The prevalence of MIH among school children residing in the district of Salem, a fluorosis endemic region

Background
This prevalence study for Molar incisor hypomineralisation (MIH) is a rare data in the literature, as this was undertaken in Salem, a fluorosis endemic district in Tamilnadu.
Aim
To evaluate the prevalence of MIH among school children residing in the district of Salem, a fluorosis endemic region.
Design
A target sample of 5000 children between 9-14 years, comprising of 250 children from 20 blocks in the district of Salem participated in this study. The examination was done in their respective school by a calibrated examiner using European Academy of Paediatric Dentistry (EAPD) criteria for MIH.
Results
Out of the 4989 children examined 384 children had MIH. The prevalence of MIH in Salem was 7.3%, MIH present in girls was 8.9% when compared to 6.1% in boys. There was a gradual increase in prevalence rate with the age. Single tooth involvement of MIH was seen predominantly in incisors (2.24%) whereas molars had three teeth (1.1%). MIH with caries involvement were found in 51% of the teeth.
Conclusions
The prevalence of MIH for an endemic fluorosis district was found to be at 7.3%.Girls had more percentage of MIH when compared to boys which was statistically significant. A gradual increase in number of MIH was seen with age due to the post enamel breakdown. Caries involvement was also seen in more than 50 % of the MIH involved teeth.
Introduction
Some minor clinical conditions, which are not adequately noticed, suddenly turn out to be a very common finding. This draws the attention of the researchers in a quest to know the history, prevalence, etiology, clinical problems, management etc. One such problem which affects the dental enamel is the molar incisor hypomineralisation (MIH).History reveals that Severe Dental Enamel Hypoplasia of molars in sub adults, excavated from a 16th – 18th Century London graveyard, exhibited quite an exceptional number of enamel disturbances with severity when compared to the other archaeological population, currently these would have been clinically diagnosed as showing MIH.1
In 1970, the first epidemiological report of 15% prevalence on idiopathic enamel hypomineralisation in permanent teeth was reported.2 Earlier all developmental defects of enamel were considered generally as hypoplasia but then in 1992, FDI Commission on Oral Health, Research and Epidemiology classified them as two distinct entities: enamel opacities/hypomineralisation which presents as qualitative defect of enamel altering the translucency of enamel appearing as white, cream, yellow, or brown in colour whereas enamel hypoplasia, a quantitative defect with a reduced or altered amount of enamel appearing as grooves and pits or with partial or total lack of surface enamel.3,4
The current term MIH was coined at the 5th Congress of the European Academy of Paediatric Dentistry (EAPD) in 2001 and was accepted for usage in 2003 at the 6th congress of EAPD.5Differential diagnoses for MIH includes mild dental fluorosis and white spot lesions. Clinically the former appears as hypomineralised defect with subsurface porosities ranging from opaque, white, or flecked appearance. The striking clinical difference of dental fluorosis is its presence throughout the enamel as diffuse opacities, whereas MIH/MH presents as a localised thickness of demarcated opacities. The incipient carious white spot lesions are demineralised areas of enamel usually associated with plaque-retentive zones of teeth.6
In an attempt to score developmental defects of enamel, FDI proposed an index called DDE index, which was later found to be suitable for scoring MIH.7 Later many indices were used like the modified Developmental Defects of Enamel by Clarkson et al8, Enamel Defect Index by Brook et al9, but with the advent of introduction of an index solely for MIH by the EAPD in 20037. This index differentiates the diffuse opacities of fluorosis from demarcated opacities of MIH and should not be scored together as single entity as clinically fluorosis differs from MIH, and MIH is not influenced by fluoride Koch, 200310 .
The worldwide prevalence rate of MIH is showing an increasing trend, with earlier studies conducted in European countries ranging from 3.6% to 25% J??levik 11.Prevalence data retrieved from PubMed search using keywords MIH and EAPD after the introduction of index in 2003 showed prevalence ranging from3.5% to 40.2%12.These values suggest, there is a definite increase in trend in the prevalence of MIH worldwide. Most of the above available prevalence data comes from developed countries, with scanty information from the world’s second largest populated country like India. Prevalence reports in India ranges from 6.3 %( 2014)13, 9.2% (2012)14 & 10% (2014)15.As there exists a paucity in the data pertaining to MIH in India this study was undertaken covering a larger district in the southern state of Tamilnadu, India. The aim of this cross sectional study is to evaluate the prevalence of MIH in a fluorosis endemic area of Salem district.
Materials and methods
Ethical approval
The institutional ethical committee and review board approved the study protocol. Permission from the
District Education Department was obtained from the chief educational officer. Written Permission from school authorities and consent from parents was sought to allow the investigator to conduct the survey in each school.
Characteristics of the Study location
The present study was conducted in Salem district, located in southern state of India, spread in an area of 5245 km2 with varied source of community water supply, as both community regulated water supply and ground water were consumed. Salem district is also plotted as an endemic fluorosis area in the map of India with fluoride level in ground water ranging from 0 to 3ppm. The total population of Salem district accounts to 3,482,055, in which children below 6 years accounts for 344,960.Out of the total population 50.95 comprises urban whereas 49.05 rural population. (Census of India 2011).
Inclusion criteria
Children between the group of 8’12 years, born and brought up in Salem district with all the permanent anteriors and permanent molars erupted.
A total of 20 schools were chosen representing, one school from each block
Exclusion criteria
Children with any other developmental defects like amelogenesis imperfect and tetracycline staining.
Children who refused to take part or absentee on the day of examination.
Children with any other special health care needs or undergoing any orthodontic treatment.
Broken clinical crown in the molars with potential unknown cause.
Sample selection
Geographically Salem district is divided into 20 blocks, one school from each block was randomly selected by lottery method to represent that area. Children between the age group of 8 ‘ 12 years from government schools of both socioeconomic status, with a target of 250 children from each school, to achieve a target total of 5000.
Study design and examination
The examination of the entire study sample was performed by a single examiner (RK) with the help of two interns who helped for data entry. Scoring was done after thorough orientation to the scoring criteria, using the pictures taken previously from outpatient records in the department. Clinical differentiation of various grades of fluorosis was also done as the study was undertaken in an endemic fluorosed area to distinguish from MIH for this study.
Calibration
Before initiation of the study, a calibration exercise was carried out for the examiner (RK) with the aid of different clinical photographs of enamel developmental defects. Intra examiner variability was taken in to account and using kappa statistics, it was found to be 0.87.
Study setting and sampling procedure
At the start of the study all the children were given a pre-printed proformas, which was filled by each participant for details like name, age, sex, address, source of drinking water etc. All the Children were examined at their respective school premises with adequate natural day light, using a mouth mirror and a blunt ended probe without drying the teeth. Prior to this all the children were asked to rinse with plain water to remove any soft and loose debris. Any other remaining debris was removed gently by scraping with the blunt probe for better visualisation.
Labial, lingual/palatal and incisal surfaces of upper and lower permanent incisors and buccal, lingual/palatal and occlusal surfaces of the first permanent molars were examined. Fully erupted teeth with visible clinical crown were only scored.
Scoring for MIH was done using the ten point system proposed by Ghanim etal 201117, as per the European academy of Pediatric dentistry recommendations. (as illustrated in Table 1)
Table1. Criteria for scoring molar incisor hypomineralisation based on the European Academy of Paediatric Dentistry recommendations.
Code Criteria
0 Enamel defect free
1 White ‘ creamy demarcated opacities, no PEB
1a White ‘ creamy demarcated opacities, with PEB
2 Yellow ‘ brown demarcated opacities, no PEB
2a Yellow ‘ brown demarcated opacities, with PEB
3 Atypical restoration
4 Missing because of MIH
5 Partially erupted (i.e., less than one-third of the crown high) with evidence of MIH
6 Unerupted ‘ partially erupted with no evidence of MIH
7 Diffuse opacities (not MIH)
8 Hypoplasia (not MIH)
9 Combined lesion (diffuse opacities ‘ hypoplasia with MIH)
10 Demarcated opacities in incisors only
Grading of tooth for MIH
As the study setting was done for a large population of children, the presence or absence of MIH was only evaluated using the EAPD scoring criteria and hence the severity was not noted. As per the scoring criteria MIH was assessed for White/creamy or Yellow/brown demarcated opacities, with or without PEB, atypical restoration, missing due to MIH from history. All diffuse opacities which were identified as dental fluorosis were noted separately along with any other type of hypoplasia other than MIH.
Statistical Analysis
The collected data were analysed using the SPSS package version 11.5 (SPSS Inc, Chicago, IL, USA).A descriptive analysis of the prevalence and distribution of the clinical recordings was performed and p value was assessed using chi square test.
Results
Out of the total available data among 4989 children, the prevalence of MIH in Salem was found to be 7.7 % (table 1). Among these children examined 2158 (43.3%) were boys and 2831 (56.7%) were girls. The MIH was present in 131 (6.1%) and 253 (8.9%) boys and girls respectively (table 2). When age wise distribution of MIH was observed, the prevalence seems to be in an increasing trend with age, with lowest percentage noted in 8years with 2.6% and highest among the age group of 11 years with 9.6%.The percentage among other age groups were 9 years (6.6 %), 10 years (4.8%), 12 years (8.6%) and 13 years (6.7%) (table 3). When age group was assessed with their sex the girls (56.7%) had more percentage of MIH when compared to the boys (43.3%), which was seen in all the age groups (table4). This study also evaluated the involvement of number of incisors with MIH, it was found that majority of the cases had one incisor involvement (2.24%) followed by two incisors (1.74%).Children having four incisor involvement was seen in (0.50%), three incisor involvement in (0.26%).The percentage of involvement of five, six, seven and eight incisors were similar with (0.04%) (table 5).
The total number of MIH in molars were also evaluated, the maximum number of molar involvement was three accounting for (1.1%) followed by one molar (1%) and two molars (0.4%).None of the cases had all the four permanent molars with MIH (table6).
Evaluation between molar to incisor showed, when there was an involvement of one or two incisors there was a simultaneous involvement of either one or three permanent molars. Single tooth involvement of MIH was neither presence in molar nor in the incisors. (table7).
The number of teeth having MIH with caries involvement, was found to be present in more than 50% of the children.MIH with one to two caries teeth were seen in 72 children (1.4%), with three to four carious lesion in 95 children (1.9%) and above four carious lesions in 31 children (0.6%) (table 8).
Discussion
Global data
The global data available regarding prevalence of MIH are still deficient and a country like India having the world’s second largest population have reports in the literature only in single digits. Even though the previous reported studies have not shown any direct relation between fluorosis and MIH, a large population of India live in endemic zones of fluorosis. So this provoked us to take up a population living in an endemic area of Salem district in the southern state of India with a previously existing developmental defect in enamel namely dental fluorosis.
As per the census of India around 35% of the population are below 15 years. Thus the sample selected for this study may be considered to be a true representation of the entire population of this region for this age group, as the target population and the rate of participation was good.
Prevalence data
The prevalence rate of MIH in the literature has been reported ranging from 2.8 % in Hong Kong (2008)18 to as high as 40.2 % amongst Brazilian subjects (2009)19.As the majority of the studies come from the European population, the prevalence ranges from 3.6 to 37.5 % (1987 to2008)19, 20.This wide disparity in reporting can be attributed to different sampling methodologies like birth cohorts, recruitment of population, convenience samples and non-uniform methods of clinical examination like the developmental defects of enamel (DDE) index (Weerheijm and Mejare 2003)7.
With the advent of EAPD index, the reported disparity in the clinical examination of MIH with other developmental defects of enamel like diffuse opacities in fluorosis, hypoplasia etc. has been addressed and hence this index was used in our study. Another problem with other indices is that they evaluate the size of the defects, whether equal to or larger than 2 mm to assess severity21,22,23,24. To ensure a uniform examination of this target population, one single trained and calibrated examiner performed the sample examination.
The present overall prevalence rate of 7.3% appears close to the previous Indian studies reported in the literature, parikh et al (9.2%)14, Mittal et al (6.3%)13 and Bhaskar et al (10%)15.This shows that MIH has not spared any part of the word, which is almost seen among one in ten children, which is found to be moderately high.
Eventhough the prevalence rate of this region was found to be moderate, these data cannot be compared with other worldwide reports due to various factors like small sample size, use of other indices, diagnostic criteria and inclusion of certain special groups. 25,26,27
MIH in molars and incisors showed increase in severity with age. Younger age group tend to have milder defects while elder one had more disintegrated defects. This was predominantly evident in molars when compared to incisors. This age dependant severity was reported similarly in other studies also suggesting that MIH a preexisting congenital defect of enamel, when exposed to oral cavity for a longer duration lead to PEB particularly in the molars where heavy masticatory forces are involved.24,28
Children from the fluorosis hit district of Salem consume water from different sources other than the community water supply regulated with fluoride. This excess fluoride during maturation stage of enamel, affects enamel crystal formation leading to diffuse opacities.But in this study dental fluorosis did not have any significant impact on the occurrence of MIH, which is in concurrence with the studies previously reported by Richard et al29where the MIH prevalence was low in fluoridated community. Similarly Koch et al 10 in a Swedish study stated that environmental factors like levels of fluoride did not have a direct impact.
Gender predilection showed, MIH was more common in girls than boys (8.1% vs 6.9%). This can be attributed to the fact that chronological eruption sequence in girls are more advanced than the boys. The early eruption of FPM with hypomineralisation can lead to PEB30.
The degree of severity of MIH involved teeth was not uniform, this was similarly noted in the previous studies and this difference in severity may be due to the timing, maturation, severity of insult or a combination of factors affecting amelogenesis.22,24,28,31 .
MIH like defect was also noticed in few cases in canines and premolars which was not large numbers, suggesting that a broader perspective of this condition is essential. A similar finding was also reported by Bhaskar et al 15.
Notable clinical findings in this study was none of the cases showed involvement of MIH only in incisors or molars. MIH with dental caries was noted in more than 50% of the cases owing to factors like PEB leading to plaque accumulation, poor brushing due to sensitivity and lack of awareness of pertaining situation. These data are very essential for the public health department in our country, as these children require complex treatment procedures.
Some of the limitations in this survey includes assessment of various etiological factors, demographic pattern and any other involvement of risk factors, which could have influenced the development of MIH either prenatally or at birth. These information can further help us to track the time at which this is initiated for early prediction and follow up.
Future direction of the study should be aimed at the age for sample selection, between 7’8 years immediately after the eruption of the first permanent molars have erupted, before its removal, a common treatment for this condition.
Conclusions
Prevalence of MIH in an endemic fluorosis region of Salem is 7.3% which is moderately high. MIH presence in girls outnumbered boys marginally. There was increase in the prevalence of MIH with age attributed mainly to the PEB, specifically in the molars.
Molar to incisor MIH involvement was found to be
Caries involvement in teeth with MIH accounted for more than 50%.
Existing endemic fluorosis did not have any direct impact in the prevalence rate of MIH, other risk factors like environmental, diet, genetic etc. need to be assessed.
What this paper adds
This is one of the largest survey carried out in this region and worldwide.
This study further enhances the International data obtained from India, where the prevalence reports for MIH are few.
This is the first study undertaken in a fluorosis endemic area showing that it has no direct relation with MIH.
Why this paper is important for paediatric dentists
Early detection of MIH can prevent the tooth from PEB.
Paediatric dentist should be able to detect and differentiate from other enamel defects.
Preventive and corrective measures can be carried out for the young permanent teeth.

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