The prevalence and factors associated with dental fluorosis among adolescents in central Sudan: a community-based cross-sectional study, 2025

Abstract

Background

Dental fluorosis is a significant public health issue in many parts of the world, including Sudan, where its prevalence and associated factors among adolescents are not well-documented. Thus, this study aimed to determine the prevalence and factors associated with dental fluorosis among adolescents in Central Sudan.

Methods

This community-based cross-sectional study was conducted from April to June 2025 in Elrikieb, East Gezira, Central Sudan. Adolescents aged 10–19 years were enrolled using a multistage, stratified random sampling approach to achieve the required sample size (343). Data on socio-demographics, anthropometrics, and environmental factors were collected using a structured questionnaire. Dental fluorosis was assessed using the Thylstrup-Fejerskov Index (TFI). Participants with a TFI score of 4 or more were classified as having dental fluorosis. Univariate binary analysis was performed, with odds ratios and 95% confidence intervals; P values < 0.05 were considered statistically significant.

Results

A total of 343 adolescents [177 (51.6%) males and 166 (48.4%) females] were enrolled in the study. The median (interquartile, IQR) age and body mass index (BMI) were 14 (12–16) years and 16.3 (14.8–18.2) kg/m², respectively. The distribution of fluorosis was as follows: questionable (0.6%), very mild (16.9%), mild (21.0%), moderate (26.2%), severe (5.5%), and 29.7% were normal. Of the total, nearly one-third (31.8%) of enrolled adolescents had moderate to severe (TF score ≥ 4) dental fluorosis, giving the overall prevalence of dental fluorosis of 31.8% (109 adolescents).

Univariate analysis revealed no significant association between dental fluorosis and any of the investigated factors, including age, gender, BMI, tobacco use, parental education, parental occupation, or the presence of a smoker in the family (all p > 0.05).

Introduction

Dental fluorosis is a dose-dependent, hypomineralization of tooth enamel resulting from excessive fluoride intake during the pre-eruptive stage of tooth development [1, 2]. While an optimal amount of fluoride is beneficial in preventing dental caries, chronic ingestion of high levels can lead to this irreversible condition [3–5]. The clinical manifestation of dental fluorosis ranges from fine, white opaque lines on the enamel surface to severe pitting, brown staining, and enamel loss, depending on the severity [2]. The aesthetic and psychological impact of dental fluorosis can be significant, particularly for female adolescents, potentially affecting their quality of life [6–8]. The etiology of dental fluorosis is primarily linked to fluoride concentrations in drinking water, but other sources of fluoride, such as fluoride toothpaste, diet, and supplements, also contribute to the total daily intake [1, 3, 5, 9]. Several indices are used to measure dental fluorosis, such as Dean‘s Index-1934, Community Fluorosis Index-1946, Thylstrup-Fejerskov Index (TFI)-1978, Tooth surface Index of Fluorosis-1984, and Fluorosis Risk Index-1990 [10–13]. However, recently, TFI-1978 has been the most used one [10, 11, 14].

The prevalence of dental fluorosis varies widely across regions worldwide, influenced by differences in water fluoride content and local public health policies [5]. In Africa, several countries have reported varying prevalence rates, even within the same country, such as Sudan [15, 16]. For example, a study conducted in two locations in Khartoum, Sudan (Treit el Biga and Abu Groon), revealed a higher prevalence of dental fluorosis in Treit el Biga than in Abu Groon [16]. Another study conducted in Khartoum found a high prevalence of dental fluorosis among adolescents (68.3%), with 9.2% having moderate to severe fluorosis, and no difference between females and males [17]. A school-based survey of 1,109 12-year-old schoolchildren in Khartoum State reported a prevalence of dental fluorosis of 11.9% [18]. Likewise, similar prevalence rates (moderate to severe) have been reported in Nigeria (11.3%) [9] and in China (12.5%) [13]. A cross-sectional study involving 585 schoolchildren aged 8–12 years conducted in Mexico revealed that more than half (56.1%) of the children had dental fluorosis (TFI ≥ 4) [14]. The wide range of prevalence rates underscores the need for region-specific data to accurately assess the problem’s magnitude and develop targeted public health interventions. Despite the known association between fluoride exposure and dental fluorosis, the roles of other factors were explored by researchers including socio-demographic characteristics such as younger age [19], being males [19], rural residence [13, 20], low adolescents’ parents education level [13], low socio-economic status [21], nutritional status such as low body mass index (BMI) [14], and other environmental exposures, such as tobacco smoke, and passive smoking remain areas of interest for research [22–24]. Furthermore, recent literature has shown that genetic predisposition plays a significant role in the development of dental fluorosis [25].

In Sudan, specifically, there’s a scarcity of recent, community-based studies on dental fluorosis, especially in central regions like Gezira State [15–18]. In addition, the majority of existing data from Khartoum [15, 17, 18] is informative, but it may not be representative of rural or semi-urban communities, where access to different water sources and socio-economic conditions can vary significantly. Understanding the local prevalence and associated risk factors is crucial for effective public health planning and for identifying at-risk populations. While the fluoride concentration in drinking water is the most likely determinant, other factors, such as socioeconomic status, dietary habits, environmental conditions, and genetic predispositions, may also play a role. Therefore, this study was designed to address this knowledge gap by providing community-based data on the prevalence of dental fluorosis and its associated factors among adolescents in Central Sudan. The findings are expected to inform local health authorities about the severity of the problem and guide the development of appropriate public health strategies, such as water defluoridation programs and community education campaigns. The study also examines the prevalence of dental fluorosis and its potential associations with various socio-demographic, anthropometric, and environmental factors, thereby providing a broader understanding of the determinants of dental fluorosis in this specific context.

Methods

Study design and setting

This community-based cross-sectional study was conducted from April to June 2025 among adolescents in Central Sudan. This study was conducted in Elrikieb, East Gezira, in Central Sudan. Gezira State is located in east-central Sudan, lying between the Blue and White Nile rivers. Elrikieb was chosen because it comprises four sub-villages, and its inhabitants resemble those of the entire Gezira State in terms of race, diet, and water sources. In this study, the authors strictly adhered to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines [26].

Study population and sampling

In the present study, 343 adolescents were recruited. Participants were recruited from the community through a systematic approach. A multi-stage stratified random sampling approach was employed to select the potential participants. Within each selected sub-village, households were randomly selected, and adolescents from eligible households were invited to participate.

Inclusion and exclusion criteria

Before data collection, informed consent was obtained from the adolescents’ parents and their guardians. The definition of adolescents was based on the WHO’s definition [27]. Therefore, all adolescents aged 10–19 years were included in the present study. Pregnant or lactating adolescents were excluded. All participants recruited were apparently healthy. Those with systemic disease (severe anemia, renal disease, thyroid disease) were excluded (self-reported).

Sample size calculation

The desired sample size was computed using OpenEpi Menu software [28]. The authors assumed that at least one-third or half of the adolescents would have dental fluorosis. The assumption was based on previous studies in other regions of Sudan [16, 29]. Thus, a sample size of 343 adolescents was computed for this study. This sample size was calculated to detect a 5% difference at α = 0.05 with 80% power.

Study variables and measures

Data were collected using a questionnaire that was developed following a thorough literature review. The questionnaire was administered face-to-face, gathering information on socio-demographic factors, such as age, gender, parental education, and occupation, as well as environmental factors, including tobacco use and exposure to passive smoking. Anthropometric measurements of weight and height were taken to compute BMI [15, 16, 30]. In this study, dental fluorosis was the primary outcome, assessed by two dental doctors (male and female) with 3 years of practice, using the TFI [2]. The dental examination was carried out in the house’s premises by the researcher. Adolescents were seated on ordinary chairs under natural daylight; examinations were carried out without prior cleaning or drying of the teeth; and the instruments used were sterilized. The TFI is a 10-point ordinal scale (0–9) that classifies fluorosis severity from normal to severe. For this study, a TFI score of 4 or higher (moderate to severe) was considered the presence of dental fluorosis and coded as (1), while scores of 3 or less were considered normal and coded as (0) [10, 11, 14]. Dental fluorosis was considered if TFI was ≥ 4) [14].

Statistical analysis

The data were entered into SPSS for Windows (version 22.0; SPSS Inc., New York, NY, USA) statistical software for analysis. The continuous data, such as age and BMI, were tested for normality using the Kolmogorov–Smirnov test and were found not to be normally distributed. Consequently, they are reported as medians with interquartile ranges (IQRs). The univariate binary analysis was performed on TFI score as the categorical dependent variable (moderate-severe dental fluorosis vs. normal fluorosis) and the socio-demographic data, anthropometric data, and environmental factors such as age, gender, BMI, parental education, parental occupation, tobacco use, and presence of a smoker in the family as the independent variables. Initially, the authors planned to shift all variables with p-values < 0.2 from the univariate to the multivariate binary analysis to adjust for covariates; however, none of the investigated variables had p-values < 0.2. Therefore, the authors confined the analysis to the univariate binary analysis. Odds ratios (ORs) and 95% CIs were computed as they were applied. A two-sided p-value of < 0.05 was considered statistically significant.

Results

In this study, 343 adolescents were recruited, comprising 177 (51.6%) males and 166 (48.4%) females. The median (IQR) age and BMI were 14(12‒16) years, and 16.3(14.8‒18.2) kg/m², respectively.

Fifty (14.6%) of the adolescents’ mothers and 91 (26.5%) of the adolescents’ fathers had ≥ education. The majority of the adolescents’ mothers were housewives 322, 93.9%), and 301 (87.8%) of the adolescents’ fathers had a job. Few adolescents (11, 3.2%) were tobacco users. One hundred and one adolescents (29.7%) reported the presence of a smoker in their families. Of the total enrolled adolescents, 102 (29.7%), 2 (0.6%), 58 (16.9%), 72 (21.0%), 90 (26.2%), and 19 (5.5%) had normal, questionable, very mild, mild, moderate, and severe dental fluorosis, respectively. Of the total, nearly one-third of enrolled adolescents had moderate to severe dental fluorosis (31.8%). In this study, the overall prevalence of dental fluorosis, including questionable, very mild, mild, moderate, and severe, was 70.3% (Table 1).

Table 1.

Socio-demographic and clinical characteristics of the studied adolescents in central Sudan (n = 343), 2025

Variable		Total (n = 343)
		Median	Interquartile range
Age (years)		14	12‒16
Body mass index (kg/m2)		16.3	14.8‒18.2
		Frequency	Percentage
Gender	Male	177	51.6
	Female	166	48.4
Mother Education	≥ secondary	50	14.6
	< secondary	293	85.4
Father education	≥ secondary	91	26.5
	< secondary	252	73.5
Mother occupation	House wife	322	93.9
	Employed	21	6.1
Father occupation	Working	301	87.8
	Not working	42	12.2
Tobacco use	No	332	96.8
	Yes	11	3.2
Presence of a smoker in the family	No	242	70.6
	Yes	101	29.4
Dental fluorosis	normal	102	29.7
	questionable	2	0.6
	very mild	58	16.9
	mild	72	21.0
	moderate	90	26.2
	severe	19	5.5

In the univariate binary analysis, no factor from the investigated variables (i.e., age, gender, BMI, tobacco use, parental education and occupation, and presence of a smoker in the family) was found to be associated with dental fluorosis among adolescents, with a p-value of > 0.05 (Table 2).

Table 2.

Univariate binary analysis of the factors associated with dental fluorosis among adolescents in central Sudan (n = 343), 2025

Variable		Adolescents with dental fluorosis (n = 109)	Adolescents without dental fluorosis (n = 234)	Univariate analysis
		Median (interquartile range)		Odds ratio (95% confidence interval, CI)	p
Age (years)		14(12‒16)	14(12‒16)	0.98(0.89‒1.08)	0.763
Body mass index (kg/m2)		16.2(14.6‒18.9)	16.3(14.8‒18.1)	0.99(0.94‒1.03)	0.723
	Frequency(proportion)
Gender	Male	53(48.6)	124(53.0)	Reference
	Female	56(51.4)	110(47.0)	1.19(0.75‒1.87)	0.451
Mother’s education level	≥ secondary level	16(14.7)	34(14.5)	Reference
	˂ secondary level	93(85.3)	200(85.5)	0.98(0.51‒1.88)	0.971
Mother’s occupation status	Housewife	101(92.7)	221(94.4)	Reference
	Employed	8(7.3)	13(5.6)	1.34(0.54‒3.35)	0.522
Father’s education level	≥ secondary level	32(29.4)	59(25.2)	Reference
	˂ secondary level	77(70.6)	175(74.8)	0.81(0.48‒1.34)	0.419
Father’s occupation status	Unemployed	13(11.9)	29(12.4)	Reference
	Employed	96(88.1)	205(85.6)	0.95(0.47‒1.92)	0.902
Adolescents’ tobacco use	No	105(96.3)	227(97.0)	Reference
	Yes	4(3.7)	7(3.0)	1.23(0.35‒4.31)	0.740
Presence of a smoker in the family	No	78(71.6)	164(70.1)	Reference
	Yes	31(28.4)	70(29.9)	0.93(0.56‒1.53)	0.780

Discussion

The findings of this community-based cross-sectional study offer critical insights into the prevalence and associated factors of dental fluorosis among adolescents in a rural setting in Central Sudan. The study’s most significant finding is the high prevalence of dental fluorosis: approximately one-third (31.8%) of the adolescents exhibit a TFI score of 4 or higher, indicating moderate to severe enamel defects. This prevalence, although lower than some reports from high-fluoride regions such as Sri Lanka (42.0%) [7] and Mexico (56.1%) [14], is considerably higher compared to the 11% prevalence reported in a recent systematic review [5]. The data also fall within the wide range of prevalence rates reported in Sudan. The overall prevalence of dental fluorosis (with all its grades) in this study (70.3%) is similar to the 68.3% found in Khartoum [17], but the moderate to severe dental fluorosis prevalence in the present study, 31.8%, is higher than the 9.2% and 11.9% reported in other studies conducted in Khartoum [18]. This variability underscores the importance of region-specific data and highlights the significant public health challenge faced by the community in the studied area (Elrikieb). The widespread nature of this condition (dental fluorosis) calls for immediate public health action to mitigate fluoride exposure and protect the dental health of the population.

A crucial and unexpected finding of this study is the complete lack of a statistically significant association between dental fluorosis and any of the investigated socio-demographic, anthropometric, and environmental factors. This includes age, gender, BMI, tobacco use, parental education, parental occupation, and the presence of a smoker in the family. The absence of a correlation between gender and fluorosis, for example, aligns with some previous studies in Sudan [16, 17] but contrasts with others who have found gender-based differences [19]. The lack of association with parental education and occupation, which often reflect socio-economic status, is also surprising, given that these factors can influence dietary habits and access to different water sources [13]. The findings suggest that the primary determinant of dental fluorosis in this specific community in Central Sudan is likely a pervasive environmental factor that affects all individuals equally, regardless of their socio-demographic background.

The most plausible explanation for these results is that the primary source of fluoride exposure, almost certainly the drinking water, is universally high throughout the community. As dental fluorosis is a dose-dependent condition [1, 2], uniform exposure to high fluoride levels would lead to a high prevalence across the board, with minimal variation across the studied factors. The results are a strong indirect indicator of elevated fluoride concentrations in the local water supply. Previous studies conducted in the nearby areas in Sudan have shown high fluoride levels in the drinking water [16, 29].

The finding that BMI was not associated with fluorosis, contrary to a study in Mexico [14]. This also supports the hypothesis, as it suggests that the etiology is not related to nutritional status but rather to environmental exposure. Other factors known to influence fluoride intake, such as the consumption of tea, which can be rich in fluoride, were also not assessed and may have contributed to the overall exposure [5, 9]. The data highlights the limitations of evaluating socio-demographic and behavioral factors alone in a context where a potent environmental determinant is present and pervasive.

Study implications

The high prevalence of dental fluorosis in this community requires a prompt and comprehensive public health response. Since no specific subgroup was identified as being at a higher risk, a universal intervention targeting the entire population is warranted. The most effective strategy would be to investigate and address the source of excessive fluoride exposure. This should begin with a systematic, rigorous assessment of fluoride levels in all local drinking water sources, including wells, boreholes, and piped water systems. After confirming the source, public health authorities should implement water de-fluoridation programs, which are a cornerstone of fluorosis prevention in regions worldwide with high fluoride levels. Community education campaigns are also crucial for increasing awareness about the causes of dental fluorosis and promoting safer water consumption habits among the population. While the study did not find associations with factors such as parental education and occupation, these remain crucial for the success of any public health campaign. Educating parents and guardians about the importance of using low-fluoride water for children, particularly during the critical years of tooth development, is crucial. Addressing dental fluorosis is not only a matter of dental aesthetics but also of enhancing the overall quality of life and psychological well-being of adolescents [6–8].

Study strengths and limitations

This study possesses several notable strengths. It is one of the first recent community-based studies to systematically assess dental fluorosis in a rural area of Central Sudan, thereby filling a significant gap in the literature. The use of a robust methodology, including a multi-stage stratified random sampling approach, enhances the representativeness of the sample and the generalizability of the findings to similar communities in the region. The assessment of dental fluorosis using the TFI, a highly detailed and internationally accepted scoring system, ensures the reliability and accuracy of the data. Moreover, the study’s strict adherence to the STROBE guidelines enhances transparency and scientific rigor. However, some limitations must be noted to improve future research. For a dose-dependent condition like fluorosis, a longitudinal study would be ideal to track fluoride exposure over time. The second, and most critical, limitation is the lack of measurement of fluoride concentration in the drinking water, which is the primary etiological factor. Without this data, the study cannot confirm the source of the high fluoride exposure. However, this study recommends that local authorities take further action, including measuring fluoride concentrations in drinking water. Other potential sources of fluoride intake, such as dietary habits (e.g., intake of fluoride-rich foods or beverages, such as tea), were also not assessed. Finally, dichotomizing the TFI score at ≥ 4 for the binary analysis may have masked more subtle relationships with the investigated factors. However, this cutoff is clinically relevant for classifying moderate-to-severe fluorosis. However, in this study, this dichotomization was justified as the first epidemiological study in the studied area to estimate the prevalence and potential associated factors of dental fluorosis.

Conclusion

This study has established that dental fluorosis is a highly prevalent public health issue among adolescents in this community in Central Sudan. The study’s finding of no significant association between fluorosis and the investigated socio-demographic, anthropometric, and environmental factors strongly suggests that a widespread and consistent environmental source of fluoride, most likely the drinking water, is the dominant determinant of the condition. These results provide critical evidence for local health authorities to prioritize a systematic assessment of fluoride levels in water sources and to implement targeted de-fluoridation and community education programs. Future research in this region should focus on quantifying fluoride levels in drinking water and other dietary sources, as well as exploring potential genetic predispositions, to gain a complete understanding of the epidemiology of dental fluorosis in Central Sudan. Moreover, exploring the impact of dental fluorosis on adolescents’ quality of life is an essential psychodental health topic that deserves further research.

Abbreviations

AOR

Adjusted odds ratio

BMI

Body mass index

CI

Confidence interval

IQR

Interquartile range

TFI

Thylstrup-Fejerskov Index

WHO

World Health Organization

Authors’ contributions

MM and IA: conception, design, acquisition of data, analysis, interpretation of data, drafting the article. JKA: conception, design, acquisition of data, analysis, interpretation of data, and revising the manuscript critically for important intellectual content. All authors have approved the final version of this manuscript.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the principles outlined in the Declaration of Helsinki and adhered to good clinical research practices. Ethical approval was granted by the Research Ethics Committee of the Faculty of Medicine and Health Sciences at the University of Gadarif in Gadarif, eastern Sudan (Ref. #2025, 07). Institutional permission to conduct the study was obtained from the Ministry of Health, Gezira State (Letter # 50/B/1; May 18, 2025). Written informed consent was obtained from all participants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.