Prevalence of Dental Fluorosis Among Primary School Children in Rural Areas of Chidambaram Taluk, Cuddalore District, Tamil Nadu, India

Background: Fluorosis is one of the common but major emerging areas of research in the tropics. It is considered endemic in 17 states of India. However, the Cuddalore district of Tamil Nadu is categorised as a fluorosis non-endemic area. But clinical cases of dental fluorosis were reported in the field practice area of Department of Community Medicine, Rajah Muthiah Medical College, Annamalai University, Chidambaram. Since dental fluorosis has been described as a biomarker of exposure to fluoride, we assessed the prevalence and severity of dental fluorosis among primary school children in the service area. Materials and Methods: Children studying in six primary schools of six villages in the field practice area of Rural Health Centre of Faculty of Medicine, Annamalai University, Chidambaram, were surveyed. Every child was clinically examined at the school by calibrated examiners with Dean's fluorosis index recommended by WHO (1997). Chi-square test, Chi-square trend test and Spearman's rank correlation coefficient test were used for statistical analysis. Results: Five hundred and twenty-five 5- to 12-year-old school children (255 boys and 270 girls) were surveyed. The overall dental fluorosis prevalence was found to be 31.4% in our study sample. Dental fluorosis increased with age P < 0.001, whereas gender difference was not statistically significant. Aesthetically objectionable dental fluorosis was found in 2.1% of the sample. Villages Senjicherry, Keezhaperambai and Kanagarapattu revealed a community fluorosis index (CFI) score of 0.43, 0.54 and 0.54 with 5.6%, 4.8% and 1.4% of objectionable dental fluorosis, respectively. Correlation between water fluoride content and CFI values in four villages was noted to be positively significant. Conclusion: Three out of six villages studied were in ‘borderline’ public health significance (CFI score 0.4-0.6). A well-designed epidemiological investigation can be undertaken to evaluate the risk factors associated with the condition in the study region.

Fluorine, a member of the halogen family, is an element essential for normal growth, development and maintenance of human health. Fluoride plays an important role in preventive dentistry due to its cariostatic potential. However, excessive intake of ß uoride leads to dental and skeletal ß uorosis. India lies in a geographical ß uoride belt, which extends from Turkey up to China and Japan through Iraq, Iran and Afghanistan; of the 85 million tons of ß uoride deposits found on the earth's crust, nearly 12 million tons are in India. (1,2) Consequently, ß uorosis is an endemic condition prevalent in 17 states of India. (3) In Tamil Nadu, ß uorosis has been reported to be endemic in the districts of Dharmapuri, Erode, Salem, Coimbatore, Trichy, Madurai, Vellore and Virudhunagar. (3,4) However, in our study area, -the Þ eld practice area of the Department of Community Medicine, Rajah Muthiah Medical College and Hospital (RMMC and H), Chidambaram, Cuddalore district, which is a non-endemic area, clinical cases of dental ß uorosis were reported when we assessed caries prevalence and treatment needs among primary school children. Clinical dental ß uorosis being the most convenient biomarker of ß uoride exposure (1) evoked the thought of conducting the present study with the following objectives: 1. To assess the prevalence and severity of dental ß uorosis among primary school children in the study area. 2. To calculate the community ß uorosis index (CFI) in the study population. 3. To provide baseline data and information about dental ß uorosis to public health authorities for planning appropriate preventive strategies.

Materials and Methods
This cross-sectional study was conducted among primary school children aged 5 to 12 years from classes 1 to 5 in the rural areas of Chidambaram taluk, Cuddalore district, Tamil Nadu.

Study population
All the primary schools located in the service area of RMMCandH were chosen as research setting. The coverage of children was confined only to primary schools as each village had a primary school and 99% of the children of primary school age group in the study area were attending schools. High school children were not included as only 85% of the children of high school age group (11-16 years) in the study area were attending schools. Moreover, children from other villages were also attending this high school. All the children present in these six primary schools formed the study population. Hence the study population comprised 531 primary school children. It was conÞ rmed that all the children were continuous residents of the study area since birth.

Clinical examination
Written consent from parents and approval from concerned school authorities were obtained. The survey was conducted from July 2003 to March 2004. Oral examination was performed by three trained and calibrated dentists (SS, CK and MPV). The presence and severity of dental ß uorosis was recorded using Dean's index (1942) according to WHO (1997) criteria. (5) Each tooth in the mouth was rated according to one of the six categories of Dean's index, and the individual's dental ß uorosis score was arrived at based on the severest form recorded for two or more teeth. CFI (6) was calculated to identify villages where dental ß uorosis has been a common public health problem. CFI was computed by summing up the scores of individual grades of dental ß uorosis as described by Dean and dividing the sum by the total sample size. The public health signiÞ cance of CFI values was as below: CFI value range Public health signiÞ cance 0.0-0. 4 Negative 0.4-0. 6 Borderline 0.6-1.0 Slight Very marked

Training and calibration of examiners
Prior to the survey, the examiners participated in a two-day training and clinical calibration exercise. Forty-eight school children were examined by each of the three investigators to assess inter-examiner reliability. Intra-examiner reproducibility was assessed by re-examining 10% of the sample. At the end of each day during the course of survey, 10 children were re-examined by each examiner to maintain intraexaminer consistency.

Sources of drinking water
Five out of six villages studied had a common public drinking water supply system. In this scheme, water was pumped from the bore well into a storage tank erected at the central location of each village and taps were provided near the tanks. Water was also distributed through a pipe network and taps provided in the streets. In one village, South Pichavaram alone, the sources of drinking water were a common well and a hand pump closely connected to the well.

Fluoride estimation in drinking water
Water samples were collected in 500-ml plastic bottles, which were doubly rinsed with distilled water. They were labeled, coded and sent to laboratory for fluoride estimation on the same day. Fluoride analysis was done at the Chemistry Department, Annamalai University, using SPADNS method. (7) Duplicate samples were taken after a month to conÞ rm the ß uoride level.

Statistical analysis
The association of dental ß uorosis with gender as well as with age was studied using Chi-square test and Chi-square trend test, respectively. Spearman's rank correlation coefÞ cient test was used to measure the correlation between water ß uoride level and CFI.

Results
Among 531 primary school children, 525 were included in the study as the remaining six children were chronic absentees. Gender distribution in the sample was 255 (48.6%) boys and 270 (51.4%) girls.
Overall, 31.4% of the sample showed some grades of dental ß uorosis. Dental ß uorosis was more prevalent among boys than girls. However, gender difference was not statistically signiÞ cant (P > 0.05, N.S.). The prevalence of dental ß uorosis was found to increase with age (P < 0.001) [ Table 1].  On enquiring the local inhabitants and the Village Administrative OfÞ cer, we came to understand that the water sources in the above two villages were changed before two to three years of the study. This could be the reason why such a low ppm was recorded in the above two villages. In the remaining four villages, the water supply was constant for 10-12 years. Hence, the degree of correlation between water ß uoride level and CFI values was measured only for those four villages. A highly positive signiÞ cant correlation was found between them (P < 0.001).

Inter-examiner consistency
Inter-examiner consistency for the presence or absence of dental ß uorosis was excellent (100%). However, the agreement regarding the degrees of ß uorosis between SS and CK, SS and MPV and CK and MPV was 83.33%, 75% and 75%, respectively.

Intra-examiner reproducibility
For the presence or absence of dental ß uorosis, the intraexaminer reproducibility was excellent (100%). However, for the degrees of ß uorosis, the agreement between the examinations by SS, CK and MPV was 100%, 60% and 80%, respectively.

Discussion
Fluorosis is endemic in almost two-third states in India. Excess ß uoride in groundwater is mainly the key factor. One in 10 villages of Rajasthan has excessive content of ß uoride in its water supply. (8) About 62 million people are   at risk of developing ß uorosis from drinking high-ß uoride ion water in India. Six million children below the age of 14 years are affected. (9) Dental ß uorosis is endemic in 150,000 villages in India. (10) In the present study, nearly one-third of children had experienced dental ß uorosis of 31.4%. This estimate is very close to the Þ ndings (29.35%) in rural school children in Lucknow district, Uttar Pradesh. (11) However, a higher prevalence of 92.73% was recorded among school children of similar age group in the village of Juai Kalan, Bhiwani district, Haryana. (12) On the other hand, a lower prevalence of 16.8% was recorded in rural school children in Kerala. (13) Not surprisingly, in the present study, dental ß uorosis revealed no significant difference between genders. This is consistent with other studies conducted among rural school children in Haryana (14) and Karnataka. (15) Similar findings were recorded in rural Tanzania. (16) However, in Kerala, a higher prevalence among girls was reported. (13) In this study, the prevalence of dental ß uorosis was found to increase with age. This trend is consistent with the Þ ndings of DCI among children in rural Tamil Nadu. (17) Similar finding was documented among rural school children in Haryana. (12) One possible reason is that most of the teeth in the 5-6-year age group are deciduous (primary teeth), and much of the mineralization process occurs in the intra-uterine phase, where the placenta serves as a partial barrier to the transfer of ß uoride to the developing primary teeth. (18) Other reasons for lower prevalence in the younger age groups may be that (i) the period of enamel formation for primary teeth is shorter and hence the exposure to ß uoride is shorter; (19) (ii) the enamel of primary teeth is thinner than that of permanent teeth (19) and (iii) the rapidly growing skeleton of foetus may absorb ß uoride at more rapid rate since fluoride is a hard-tissue seeker and is thus less available for primary teeth. (20) On the other hand, the greater body size and weight, the increased physical activity and the kind of food consumed may lead to a higher water intake and thus a higher prevalence in older age groups. (11) Our study reports higher CFI values of 0.43, 0.54 and 0.54 in Senjicherry, Keezhaperambai and Kanagarapattu villages, respectively, indicating a 'borderline' (CFI score 0.4-0.6) (6) public health signiÞ cance at one end and a 'negative' (CFI score less than 0.4) (6) (6) In the present study, we observed a highly positive signiÞ cant correlation between ß uoride ion concentration in water and CFI scores, i.e., as the ß uoride level in water increases, the CFI value also increases indicating the increase in the percentage of objectionable dental ß uorosis. This is in accordance with the previous Þ ndings. (15) Galagan and Lamson (21) reported 0% objectionable dental ß uorosis at 0.5 ppm of ß uoride in drinking water with a CFI score of 0.3 at a mean annual temperature of 21°C (70°F) in Arizona communities. According to Dean, the threshold of objectionable dental ß uorosis lies between a CFI value of 0.4 and 0.6. (6) However, the present study shows 0.8% and 1.7% of objectionable dental ß uorosis at 0.56 ppm (CFI value = 0.18) and 0.66 ppm (CFI value = 0.27), respectively, at a mean maximum annual temperature of 36.3°C (97.3°F). (22) This clearly indicates that even at a minimal ß uoride concentration of 0.56 ppm in drinking water, with a CFI score of 0.18, unacceptable dental fluorosis was noticed due to considerable intake of water (resulting in higher ß uoride ingestion) following a higher daily temperature. In addition, deÞ nite dental ß uorosis had been noticed in signiÞ cant number of children in Lucknow even at a fluoride level of 0.4 ppm. (11) Hence a CFI value of less than 0.4 -a 'negative' public health significance as described by Dean (6) -may not be appropriate for our climatic condition.
Thus, the 'upper' permissible limit of ß uoride in drinking water has to be calculated based on temperature so as to prevent the occurrence of objectionable dental ß uorosis in the study area. However, some additional factors were found to be of importance in the development of dental ß uorosis such as the consumption of Þ sh (as these were coastal areas) and tea, the nutritional status of individuals, the environmental factors, nature of dentifrices used and average water intake, which requires further investigation.

Limitations of the study
The present study reports dental fluorosis in the mixed dentition on examining primary school children. However, reporting ß uorosis in mixed dentition is not very straightforward. Data about dental ß uorosis on permanent dentition (i.e., high school children) is more appropriate. However, information furnished in the present study can be utilized as preliminary data.

Implications of the present study
Cuddalore district in Tamil Nadu is categorized as a ß uorosis non-endemic area. As per the Þ ndings of the present study, it is evident that three villages in the study area are in the 'borderline' category of public health signiÞ cance. Our study underscores the need for conducting detailed ß uoride mapping and geochemical surveys of existing water sources of Cuddalore district. Nagarajan et al. (23) reported a maximum concentration of 1.2 ppm of ß uoride in groundwater samples collected in and around Chidambaram town (12 km from the study area). Moreover, groundwater samples collected at different locations in and around Cuddalore SIPCOT area (around 40 km from the study area) showed up to a maximum concentration of 2.6 ppm of ß uoride. (24) Hence periodic surveys are needed to monitor dental ß uorosis and to conduct routine water analyses to identify the high-risk communities.

Conclusion
The present study acts as a pointer to public health physicians, dentists, chemists, planners, administrators, engineers and water supply authorities. The information furnished can be utilized as preliminary data, and a well-designed epidemiological investigation can be undertaken at taluk level and district level to conÞ rm and assess dental ß uorosis and to evaluate the risk factors associated with the condition in the study region.