barcelos et al. immersed stainless steel and NiTi wires in the solution of artificial saliva and fluorides for 15 and 30 days after which they investigated the release of Ni(II) ions and the open circuit potential (OCP). The authors found that corrosion depended on a combination of the pH of saliva, contact time, and the concentration of F− ions, and they also found out that the critical pH for NiTi corrosion was 3 [14]. Danaei et al. investigated the effect of mouthwashes on the release of metal ions (Ni, Cr, Fe, Cu, and Mn) from stainless steel brackets under in vitro conditions. The brackets were incubated at 37 ◦ C for 45 days. The concentration of metal ions was determined by ICP-OES. The most intense dissolution of metal ions was found to occur in the control group (water). The lowest dissolution was observed in the chlorhexidine group as compared with Oral B and Persica (Iranian mouthwash) groups [15]. The magnitude of pH could provide another explanation of the results: orange juice (3.765), artificial saliva (6.752), and Coca Cola® (2.465). pH remained stable over the 28 days of the experiment. The difference could also be associated with the reduction of (antioxidative) properties of orange juice and oxidative properties of Coca Cola® as the medium. Coca Cola® is a carbonated soft drink, containing very high sugar levels and a low pH. Low pH intensifies the cathodic reaction of corrosion. The postulated mechanism is that at first the passivation layer of oxides is formed, which is further dissoluted by the action of protons in acidic pH, leading to the release of metal ions [16]. Theoretically, the acidic pH (ca. 3) of sugar-rich carbonated beverages can lead to the breakdown of the protective layer that is formed on the surface of stainless steel. Also Kao and Huang [17] stated that lower pH enhances corrosion of orthodontic stainless steel wires. In another study it was found that acidic
Table 2 The total mass of metal ions released during experiments (g). Metal ion
Ni Cr Fe Cu Mn Mo Cd
Artificial saliva [10]
15.54 4.435 8.923 53.45 0.8690 2.124 0.3870
Coca Cola® and artificial saliva
Orange juice and artificial saliva Orange juice
Artificial saliva
Total
Coca Cola®
Artificial saliva
Total
4.355 1.553 23.96 12.27 5.598 1.873 0.2385
10.97 2.051 24.46 45.60 3.566 8.126 0.3582
15.33 3.604 48.42 57.87 9.164 9.999 0.5967
22.51 0.9810 156.1 1.709 36.49 27.38 0.8917
15.24 0.0711
37.75 1.052 ≥156.1 32.91 41.16 30.12 2.173
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pH strongly intensified the release of metal ions from orthodontic archwires. The majority of ions were released during the first week of the experiment [18]. The total quantity of the released Cr ions was higher in artificial saliva (4.44 g) than in orange juice (3.60 g), and the lowest in Coca Cola® (1.05 g). Coca Cola® intensified the release of Fe ions (a mass 18 times as large as that released in artificial saliva). In the environment of orange juice, more Fe solubilized (5 times). The release of Cu ions was similar in orange juice and slightly lower in Coca Cola® . Significantly more Mn was released in juice (10 times) and Coca Cola® (47 times), although the dose was low. Similarly to Mo: in orange juice (5 times) and Coca Cola® (15 times). In the case of Cd, also soft drinks increased the solubilization: orange juice (54%), and Coca Cola® (5.6 times). These doses were also at a very low level. The formulation of different brands of orange juice differs. This may have an impact on the dissolution process of stainless steel components. The juice in this study was exemplary, to show the effect of orange juice on solubilization of metal ions from the orthodontic appliance. The general outcome of the studies was that Coca Cola® environment facilitates solubilization of Ni(II) ions from alloys (in particular stainless steel), which was also observed in the present work. This is of particular concern, since Ni can pose toxic effects [19]. It must be admitted, though, that in vitro studies have limitations in simulation of real oral cavity conditions. The daily doses (RDD) recommended by WHO for Cr and Ni are as follows: Cr 50–200 g/day, and Ni 25–35 g/day [20]. In the present study, the mass of released Cr and Ni ions daily into different media was: Cr 0.159 (artificial saliva), 0.129 (orange juice), 0.0375 (Coca Cola® ) g/day, Ni: 0.554 (artificial saliva), 0.548 (orange juice), and 1.35 (Coca Cola® ) g/day. Conclusions The present in vitro study showed that acidic soft drinks contributed to more intense solubilization of stainless steel of which orthodontic appliances are manufactured only to a certain extent. Coca Cola® intensified the release of Ni ions, while orange juice did not seem to have a significant impact on the release of metal ions from orthodontic appliances. The ions released from orthodontic appliances were far below RDD, which means that the dissolution of stainless steel did not provide a substantial increase of released metal cations and as a result of which the daily dose of Cr and Ni did not remarkably increase in all tested media. Conflict of Interest The authors declare that there is no conflict of interest.
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Acknowledgment This research was financially supported by The National Centre for Research and Development in Poland (NR13000610).
References [1] Mikulewicz M, Chojnacka K. Release of metal ions from orthodontic appliances by in vitro studies: a systematic literature review. Biol Trace Elem Res 2011;139:241–56. [2] Yip HHY, Wong RWK, Hägg U. Complications of orthodontic treatment: are soft drinks a risk factor? World J Orthod 2009;10:33–40. [3] Shenkin JD, Heller KE, Warren JJ, Marshall TA. Soft drink consumption and caries risk in children and adolescents. Gen Dent 2003;51:30–6. [4] Aptekmann NP, Cesar TB. Long-term orange juice consumption is associated with low LDL–cholesterol and apolipoprotein B in normal and moderately hypercholesterolemic subjects. Lipids Health Dis 2013;12:119. [5] Foroudi S, Potter AS, Stamatikos A, Patil BS, Deyhim F. Drinking orange juice increases total antioxidant status and decreases lipid peroxidation in adults. J Med Food 2014;17:612–7. [6] Shahabi M, Jahanbin A, Esmaily H, Sharifi H, Salari S. Comparison of some dietary habits on corrosion behavior of stainless steel brackets: an in vitro study. J Clin Pediatr Dent 2011;35:429–32. [7] Parenti SI, Guicciardi S, Melandri C, Sprio S, Lafratta E, Tampieri A, et al. Effect of soft drinks on the physical and chemical features of nickel–titanium-based orthodontic wires. Acta Odontol Scand 2012;70:49–55. [8] Kusy RP. Orthodontic biomaterials: from the past to the present. Angle Orthod 2002;72:501–12. [9] Eliades T, Bourauel C. Intraoral aging of orthodontic materials: the picture we miss and its clinical relevance. Am J Orthod Dentofacial Orthop 2005;127:403–12. [10] Mikulewicz M, Chojnacka W, Wołowiec P. Release of metal ions from fixed orthodontic appliance: an in vitro study in continuous flow system. Angle Orthod 2014;84:140–8. [11] Amini F, Jafari A, Amini P, Sepasi S. Metal ion release from fixed orthodontic appliances – an in vivo study. Eur J Orthod 2012;34:126–30. [12] Mikulewicz M, Wołowiec P, Janeczek M, Gedrange T, Chojnacka K. The release of metal ions from orthodontic appliances: animal tests. Angle Orthod 2014;84:673–9. [13] Tahmassebi JF, Duggal MS, Malik-Kotru G, Curzon ME. Soft drinks and dental health: a review of the current literature. J Dent 2006;34:2–11. [14] Barcelos AM, Luna AS, Ferreira NA, Braga AVC, Lago DCP, Senna LF. Corrosion evaluation of orthodontic wires in artificial saliva solutions by using response surface methodology. Mater Res 2013;16:50–64. [15] Danaei SM, Safavi A, Roeinpeikar SM, Oshagh M, Iranpour S, Omidkhoda M. Ion release from orthodontic brackets in 3 mouthwashes: an in-vitro study. Am J Orthod Dentofacial Orthop 2011;139:730–4. [16] Huang HH, Chiu YH, Lee TH, Wu SC, Yang HW, Su KH, et al. Ion release from NiTi orthodontic wires in artificial saliva with various acidities. Biomaterials 2003;24(20):3585–92. [17] Kao CT, Huang TH. Variations in surface characteristics and corrosion behaviour of metal brackets and wires in different electrolyte solutions. Eur J Orthod 2010;32(5):555–60. [18] Kuhta M, Pavlin D, Slaj M, Varga S, Lapter-Varga M, Slaj M. Type of archwire and level of acidity: effects on the release of metal ions from orthodontic appliances. Angle Orthod 2009;79(1):102–10. [19] Schaumlöffel D. Nickel species: analysis and toxic effects. J Trace Elem Med Biol 2012;26(1):1–6. [20] Kabata-Pendias A, Pendias H. Biogeochemistry of trace elements. Warsaw: PWN; 1993. p. 53–66 (in Polish).