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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 6  |  Issue : 2  |  Page : 77-80

Incidence of attention-deficit and hyperactivity disorder among school children in Riyadh city and its association with body burden of mercury leached from dental amalgam fillings: A cross-sectional study


1 Department of Preventive Dental Sciences, Riyadh Elm University, Riyadh, Saudi Arabia
2 Department of Microbiology, Abyat Medical Center 2, Riyadh, Saudi Arabia
3 Department of Dentistry, King Saud University, Riyadh, Saudi Arabia
4 Department of Psychology, University Medical Center, Riyadh, Saudi Arabia

Date of Web Publication19-Aug-2019

Correspondence Address:
Dr. Fatmah Nasser Almotawah
Department of Preventive Dental Sciences, Riyadh Elm University, Riyadh 5321
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sjos.SJOralSci_20_19

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  Abstract 


Objectives: The objectives of this study are to determine the association between the incidence of attention-deficit and hyperactivity disorder (ADHD) in children of mothers with and without amalgam fillings.
Design: The study design was a cross-sectional descriptive study.
Setting: The study was conducted at a dental college's clinic in Riyadh, Saudi Arabia.
Participants: In total, 869 children (512 males and 357 females) aged 6–12 years and 796 mothers were included. Children suffering from hearing impairment, language impairment, or learning disabilities or those diagnosed with mental health problems were excluded from the study.
Primary and Secondary Outcome Measures: The primary outcome measures included the results of the Vanderbilt scale used for ADHD diagnosis in children and the mercury concentration in 1 ml saliva samples obtained from both the mother and the children. The secondary outcome measures included the number of dental amalgam restorations in the oral cavity determined through a dental examination of children and their mothers.
Methodology: A consent form was signed by the mothers who agreed to participate in our study, they were all examined for amalgam presence and a saliva samples were collected and digested.
Results: Children with ADHD showed significantly higher levels of mercury in saliva than did children without ADHD. The mothers who had dental amalgam fillings during pregnancy had significantly higher mercury levels than did the mothers who did not have dental amalgam fillings.
Conclusion: Prenatal mercury exposure is associated with a higher risk of ADHD behavior. Further research can be carried out to identify the toxic effects of mercury on different body organs owing to dental amalgam fillings. The study scale can be further increased to obtain a more accurate percentage of ADHD cases in Saudi Arabia.

Keywords: Amalgam, attention-deficit and hyperactivity disorder, children, dental, maternal, mercury


How to cite this article:
Almotawah FN, Abdullateef M, Alkanhal H, Albukairi M, Alsaif R, Almejrad L, Alzahrani A. Incidence of attention-deficit and hyperactivity disorder among school children in Riyadh city and its association with body burden of mercury leached from dental amalgam fillings: A cross-sectional study. Saudi J Oral Sci 2019;6:77-80

How to cite this URL:
Almotawah FN, Abdullateef M, Alkanhal H, Albukairi M, Alsaif R, Almejrad L, Alzahrani A. Incidence of attention-deficit and hyperactivity disorder among school children in Riyadh city and its association with body burden of mercury leached from dental amalgam fillings: A cross-sectional study. Saudi J Oral Sci [serial online] 2019 [cited 2019 Sep 16];6:77-80. Available from: http://www.saudijos.org/text.asp?2019/6/2/77/264759




  Introduction Top


Attention-deficit and hyperactivity disorder (ADHD) is one of the most common neurodevelopmental childhood disorders, affecting 8%–12% of children worldwide,[1] with its incidence being increased in Saudi Arabia;[2] however, the etiology is not well understood.[3] It is characterized by developmentally atypical levels of inattention, overactivity, and impulsivity that can significantly affect many aspects of behavior and performance, both at school and at home.[4],[5] The association between metal toxicity, including prenatal and postnatal lead exposures, and ADHD-related behaviors has been supported by increasing evidence.[6]

The developmental neurotoxicity of mercury is well established and demonstrated by mass poisoning episodes in Japan and Iraq.[7] Effects of mercury on the central nervous system have been shown in animal models,[8] including changes in rodent dopaminergic function, which provide a biologic basis for its effects in ADHD cases. Epidemiologic studies of lower-dose mercury exposure are however inconsistent,[9] with some studies showing associations between mercury and the ADHD-related behaviors while others not.[9]

Nonetheless, there is much controversy about the effect of mercury released from dental amalgam restorations in pregnant mothers on the neurodevelopment of infants, leading to conditions such as ADHD and learning impairments. Studies on increased mercury levels in the saliva of such individuals, where dental amalgam restorations represent a greater proportion of the total exposure, recognize it as a valuable material for assessing the mercury body burden.[10] There have also been reports of increased mercury levels being associated with increased levels of neurological disorders. However, there is far less literature available on the association between maternal dental amalgam restorations and the development of ADHD in children.

The study aimed to determine the association between the presence of maternal dental amalgam restorations and the development of ADHD in school children in Riyadh, the capital city of Saudi Arabia.


  Methodology Top


The study was registered with the research center at the Riyadh Elm University, and the ethical approval was obtained from the Institutional Review Board of the institute. The study was also approved by the King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia. Informed consent was obtained from all parents before the administration of the questionnaire and collection of saliva. Verbal assent was obtained from all children before the collection of saliva.

This was a cross-sectional descriptive study that assesses the effect of the presence of dental amalgam in mothers on the incidence of ADHD in their children. Eight hundred and sixty-nine elementary school children who were medically fit, aged 6–12 years (Grades 1–6), and their mothers (796 mothers) were selected from the pedodontics' clinics of Riyadh Colleges of Dentistry and Pharmacy. Children with hearing impairment, language impairment, or learning disabilities or those diagnosed with mental health problems were excluded from the study. Consent form was signed by the mothers who agreed to participate in our study, entailing her and her child's/children's acceptance to participate in the study.

The study participants were interviewed in person by the researchers. This interview included a questionnaire that comprised both the child's and mother's demographics, as well as their past medical and dental histories. It is generally accepted that the Vanderbilt ADHD rating scale is a reliable psychological tool to assess the ADHD symptoms in children aged between 6 and 12 years and its effect on their behavior and academic performance. An Arabic version of this scale was used in our study to assess the participant child's condition through the parents' version. The teacher's version was used for further evaluation after taking permission from the parents, once the parents' version indicated ADHD. ADHD was diagnosed if both the parents' and the teacher's versions of the scale indicated ADHD. The translated version was validated by assessing 10 children previously diagnosed with ADHD, regarded as the control children.

Mothers were examined for the presence of amalgam filling in their mouths, and it was documented if the filling was done during pregnancy or after pregnancy. Saliva samples were taken from both the mother and the child. About 1 ml of saliva samples were collected after stimulating saliva secretion in participants by making them suck a clean, sterile bead for 5 min. The samples were preserved in a sterile plastic packet and sent for analysis.

Saliva samples were digested with 10 ml of 6:1 mixture of concentrated nitric acid and perchloric acid, and the mixture was heated until completely evaporated to obtain a water-clear solution. Each digested sample was transferred into a 100 mL volumetric flask and made up to the mark with distilled water followed by spectrofluorometer analysis to measure mercury concentration (Shimadzu RF– 540– Japan) according to the procedure given by Mudakavi (1984) at 555 nm wavelength. All the collected data were statistically analyzed by the unpaired t-test using the SPSS ver 25 data processing software (IBM Inc., Armonk, NY, USA).


  Results Top


The present study shows that children of mothers with dental amalgam filling have higher mercury level in the saliva than in children of mothers without amalgam filling [Table 1] and [Table 2]. It also shows that the incidence of ADHD is higher in children with higher mercury levels than in children with lower mercury levels [Table 2].
Table 1: Sample of mothers (with/without filling) and children (with/without attention-deficit and hyperactivity disorder)

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Table 2: Comparison of saliva Hg levels in children from mothers with versus without fillings

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Moreover, the present study indicates a sex bias with respect to instances of ADHD. The number of ADHD cases was higher in girls than boys [Table 3].
Table 3: Comparing saliva Hg levels in boys and girls

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  Discussion Top


The higher number of ADHD instances in children with higher mercury levels in the saliva may be linked. The high mercury level may affect the central nervous system, leading to dopaminergic disorders, which can provide the biologic basis for the effects of ADHD. This study in occurrence of ADHD, with the number of cases being higher in girls than boys. However, the mechanism underlying this sexual difference in exposure-related neurotoxicity is unknown.[11] A growing literature indicates that these differences may arise due to impact of endocrine-disrupting chemicals, such as bisphenol A, phthalates, and mercury on neurodevelopment among males and females.[12]

Increasing evidence supports associations between metals and ADHD-related behaviors, including prenatal and postnatal lead exposures.[6] The amount of patients and samples taken is a point of strength in this study, while on the other hand, some patients were excluded because we could not follow-up with them.

The developmental neurotoxicity of mercury is well established and demonstrated by mass poisoning episodes in Japan and Iraq.[7] The central nervous system effects of mercury have been shown in animal models,[8] including changes in rodent dopaminergic function, providing a biologic basis for effects on ADHD. Epidemiological studies of lower-dose mercury exposure are inconsistent,[9] with some studies showing associations between mercury and ADHD-related behaviors and others reporting null associations.[9]


  Conclusion Top


Pre-natal mercury exposure is associated with a higher risk of ADHD behavior. Further research can be carried out to identify the toxic effects of mercury on different body organs owing to dental amalgam fillings. The study scale can be further increased to obtain a more accurate percentage of ADHD cases in Saudi Arabia.

Strengths and limitations of this study

  • The large sample size of this study is a strength
  • Sources of mercury other than the dental amalgam filling during the same period can induce a higher risk of ADHD.


Financial support and sponsorship

Funding for this study was obtained from Grant No GX-35–267, King Abdulaziz City for Science and Technology, the Kingdom of Saudi Arabia.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Karagas MR, Choi AL, Oken E, Horvat M, Schoeny R, Kamai E, et al. Evidence on the human health effects of low-level methylmercury exposure. Environ Health Perspect 2012;120:799-806.  Back to cited text no. 1
    
2.
Al Hamed JH, Taha AZ, Sabra AA, Bella H. Attention deficit hyperactivity disorder (ADHD) among male primary school children in Dammam, Saudi Arabia: Prevalence and associated factors. J Egypt Public Health Assoc 2008;83:165-82.  Back to cited text no. 2
    
3.
Llop S, Guxens M, Murcia M, Lertxundi A, Ramon R, Riaño I, et al. Prenatal exposure to mercury and infant neurodevelopment in a multicenter cohort in Spain: Study of potential modifiers. Am J Epidemiol 2012;175:451-65.  Back to cited text no. 3
    
4.
Scheffler RM, Brown TT, Fulton BD, Hinshaw SP, Levine P, Stone S. Positive association between attention-deficit/hyperactivity disorder medication use and academic achievement during elementary school. Pediatrics 2009;123:1273-9.  Back to cited text no. 4
    
5.
Faraone SV, Sergeant J, Gillberg C, Biederman J. The worldwide prevalence of ADHD: Is it an American condition? World Psychiatry 2003;2:104-13.  Back to cited text no. 5
    
6.
Mergler D, Anderson HA, Chan LH, Mahaffey KR, Murray M, Sakamoto M, et al. Methylmercury exposure and health effects in humans: A worldwide concern. Ambio 2007;36:3-11.  Back to cited text no. 6
    
7.
Bose-O'Reilly S, McCarty KM, Steckling N, Lettmeier B. Mercury exposure and children's health. Curr Probl Pediatr Adolesc Health Care 2010;40:186-215.  Back to cited text no. 7
    
8.
Fernandes Azevedo B, Barros Furieri L, Peçanha FM, Wiggers GA, Frizera Vassallo P, Ronacher Simões M, et al. Toxic effects of mercury on the cardiovascular and central nervous systems. J Biomed Biotechnol 2012;2012:949048.  Back to cited text no. 8
    
9.
Sagiv SK, Thurston SW, Bellinger DC, Amarasiriwardena C, Korrick SA. Prenatal exposure to mercury and fish consumption during pregnancy and attention-deficit/hyperactivity disorder-related behavior in children. Arch Pediatr Adolesc Med 2012;166:1123-31.  Back to cited text no. 9
    
10.
Yilmaz S, Adisen MZ. Ex vivo mercury release from dental amalgam after 7.0-T and 1.5-T MRI. Radiology 2018;288:799-803.  Back to cited text no. 10
    
11.
Wang BQ, Yao NQ, Zhou X, Liu J, Lv ZT. The association between attention deficit/hyperactivity disorder and internet addiction: A systematic review and meta-analysis. BMC Psychiatry 2017;17:260.  Back to cited text no. 11
    
12.
Arbuckle TE, Davis K, Boylan K, Fisher M, Fu J. Bisphenol A, phthalates and lead and learning and behavioral problems in Canadian children 6-11 years of age: CHMS 2007-2009. Neurotoxicology 2016;54:89-98.  Back to cited text no. 12
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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