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With great interest, we have read the article by Shahidi et al1 entitled “Effect of magnetic resonance imaging on microleakage of amalgam restorations: an in vitro study” that is published in Dentomaxillofacial Radiology. The first report on the role of exposure to MRI or microwave radiation emitted by mobile phones in enhancing the release of mercury from dental amalgam restoration waspublished in 2008.2

Although the paper authored by Daokar et al. addresses a challenging issue, it has some shortcomings. One of the shortcomings of this study comes from this point that the authors have ignored substantial evidence which indicates the role of exposure to electromagnetic fields (e.g. mobile phones, Wi-Fi and cordless phones) on oxidative stress induction [20-23]. It should be noted that in modern life, due to rapid advances in telecommunication technology, we are all surrounded by electromagnetic fields produced by a variety of sources. Daokar et al. in their study collected saliva samples before restoration and 24 h, 7 days, and 14 days after restoration. Therefore, alterations observed in salivary oxidative stress (MDA levels) could be simply due to frequent use of mobile phones or cordless phones.

Amalgam was banned as a dental restorative material in Norway in 2008 due to environmental considerations. An electronic questionnaire was sent to all dentists in the member register of the Norwegian Dental Association (NTF) one year later, to evaluate dentists’ satisfaction with alternative restorative materials and to explore dentists’ treatment choices of fractured amalgam restorations. Replies were obtained from 61.3%. Composite was the preferred restorative material among 99.1% of the dentists. Secondary caries was the most commonly reported cause of failure (72.7%), followed by restoration fractures (25.1%). Longevity of Class II restorations was estimated to be ≥10 years by 45.8% of the dentists, but 71.2% expected even better longevity if the restoration was made with amalgam. Repair using composite was suggested by 24.9% of the dentists in an amalgam restoration with a fractured cusp. Repair was more often proposed among young dentists (p < 0.01), employees in the Public Dental Service (PDS) (p < 0.01) and dentists working in counties with low dentist density (p = 0.03). There was a tendency towards choosing minimally invasive treatment among dentists who also avoided operative treatment of early approximal lesions (p < 0.01). Norwegian dentists showed positive attitudes towards composite as a restorative material. Most dentists chose minimally- or medium invasive approaches when restoring fractured amalgam restorations.

Methods: Twenty-eight patients as the study group with amalgam fillings, and 32 of them as the control group were included in this prospective case–control study. The mercury levels were measured in the maternal and cord venous sera, and the placental samples. Two groups were compared in terms of these and the fetal/neonatal biometric measurements.

Results: In the study group, the maternal and umbilical cord mercury levels were found to be significantly higher than those from the control group (p = 0.006 and p = 0.010, respectively). These high levels did not affect the fetal biometric measurements.

Conclusions: The presence of high serum mercury levels in pregnant women with amalgam fillings is important, and warrants further long-term studies in order to investigate the fetal neurological effects as well.

RESULTS:
Among 115 patients, 67.8% patients reacted positive to a dental material and nearly a quarter to mercury or amalgam. No correlation was found between pathology and skin patch testing results (P = 0.44). A total of 87 patients were followed up in clinic, and among 26 patch-test-positive patients who had their amalgam fillings replaced, moderate to complete resolution was noted in 81%.

CONCLUSIONS:
Skin patch testing is a valuable tool to confirm clinically suspected oral lichenoid reactions. Pathology diagnoses of oral lichenoid reactions did not correlate with patch test results. Prospective studies are needed to ascertain that a clinically suspected oral lichenoid reaction with a positive patch test result may resolve after the replacement of amalgam fillings.

We have found that dental surface restorations significantly contributed to the blood concentrations of THg and IHg in both periods of study, as well as MeHg in 2011–2012, after adjusting covariates such as age, education, race/ethnicity, gender, smoking, and fish consumption history. However, no association between the dental fillings and urinary BPA was found.This is the first study to demonstrate the relationship between dental fillings and body level of Hg and/or BPA in a nationally representative population. Our findings did not address the potential adverse health effects at low thresholds of mercury exposure; however, a significant correlation between the blood level of mercury and dental restoration raises major concerns about potential mercury exposure. This study provides the scientific basis for the on-going population-based risk assessment of exposure to Hg and/or BPA from dental surface restorations for the selection of safe, effective re-storative materials, especially for sensitive populations.

Results: The mercury-exposed and control groups were similar in age (37.2 ± 6.6 vs. 36.9 ± 9.0 years), had an identical gender distribution (16 females and 12 males) and similar left ventricular ejection fractions (65.5 ± 3.1 vs. 65.4 ± 3.1%). The mean HRR1 [25.6 ± 6.5 vs. 30.3 ± 8.2 beats per min (bpm); p = 0.009], HRR2 (43.5 ± 5.3 vs. 47.8 ± 5.5 bpm; p = 0.010) and HRR3 (56.8 ± 5.1 vs. 59.4 ± 6.3 bpm; p = 0.016) values were significantly lower in the mercury-exposed group than in the healthy controls. However, there were no significant correlations between blood, urine and hair mercury levels and exercise test parameters. Conclusions: Mercury-exposed individuals had lower HRR indices than normal subjects. In these individuals, mercury exposure measurements did not show correlations with the exercise test parameters, but age did show a negative correlation with these parameters. Therefore, cardiac autonomic functions might be involved in cases of mercury exposure.