The aim of this study was to evaluate the effect of exposure to radiofrequency electromagnetic fields emitted by mobile phones on the level of nickel in saliva.
Fifty healthy patients with fixed orthodontic appliances were asked not to use their cell phones for a week, and their saliva samples were taken at the end of the week (control group). The patients recorded their time of mobile phone usage during the next week and returned for a second saliva collection (experimental group). Samples at both times were taken between 8:00 and 10:00 pm, and the nickel levels were measured. Two-tailed paired-samples t test, linear regression, independent t test, and 1-way analysis of variance were used for data analysis.
The 2-tailed paired-samples t test showed significant differences between the levels of nickel in the control and experimental groups ( t  = 9.967; P <0.001). The linear regression test showed a significant relationship between mobile phone usage time and the nickel release (F [1, 48] = 60.263; P <0.001; R 2 = 0.577).
Mobile phone usage has a time-dependent influence on the concentration of nickel in the saliva of patients with orthodontic appliances.
Radiofrequencies from mobile phones and nickel concentrations in saliva were examined.
Mobile phone radiation is positively correlated with nickel concentration in saliva.
Nickel concentrations in saliva were different in men and women.
An integral part of modern telecommunication is the mobile phone, which may have negative effects on different organs and cells. These negative impacts culminate from radiofrequency electromagnetic radiation (RFER) emitted from mobile phones. From 1990 to 2011, worldwide mobile phone subscriptions grew from 12.4 million to over 5.6 billion, and the global pandemic usage of mobile phones was about 70% as of 2011. Insufficient understanding of the potential adverse health effects of mobile phones have raised concerns among health care professionals.
According to the proximity of mobile phones to the oral cavity during the conversation period and the metallic orthodontic appliances in the mouth, there might be a serious risk in exposure of these appliances to the mobile phone radiation. Archwires, headgear, bands, and brackets used in orthodontics mainly consist of nickel. The harmful effects of nickel have been systematically investigated at the levels of the cells, tissues, organs, and organisms. According to the International Agency for Research on Cancer, nickel compounds are classified as carcinogenic to humans, but it is still unclear which forms of nickel pose the greatest risk. Nickel complexes in the form of arsenides and sulphides are carcinogenic, allergenic, and mutating substances even at nontoxic concentrations. Nickel might induce DNA alterations mainly through basic damage and DNA-strand scission in G12 cultured cells. Empirically, a biologic limit of 30 μg per gram has been proposed for nickel in the urine of workers exposed to soluble nickel compounds at the end of their shifts.
Nickel is a common metal that can cause allergic contact dermatitis more than all other metals. Previous studies have indicated that approximately 10% of the population is sensitive to nickel, and this sensitivity is more commonly seen in female patients. The authors of an in-vitro study mentioned that if nickel leached out from orthodontic appliances, type IV (delayed hypersensitivity) due to the allergic contact dermatitis could occur. In conventional orthodontic treatments, the nickel-titanium alloy containing approximately equi-atomic nickel and titanium is common in orthodontic wires used clinically because of its good working and mechanical properties. Because titanium is mainly inert and not cyctotoxic, the main potential risk of cytotoxicity is due to the biologic side effects of nickel, which is associated with the corrosion process.
The amount of metal ion release from dental alloys has become of increased interest in both in-vivo and in-vitro studies. Appliances and additional devices used during orthodontic treatments are exposed to various factors, such as temperature, pH, mechanical stress, and microflora (biocorrosion). All of these factors may lead to the release of toxic metal ions such as nickel as shown in an in-vitro study. Several authors have questioned the effect of temperature changes on different properties of orthodontic alloys.
The anatomic location of the parotid gland (at the anterior border of the external ear and between the mandibular ramus and the sternocleidomastoid muscle, 4- to 10-mm deep under the skin surface) makes it a conceivable candidate to be influenced by exposure to RFER on the side of the head where the mobile phone is held. Some researchers, in both human and animal studies, have confirmed that mobile phones cause significant increases in salivary oxidative stress, salivary flow, total proteins, and albumin, whereas amylase activity was decreased. In a nationwide case-control study, Sadetzki et al examined the correlation between parotid gland tumors and mobile phone usage and indicated a positive dose-dependent response trend. Thus, the RFER emitted from mobile phones may influence the amount of nickel released from the fixed orthodontic appliances.
The rate at which the human body absorbs RFER is measured by the specific absorption rate (SAR). The amount of radiation emitted by a mobile phone depends on the model. Different handsets have different SAR ratings, and different countries have placed radiation exposure limits on the maximum levels of SAR for modern handsets. These limits vary according to the country; for example, in the United States, the Federal Communications Commission has set a maximum SAR limit of 1.6 W per kilogram. However, in Europe, this limit is 2.0 W per kilogram. It is therefore expected that the level of RFER emitted will correlate with the biologic impact induced, which in turn depends on the different mobile phone technologies.
According to the aforementioned reasons, the aim of this study was to test the hypothesis that exposure to RFER emitted by mobile phones can affect the level of nickel in saliva. In addition, the effect of different times of exposure to the RFER was evaluated on the concentration of nickel in saliva.
Material and methods
Fifty healthy patients (25 men, 25 women; average age, 25.2 years; range, 23-26 years) who had fixed orthodontic appliances were selected for the study. Candidates needed placement of full orthodontic appliances for at least 2 months and no more than 4 months to satisfy the inclusion criterion. The exclusion criteria were patients with systemic diseases or medication intake; those who smoked or consumed alcohol; those with any metallic restoration material such as an amalgam or a fixed prosthesis, which was checked with panoramic x-rays; those with missing or extracted teeth (except for third molars); and those who were unwilling to participate. The women were asked about menstruation; if they were currently menstruating, the session was postponed for a week. The patients were asked, orally and in writing, not to eat seafood and canned food, not to drink hot tea and coffee, and not to smoke tobacco for 3 days before the checkups. The next visit was scheduled for 3 days later at the same time of day, and the patients were asked to be careful about the time they were using their mobile phones. They were also told to avoid brushing their teeth and rinsing their mouth with fluoridated products for 3 nights before the visits.
During the regular checkups, the patients were asked not to use their cell phones for 1 week, and saliva samples were taken from them at the end of the week (this was considered the control group). For the next visit, a chronometer was given to the patients to calculate how many minutes they used their cell phone during the second week of the experiment. At the end of the second week, saliva samples were again collected, and the sexes, ages, and cell phone usage times were also recorded; this was considered the experimental group. The saliva samples were sent to the laboratory for further analysis.
Briefly, similar to the method of Saghiri et al, sampling was carried out in the office to collect uncontaminated specimens between 8:00 and 10:00 pm . The patients were instructed to collect their salvia in sterile nickel-free, 20-mL plastic containers, which were stored at −20°C. Inductively coupled plasma-mass spectrometry was used to measure the amount of nickel in the saliva samples. The average of 3 measurements for each sample was used.
Data were entered into an Excel spreadsheet (Office 2010; Microsoft, Redmond, Wash). Differences between the nickel levels in the patients’ saliva and their controls, the correlation of time of using the mobile phones, their sexes, and the types of mobile phones were analyzed in relation to the nickel levels in the saliva samples. The Kolmogorov-Smirnov goodness-of-fit test was used to assess the normality of the nickel values; if the distribution was not normal, the equivalent nonparametric test was used. Two-tailed paired-samples t test, linear regression, independent t test, and 1-way analysis of variance were used for data analysis. All statistical analyses were done using SPSS statistical software (version 20; IBM, Armonk, NY), and P <0.05 was considered to be statistically significant.
The data were not divided based on sex (N = 50) in the analysis of nickel level differences between the subjects and their controls to assess the overall effects of speaking time. To compare the mean values of nickel release in the control group and the experimental group, paired-samples t tests were used. The tests showed significant differences between the levels of nickel in the control and experimental groups (t  = 9.967; P <0.001). The linear regression tests on all samples showed significant positive difference on the effect of speaking time on nickel release (F [1, 48] = 60.263; P <0.001; R 2 = 0.577). Means, standard deviations, maximums, minimums, and P values of the measured concentrations of nickel are presented in the Table .
|Experimental group||n||Nickel release (ng/L)|
|Speaking time (min)||Control group||First-visit group||Difference||P value|
|Min||Max||Mean||SD||Min||Max||Mean||SD||Min||Max||Mean||SD||Min||Max||Mean||SD||Paired-samples t test||Linear regression|