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ORIGINAL ARTICLE
Year : 2021  |  Volume : 24  |  Issue : 12  |  Page : 1808-1813

Relation between molar-incisor hypomineralization (MIH) occurrence and war pollutants in bombarded regions: Epidemiological pilot study in Lebanon


1 Department of Pediatric Dentistry and Public Dental Health, Faculty of Dental Medicine, Lebanese University, Beirut, Lebanon
2 Medical Genetics Unit, Faculty of Medicine, Saint-Joseph University, Beirut, Lebanon
3 Department of Biological Sciences, Laboratory of Cancer Biology and Cellular Immunology, Faculty of Sciences, Beirut, Lebanon
4 Department of Forensic Odontology, Human Identification and Anthropology, Faculty of Dental Medicine, Lebanese University, Beirut, Lebanon

Date of Submission30-Dec-2020
Date of Acceptance22-Jun-2021
Date of Web Publication09-Dec-2021

Correspondence Address:
Dr. R Elzein
Department of Pediatric Dentistry and Public Dental Health, Faculty of Dental Medicine, Lebanese University, Hadath
Lebanon
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_702_20

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   Abstract 


Background: Molar-incisor hypomineralization (MIH), a developmental enamel defect affecting one or more first permanent molars (FPMs) and sometimes incisors (PIs), is one of the most common pandemic health problems in the world. MIH etiology is still unclear and has been suggested to be related to exposure to environmental toxicants during enamel mineralization. Aims: To assess the susceptibility to MIH occurrence in regards to war pollutants through the investigation of the prevalence and the clinical characteristics of MIH in a group of Lebanese children whose FPMs and PIs enamel mineralization coincides with the 2006 Lebanese war. Patients and Methods: This cross-sectional study was performed in schools from different regions of Lebanon. Schoolchildren born in 2004, 2005, 2006, and 2007 were examined for MIH. Clinical status, lesion type, extension, and severity were recorded using the short form chart of the MIH index. Pearson's Chi-square or Fischer's exact test were used to determine if there is a significant relationship between categorical variables. Results: An overall MIH prevalence of 22.93% has been reported. Forty-seven point seventy-five per cent had both molars and incisors affected. Demarcated opacities were the most frequently observed clinical status. Most of the MIH FPMs and PIs were mildly affected with lesions extended on less than the third of the tooth surface. Conclusions: MIH prevalence among children born around 2006 Lebanese war is high. The hypothesis of a relation between MIH susceptibility and war pollutants in bombarded regions is legible but requires to be elucidated via additional in vitro and in vivo studies for accurate risk assessment.

Keywords: Epidemiology, Lebanon, molar-incisor hypomineralization, toxicology, war pollutants


How to cite this article:
Elzein R, Chouery E, Abdel-Sater F, Bacho R, Ayoub F. Relation between molar-incisor hypomineralization (MIH) occurrence and war pollutants in bombarded regions: Epidemiological pilot study in Lebanon. Niger J Clin Pract 2021;24:1808-13

How to cite this URL:
Elzein R, Chouery E, Abdel-Sater F, Bacho R, Ayoub F. Relation between molar-incisor hypomineralization (MIH) occurrence and war pollutants in bombarded regions: Epidemiological pilot study in Lebanon. Niger J Clin Pract [serial online] 2021 [cited 2022 Jan 20];24:1808-13. Available from: https://www.njcponline.com/text.asp?2021/24/12/1808/332089




   Introduction Top


Molar-incisor hypomineralization (MIH) describes a developmental defect affecting the enamel of the first permanent molars (FPMs) often associated with the permanent incisors (PIs).[1] MIH teeth present well-demarcated[2] asymmetric soft and porous hypomineralized enamel opacities leading to tooth hypersensitivity,[1] esthetic concerns,[3] susceptibility to caries development,[4] chronic pulp inflammation,[5] post-eruptive enamel breakdown (PEB) soon after the eruption[6] and early loss of the tooth.[7] MIH presents a worldwide pandemic health issue,[8] negatively affecting patients' oral self-perception,[9] and parents' thoughts about their children's oral health status,[10] in addition to challenging therapeutic interventions for clinicians.[11] MIH can be diagnosed at 6 to 8 years of age, time of eruption of FPMs and PIs. These concerned teeth begin to mineralize within the last period of pregnancy and the first three years of the child's life, which identifies the window of susceptibility to MIH.[12] During this period, any systemic or environmental factor can insult the highly sensitive enamel-forming cells, the ameloblasts, and lead to hypomineralization of the developing enamel.[13] However, the etiology of MIH is still unclear. The reported multifactorial pathogenesis included genetic component,[14] prenatal, perinatal, and postnatal exposures[15] and risk of environmental toxicants like dioxin,[16],[17],[18] and endocrine disruptors, essentially bisphenol A (BPA).[19],[20]

In war regions, different environmental toxicants are liberated due to the explosion of ammunition. In addition, high heavy metals accumulated in pregnant women are disseminated to their newborns; causing peril for pregnancies and children health.[21],[22] Besides, the incorporation of metals into teeth has been used as indicator for environmental exposure to metals and as biomarker for consecutive disease manifestation.[23] But, in the literature, war pollutants have not yet been widely considered as implicated in dental defects, such as MIH susceptibility; the effects of the accumulation of such heavy metals in teeth need to be better explored.

Lebanon has been a war zone during July-August 2006 that resulted in a severe environmental damage due to the heavy metals included in used weapons.[24],[25] Therefore, it would be interesting to appraise the prevalence of MIH among Lebanese population whose FPMs and PIs enamel mineralization coincides with the 2006 Lebanese war.

This study aimed to assess the prevalence and the clinical characteristics of MIH in a group of 10 to 13-year-old Lebanese children, (born in 2004-2005-2006 and 2007) and to overview a possible relation between MIH occurrence and the war of 2006.


   Materials and Methods Top


Protocol and ethical approval

The ethical approval for this cross-sectional study was delivered by the Institutional Review Boards of the Lebanese University (#76/2017) and of the Saint-Joseph University of Beirut (#USJ-2017-143) in accordance with the Helsinki Declaration. Authorization to access public schools was delivered from the Lebanese Ministry of Education and Higher Education. For private schools, access was facilitated by the corresponding institutions' administrations. It was reported according to the STROBE statement and operated during 2017-2018 academic year in randomly selected eight schools from different Lebanese regions The approval from the ethics committee is obtained in 2 May 2017 (from Lebanese University) and 7 November 2017 (from Saint-Joseph University) . It is mentioned in the paragraph Materials and methods (protocol and ethical approval).

Studied population

It comprised Lebanese schoolchildren aged 10 to-13-years old (born in 2004, 2005, 2006 and 2007). Starting from a random point of the list of children names, each second child was sampled. All parents of the enrolled children consented voluntary before their participation. Exclusion from the study concerned non-Lebanese children, the uncooperative participants during examination, the absent on the day of the study, and the ones that their parents declined consent.

Study settings

One calibrated pediatric dentist performed dental examinations. The single examiner assisted to extensive theoretical and clinical training in MIH, and has been twice calibrated, 20 days apart, using 30 photographs of 15 patients with different types of enamel defects. The reproducibility index was then calculated using Cohen's Kappa coefficient (0.96). Examination occurred in schools (classrooms, infirmary or dental chair if available) using individually wrapped and sterilized examination equipment. Dental light source or daylight supplemented with a portable penlight torch was used to ensure vision. The same trained dental assistant recorded the notes on individual chart form.

Data measurement

Teeth were examined wet. Sometimes, teeth surfaces were cleaned using gauzes from food remains to ensure a better visualization. MIH clinical diagnosis was based on the MIH index criteria.[26] Short-form chart was used to record the clinical status and extension of the defect. Demarcated opacities, post-eruptive enamel breakdown (PEB), atypical restorations, atypical caries, missing due to MIH (by comparing to other teeth of same group) were the clinical variable configurations. Lesion extent was recorded as following: less than one-third (1/3), between one-third and two-thirds (2/3), and more than two-thirds, of the tooth surface. MIH lesion of 1 mm or less in diameter was not taken in consideration. The severity was deducted from the scores. A tooth presenting only color variations was classified as “mildly affected” and the one affected by PEB and/or atypical restoration/atypical caries/missing was categorized as “severely affected”.[26]

Data management and analysis

De-identified and re-coded examined children were recorded using Microsoft Excel 2007. Statistical Package for Social Sciences Computer Software (SPSS 21.0, Inc., Chicago, IL, USA) to analyze the data. Pearson's Chi-square or Fischer's exact test were used to determine if there is a significant relationship between MIH and non-MIH categories. The significance threshold was set at .05.


   Results Top


Sample selection

In total, 740 participants were available for the study. Only 697 of guardians provided approval for examination but 15 subjects, being uncooperative during examination, were not compliant which resulted in the examination of 682 children during a 9-month period.

Prevalence

As result, 178 participants had been diagnosed by MIH, distributed as 81 males (45.51%) and 97 females (54.49%) with a mean age of 11.3 ± 0.88 years. An overall prevalence of 22.93% was recorded. A significantly higher percentage was revealed in 13 years old children (52.38%) compared to 12 years (30.77%), 11 years old (25.82%) and 10 years' children (21.87%) (P < 0.0001).

Distribution of the affected teeth in all MIH children

Among the 178 MIH cases, there were 642 affected teeth: 484 FPMs and 158 PIs. Forty-seven point seventy-five per cent of cases presented MIH on FPMs and PIs while 52.25% had only molars with MIH. [Figure 1] illustrates the affected specific teeth. Lower molars were not significantly (P = 0.26) more frequently affected (65.73/74.16%) than the uppers (64.61/67.41%). Left side FPMs were not significantly (P = 0.108) more affected (67.41/74.16%) than the right ones (64.61/65.73%). Total upper incisors (N = 124) were significantly (P < 0.0001) more affected than the mandibular (N = 34) and the centrals (N = 113) significantly (P < 0.0001) more affected than the laterals (N = 45). No significant (P = 0.06) difference was found between total left and total right PIs. Globally, the lower left FPM was the most frequently affected tooth (74.16%), while the least was the mandibular right lateral PI (1.68%). The mean number of hypomineralized teeth per MIH child was 3.61; 2.72 for molars and 0.88 for incisors.
Figure 1: Distribution of affected FPMs and PIs in 10 to-13-year-old Lebanese MIH children

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Distribution of MIH defect by its type and its extension on affected teeth

The most frequently noted defects were respectively: demarcated opacities (74.45%), PEB (17.86%) and atypical restorations (7.68%). The majority of defects (66.45%) were extended on less than the third of the tooth surface. Moreover, for molars group, the extension of defects correlated significantly with the number of affected FPMs (P = 0.0005).

Distribution of MIH FPMs and PIs according to the degree of severity

Most of the FPMs (58.30%) and PIs (96.21%) were mildly affected without significance regarding gender. The degree of severity of FPMs and age were not in significant relationship (P = 0.054).


   Discussion Top


The population studied herein included a sample of children whose FPMs and PIs enamel mineralization synchronized with the war of 2006. An overall MIH prevalence of 22.93% has been reported with a mean value of 3.61 MIH teeth per affected child; 2.72 for molars and 0.88 for incisors. For the same mean age, our results were higher than those obtained in Hong Kong (2.8%),[27] in Northern England (15.9%),[28] in Karnataka India (13.12%)[29] and in Bosnia Herzegovina (12.3%).[30] In addition, the mean global prevalence of MIH has been reported as 13.1%.[8] Analyzing the diversity of the results is difficult to achieve due to variability of many factors: sample selection methods, examination conditions, selected age groups, adopted indices. Environmental and genetic components among the studied populations are also critical determinants concerning the enamel hypomineralization occurrence.[31] The environmental toxicants have not been widely explored in MIH etiology unlike systemic factors.

In fact, children's exposure to environmental toxic chemicals contributes to a change in the patterns of pediatric diseases.[32] The pre-and post- natal environment affect the tissue physiology and homeostasis.[33] Pregnancy and fetal development are sensitive to mothers' exposure to environmental chemical, biological and physical elements.[22],[34] Particularly, the ameloblasts are susceptible to unusual variations in their environment during early childhood and any insult may disturb the enamel hard tissue structure.[13] Teeth have been used to rate lifelong accumulative exposure to metals;[23] and the existence of trace elements in the enamel could negatively impact its physical properties and consequently its hardness and shade lightness.[35] So far, the implication of multiple molecules in teeth shape and development has been investigated. Data suggest that the BPA is a potential causative agent of MIH.[19],[20] Moreover, chronic perinatal exposure to low-dose BPA affects dental enamel mineralization in rats.[36] It has been noticed that incidental exposure of children to large load of dioxins was linked with developmental enamel defects and dental agenesis.[37] Furthermore, it has been found that 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin affects tooth development by triggering apoptosis in cells of the dental epithelium.[38]

However, few researches have been conducted on the possible effect of war pollutants on developing teeth. Savabieasfahani et al.[21] discussed the imprint of war on the deciduous teeth of the children of the Middle East after prenatal metal exposure. Al-Sabbak et al.[39] also concluded that the enamel of a primary tooth from a child with birth defects from Al Basrah, a bombarded city in Iraq, had greater lead than the teeth of children living in unblasted zones. No studies have been conducted on the effect of these war metals on the developing enamel of permanent teeth. But primary and permanent teeth have similar morphology and histology, so environmental risk of metals may also be investigated by analyzing permanent teeth.[40]

Lebanon, being a recurrent war country in the Middle-East between 1975 and 2006, suffers from suspicious environmental conditions. Particularly in July 2006, the bombing raids against Lebanon resulted in severe destructions and infrastructure demolitions as well as in environmental damages due first to the heavy metals used weapons[25] and second to the oil spill in the Mediterranean Sea.[24] New-generation weapons include mercury, vanadium, chromium, strontium, and uranium. Many of the toxic, teratogen, and carcinogen effects of these heavy metals on health are known.[41] They penetrate in human tissues by various routes: inhalation, diet or touch, and they can disrupt the human body vital functions even in small quantities.[42] In addition, they can induce epigenetic variations in the genome altering the mother and the fetus, through crossing the placental barrier, acting as prenatal endocrine disruptors or affecting the transfer of nutrients to the fetus.[22] All these facts have the power to produce long-term undesirable outcomes on children's in all stages of their development. In addition to the cited exposure risks, the persistence of these toxicants in post-war environments can result on extended exposure, causing their accumulation in the body organs.[22],[43] In Lebanon, post-war reconstruction dust residues rich with heavy metals have possibly been discharged in the environment, polluting various features of human life. The characterization of heavy metal exposure of the Lebanese population is still broadly uninvestigated.[44] This might contribute to the persistence of high prevalence of MIH in Lebanon even after 2006 war, as MIH prevalence amongst 7–9 years old Lebanese children (born in 2008, 2009, and 2010) is 26.7%.[45] Therefore, in addition to the risk factors previously found to be associated with MIH in Lebanon[20] and as prevalence of MIH being high, the hypothesis of MIH susceptibility related to war heavy metals needs to be explored.

Experimental approaches for toxicology assessment of MIH-War pollutants are needed. In fact, there are many approaches that can be considered to estimate the toxic effects of inhaled complex assortments, like air pollution particles: epidemiology-, human clinical-, animal-, and in vitro- studies.[46] The proposed pyramid in [Figure 2] represents a scheme of the importance of each experimental approach for a complete assessment of the toxic effects of war pollutants on MIH occurrence. The current research represents an epidemiology investigation. One of the main objectives of epidemiology is to quantify different features of a population's health, diseases, death status and the risk factors by calculating health indicators. A morbidity indicator describes the presence of a disease in a population, or the degree of risk of an event. The prevalence is one of the frequent uses of this notion in epidemiology.[47] The prevalence indicator in our study revealed a high morbidity of MIH comparing to worldwide estimation. But further evaluations based on the Lebanese regional and group differences (age range) are needed in order to ensure more accurate information about the MIH occurrence related to war pollutants in Lebanon specially that some regions were more bombarded than others. Sadly, there is no official data related to the prevalence of MIH in children born before 2006 war although observational MIH clinical cases are rarely seen in older group age (14 years and up at the time of examination). In addition, controlled human exposure studies such as comparison of our group, exposed to the war pollutants, to other groups born at the same years but in clean air conditions (not bombarded countries) is important to complement the epidemiological study. Oddly, in published studies exploring the MIH prevalence, there is a lack in mentioning the year of birth of the MIH examined children making impossible to compare our results with other data from “clean” countries. Furthermore, animal toxicology studies are also needed to assess causality, biological credibility and underlying mechanisms of war pollutants on MIH. Because their dentition is highly specialized, mice are the most frequently used model to study tooth development and subsequent pathologies. Human and rodent follow similar stages of amelogenesis.[48] Finally, in vitro studies are a very helpful approach to identify fundamental mechanisms by which war pollutants affect ameloblasts cell lines. In vitro studies allow rapid screening of many pollutants, or of components of complex mixtures which is very helpful in the Lebanese suspicious environmental conditions; indeed, in addition to war pollutants, Al-Alam et al.[49] showed that four analyzed Lebanese regions were polluted with Polycyclic aromatic hydrocarbons, known as hazardous organic pollutants. Baalbaki et al.[50] also showed that the levels of the Benzo[a]pyrene in Lebanon are much higher than those in most cities around the world.
Figure 2: Pyramid proposal for MIH - War pollutants experimental approaches

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   Conclusion Top


This is the first epidemiological study that supports the possible toxic effect of heavy metals weapons used in wars on MIH susceptibility. Based on it, the hypothesis of a relation between MIH susceptibility and war pollutants is legible but requires to be elucidated via additional in vitro and in vivo studies for accurate risk assessment. The current investigation represents a key starting point for future experiments in MIH toxicology.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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