Abstract
Background:
Fluoride, while protective against dental caries at optimal levels, can cause fluorosis at higher concentrations. Limited data on fluoride levels and related dental health issues in Coimbatore necessitated this study.
Aim:
The present study aimed to estimate fluoride concentrations in drinking water and the prevalence of dental caries and fluorosis in Coimbatore district, Tamil Nadu.
Materials and Methods:
Fluoride concentration was assessed in 100 randomly selected drinking water sources across five zones of Coimbatore using the color comparator technique. A total of 933 residents were examined for dental caries (Decayed, Missing, and Filled Teeth (DMFT) index) and fluorosis (Dean’s Fluorosis Index).
Statistical Analysis:
Data were analyzed using SPSS version 21.0 (IBM Corp., USA). Descriptive statistics and Spearman’s correlation test was used and P < 0.05 was considered statistically significant.
Results:
Corporation-supplied water was the main drinking source in Coimbatore. The mean fluoride concentration was 0.48 parts per million (ppm). Dental caries prevalence was 65%, while dental fluorosis was observed in 4% of the population.
Conclusion:
Suboptimal fluoride levels in drinking water may contribute to the high prevalence of dental caries. Water fluoridation is recommended to improve oral health in Coimbatore.
Keywords: Fluoride level, Dental caries, Dental fluorosis, Dean’s Fluorosis Index, DMFT index
INTRODUCTION
Dental caries remains a major oral health issue in developing countries like India.[1] Optimal fluoride levels in drinking water help prevent caries by promoting enamel remineralization, but excessive intake can cause dental and skeletal fluorosis.[2] The World Health Organization (WHO) recommends a fluoride concentration of 0.7–1.5 parts per million (ppm) in drinking water to balance benefits and risks.[3]
Fluoride can be attributed mainly to its influence on de- and remineralization kinetics of dental hard tissues.[4] Dental caries result from enamel demineralization caused by acids from bacterial fermentation of sugars, leading to cavitated or non-cavitated lesions often linked to pain.[5,6] Prevention includes fluoride use, oral hygiene, and diet control. Fluoride strengthens enamel and reduces demineralization.[7] Excessive fluoride during tooth development can cause dental fluorosis; prolonged high intake may lead to skeletal fluorosis.[4,8] Guidelines restrict fluoride levels in drinking water to reduce these risks.
In India, the permissible fluoride level in treated water is 1 mg/dL to limit dental fluorosis.[3,9] Studies in Coimbatore show fluoride levels in underground and municipal water are below WHO standards.[10] A study conducted in 2018 reported dental caries and dental fluorosis prevalence of 43.6% and 14%, respectively, in a tertiary hospital in Coimbatore’s outskirts.[11] With the growing use of borewell and packaged water, the current fluoride levels are uncertain. This is the first study to assess fluoride levels across all Coimbatore zones and their link to dental caries and fluorosis.
MATERIALS AND METHODS
Study design
A descriptive cross-sectional study was conducted among 933 individuals in Coimbatore from July to September 2019, along with a relative estimation of fluoride levels in drinking water sources. Ethical clearance was obtained (EC/2019/0706/CR/27), and informed consent was secured from all participants.
Sampling size, population, and characteristics
Random sampling was used. Zone and ward data (East, West, North, South, Central) were obtained from Coimbatore City Municipal Corporation. Corporation water samples were collected from 10 randomly selected wards across five zones; borewell samples from five randomly selected wards per zone; and 25 packaged water samples from various brands were collected.
Based on a 2015 study by Thaufiq Ahmed et al.[11] reporting 14% fluorosis in southern Coimbatore, the sample size was calculated using the formula:
n = [(Z1-α/2)² × p (1-p)]/d²,
where Z = 1.96 (P < 0.05), P = 0.14, and d = 0.05.
The estimated sample was 184 per zone (total 920). Of 1,000 screened, 933 met the inclusion criteria.
Inclusion criteria
Adult (male and female) aged 18-44 years
Residents of Coimbatore district since birth
Exclusion criteria
Daily consumers of multiple water sources
Individuals with systemic disease affecting oral health
Age and sex distribution of the population
A total of 933 participants (Male: 454 (49%), Females: 479 (51%)) were examined for dental caries and fluorosis. Detailed distribution of age by zone is provided in Table 1.
Table 1.
Age and sex distribution of studied population
| Age (Years) | 18-22 | 23-33 | 34-44 | Total (M+F) | |||
|---|---|---|---|---|---|---|---|
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| Zone | M | F | M | F | M | F | |
| East | 23 | 36 | 32 | 27 | 37 | 32 | 187 |
| West | 46 | 38 | 26 | 27 | 17 | 32 | 186 |
| North | 35 | 39 | 33 | 25 | 26 | 25 | 183 |
| South | 33 | 47 | 21 | 32 | 25 | 30 | 188 |
| Central | 31 | 36 | 35 | 27 | 34 | 26 | 189 |
M: Male; F: Female
Water sample collection and fluoride estimation
About 100 ml water samples were collected in clean, labeled plastic bottles. Fluoride levels were measured using the cost-effective color comparator method, which uses bleached zirconium xylenol reagent to form an orange complex. The shade, indicating fluoride concentration, was matched to a comparator chart using a double-blind procedure to reduce observer bias.
Clinical examination and data collection
Trained dentists examined 933 eligible participants seated under natural light, using sterilized explorers and mouth mirrors. A second person recorded the clinical findings (DMFT scores and DFI). Demographic details and primary source of drinking water were collected using a structured, closed-ended questionnaire.
Assessment of dental caries and fluorosis
Dental Caries: Graded using the Decayed, Missing, and Filled Teeth (DMFT) index. A higher DMFT score indicates a greater prevalence of dental caries.
Dental Fluorosis: Evaluated using Dean’s Fluorosis Index (DFI). (0-Normal, 1-Questionable, 2-Very Mild, 3-Mild, 4-Moderate, 5-Severe).
Statistical analysis
To analyze the data, SPSS version 21.0 (IBM Corp., USA). was used. Descriptive analysis and Spearman’s correlation test were applied to assess the association between fluoride concentration in drinking water and dental caries (DMFT index) as well as DFI. A p < 0.05 was considered statistically significant.
RESULTS
Primary source of drinking water of the studied population
A survey of 933 Coimbatore residents found 75% used corporation water, 13% relied on packaged water, 11% on borewell water, and 1% on other sources [Figure 1].
Figure 1.
Primary sources of drinking water in Coimbatore district
Estimation of fluoride in drinking water
The study measured the mean fluoride levels in Coimbatore’s drinking water sources: Corporation water – 0.35 ppm, Borewell – 0.9 ppm, and Packaged water – 0.2 ppm. The overall average was 0.48 ppm, below the ADA’s (American Dental Association) recommended 0.7 ppm for optimal dental health.
Prevalence of dental caries in relation to the type of drinking water sources available in Coimbatore district
The prevalence of dental caries is presented in Table 2. Dental caries affected 65%, i.e., 607 out of 933 subjects. Age-wise, 193 cases: 18–22 group, 205: 23–33, and 209: 34–44 years. Zone-wise prevalence was highest in the East and South (70%), followed by Central (67%), North (62%), and West (57%). The highest prevalence (83%) was among South Zone females aged 34–44, lowest (41%) was among West Zone males in the same age group. Caries prevalence by water source: 50% consumed packaged water, 46% corporation water, 3% borewell water, and 1% other [Figure 2]. DMFT index scores with 95% confidence intervals are detailed in Table 3.
Table 2.
Prevalence of dental caries
| Age Years | 18-22 | 23-33 | 34-44 | Total n (%) | |||
|---|---|---|---|---|---|---|---|
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| Zone | Male n (%) | Female n (%) | Male n (%) | Female n (%) | Male n (%) | Female n (%) | |
| East | 11 (48) | 20 (56) | 26 (81) | 20 (74) | 29 (78) | 24 (75) | 130 (70) |
| West | 27 (59) | 16 (42) | 16 (62) | 16 (59) | 7 (41) | 24 (75) | 106 (57) |
| North | 19 (54) | 21 (54) | 23 (70) | 16 (64) | 17 (65) | 18 (72) | 114 (62) |
| South | 18 (55) | 29 (62) | 16 (76) | 25 (78) | 18 (72) | 25 (83) | 131 (70) |
| Central | 14 (45) | 18 (50) | 26 (74) | 21 (78) | 27 (79) | 20 (77) | 126 (67) |
| Total | 193 (53) | 205 (72) | 209 (74) | 607 (65) M-294, F-313 |
|||
M: Male; F: Female: n: number
Figure 2.
Prevalence of dental caries in relation to the type of drinking water sources
Table 3.
DMFT index and Dean’s fluorosis index (DFI) of study population (Mean±SD)
| Age years | Zone | East | West | North | South | Central | All Zones |
|---|---|---|---|---|---|---|---|
| 18-22 | DMFT | 2.29±2.97 | 2.2±2.51 | 2.68±3.53 | 2.85±3.3 | 1.9±2.39 | 2.38±2.94 |
| DFI | 0.07±0.24 | 0.07±0.32 | 0.1±0.22 | 0.07±0.27 | 0.07±0.3 | 0.08±0.27 | |
| 23-33 | DMFT | 4.21±2.98 | 3.65±3.67 | 4.3±3.75 | 4.15±3.1 | 5.13±3.69 | 4.31±3.46 |
| DFI | 0.06±0.31 | 0.06±0.31 | 0.03±0.16 | 0.02±0.15 | 0.04±0.21 | 0.04±0.23 | |
| 34-44 | DMFT | 4.48±3.07 | 4±3.41 | 4.72±3.48 | 5.69±4.58 | 5.82±3.86 | 4.97±3.75 |
| DFI | 0.05±0.27 | 0.01±0.07 | 0.02±0.11 | 0±0 | 0.02±0.14 | 0.02±0.12 | |
| All Age groups | DMFT | 3.71±3.14 | 3.88±3.2 | 3.74±3.68 | 4.02±3.85 | 4.19±3.75 | 3.75±3.55 |
| DFI | 0.06±0.27 | 0.05±0.27 | 0.02±0.12 | 0.04±0.2 | 0.04±0.23 | 0.04±0.22 | |
| DMFT 95% CI | 3.26-4.16 | 3.42-4.34 | 3.20-4.27 | 3.47-4.57 | 3.65-4.72 | 3.52-3.97 | |
| DFI 95% CI | 0.02-0.10 | 0.01-0.09 | 0.003-0.04 | 0.01-0.07 | 0.01-0.07 | 0.03-0.05 |
DMFT: Decayed, Missing, and Filled Teeth; SD: Standard deviation; CI: Confidence interval
Prevalence of dental fluorosis relative to the type of drinking water source available in Coimbatore
The study found an overall dental fluorosis prevalence of 4% (41 cases). By age, 21 cases were in the 18–22 group, 11 in the 23–33, and 9 in the 34–44. Zone-wise prevalence was: East 6%, West 5%, North 4%, South 4%, and Central 4%. The highest rate of 12% was observed in West Zone males aged 34–44 [Table 4].
Table 4.
Prevalence of dental fluorosis
| Zone | 18-22 years | 23-33 years | 34-44 years | Total n (%) | |||
|---|---|---|---|---|---|---|---|
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| Male n (%) | Female n (%) | Male n (%) | Female n (%) | Male n (%) | Female n (%) | ||
| East | 0 (0) | 4 (11) | 1 (3) | 2 (7) | 1 (3) | 3 (9) | 11 (6) |
| West | 2 (4) | 2 (5) | 2 (8) | 1 (4) | 2 (12) | 0 (0) | 9 (5) |
| North | 0 (0) | 3 (8) | 0 (0) | 2 (8) | 1 (4) | 1 (4) | 7 (4) |
| South | 1 (3) | 5 (11) | 1 (5) | 0 (0) | 0 (0) | 0 (0) | 7 (4) |
| Central | 2 (6) | 2 (5) | 2 (6) | 0 (0) | 1 (3) | 0 (0) | 7 (4) |
| Total | 21 (6) | 11 (4) | 9 (3) | 41 (4%) M-16, F- 25 | |||
M: Male; F: Female: n: number
The DFI showed a mean score of 0.04. The highest (0.6) was in the East Zone, which also had the highest fluoride levels; the lowest (0.02) was in North [Table 3]. Among affected individuals, 61% consumed corporation water, 28% borewell, and 11% packaged water. No cases of concurrent dental caries and fluorosis were observed [Figure 3].
Figure 3.
Prevalence of dental fluorosis in relation to the type of drinking water sources
Correlation between decayed, missing, and filled teeth (DMFT) Score and Dean’s fluorosis index with fluoride concentration in drinking water
Spearman’s correlation test was applied to assess the association between the variables. Results showed a negative association between fluoride concentration and dental caries (Spearman’s rank correlation coefficient (rs) = -0.235, P = 0.653), suggesting reduced caries risk with higher fluoride. A positive correlation was found with DFI (rs = 0.28, P = 0.275), indicating increased fluorosis prevalence at higher fluoride levels. These results underscore the need to maintain optimal fluoride levels to balance caries prevention and fluorosis risk [Table 5].
Table 5.
Prevalence of dental caries and dental fluorosis and correlation between DFI and DMFT score with fluoride concentration
| ZONE | Fluoride Conc. (ppm) | Dental caries | Dental fluorosis | ||||
|---|---|---|---|---|---|---|---|
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| Prevalence % | DMFT Index | Spearman Correlation b/w Fluoride Conc. and DMFT | Prevalence % | Dean’s Fluorosis Index | Spearman Correlation b/w Fluoride Conc. and DFI | ||
| East | 0.55 | 70 | 3.71±3.14 |
rs=-0.235 P=0.653 |
06 | 0.06±0.27 |
rs=0.281 P=0.589 |
| West | 0.45 | 57 | 3.88±3.2 | 04 | 0.05±0.27 | ||
| North | 0.47 | 62 | 3.74±3.68 | 03 | 0.02±0.12 | ||
| South | 0.48 | 70 | 4.02±3.85 | 04 | 0.04±0.2 | ||
| Central | 0.47 | 67 | 4.19±3.75 | 04 | 0.04±0.23 | ||
| All Zones | 0.48 ppm | 65% | 3.75±3.55 | 04% | 0.04±0.22 | ||
DMFT: Decayed, Missing, and Filled Teeth; DFI: Dean’s fluorosis index, rs: Spearman’s rank correlation coefficient
DISCUSSION
The study was conducted in Coimbatore, a densely populated tier-2 city with limited literature on the prevalence of dental caries and fluorosis linked to fluoride in drinking water. Fluoride is crucial for dental health at optimal levels, strengthening enamel and preventing caries. However, excessive fluoride intake during tooth development can lead to dental fluorosis, causing enamel hypomineralization and esthetic issues if untreated in childhood.[4,7,12] Our study found the average fluoride concentration in drinking water across all zones to be 0.48 ppm. Uma et al.[13] (2016) reported fluoride levels of 0.2–1.2 ppm in Coimbatore’s West Zone, aligning with our findings. Fluoride concentrations in corporation and packaged water, however, fall below the ADA’s recommended 0.7 ppm.[14]
Dental caries affects about 3.6 billion people globally, making it the most common oral disease.[15] In our study, caries prevalence was 65%, with a mean DMFT index of 3.75, possibly linked to suboptimal fluoride levels in drinking water. A study in Nalgonda, Andhra Pradesh, showed 60.5% caries prevalence in areas with fluoride below 0.7 ppm, compared to 17.6% in optimally fluoridated areas.[16] Similarly, a study conducted in Brazil found that caries progression in school-children living in fluoridated areas was found to be lower than that in fluoride-deficient areas.[17] In Coimbatore, caries prevalence rose from 41% in 2018 (Thaufiq Ahmed et al.)[11] to 65% in the current study, likely due to reduced fluoride levels affecting hydroxyl-fluorapatite formation in enamel.
In our study, dental fluorosis prevalence in Coimbatore was 4%, with a mean Dean’s Index of 0.04, indicating minimal cases. This aligns with studies from low-fluoride areas in Kerala—2.2% in Kollam and 4.4% in Thrissur.[18,19] Similarly, in Lithuania, 4% of fluorosis cases were reported in low-fluoride areas.[20] These findings suggest that low fluoride levels in drinking water reduce fluorosis risk. The current study shows a lower fluorosis rate than the 2018 study by Thaufiq Ahmed et al.[11] in Coimbatore’s southern region, likely due to very low fluoride levels in drinking water. The prevalence of fluorosis, in spite of low fluoride concentrations in drinking water, may be because of the systemic uptake of fluoride through polluted air, consumption of fluoridated food like tea and fish, and consumption of well water.[21]
CONCLUSION
Coimbatore’s district average fluoride concentration in drinking water is 0.48 ppm, and this suboptimal fluoride level likely contributes to the high prevalence of dental caries (65%) and low incidence of dental fluorosis (4%) observed in the study population.
Limitations
The results may be affected by recall bias and unmeasured dietary fluoride.
Recommendations
Coimbatore’s average drinking water fluoride concentration (0.48 ppm) is below the ADA’s recommended 0.7–1.5 ppm. As the majority of the Coimbatore residents are relying on the centralized municipal water supply, it will be easier for the authorities to monitor the fluoride level and implement controlled water fluoridation to reach the optimal (0.7–1.5 ppm) range, mirroring successful public health models in the USA and Singapore. Additional strategies include public education, promoting fluoride toothpaste, and mandating fluoride labeling on packaged water.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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