Defining the Prevalence of Molar Incisor Hypomineralization in Brazil

Objective: To define the prevalence of Molar Incisor Hypomineralization (MIH) in Brazil since the reports ranged from 2.5% to 40.2%. Material and Methods: We studied 407 children from 7 to 14 years of age. MIH was measured using the European Academy of Paediatric Dentistry criteria of 2003. Clinical data were collected by a calibrated dentist (Kappa=0.88) and included affected teeth and degree of MIH severity (mild/severe). Mild MIH cases were considered when the tooth presented demarcated opacity ≥ 1.0mm, without any loss of structure. While severe cases were defined by teeth in which loss of structure was present, or past or current lesion that required treatment, or presence of atypical restorations. In addition, published data (nine studies) reporting MIH in Brazilians were identified, and the heterogeneity of these studies was tested (I2 index/ p≤0.01). Results: In the original sample studied, the majority of patients were males (55.3%; n = 225), with an average age of 10.1 years (± 2.1 years). The prevalence of MIH in this group was 14.5% (59 affected in 407), and most of the affected teeth had a mild degree of alteration (77.4% or 202 in 261 teeth). Conclusion: A meta-analysis including nine published reports, and our original data showed that MIH prevalence in Brazil is 13.48 (95% CI, 8.66% -18.31%).


Introduction
Molar Incisor Hypomineralization (MIH) is defined as a qualitative enamel defect that occurs during different stages of amelogenesis [1]. This condition usually affects at least one of the first permanent molars and may be associated with permanent incisors [2]. However, some studies report the association of MIH with permanent canines and primary second molars [3,4].
Disturbances during pregnancy, severe infections, the frequent use of antibiotics in childhood [5], and other exposures [6] have been investigated as etiologic factors and the genetics play role [7]. One of the main characteristics of MIH is enamel porosity and opacity, which may vary from white/yellowish to brown [2]. In some cases, MIH may cause the loss of tooth structure, resulting in functional (pain, tooth sensitivity and dental caries), and aesthetic problems for the individual [8].
It is suggested that the diagnosis of MIH should be performed on clean and wet teeth, and epidemiological studies of MIH should be based on 8-year-olds since, at this age, all permanent molars and incisors have erupted [2,9]. Likely due to different criteria of diagnosis, the prevalence of MIH varies considerably in different parts of the world ranging from 2.4 to 37% in European countries [10][11][12], 2.5% in China [13], and 2.5% to 40% [14][15][16][17] across Brazil. Due to these facts, the present study aimed to define the prevalence of MIH in Brazilians, which shows the widest range reported in the literature.

Sample and Calibration
A sample consisting of 407 individuals of both sexes from 7 to 14 years of age treated at the Paediatric Dentistry. The inclusion criteria for this study was the patients having all first permanent molars erupted.
Children with syndromes known to affect the enamel development were not included in the study.
To assess the intra-examiner reliability, an exercise was first applied to the examiner (F.M.F.S) and the gold standard evaluator (M.C.C.). Twenty clinical pictures of dental enamel defects (eight with MIH) were shown to the two individuals. Two weeks after the first assessment, a new assessment was carried out with the examiner, and the resulting Kappa was 0.88.

Clinical Examination
The clinical examination was performed by the calibrated dentist (F.M.F.S) carried out with a mirror and a probe in the dental chair using artificial light. MIH was evaluated using the European Academy of Paediatric Dentistry (EAPD) [2,9]. Mild MIH cases were considered when the tooth presented demarcated opacity ≥ 1.0mm, without any loss of structure. While severe cases were defined by teeth in which loss of structure was present, or past or current lesion that required treatment, or presence of atypical restorations [2]. The study included 225 males (55.3%) and 182 (44.7%) females, with an average age of 10 years.

Bibliographic Sources
A database search was performed in PubMed, Lilacs (Latin American and Caribbean Health Sciences Literature) and BBO (Brazilian Bibliography of Dentistry) using the following terms: "Dental Enamel Hypoplasia", "Molar Incisor Hypomineralization", "MIH", Hypomineralization Molar Incisor", "First permanent molars and incisors", "Prevalence", "Epidemiology", "Epidemiol" and "Brazil". A total of 383 references were identified and after excluding the publications that did not report denominators to allow calculation of frequencies, case reports, and studies that included the same sample of other publications, nine articles were selected (Table 1).

Results
The prevalence of MIH in the studied sample was 14.5 % (59 affected in 407 individuals studied), and there was no statistically significant difference in MIH affection by sex (p=0.914).
A total of 261 teeth were affected by MIH, 33% of them (n=86) were first permanent maxillary molars, 28.3% (n= 74) first permanent mandibular molars, 22.2% (n=58) permanent maxillary incisors, and 16.5% (n=43) permanent mandibular incisors. According to the degree of severity, it was observed that most teeth were mildly affected by MIH (77.4%; 202 in 261 affected teeth). Among the most severely affected teeth, most of them were first permanent molars (84.7%; 50 in 160 affected molars) ( Table 2). Meta-analysis was performed on data from nine articles results in addition to our original data. Figure   1 shows the estimates of MIH reported by the ten studies, which yielded a summary prevalence of 15.92 (95% CI, 10.85%-21.00%) with significant evidence of between study heterogeneity (Q = 521.81, p<0.01, I2 = 98) ( Figure 1). In an attempt to reduce heterogeneity, the sensitivity analysis was performed by removing the study that reported a different clinical diagnostic (the size of the lesions was not taken into consideration and used two methods for diagnostics). The new estimate was 13.48 (95% CI, 8.66% -18.31%) (Figure 2).

Discussion
There is great interest in understanding why MIH occurs, but this is a difficult task if we do not have even a decent estimate of the prevalence of the condition. However, it is notable that over the years, prevalence studies of MIH have been increasing mainly in Brazil.
The prevalence of MIH in the present study was 14.5%, which was consistent with most of the literature [22,23]. Not surprising, the prevalence estimate in our sample is close to the one found in the city of São Paulo (12.3%) [15], which is just 400 kilometers from downtown Rio de Janeiro. This may also be due to the diagnostic criteria that was similar among these studies. The frequency in the north-eastern region of Brazil appears to be lower [18,14]. This may be due to the inclusion of opacities greater than 2 mm in studies conducted in the region, which makes it more a strict criterion.
The meta-analysis showed high heterogeneity among the studies included. This is probably related to the use of different indexes, diagnostic criteria, and age groups. All selected articles had their examiners calibrated, but in different types of photographic training, clinical examination, or both. Eight studies, included our original data, used the same diagnostic criteria. Some studies included in the meta-analysis [14,19,20], except for one [16], reported lower prevalence compared to our study, probably because they considered only opacities that were larger than 2 millimeters of diameter.
In our sample, most cases had mild MIH, although more than 50% of affected teeth were first permanent molars with some degree of loss of structure. Such cases can have discomfort, caries lesion development, and esthetic concerns [14]. Prevalence studies are important to help formulate strategies to prevent or reduce the possibility of the consequences of MIH.

Financial Support
This study was financed in part by the Coordenação de Aperfeiçonamento de Pessoal de Nivel Superior Brasil -(CAPES) -Finance Code 001.