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.