Enamel defects among Syrian schoolchildren in Damascus city: A cross-sectional epidemiological survey

Abstract

Background:Enamel defects EDs can affect the quality of life due to poor aesthetic appearance, post-eruptive caries and breakdown. Therefore, there is a need to provide further understanding about prevalence of EDs among Syrian children and etiological factors. Therefore, this study was undertaken to determine the prevalence and etiological factors of EDs among Syrian children aged 7 to 12 years in Damascus. 

Methods: a cross-sectional observational study was undertaken. A total of 2000 schoolchildren (934 boys and 1066 girls) were firstly examined to detect EDs. Using the Enamel Defect Index (EDI), a second clinical examination was performed to 240 children with EDs. All surfaces of affected teeth were examined individually. A following telephone interview with parents was performed to investigate the etiological factors of EDs. 

Results: The prevalence of EDs was 16.1%. Percentages of Localized enamel defects LEDs, Molar incisor hypomineralization MIH, amelogenesis imperfecta AI and EDs related to high fluoride intake were 51.7%, 42.7%, 5% and 0.6% respectively. The highest prevalence of EDs was observed in the upper incisors followed by the lower first molars, whilst EDs were least prevalent in upper lateral incisor. The etiological factors that significantly contribute to EDs type, were the place of residence and educational level of parents. Having higher educational level of parents was significantly associated with higher prevalence of MIH of children whilst LEDs were significantly associated with low educational level of parents. Other factors including gender, age, consanguineous marriage, economic status of family, medical problems and medications during pregnancy, nature of delivery, timing of birth, child's birth weight, type of feeding, genetic and systemic diseases and allergic problems, injuries, bruises and surgeries during childhood, were not associated with EDs. 

Conclusions: information about the prevalence of EDs and etiological factors have been provided. Educational level of family and place of residence can be predisposing factors for the presence of EDs among Syrian children. There is a need for raising awareness towards EDs among Syrian community to take preventive measures in order to preserve the rest of intact dental tissues and prevent post-eruptive breakdown of affected teeth.

Introduction

Enamel formation begins around the twentieth week of uterine life in the crowns of the first permanent molars. The process of forming the crowns continues until completed by age three [1, 2].

The ameloblast cells are highly sensitive, so any disturbance that occurs, during the stage of tissue differentiation such as loss of metabolic activity, can lead to decrease in the normal thickness of enamel and called hypoplasia. Enamel hypoplasia can manifests clinically in several forms including thin enamel, pitted or grooved enamel [3, 4]. In addition, any disturbance that occurs during the development period manifests as permanent defects in the erupting teeth [1]. 

The clinical manifestations of these EDs vary according to the time in which the disorder occurred [5]. Enamel hypomineralization, which can be either a lack of maturity (Hypomaturation) or a lack of calcification (Hypocalcification (appear when the disturbance occurs in one of the stages of enamel crystals deposition or maturation [3]. It manifests clinically as discolored enamel on the surface of the enamel and it varies according to the severity of the defect, ranging from yellowish-brown color when the defect is severe, to changes in the opacity of the enamel [3]. When the defect is of moderate severity, clinical manifest can be less severe and enamel has mottled appearing [3].

Developmental defects can affect dental enamel in both primary and permanent teeth. These defects may be due to genetic reasons such as (AI) or environmental [4].  Researchers found that AI is associated with the occurrence of various mutations in the genes responsible for the proteins and enzymes of enamel formation [6, 7]. They have isolated six main classes of genes responsible for enamel morphogenesis including ENAM-AMBN-AMELX-MMP20-KLK4 and Amelotine [8]. Dashash and colleagues (2010) have investigated Syrian families with AI and found homozygous/heterozygous mutation in the ENAM and ameloblastin gene in affected families with AI [9]. 

On the other hand, environmental reasons of EDs can be subsequent to systemic diseases related to nutritional deficiency, febrile diseases, and systemic fluoride overdose. Dental fluorosis has been an environmental developmental defect that affects the enamel and characterized by diffused opacities that vary from white transverse lines to extensive opaque areas associated with post-eruptive staining and shallow pits in severe cases [10].  Molar Incisor Hypomineralization MIH is an example of acquired idiopathic EDs [11] that can cause systemic hypomineralization to one or more permanent first molars and incisor. MIH was classified based on clinical appearance into hypoplasia demarcated opacities, and post-eruptive breakdown [12].

Other environmental EDs can be resulting from local causes affecting the single tooth or several teeth at the site of defect such as local infection (Turner's teeth), local trauma, and prolonged stay of the primary tooth. Researchers have demonstrated that 10% of EDs affecting permanent incisors are caused by trauma to the preceding incisor [10, 13].

The prevalence of EDs has increased among different populations, ranging from 63 to 68% in New Zealand, Ireland and England, to 99% in Hong Kong in China [14, 15]. The prevalence of MIH ranges from 3.5 to 40.3%, and the number of affected molars varies among people, ranging from a single molar defect to defects including, incisors and other permanent first molars [15, 16]. In the Netherlands, MIH was seen on the primary second molars in 4.9% of children, and 87% of the affected molars showed specific opacity [17]. 

Jan and colleagues in 2006 showed that 57.5% of children had at least one permanent tooth with EDs in children in eastern Slovakia [18]. This reflects the presence of multiple diagnostic patterns for this defect.

Recently, the number of cases of children suffering from various EDs, including MIH, has increased, and due to the absence of previous studies showing the prevalence rates of such EDs in children of the Syrian community and the factors related to this defect, it was found that it is necessary to conduct a study on this topic. Therefore, this study was firstly undertaken to determine the prevalence of various types of EDs (MIH, AI, LEDs, and EDs caused by systemic fluoride) among schoolchildren aged 7 to12 years in Damascus city. In addition, the objective was to identify etiological factors that may cause EDs, such as child’s weight at birth, the child’s nutrition, systemic diseases in childhood, genetic diseases, allergic problems, and vaccination.

Materials And Methods

This study has a cross-sectional observational design in which the first clinical examination of schoolchildren was undertaken to assess the prevalence of EDs and a second clinical examination was performed to assess the type and degree of EDs. A following telephone interview was also undertaken to families of children with EDs to investigate the etiological factors of EDs. 

Ethical approval was obtained from the Faculty of Dentistry at Damascus University, and the Department of School Health of the Ministry of Education in Damascus in order to conduct a clinical examination for children aged between 7-12 years.

The study was undertaken in the city of Damascus, where it was divided into eleven regions, according to the distribution of the statistical office in the Directorate of Education of Damascus Governorate. Children were randomly selected taking into consideration the number and age of children in each region, so the number of students in each region was  in Region A, B, C, D, E, F, G, H, I, J, and K ( 134, 245, 133, 209, 159, 171, 210, 156, 174, 317, and 92). The study included all cooperative children within aged 7 to 12 years, who had at least one permanent incisor and/or at least one erupted first permanent molar, whilst uncooperative children, those who had orthodontic treatment, which can interfere with clinical examination or who had missed or extracted permanent teeth, were excluded from the study. The original population of the research sample was determined from a group of schoolchildren in Damascus between the ages of 7 and 12 years. Then, the sample size was calculated based on the number of children in Damascus schools, which numbered 159 thousand boys and girls according to the statistics of the Oral Medicine Center in the Ministry of Education. For a power of study of 95% and an accuracy level of 5%, 1500 boys and girls were selected and 25% (500) boys and girls were added to consider the confounding factors. The final sample size became 2000 boys and girls. 

Oral examination was undertaken, by one examiner RAJ in the classroom using disposable mirrors with the illumination of a flashlight to identify affected and healthy children. Children were examined according to their sequential numbers, using specific tables.  A specific questionnaire was designed to record personal information such as name, age, gender, school, address (place of residence), and telephone number. In addition, all healthy and affected erupted teeth were recorded together with the type of EDs. Then, a second clinical examination was performed for children who had EDs using the Enamel Defect Index (EDI). 

Each dental surface examined was scored using a three-digit index ranging from 000 to 111, and having 8 scores per tooth surface according to Elcock and colleagues (2006) in which the first number refers to hypoplasia(Fig. 1-A), the second and third numbers refer to opacity(Fig.1-B), and post-eruptive breakdown (Fig. 1-C)respectively[14]. Each affected tooth was examined individually, and the index was recorded for all surfaces. For instance, buccal, palatal, medial, lateral, occlusal, cervical surfaces were examined in the upper molars.   In the upper incisors, cervical buccal, buccal, incisal buccal, incisal palatal, palatal and cervical palatal surfaces were examined. The surfaces adjacent to incisors were neglected due to their smallness, and if they were affected, the defects often included the adjacent buccal and lingual or palatal surfaces. 

In addition, the index was expanded with sub categories to determine the type of hypoplasia (single or multiple pits, single of multiple grooves, partial or complete loss of enamel area), opacity(white cream or brown demarcated boundary, diffuse patchy boundaries) and post-eruptive breakdown(present/ absent)[19]. Moreover, a telephone call was performed to all children, who had EDs when the telephone line for the parents was available in order to obtain information about general health of the child, and conditions of pregnancy. These included pregnancy period (normal/ associated with health problems), medications to be taken during pregnancy (existing/ non-existent) childbirth (natural/surgical), timing of birth (normal 9 months/ early), baby's weight at birth (normal/low weight baby), and breastfeeding (natural/ artificial/ mixed) was recorded. In addition,  research also recorded answers of questions about   general diseases affecting child, presence of  genetic diseases in the family, allergy to certain medicines or foods, vaccination (complete/incomplete regular), reasons behind missing teeth (congenital/extraction, and trauma), injuries and accidents in early life, number of brushing times and the presence of consanguineous marriage.

Statistical Analysis

Data were coded and entered into the computer, using the Statistical Package for the Social Science N0. 24.0 (SPSS Inc, Chicago, III). Frequencies mean and standard deviations were calculated and categorized according to age, gender, regions examined affected teeth and type of EDs. The (chi-square) test was also used to conduct an analytical study of the proportions of the distribution of all EDs among children and their relationship to age, gender and factors to determine the statistically significant differences.

Results

The sample consisted of 2000 including 934 boys (47%) and 1066 girls (53%) between 7 and 12 years (9.84±1.56), who were selected from all regions. The number of children examined from the age of 10 years was 412 boys and girls, who constituted (21%) of the sample, which is the highest percentage, while the lowest percentage (8%) was for children from the age of 7 years (153). other children. The number of children aged 8 years and 9 years were 327 (16%) and 348 (17%) respectively. The number of children aged 11 and 12 years were 384(19%) and 376 (19%) respectively. 

The prevalence of EDs, based on the first clinical examination, was 16.1%. Findings of the study indicated that the LEDs was more frequent  (51.7%) than MIH (42.7%), AI (5%), and also than EDs related to high doses of systemic fluoride (0.6%). 

Table 1 presents the distribution of EDs in males and females in different age groups. There was no significant difference between males and females in the prevalence of EDs (P= 0.45) as it was observed in 156 (17%) of males and 165(16%) females. There was no significant difference between males and females in the frequency of different EDs (P=0.69) despite the increased cases of LEDs among male children when compared to females (55% versus 48%). In addition, the MIH were more frequent in female children than males (45% versus 40%) and the percentage of AI in female children was more than males with no significant difference (5% versus 4%). Findings are presented in Table 1.  

The findings indicated that highest frequency of EDs was observed among children aged 9 years. However, there was no significant difference between different age groups in the frequency of EDs (P= 0.116). Results also indicated that the highest percentage of LEDs was observed in children at the age of (7 years) and reached (77.8%), and at the age of 11 years (56.7%). However, there was no significant difference or relationship between the types of EDs and the age of the affected children (P= 0.463). In contrast, there was a statistically significant difference between the types of EDs and the region examined in Damascus (P= 0.00061) as one of the regions in Damascus had the highest percentage of MIH (16.7%) and AI (22.2%). When investigating the etiological factors of EDs through the phone, it was found that the response rate was 53.6%.

There was no significant relationship (P= 0.13) between the type of EDs and the economic status of the parents, despite the high percentage of MIH  among children who had families with good economic status (57.7%), and increased frequency of LEDs among children from families with low economic income (47.1%).

A statistical significant difference between the educational status of parents and the type of EDs was observed (P=0.005). The percentage of MIH increased in children from families with a good educational level (52.6%), while the percentage of LEDs increased in children from families with low educational level (45.5%).

The presence of consanguineous marriage was observed in 51 out of 139 children with EDs (36.6%). The presence of MIH was more common than any other defects. However, there was no significant difference between the type of EDs and the presence of consanguineous marriage (P=0.44). 

The number of children who had mothers with medical problems during pregnancy was eight out of 128(6.2%). However, no significant difference was observed between the presence of medical problems during pregnancy period and type of defect (P= 0.89). 

In addition, the number of mothers who took medications during pregnancy was 13 (10.2%). MIH (69.2%) was more frequent in children of mothers who took medications during pregnancy. However, this difference was not significant 

It was also noted that there was no significant relationship between the type of EDs and the nature of delivery (natural, cesarean) (P= 0.85).

The rate of premature birth among mothers of children with EDs was (3.1%). It was noticed that there was no significant relationship between the type of EDs and the timing of birth.

In addition, there was no significant difference between the type of EDs and the child's birth weight (P=0.93). The percentage of children with EDs who were breastfed reached (80.2%), were artificially fed was (7.1%) and who had mixed feeding (12.7%) with no significant difference between the type of EDs and the nature of the baby's feeding (natural - artificial - mixed). 

The percentage of systemic diseases in childhood in children with EDs was (28.6%).  High prevalence of MIH was observed in children who had systemic diseases in their early childhood (72.2%). However, the P value did not show statistically significant relationship between EDs type and systemic diseases in childhood (P=0.085). 

The percentage of genetic diseases in the family of children with EDs was (16.7%). It was noted that the prevalence of MIH was higher in children with genetic diseases (57.1%), compared to healthy children (54.3%). However, there was no statistical significance (P=0.26).

The rate of allergic problems in children with EDs was present in 13.5%.  However, there was no significant relationship between the type of EDs and the presence of allergic problems (P=0.582).

The percentage of children with EDs who were exposed to injuries, bruises or surgeries during childhood was (23%). The percentage of local defect in children who have been exposed to injuries, bruises or surgeries was high (55.2%), as well as the percentage of MIH (44.8%) compared to those who were not exposed to any injuries. However, there was no significant difference between the type of EDs and the presence of injuries, bruises or surgeries during childhood (P= 0.21). No relationship between the type of EDs and the regularity of the vaccination schedule in children was observed (P= 0.68) as only one case with EDs, did not complete the vaccination program (0.8%).

Most children with EDs had their primary teeth replaced naturally, as their percentage reached (89.7%), while 10.3% of children with EDs had pulpitis, necrosis, abscesses, trauma or long stay of their primary teeth. All LEDs (100%) and 66.7% of MIH cases were observed in children who had trauma on their primary teeth. However, there was no significant relationship between the status of primary teeth and type of EDs.   In contrast, there was a significant relationship between the type of EDs and oral health (P=0.01). LEDs were significantly more frequent in children with good oral health (66.6%), whilst MIH was more frequent in children with poor oral health (57.1%). Findings are presented in Table 2.

The number of children with EDs who underwent a second clinical examination was 240 out of 321(74.8%). It was not possible to preform clinical examination to 25.2% of children with EDs.  The highest prevalence of EDs was observed in the upper incisors (61%) followed by the lower first molars(43.3%), the upper first molars(37.05%), then the lower central incisor(30.95%), lower lateral incisor(17.8%), and the upper lateral incisor(15%), which had the lowest prevalence. Table 3 presents the distribution of EDs in right and left sides of incisors and molars.

The summary of the assessment of EDs according to the EDI index on the incisors and molars is presented in Table 4.  The prevalence of hypoplasia was generally low, although it was generally high in the upper incisors and lower lateral incisors. In most cases, it was continuous with grooves seen in 8% of the cases on the incisal buccal surface of the upper incisors associated with rare pits. 

The sub categories of EDI indicated that the highest prevalence of opacity was on the right and left upper incisors. It was white with demarcated edges and more common on incisal buccal surface, except for the lower incisors, which was more obvious on its buccal surface and then on incisal buccal surface.  The opacity on molars ranged from white to yellowish white and yellow, and its edges were demarcated or diffused in equal proportions.

The opacity was common on all surfaces, and the highest percentage was on the buccal surface (40%), then the occlusal (36%) and the palatal (30%). The highest percentage of opacity was seen more common on the buccal surface than the occlusal surface of the upper molars, while it was the opposite in the lower molars, as it was more frequent in occlusal than buccal surface. In addition, the opacity seen on the buccal surface was yellow (43%), demarcated (49%) or diffused (51%). The opacity seen on the palatal surface was yellow (31%) with demarcated edges in 34% or diffuse in 66% of the cases. The opacity seen on the occlusal surface was yellowish-white in 33% of the cases, with demarcated edges in 44% or diffused in 56% of the cases.

Regarding post-eruptive breakdown, it was more frequent in molars and almost non-existent in incisors. The prevalence of post-eruptive breakdown increased in the lower molars compared to the upper molars.

The post-eruptive breakdown was observed on the occlusal surface in 15% of all cases. 

Discussion

EDs are disturbances of hard tissues during odontogenesis that can negatively affect the health of children. It can cause several adverse effects such as dental sensitivity and caries. It can also reduce social interaction due to compromised appearance of patients, cause low self- esteem and absence from school [2]. Therefore, understanding the prevalence and etiological factors of EDs can enable dentists to provide early and appropriate preventive and successful restorative care which in turn can improve the psychological well-being of affected children [20].

The number of EDs cases among Syrian children is increasing. However, there is a lack of sufficient national information about its prevalence and etiological factors. Therefore, the objective of this study was  to investigate the prevalence of EDs among Syrian children, and provide further understanding about the etiological factors.

 A comprehensive clinical examination was conducted for children in order to identify the EDs. Then, these EDs were evaluated using the EDI. About 240 (74.8%) had EDs and 25.2% were not examined due to their refusal, lack of cooperation or absence of the follow-up visit.

Children between 7 and 12 years were selected, as this age group corresponds to the ages of primary school children in the Syria and would be the most suitable age group for identifying EDs on incisors and molars. Children were selected from all regions of the city of Damascus. The EDI index was used as a simple tool that does not require a long period. It does not prevent the educational process of children and enable comparisons with other previous studies [14,19,21]. It enabled obtaining rich clinical information about dental surfaces of each tooth, facilitating recording of the sub-patterns of each major EDs. 

Elcock and colleagues indicated in their 2006 study [14] that the use of the EDI index in the evaluation of EDs clinically is equivalent to or exceeds the The Fédération Dentaire Internationale Developmental Defects of Enamel index (FDI  DDE index). Their studies also showed that the EDI parameter requires a shorter application time compared to the FDI DDE by a significant difference (P < 0.05), while comparisons in the frequencies of EDs were possible when using both indicators, although it was not possible to record the post-emergence breakdown when using the FDI DDE index[14].

The investigation of etiological factors was based on communication with parents through phone. The response rate was only 53.6% due to the absence of telephone line (nonexistent, broken, closed), related to the non-cooperation of parents, or the number is originally wrong.

The methodology used, for communication with parents to investigate the etiological factors of EDs, was based on previous nutrition studies, as nutrition researchers conducted telephone call to assess the amount of food and drinks consumed at home during the past twenty-four hours. The method was found to be easy and inexpensive compared to other methods, but it requires cooperation by the person due to its total dependence on personal memory with the absence of accurate records of information [22]. This method was convenient for the parents because it did not require them to come to the dental clinic or answer the questions in absentia. The communication with them brought a feeling of relief and gave them impression of the doctor's interest in their child. It enabled direct explanation and understanding of what is required accurately in a gentle and simple way.

Talking to the mother was found to be effective in most cases. This is consistent with Whatling and Fearne (2008) study who concluded that questioning father of a child with MIH is insufficient, especially about pregnancy [1]. Alternatively, they interviewed affected and healthy children with their mothers to obtain sufficient and accurate information regarding the period of pregnancy. Children who were accompanied by fathers, a family member, adopted children, or legal guardians were excluded from the study [1].

During the questioning of mothers, the focus was on the health status of the child during the first four years of his life, as this period coincides with the process of dental development. This is consistent with the research conducted on the epidemiology of MIH, which focuses on environmental disorders that occur in the first three years of life [1].

The results of this study showed a high prevalence of EDs (16.1%) among Syrian children. To our knowledge, this study has been the first that provided number about EDs among Syrian community. 

Previous studies have reported prevalence of EDs among different populations, ranging from 63 to 68% in New Zealand to 99% in Hong Kong in China according to diagnostic tools they have used[14, 15]. 

In addition, the percentage of LEDs was higher in males (55.1%) than females (48.5%), while the percentage of MIH was more frequent in females (45.4%) than males (39.7%), with no significant difference between males and females in the frequency EDs. 

Previous studies showed no relationship between a child's gender and the prevalence of EDs in permanent first molars[23,24]. For instance, Almuallem and co-workers (2022) did find any relationship between MIH and gender when investigating the prevalence and etiological factors among Saudi schoolchildren aged 8-12 years in Riyadh[23].

Our study indicated that EDs were not related to age. However, the prevalence of EDs varied significantly according to the region investigated in the city of Damascus. The highest prevalence of EDs was seen in the region (22%), which had lower educational economic status (n=39) whilst, Muhajirin region, which had better socio-economic status had the lowest prevalence of EDs (P = 0.00023). This might indicate that regions with low economic and social levels, can reflect poor nutritional status of these children, poor cultural situation, poor health awareness towards the importance of regular checkup, and dental treatment of primary teeth. The difference in the prevalence rates of EDs in different regions in Damascus may also be due to the different percentages of fluoride in drinking water in those regions with the absence of relevant local studies showing the exact fluoride level in drinking water in each region.

It is worth mentioning that environmental pollution can have also a role in causing EDs. Jan and colleagues (2006) reported a high prevalence of developmental EDs in permanent teeth of children exposed to high rate of polychlorinated biphenyls [18]. The results of their study concluded that there is a significant dose-dependent relationship between the occurrence of EDs on permanent teeth and the duration of exposure to environmental pollutants. 

Previously, Arrow (2009) showed a relationship between the occurrence of EDs of permanent first molars and the place of residence of the child [24].

In this study, our findings showed that LEDs were more common (51.7%), than MIH (42.7%), AI (5%), and EDs resulting from high doses of systemic fluoride (0.6%).  The high percentage of LEDs could be due to the parents’ lack of awareness towards the importance of promoting oral health of their children during primary dentition and their belief that treating caries of primary teeth would not be essential. Consequently, this lack of interest and care can cause pulpal infection, subsequent abscesses and apical lesions that subsequently affect the enamel of permanent posterior tooth.

Findings of this study also showed that the highest percentage of LEDs was 77.8% at the age of 7 years, followed by the age of 11 years with 56.7% without a significant relationship between different EDs and age. The increased prevalence of LEDs may be due to the lack of health awareness towards the importance of primary teeth and their treatment in the case of traumatic injuries and caries.  Jälevik and co-workers (2018) who previously found that dental injuries to primary anterior teeth could raise the risk for developmental EDs in the permanent teeth [10]. A recent systematic review has indicated that intrusive trauma affecting primary tooth can cause the highest proportion of consequences presenting, as EDs and that younger patients experiencing primary trauma are more likely to obtain damage to the succeeding dentition. However, the same review indicated to poor quality of evidence due to the observational nature of the studies available [25]. 

Our study indicated that MIH was more common in children from families with good economic status whilst LEDs were more common in children from families with low economic income (47.1%). However, there was no significant relationship between the type of EDs and the economic status of the family. Previous study undertaken by Montero and colleagues (2003) reported high prevalence of EDs in a group of children aged 3 to 5 years, who related to poor families and attributed this to the low socio-economic level of this group [26]. Development of EDs were found to be more frequent among children from economically underprivileged families [27]. Similarly, Tourino (2018) found that children from families with a lower income had a greater frequency of EDs as they are more prone to low birth weight, premature birth and nutritional problems during enamel formation [28]. The differences existed between our findings and other studies may be related to the index used or to the depth to which the EDI was used [14]. 

In addition, our findings indicated that EDs were very common in children descended from families with a medium educational status (75.1%). There was a significant relationship between educational status of parents and type of EDs (P = 0.005). The percentage of MIH increased in children from families with a good educational level 52.6%. The percentage of LEDs in children from families with a low educational level increased 45.5% (n = 10). This confirms to what was previously mentioned in terms of high rate of untreated caries and abscesses among children from families with low educational level [29]. 

In contrast, Arrow (2009) showed no relationship between the prevalence of EDs in permanent first molars and the educational level of the mother [24].

Consanguineous marriage is a relationship between biologically related individuals. Previous studies have provided evidence about the significant association between consanguineous marriage and congenital dental anomalies in which genetic factors can have a role in gene environment interactions that affect oral health [30, 31, 32, 33, 34]. For instance, Lakshmayya and colleagues (2010) found that malocclusion, no syndromic oligodontia, and enamel hypoplasia were more frequent in individuals born from consanguineous marriage [35].

In contrast, the results of this study indicated that consanguineous marriage was present in 36.7% (n=51) of children with EDs. However, there was no statistically significant relationship between the types of EDs and the presence of consanguineous marriage. Similarly, Arrow (2009) showed no relationship between the occurrence of EDs in permanent first molars and the presence of consanguineous marriage [24].

The percentage of mothers who suffered from health problems during pregnancy and had children with EDs constitutes 6.2%. However, there was no significant relationship between the type of EDs and pregnancy period. Similarly, Arrow (2009) showed no relationship between the occurrence of EDs in permanent first molars and health status of the mother during pregnancy [24]. In contrast, Whatling and Fearne (2008) noticed that the prevalence of MIH was significantly more common in children of mothers who suffered from health problems during pregnancy [1].

Similar to previous work [11, 24], our findings showed no significant relationship between the type of EDs and medications taken by mothers during pregnancy. The present study also found no significant relationship between the type of EDs and the nature of delivery. Previous researchers did not find any relationship between EDs and type of delivery (natural, caesarean) or birth complications such as hypoxia at birth [1, 11, 24].   Arrow (2009) also showed no relationship between the occurrence of EDs on the permanent first molars and the age of the mother at birth, the state of birth, whether it was natural or caesarean, whether it was planned or unplanned [24]. 

However, a recent systematic review has indicated that caesarean delivery and delivery complications were associated with increased risk of developing MIH [36]. In another recent systematic review investigating the etiological factors of hypomineralization MIH, Garot and co-workers (2022) found that perinatal factors that lead to hypoxia such as prematurity, caesarean delivery, and birth complications are associated with an increased risk of developing MIH [37]. 

The present findings were consistent with previous studies, which did not find significant relationship between the type of EDs and the timing of birth (normal, cesarean) or gestational age [1, 11]. However, the results of a recent meta-analysis showed a three times increased risk of developmental defects of enamel in preterm children [38].

When investigating the relationship between the types of EDs and the child's birth weight, we did not find any significant relationship between children with MIH and birth weight and this was in agreement with findings of previous studies [1, 11]. In contrast, Arrow (2009) showed a relationship between EDs and the health status of the child at birth [24].

The present study showed no significant relationship between the type of EDs and the nature of the child's feeding (natural - artificial - mixed). Likewise, previous studies did not find a relationship between EDs and the duration of breastfeeding [1, 11, 18, 24].

Previous study undertaken by Ortega Páez and colleagues (2008) showed that the prevalence of EDs among children with celiac disease was 83.3% versus 53.3% of the control children in Spain [39].   Whatling and Fearne (2008) showed that MIH was more common in children taking Amoxicillin [1]. In addition, Beentjes and colleagues (2002) showed that children with MIH were more susceptible to recurring systemic diseases during the first four years of their life compared to healthy children. Children with MIH were more likely to develop systemic diseases during the first four years of their life such as middle ear infections, cystitis, diarrhea, measles, smallpox, whooping cough, pneumonia, respiratory tract infections, non-specific respiratory diseases, asthma, bronchitis, gastrointestinal infections, and hyperthermia [11].  

In a recent systematic review, researchers found that postnatal factors such as measles, urinary tract infection, otitis media, gastric disorders, bronchitis, kidney diseases, pneumonia and asthma are associated with MIH [37]. Fever and antibiotic use, which may be considered as consequences of childhood illnesses, were also associated with MIH. Arrow (2009) showed a relationship between the occurrence of EDs on permanent first molars and medical treatments received by the newborn [24], where the prevalence of EDs increased among children who received medical treatments at birth (84%) compared with healthy children (69%).

Our hypothesis were that systemic diseases in childhood might play a role in Eds. However, there was no relationship between the occurrences of EDs on the permanent first molars, the presence of childhood diseases, the type of these diseases, the medical treatments during childhood, and the type of medicines. Therefore, further studies in this matter are still required to elucidate the role of systemic diseases and EDs. 

In this study, no relationship was observed between the type of EDs and the regularity of vaccination schedule in children. In contrast, Whatling and Fearne (2008) showed that MIH was more common in children who had chickenpox (varicella) between the ages of three to four years, as this period of infection is more important in causing MIH than the occurrence of the infection itself [1]. They have suggested implementing routine national vaccinations against varicella-zoster virus in order to decrease the MIH. However, this study did not find any relationship between the MIH and the measles, rubella, mumps or other diseases.

In agreement with the Whatling and Fearne (2008), our study did not find any relationship between the type of EDs and the presence of genetic diseases among the family of affected child [1]. 

When investigating allergic problems in the affected child, the results indicated that the percentage of children with EDs who suffer from allergic problems was 13.5% with no significant relationship between the type of EDs and the presence of allergic problems. Whatling and Fearne (2008) study found no relationship between MIH and childhood allergies. This research showed that no significant relationship between the type of EDs and the injuries, bruises and surgeries that the child had during childhood[1]. Whatling and Fearne's (2008) did not find any relationship between the prevalence of MIH and being under general anesthesia during childhood [1]. Arrow (2009) showed no relationship between the occurrence of EDs on permanent first molars and traumatic injuries to the child in the facial area [24].

This study reported no significant relationship between the type of EDs and the condition of primary teeth before the exfoliation. Whatling and Fearne's (2008) did not find a relationship between MIH and traumatic injury or abscesses in primary teeth [1]. Arrow (2009) showed no relationship between EDs in permanent first molars and caries in the primary teeth [24]. However, Quintero and co-workers (2022) found a significant association between the severity of hypomineralization in permanent molars and the activity of dental caries lesions [40].

The results of this research showed that most children with EDs had moderate oral health (76.4%), whilst the percentage of children with EDs with poor oral health was 14.8%.  Higher percentage of LEDs was observed in children with good oral health (66.6%), while MIH was more frequent in children with poor oral health (57.1%), with a significant relationship between the type of EDs and oral health status. This may be due to several reasons such as lack of interest of affected children in oral health measures in which enamel becomes more susceptible to infection due to both lack of mineralization and plaque accumulation that find in addition to post-eruptive breakdown which results in exposure of the dentin.

In addition, hypersensitivity of teeth with EDs due to poor enamel mineralization, the thickening of the enamel layer or the exposure of dentin can worsen oral health, as it can prevent appropriate brushing process to avoid discomfort or mainly the young  age of a child may not enable him/her  to perform the correct and effective brushing process.

Previously, Li and colleagues (1994) reported an association between enamel hypoplasia and a higher number of mutans Streptococcus MS in the saliva of children with EDs when compared to controls [41]. This was attributed to surface irregularities of affected enamel that can foster the colonization of MS [41]. In addition, Montero and colleagues (2003) found high prevalence of dental caries in children between the ages of 3 to 5 years who had EDs [26].  Arrow (2009) also showed that children with EDs of the specified type suffer from a high rate of caries on their primary teeth with no significant relationship [24]. The study did not show any association between EDs and the age at which the child started using toothpaste. There was no relationship between the occurrence of EDs on the first permanent molars and the EDs of primary teeth [24].

When investigating the etiological factors of EDs through the phone, no specific etiological factor for EDs was precisely identified, and this result is consistent with the results of several previous studies. For instance,  Whatling and Fearne (2008), indicated to the lack of evidence about specific causative factor of MIH, and suggested that EDs is a multi-causal disease that may be genetically predisposed, which reflects the importance of conducting family-level studies to obtain additional information[1]. They have not found any significant associations between MIH and delivery and birth complications, breastfeeding, immunization history, other illnesses and allergies, general anesthetics, fluoride history, and trauma or abscesses affecting the primary predecessors. However, they indicated that MIH has been significantly more common among those whose mothers had experienced problems during pregnancy (P = 0.025), those who had chickenpox between the ages of 3 and 3.99 (P = 0.047), and those who received amoxicillin (P = 0.028). The total number of molars with EDs was 383 out of 952 examined (40.2%) whilst the number of incisors with EDs was 603 out of 1864 (32.3%).

In this research, EDs of the permanent incisors and the first permanent molars was evaluated in detail, while other studies evaluated the prevalence rates in all erupting teeth without considering the type of tooth. For instance, Jan and colleagues (2006) found after investigating 6340 permanent teeth, using the FDI index, that the prevalence rate was 65%. They also found that the prevalence of EDs in primary teeth was 4.5% after examination of 3523 primary teeth [18]. Ortega Páez and co-workers (2008) studied the prevalence of EDs in young children (mean age=3.6yrs), and found that the prevalence of EDs affecting molars was 45.1%, prevalence of defects affecting incisors was 31.7%, and prevalence affecting canines was 2.3% [39].

In this research, a dental examination was conducted to all teeth of the affected child. The main patterns of the defect were recorded for all surfaces of affected teeth (hypoplasia, opacity and post-eruptive breakdown). The sub-patterns were also recorded for each tooth (hypoplasia, edges of opacity, and the color of opacity).

The upper incisors had the highest defect, followed by the lower first molars, then the upper first molars, the lower central incisors, lower lateral incisors, and then the upper lateral incisors, which had the lowest prevalence. Arrow (2009) showed that the percentage of diffused white opacity on the right upper first molar was 47%, while the percentage of diffused white opacity associated with hypoplasia on these molars was 1%. The percentage of demarcated opacity was 8% and the percentage of demarcated opacity associated with hypoplasia was 3% [24]. The rate of hypoplasia of the craters pattern was 1%. Arrow (2009) showed that the percentage of diffuse white opacity on the left upper first molar was 49%, while the percentage of diffused white opacity associated with hypoplasia on these molars was 1%, the percentage of demarcated opacity was 12% and the percentage of demarcated opacity associated with hypoplasia 2%. The rate of pitted hypoplasia 1% [24].  Arrow (2009) showed that the percentage of diffused white opacity on the left lower first molar was 41%, while the percentage of diffused white opacity associated with hypoplasia on these molars was 1%. It was also found that the percentage of demarcated opacity was 7%, the percentage of specific opacity associated with hypoplasia was 3%, and the hypoplasia rate of the pitted pattern was 3%. He indicated that the percentage of diffused white opacity on the right lower first molar was 42%, while the percentage of diffused white opacity associated with hypoplasia on these molars was 2%, the percentage of demarcated opacity was 8% and the percentage of demarcated opacity associated with hypoplasia 2% The rate of hypoplasia of the craters pattern was 2%.

After using the EDI index, a high percentage of opacity was observed in general, where the highest percentage of opacity was seen on the upper incisors. Post-eruptive breakdown was seen on molars at high rates, and it was seen on the lower molars more than upper molars. Hypoplasia was seen at low rates in the upper central incisors and the lower lateral incisors. 

In other studies, Elcock and colleagues (2006) showed, through using the EDI index, a significantly higher frequency of both opacities (93% vs. 78%; P < 0.05) and post-eruptive breakdown (28% vs. 1%; P < 0.05) in the Sydney schoolchildren when compared with those in Sheffield [14].

Due to the variety of indices used to measure EDs, studies provided different information and data about the prevalence of opacity, hypoplasia and post-eruptive- breakdown. For instance, Jan and colleagues (2006) who used the FDI index, found that the prevalence of well defined-opacity  was 49.4% with or without hypoplasia, while the percentage of diffuse opacity recorded on permanent teeth was 33.4%[18].

In this study, the use of the EDI index enabled us to obtain information about the secondary patterns of EDs.  Presence of white and demarcated opacity on the incisal buccal surface of the upper and lower incisors was observed. The opacity on molars was white to yellowish-white or yellow, demarcated or diffused on the buccal and occlusal surface of upper and lower molars. The post-eruptive breakdown was high on surfaces of molars.  Hypoplasia was mostly extended with groves presented in only 8% of the incisal buccal surface of the upper incisors.

In the study undertaken by Montero and colleagues (2003), types of EDs differed according to the site of defect, where the percentage of hypoplasia was 70% on the buccal surface of the canine, while linear opacity reached 50% of  the upper anterior incisors, and hypoplasia in 14% of defects[26]. Smith and colleagues (2009) showed a high frequency of pitted hypoplasia on occlusal surfaces (82.6%), and a high rate of post-eruptive breakdown on the occlusal surface when compared to the other surfaces (39.13%)[19]. The incisal third of buccal surfaces had a high percentage of diffused opacity (53.4%), whilst demarcated opacity associated with post-eruptive breakdown was more frequent. This discrepancy with the results of this study is attributed to the selected sample, which was a group of primary or permanent anterior and posterior teeth taken from families with AI, in which the assessment was undertaken on the images taken for theses teeth [19]. Arrow (2009) showed that the percentage of diffuse white opacity was 45%, while the percentage of diffuse white opacity associated with hypoplasia was 3%, the percentage of demarcated opacity was 16%, the percentage of demarcated opacity associated with hypoplasia was 6%, and the percentage of hypoplasia associated with grooves was 3%[24].

It should be emphasized that during the clinical examination, about 9.2% of isolated cases of EDs were observed on other than the incisors and molars. These were seen on premolars as demarcated opacity ranging from white to yellowish white and were located on the occlusal surface or cusps only. These defects can be attributed to local infections such as abscesses on the precursors of the primary molars or traumatic extraction of these molars, which is called Turner's hypoplasia.

The EDs affecting permanent canines were demarcated white or yellow opacity on the buccal surface or on the incisal buccal surfaces, and it was due to the coincidence of the environmental disturbance with the period of development of the permanent canine. 

It should be emphasized  that this study included children up to the age of 12 years before the eruption of canine and because the canine is not emerging at the time when MIH was examined and detected. The permanent canine coincides with the development of the permanent incisors. Therefore, in theory, it might be suggested that the nature of defect of canine is similar to the nature of defect of incisors in MIH and permanent canine defect can be considered as part of MIH if the cause of MIH is environmental [1].

In addition, the only one case had EDs affecting second permanent molars with a demarcated white spot on the buccal surface due to developmental systemic disorders that coincided with the period of mineralization of the enamel of these molars. The defect was symmetrical, and this is consistent with what was reported by Whatling and Fearne (2008) who indicated that developmental EDs is symmetric in most cases, while MIH may be asymptomatic [1].  A case of primary second molar defect has also been seen and this may be part of MIH.   Elfrink and co-workers (2008) showed that the prevalence of hypomineralization in primary second molars was 9.4 % in children and 3.6% on the level of defect of one dental unit [17].

Among the studies that dealt with EDs on the primary teeth is the study of Montero and colleagues (2003), which showed that the prevalence of EDs on the buccal surface of primary canine was 33% and on the maxillary primary anterior incisors was 17% [26].

It should be emphasized that this study might has some limitations. One of which is the absence of genetic analysis and measurement of water fluoridation levels that can ascertain our findings. Future work should consider these issues to enable further understanding about the etiological factors of EDs among Syrian children. It should also be emphasized that conducting a dental examination for the rest of the family members when assessing EDs of hereditary origin would be of particular importance to provide appropriate treatment and monitor  cases in the long term[42]. Moreover, it is also essential to conduct radiological and histological studies to improve understanding about other etiological factors implicated in EDs. 

Conclusion

To our knowledge, this study has provided a local number about the prevalence of EDs among Syrian community. It also improved understanding about the etiological factors of EDs. The present study provided evidence about the need for raising awareness of all families of children with EDs, through the establishment of integrated home oral health programs, and dental campaigns, about the importance of oral health, the necessity for visiting dental clinics for dental examination and assessment, application of appropriate restorations. This would prevent post-eruptive caries and breakdown, reduce factors causing tooth caries and preserve the rest of dental tissues intact. 

Future work should also consider investigating the prevalence of EDs among other age groups. There is also a need for improving knowledge of general practitioners about modern patterns of EDs, especially the MIH to recognize any symptoms that indicate the possibility of severe breakdown. This would be of particular importance to provide early diagnosis of the condition, assessment of the risk of non-erupting teeth, monitoring their emergence and early management. 

Abbreviations

AI:    Amelogenesis Imperfecta

EDI : Enamel Defect Index

EDs: Enamel Defects

FDD:  Fluoride Enamel Defect 

LEDs: Localized Enamel Defects

MD:  Mayssoon Dashash

MIH : Molar Incisor Hypomineralization MIH

RA J: Rania Al Jeghami

SPSS: Statistical Package for the Social Science

Declarations

Ethics approval and consent to participate

Ethical Approval was obtained from the ethics committee of the Faculty of Dentistry in Damascus University, Syria. All methods were carried out in accordance with relevant guidelines and regulations(eg. Helsinki declaration. In addition, a formal permission was obtained from the Ministry of Education in order to get access to schools and perform the required examinations on children. A written informed consent was obtained from all parents of the study participants.

Consent for publication

All pictures have consent for publication. 

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

The project was funded by Damascus University, Syria, which is a public University. 

Authors' contributions

RAJ collected the data and did the field work and statistically analyzed data. MD supervised the study, participated in study design, data analysis and interpretation, writing the manuscript and revising it. RAJ and MD read and approved the final manuscript.

Acknowledgements

Authors would like to thank all children and parents who accepted to take part in this study. This study is part of MSc dissertation to obtain master degree in pediatric Dentistry and is financially supported by Damascus University.

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Tables

Table 1: the distribution of EDs among males and females 

Table 2: the relationship between the type of EDs and oral health

Table 3: the distribution of EDs in right and left teeth

Table 4: The EDs Index for incisors and molars