The influence of endodontic broken stainless steel instruments on the urinary levels of iron

Effect of radiofrequency electromagnetic fields (RF-EMFS) from mobile phones on nickel release from orthodontic brackets: An in vitro study

BACKGROUND

The worldwide dramatic increase in the use of cell phones has generated great concerns about their potential adverse health effects.

OBJECTIVE

The aim of the present study was to evaluate the effects of radiofrequency electromagnetic fields (RF-EMFs) emitted from mobile phones on the level of nickel release from orthodontic brackets.

METHODS

Twenty stainless steel brackets were divided randomly into experimental and control groups (n=10). Brackets were immersed in artificial saliva at 37°C for 6 months. Experimental group were exposed to GSM 900MHz RF-EMFs emitted from a mobile phone stimulator for 4hours. The specific absorption rate (SAR) was 2.287W/kg. The concentration of nickel in the artificial saliva in both groups was evaluated by using the cold-vapour atomic absorption spectrometry. The Mann-Whitney test was used to assess significant differences in nickel release between the exposed and non-exposed groups.

RESULTS

The mean nickel levels in the exposed and non-exposed groups were 11.95 and 2.89μg/l, respectively. This difference between the concentrations of nickel in the artificial saliva of these groups was statistically significant (P=0.001).

CONCLUSION

Exposure to RF-EMFs emitted from mobile phones can lead to human exposure to higher levels of nickel in saliva in patients with orthodontic appliances. As nickel exposure can lead to allergic reaction in humans and considering this point that about 10-20% of the population can be hypersensitive to nickel, further studies are needed to evaluate the effects of radiofrequency electromagnetic fields (RF-EMFs) emitted from common devices such as mobile phones or Wi-Fi routers on the level of nickel release from orthodontic brackets.

Effect of mobile phone use on metal ion release from fixed orthodontic appliances

INTRODUCTION

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.

METHODS

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.

RESULTS

The 2-tailed paired-samples t test showed significant differences between the levels of nickel in the control and experimental groups (t [49] = 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).

CONCLUSIONS

Mobile phone usage has a time-dependent influence on the concentration of nickel in the saliva of patients with orthodontic appliances.

Effect of thermocycling on nickel release from orthodontic arch wires: an in vitro study

The amount of daily intake of metals from orthodontic appliances over time is a matter of great concern. Nickel results in one of the most common metal-induced allergic contact dermatitis in humans; it produces more allergic reactions than all the other metals combined together. The purpose of this study was to evaluate the effects of thermocycling on the nickel release from orthodontic arch wires stored in artificial saliva with different pH values. Forty new wire pieces were selected. Each wire piece was placed in a special capillary Pyrex tube filled with artificial saliva, which was sealed and immersed in deionized water at 37 °C. The samples were divided into four groups of ten. Group I received no treatment; group II was subjected to thermocycling. The pH of storage in groups III and IV was reduced to 4.5, and group IV was subjected to thermocycling. Thermocycling was carried out between 5 and 55 °C for 500 cycles. The release of nickel ions was statistically analyzed by two-way ANOVA for the effects of two variables: pH and thermocycling. The interaction between pH and thermocycling was found to be statistically significant (F = 12.127, P = 0.001). Two-way ANOVA showed that different storage media or pH and thermocycling had a significant effect on the nickel release (F = 52.812, P < 0.001 and F = 197.035, P < 0.001, respectively). Thermocycling and pH can adversely affect the release of nickel from orthodontic wires, while thermocycling is clearly the dominant factor.

The effect of social stress on salivary trace elements

Social stress can alter the saliva in favor of metabolism of trace elements. This study aimed to assess the effect of social stress on salivary copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) contents in dental students before and after a comprehensive English test. Twelve students with an average age of 27 years were selected from three dental schools. The students were carries-free, and salivary samples were collected 1 week before the test day and right before the comprehensive English test. Unstimulated saliva was collected from the participants. The pH of the saliva samples was measured using a portable pH meter, and the salivary trace element contents were determined using an atomic absorption spectrophotometer. After checking data to be normally distributed, Student's paired t test was used for statistical analysis. Salivary pH significantly increased right before the English test. Salivary Cu concentration decreased in students after the test (P > 0.05). The level of Zn, Mn, and Fe increased, while only Mn change was statistically significant (P < 0.001). Under the limitations of this study, induction of social stress led to a significant increase in Mn concentration in the saliva. The salivary Cu, Zn, and Fe contents, however, did not exhibit significant changes. Changes in salivary inorganic trace element content, as a result of physiological stress, might influence health of teeth, enamel, and oral mucosal tissues.

The effect of electrical treatment on cyclic fatigue of NiTi instruments

Dentists desire to use NiTi rotary instruments, which do not break inside the root canals of teeth, since the pieces from broken files are difficult to remove. The NiTi rotary instrument breakage is because of cyclic and torsional fatigue. Here the low-voltage (12 V) and high voltage (24 V) electrical treatments were used to enhance the cyclic fatigue of NiTi rotary instruments and increase their durability. In excremental groups, following electrical treatment samples of the NiTi instruments were rotated inside artificial root canals until they broke. Our results showed that electrical treatment with 12-V DC was effective in restoring NiTi instrument's resistance to cyclic fatigue. The scanning electron microscopy images and fractograph of samples exposed to 12-V electrical treatment showed a more regular texture over the surface with less dimpling on fractured site. These patterns can improve the super elasticity of tested devices during rotational movement, and delay the NiTi instruments separation in root canal preparations.