Relationship between Molar Incisor Hypomineralization and dental caries at eight-year-old children

Summary Introduction The aim of the present study was to determine the relationship between Molar Incisor Hypomineralization (MIH) and caries in school children from Banja Luka region, Republic of Srpska. Materials and methods One calibrated dentist evaluated a sample of 529 schoolchildren, eight years old, according to the European Academy of Pediatric Dentistry (EAPD) criteria on MIH presence. Dental caries was assessed using the DMFT (Decayed, Missing, Filled Teeth) criteria. Results DMFT/dmft was significantly higher in children with MIH than without MIH (p < 0.001). In the MIH group of children, high values of caries indices (%DMFT/%dmft and mean DMFT/dmft) were found. Conclusion Significant association between MIH and dental caries in eight-year-olds was found.


INTRODUCTION
Oral health is an essential part of the overall health. Regardless the knowledge of dental caries causes, it is still the most widespread disease of civilization and global problem. During the past decades in many developed countries it has been noticed a decline in caries prevalence of children and adolescents. Opposite to reduced prevalence of dental caries, developmental anomalies of enamel are increasingly drawing attention in clinical practice and becoming more prominent public health problem [1].
An increased frequency of structural anomalies of enamel has been noticed in the past years mainly affecting first permanent molars and incisors. For better understanding of these changes and their impact on overall oral health, Karin Werheijm et al. (2001) suggested a single term -Molar Incisor Hypomineralization (MIH), which was accepted at the meeting of the European Academy of Paediatric Dentistry in Athens in 2003 [2]. This condition is characterized by hypomineralization of systemic origin that affects one or more first permanent molars in association with defects of permanent incisors [3].
Beside clinical implications of MIH (thermal, chemical and mechanical hypersensitivity, lack of esthetics -appearance of white, yellow or brown opacity), hypomineralized changes are strong predictors of dental caries. Affected teeth, in particular first permanent molars, are susceptible to dental caries, not only because of enamel porosity, but also increased teeth sensitivity that make effective oral hygiene difficult [4]. Furthermore, low sali-vary flow rates and low pH have been observed in MIH children, as another factor that could possibly contribute to higher caries risk [5]. In more severe cases, hypersensitivity may be increased to the level that is hard to achieve efficient dental analgesia during preparation. What is even worse is that children with this type of defect require extensive and often repeated restorative treatments. Conservative treatments of these teeth are challenging for both, a patient and a dentist. In many cases, dental fear and anxiety is present which complicate treatment additionally [6,7]. For these reasons, monitored tooth eruption, adoption of timely and accurate diagnosis of MIH is crucial for proper selection of therapeutic procedures and prevention of further damage.
The aim of the present study was to determine the prevalence of dental caries in children with MIH, and relationship between MIH and caries development in permanent and primary teeth.

MATERIALS AND METHODS
A cross-sectional study was conducted in Banja Luka region, where 540 school children, aged 8 years were screened for MIH and decayed, missing and filled teeth (DMFT). Study was conducted between September 2015 and March 2016. Age of eight was chosen because first permanent molars and incisors erupted recently, so caries prevalence should still be low and therefore lower possibility for caries lesion to mask hypomineralisation [2].
The Ethical Committee of the Institute for Clinical Dentistry of Banja Luka and the Ethical Committee of Public Health Centre, Banja Luka approved the study.
Two stage sampling procedure was adopted for sample selection. In the first stage, 9 schools of all 30 were selected by random sampling. In the second stage, children were recruited, from the selected schools, by proportionate stratified random sampling. Children without parental informed consent signed and children with fixed orthodontic appliances were excluded from the study. A written informed consent was obtained from parents before clinical examination of their children.
One calibrated dentist, using a dental mirror and a probe, examined children in dental chair under artificial light. If necessary, cotton rolls were used to remove any residual debris. The criteria proposed by the European Academy of Pediatric Dentistry (EAPD) were used for the diagnosis of MIH, which included the presence of demarcated opacities, post-eruptive enamel breakdown, atypical restorations and extraction due to MIH of at least one first permanent molar [3]. Tooth lesions that were less than 1 mm in diameter were not included in the study, the opacities that were only observed on the incisors without the involvement of the molars were not diagnosed as MIH. The cases of excessive caries lesions haloed with opacities were diagnosed as MIH.
Dental caries experience was recorded using the WHO (World Health Organization) criteria for diagnosis of decayed (D), missing (M) and filled (F) teeth (DMFT/dmft Index) [8]. The caries prevalence was expressed in statistical coefficients: %DMFT/%dmft index and mean DMFT/ dmft index. The examination of dental caries included all permanent and primary teeth. According to clinical features of MIH, required treatment needs were presented in five groups: no treatment required, one-surface filling, two-or multi-surface filling, endodontic treatment and tooth extraction.
The data were analyzed using the IBM SPSS Statistics 21.0. A comparison between groups was carried out using the Pearson's correlations and Mann-Whitney U-test. For all tests the P-value of 0.05 or less was considered statistically significant.

RESULTS
Out of 540 children, nine did not have signed permission by their parents and therefore were not examined. Two children had partially erupted or unerupted all four permanent molars and were excluded as well. Finally, a total of 529 (97.96%) children (254 boys and 275 girls) were included in the study. Analysis of results about the prevalence of dental caries showed DMFT/dmft in permanent and primary teeth was significantly higher in children with MIH than without MIH (p < 0.001) ( Table 1). In the examined groups, high values of analyzed parameters for caries prevalence %DMFT/dmft and mean DMFT/dmft were found, but both significantly higher in the group with MIH (Table 2). Table 3 shows evaluation of the need for dental treatment of teeth affected by hypomineralization changes.

DISCUSSION
Our study evaluated the relationship between MIH and dental caries in school children of Banja Luka region, Republic of Srpska. Increased porosity of tooth structure and consequently reduced mechanical resistance of hypomineralized changes pose great risk for dental caries, even in populations with low caries prevalence.
Statistically significant correlation between DMFT (1.41 ± 1.62) and hypomineralized changes was found. This finding is consistent with the research of most au-  [13].
These results are on the other hand in contrast to a recent study of Heitmüller et al. where the association between dental caries and MIH in children aged 10 years was not found. However, the authors did not consider atypical restorations (due to hypomineralized changes) as restorations associated to caries and as such were not part of DMFT, which probably resulted in such finding [14].
The present study found statistically significant correlation between dmft (5.80 ± 3.48) and hypomineralized changes. This is not consistent with the majority of scientific research, where higher caries experience in permanent teeth with hypomineralized changes was found, but not in primary teeth [5,13].
Further analysis showed that 80% of our respondents with hypomineralized changes had at least one DMFT, compared to 50% in the group of children without MIH, which clearly implicate increased tendency for caries development in teeth with hypomineralization changes. A study conducted in India in 2015, by Tadikonde et al. demonstrated positive correlation between dental caries and MIH, where the prevalence of caries was 27% in children with MIH [15].
In the present study, mean DMFT/dmft in children with hypomineralized teeth was 2.3, which was statistically significant compared to the group of children without hypomineralization (1.2). Keeping in mind that the study included eight years old children who had small number of permanent teeth recently erupted, this result can be considered very high. This is in accordance with other studies [10,16]. Kirthiga et al. in their study found that the mean DMFT value in respondents affected with MIH was 3.2, which was significantly higher than the mean DMFT value of controls (0.8) [17].
MIH is associated with structural weakness and tooth hypersensitivity; therefore, there is high chance for performing poor oral hygiene and subsequently more chance for dental caries development. Histological examinations of hypomineralized teeth showed that oral bacteria can get embedded deeper into dentin of affected teeth, which obviously increase risk for dental caries [18].
Since dental treatment of MIH can pose a lot of difficulties, in our study the need for dental treatment of teeth affected by hypomineralized changes was estimated. It was determined that more than 70% of teeth with hypomineralized changes did not require treatment. This result can be interpreted as moderate and in accordance with similar results of other authors [19,20]. The study conducted in Spain in 2014 recognized the need for treatment in eight-year-old children with MIH in accordance with WHO criteria classifying them as examinations, urgent treatment and necessary treatment-but not urgent. They found that 3.8% of children with MIH required urgent treatment because of the severity of defects, while 27.9% required some type of treatment that was not an emergency [11].

CONCLUSION
Significant association between MIH and caries was found in the current study. Dental caries was more common in hypomineralized teeth, thus playing role in further deterioration of affected teeth. This finding implicates need for increased awareness in regards to hypomineralization, early dental treatment and adequate prevention.