Dental Caries in Patients with Fluorosis among Local Population of Hyderabad

By Feroze Ali Kalhoro, Saima Yousif, Muhammad Muhtassim, Sarang Suresh, Priya Rani, Naresh Kumar

Affiliations

1. Department of Operative Dentistry and Endodontics, Liaquat University of Medical and Health Sciences, Jamshoro, Pakistan

doi: 10.29271/jcpsp.2025.07.837

ABSTRACT
Objective: To assess the frequency of dental caries among individuals with dental fluorosis and to examine the relationship between fluorosis severity with the Thystrup-Fejerskov (TF) index and caries experience with the decayed, missing, and filled teeth (DMFT) index.
Study Design: A cross-sectional, observational study.
Place and Duration of the Study: Department of Operative Dentistry and Endodontics, Liaquat University of Medical and Health Sciences, Jamshoro, Pakistan, from October 2023 to December 2024.
Methodology: A convenience sample of 165 participants, aged 10-40 years and living in Hyderabad, was recruited. Participants with a TF score >1 were included. Intra-oral examinations assessed dental caries using the WHO DMFT index and fluorosis using the TF index. Non-parametric methods and logistic regression were employed.
Results: Moderate fluorosis predominated (TF scores 3-4: 66%), while severe fluorosis (TF score = 6) was seen in only 2.4% of cases. Dental caries was highly prevalent, with 90.3% of subjects exhibiting DMFT >0. A weak positive association was seen between TF and DMFT scores (r = 0.147, p = 0.059), and significant differences in DMFT across TF groups were noted (χ² (4) = 19.260, p = 0.001). Logistic regression did not prove an independent association found between fluorosis severity and caries risk after adjusting for confounders.
Conclusion: Moderate fluorosis predominated among the participants and dental caries were highly prevalent, with 90.3% of subjects exhibiting DMFT scores greater than zero. There is no association between fluorosis severity and caries risk after adjusting for confounders.

Key Words: Dental caries, Dental fluorosis, DMFT index.

INTRODUCTION

Dental caries is still a universal oral health concern worldwide, exerting a significant burden on public health and clinical practice. Fluoride has long been proven as the best method in caries prevention, yet its excessive intake during tooth development can lead to dental fluorosis; characterised by enamel hypomineralisation and altered aesthetics that may also affect caries’ susceptibility. Globally, studies have demonstrated that the relationship between fluorosis and caries is multifaceted and varies with fluoride exposure levels; in certain high-fluoride areas,^1,2 nearly all children exhibit fluorosis, but the associated caries prevalence can differ markedly. For instance, while some regions report increased caries prevalence in the presence of severe fluorosis,³ other studies indicate that mild fluorosis might confer a protective effect against decay.^4,5

In moderate fluoride regions,⁶ the occurrence of significant fluorosis often coincides with higher caries severity, whereas in low-fluoride areas,^7,8 the prevalence of dental caries tends to be elevated. These divergent findings underscore the influence of additional factors, including socioeconomic status,⁶ dietary habits,⁹ and oral hygiene practices, on the interplay between fluorosis and caries.¹⁰ The use of standardised measures, such as the Thystrup-Fejerskov (TF) index for fluorosis severity and the DMFT (decayed, missing, and filled teeth) index for caries experience, has enabled researchers to quantify this complex relationship, yet discrepancies persist across different populations.^2,11

Within Pakistan, the burden of dental caries is notably high, with a recent meta-analysis estimating a national prevalence of approximately 56.62%¹² and studies from Karachi reporting a caries prevalence of 51% among preschool children.¹³ Despite these concerning statistics, there is a paucity of research directly addressing the relationship between dental fluorosis and caries in the Pakistani context. Studies suggest that fluoride levels in drinking water and other exposures can significantly influence both the prevalence and severity of fluorosis and caries.¹⁴ Given Pakistan’s diverse regional fluoride exposures and varied socioeconomic landscapes, a focused investigation into the interaction between fluorosis and caries is both prompt and called for.

To address this gap, the present study looked to reveal the complex relationship between dental fluorosis and caries within the Pakistani population. Specifically, the authors aimed to assess the prevalence of dental caries in individuals with dental fluorosis using the TF index, investigate the correlation between fluorosis severity (TF score) and caries experience as measured by the DMFT index with particular attention to potential dose-response effects, and evaluate whether fluorosis functioned as a protective factor or as a risk indicator for caries. Furthermore, they examined the extent to which this association was changed by age, gender, and socioeconomic status. By exploring these aspects, the study will provide dentists and public health practitioners with evidence to inform targeted interventions and improve fluoride use in caries prevention strategies. The aim of this study was to assess the frequency of dental caries among individuals with dental fluorosis and to examine the relationship between fluorosis severity with the TF index and caries experience with the DMFT index.

METHODOLOGY

This cross-sectional observational study was conducted at the Department of Operative Dentistry and Endodontics, Liaquat University of Medical and Health Sciences, Jamshoro, Pakistan, from October 2023 to December 2024. The sample size was found using OpenEpi with a finite population correction factor, assuming a population size of 1,000,000 and a hypothesised outcome frequency of 50% ± 5%, which yielded a required sample size of 165 participants at an 80% confidence level. Participants were selected through a convenience sampling and included individuals of either gender, aged between 10 and 40 years with permanent dentition, born within the Hyderabad’s geographical area, and showing a TF score greater than 1. Individuals with a positive medical history, those who were pregnant, or those who had received recent dental treatment were excluded from the study.

Following approval from the Research Ethics Committee of Liaquat University of Medical and Health Sciences, Jamshoro, Pakistan (Letter No: LUMHS/REC-152), eligible participants received an explanation of the study’s goals, procedures, risks, benefits, and their rights, and provided informed consent prior to enrolment. Sociodemographic data, including employment status, education level, and family income were collected through a structured questionnaire. Intra-oral examinations were performed by the investigators in the outpatient department, with an assistant recording the findings. Dental caries experience was recorded using the WHO 2013 criteria for DMFT in permanent dentition. Decayed (D): A tooth was scored “D” if there was a frank cavitation into dentine, visualised either clinically or confirmed on bitewing radiographs when the surface was ambiguous. Non-cavitated white-spot lesions were not included. Missing (M): A tooth was scored “M” if it was extracted due to caries. Teeth missing for other reasons (trauma, orthodontics) were excluded, and filled (F): A tooth was scored “F” if it had one or more permanent restorations placed in response to caries. Dental fluorosis was evaluated on the vestibular, occlusal, and lingual surfaces using the TF index (Table I). All fully or partially erupted teeth, except third molars, were examined, and caries were recorded upon detection of a softened floor, undermined enamel, or softened wall; teeth with temporary fillings or a history of caries-related pain and/or cavities before extraction were included. The DMFT score for each participant was found by summing the highest DMFS scores across permanent teeth, and for logistic regression analyses, caries were categorised as 0 (DMFT = 0) and 1 (DMFT >1). A median TF-score was computed per patient from the highest score among permanent teeth, with additional TF-scores derived for each tooth type based on the median of the scores within that category; fluorosis severity was further categorised as 0 for TF scores 1–4 and 1 for TF scores greater than 5 (Table I).

Data analysis was performed using SPSS. Initially, the normality of the data was assessed using the Kolmogorov-Smirnov and Shapiro-Wilk’s tests for DMFT scores (Kolmogorov-Smirnov = 0.265; Shapiro-Wilk’s = 0.866; p <0.001) and TF scores (Kolmogorov-Smirnov = 0.202; Shapiro-Wilk’s = 0.901; p <0.001), which indicated that these variables were non-normally distributed. Consequently, non-parametric methods were employed. Descriptive statistics were summarised using medians and frequency distributions to capture the prevalence of dental caries and fluorosis. Spearman’s rank correlation coefficients were calculated to evaluate the association between the ordinal TF scores and the DMFT index, and the Kruskal-Wallis test was applied to compare median DMFT scores across different TF score groups. Furthermore, logistic regression analysis was used for dichotomised caries outcomes (DMFT ≥1 versus DMFT = 0) to assess whether fluorosis functioned as a protective factor or risk factor for caries. In these regression models, demographic and socioeconomic variables including age, gender, employment status, education level, and family income were included as covariates and interaction terms were incorporated to examine whether the relation- ship between fluorosis severity and caries experience varied by these factors. Subgroup analyses were also performed accordingly, with the significance level at 0.05.

RESULTS

Table I shows that the most common TF scores were 4 (36.4%) and 3 (29.7%), showing that moderate fluorosis predominated among the study participants, while only a small fraction (2.4%) showed a TF score of 6, reflecting severe fluorosis. In terms of dental caries, only 9.7% of participants were caries-free (DMFT = 0), while a large majority (90.3%) had DMFT scores greater than 0, underscoring a high prevalence of caries. When fluorosis severity was categorised, 83.0% of the subjects had TF scores between 1 and 4, while 17.0% had TF scores greater than 5. The DMFT scores ranged from 0 to 13, with the most often seen score being 2 (36.4%), followed by scores of 6 (13.9%) and 5 (10.3%). These findings highlight a population burdened by both a high prevalence of dental caries and a predominance of moderate dental fluorosis (Table II).

Table I: Thystrup-Fejerskov (TF) index table for dental fluorosis, showing the score, key clinical features, and corresponding severity category.

TF scores	Clinical description	Severity
0	Normal enamel translucency; no opacity or change	None
1	Fine, thin opaque white lines following the perikymata	Very mild
2	Opaque white areas merging less than half of the tooth surface	Very mild
3	Entire enamel surface is opaque white, but no brown staining	Mild
4	As for TF3, plus small brown stains covering less than 25% of the surface	Mild
5	Brown stains covering 25–50% of the surface	Moderate
6	Brown stains covering more than 50%; occasional surface pitting	Moderate
7	Discrete pitting of the enamel surface, with brown stains	Severe
8	Confluent pitting, loss of outer enamel; brown stains common	Severe
9	Loss of outer enamel and change of tooth morphology (e.g., coronal alteration)	Severe

Table II: Frequency distributions of TF score, dental caries, fluorosis severity, and DMFT scores (n = 165).

Parameters	Categories	Frequencies	Percentages (%)	Valid percentages (%)	Cumulative percentages (%)
TF scores	2	28	17.0	17.0	17.0
	3	49	29.7	29.7	46.7
	4	60	36.4	36.4	83.0
	5	24	14.5	14.5	97.6
	6	4	2.4	2.4	100.0
Dental caries (DMFT categories)	DMFT = 0	16	9.7	9.7	9.7
	DMFT >0	149	90.3	90.3	100.0
Fluorosis severity	TF score 1–4	137	83.0	83.0	83.0
	TF score >5	28	17.0	17.0	100.0
DMFT scores	0	16	9.7	9.7	9.7
	1	16	9.7	9.7	19.4
	2	60	36.4	36.4	55.8
	3	8	4.8	4.8	60.6
	4	4	2.4	2.4	63.0
	5	17	10.3	10.3	73.3
	6	23	13.9	13.9	87.3
	7	4	2.4	2.4	89.7
	8	4	2.4	2.4	92.1
	9	8	4.8	4.8	97.0
	12	1	0.6	0.6	97.6
	13	4	2.4	2.4	100.0

Table III: Kruskal-Wallis test results for DMFT scores by TF score group (n = 165).

TF scores	Frequencies	Mean rank	Chi-square	p-value
TF 2	28	67.21	19.260	0.001
TF 3	49	78.43
TF 4	60	93.23
TF 5	24	97.58
TF 6	4	8.50

Spearman’s rank correlation coefficient between DMFT score and TF score was 0.147 (p = 0.059), suggesting a weak positive association between dental caries experience and dental fluorosis severity. Although the correlation shows that higher TF scores tend to be associated with higher DMFT scores, the p-value slightly exceeds the conventional significance thre-shold of 0.05, meaning this relationship did not reach statistical significance. A Kruskal-Wallis test was conducted to compare DMFT scores across different TF score groups. The analysis revealed a statistically significant difference in DMFT scores among the groups (Table III).

Present findings showed that there was a potential dose- response trend between increasing fluorosis severity and higher DMFT scores. The logistic regression analysis suggested that the study population exhibited a high prevalence of dental caries (with 90.3% of subjects having DMFT >0), the model did not provide statistically significant evidence that fluorosis severity, as measured by the TF index, was independently associated with caries risk after cont-rolling age, gender, employment status, education level, and family income (Figure 1).

Figure 1: Forest plot of logistic regression predictors for dental caries.

Figure 2: Forest plot of sociodemographic predictors of severe fluorosis.

In contrast, a separate logistic regression analysis was performed with fluorosis severity to assess the influence of demographic and socioeconomic factors on the likelihood of showing severe fluorosis. The omnibus test was statistically significant (χ² (9) = 38.344, p <0.001). Education level showed a notable effect; specifically, the comparison between participants with high school education and those with university education was statistically significant (B = -1.541, p = 0.045, Exp(B) = 0.214), suggesting that individuals with high school education had substantially lower odds of severe fluorosis (Figure 2).

DISCUSSION

Although the study was not designed to assess the causal effect of fluoride exposure on caries prevalence, an inverse association was seen between fluorosis severity and DMFT scores in the sample. The results revealed that moderate fluorosis predominated among the participants and that dental caries were highly prevalent. Although results indicated a weak positive association between TF scores and DMFT scores and showed significant differences in caries experience across fluorosis severity groups, results did not provide statistically significant evidence that fluorosis severity independently predicted caries risk after adjusting for age, gender, employment status, education level, and family income. These findings partially addressed the knowledge gap by suggesting a potential dose-response trend between fluorosis severity and caries; however, they also underscored the complex interplay of fluoride exposure and socioeconomic factors.

The analysis showed a slight trend where severe fluorosis (higher TF scores) is linked to a higher DMFT scores, meaning that as fluorosis worsens, dental decay tends to increase. This pattern is similar as, what has been seen in high-fluoride areas in Ethiopia² and hints at a possible dose-response relationship, where the severity of fluorosis is related to the extent of dental decay, even though the connection is not very strong.

When demographic and socioeconomic factors were accounted for, the severity of fluorosis alone did not significantly increase the risk of caries. Initially, before those adjustments were made, the data appeared to show that as fluorosis severity increased, the risk of caries had also risen. However, after other factors had been considered, that trend was not confirmed. This finding suggested that the relationship between fluorosis and caries was more complex than had initially appeared. Other studies have shown mixed results; some suggest that severe fluorosis makes teeth more prone to cavities due to enamel defects,¹⁵ while others suggest mild fluorosis may help prevent cavities by providing more fluoride exposure.¹⁶ Current findings add to existing research by showing that, in the Pakistani population, the impact of fluorosis on caries risk is not as simple as the authors initially thought. The trend may be explained by several factors. Demographic and socioeconomic variables can confound the relationship, influencing both the exposure to fluorosis and the risk of caries,¹⁷ so, when these factors are controlled, the apparent dose-response relationship between fluorosis severity and caries risk diminishes. Additionally, mild fluorosis might be indicative of beneficial fluoride exposure that strengthens enamel, while severe fluorosis can lead to enamel defects that predispose teeth to decay, thus complicating the overall picture. Other influential factors, such as oral hygiene practices, diet, and access to dental care, often associated with socioeconomic status, may have a more dominant effect on caries risk.¹⁸ Moreover, unique environmental or genetic factors within the Pakistani population studied could further modulate this relationship, underscoring the complex interplay between fluorosis and caries risk.¹⁹

Furthermore, it was seen that individuals with lower educational backgrounds might have reduced the odds of showing severe fluorosis. This finding, though intriguing, contrasts with some earlier studies that have documented higher fluorosis risk in populations with lower socioeconomic status.²⁰ One possible explanation is that individuals with higher educational backgrounds often have greater access to fluoride-containing dental products and preventive care. A study on parental knowledge and awareness of fluoride varnish found that better-educated parents tend to be more informed about dental hygiene and the role of fluoride in preventing cavities. Consequently, their children may receive higher overall fluoride exposure during childhood.²¹ This increased exposure may inadvertently raise the risk of developing severe fluorosis. In contrast, individuals with lower educational backgrounds might have less access to these products or may use them less frequently, thereby reducing their cumulative fluoride intake and, in turn, their likelihood of severe fluorosis.²² Several studies support this idea, for instance, research has indicated that higher socioeconomic status and education are sometimes linked to increased fluorosis prevalence, as families with more resources are more likely to use fluoride toothpaste and supplements, or have access to well-regulated, fluoridated water supplies, which, if overused, may lead to fluorosis.²³ Conversely, other research emphasises that regional factors such as the actual fluoride levels in drinking water and local public health practices can modify these associations, underscoring the complexity of the relationship between education, socioeconomic factors, and fluorosis risk.²⁴

Present findings contribute to the field by illustrating the complexity of the association between dental fluorosis and caries, and by emphasising the influence of socioeconomic factors. However, the study has several limitations that should be acknowledged. First, the cross-sectional design prevents any causal inferences about the relationship between dental fluorosis and caries risk. The use of convenience sampling from a single outpatient department may limit the generalisability of the present study’s findings to the broader population. Additionally, limited data led to unstable estimates and convergence issues in the logistic regression models, which may have obscured true associations. Finally, unmeasured confounding factors, such as dietary habits and oral hygiene practices, could have influenced the observed outcomes. Future research should consider larger, more diverse samples, and longitudinal study designs to address these limitations and further elucidate the complex interplay between fluoride exposure, dental fluorosis, and caries risk.

CONCLUSION

Rather than providing definitive causal links, the research highlighted the multifactorial nature of caries risk by showing that the relationship between fluorosis severity and caries was moderated by demographic and socioeconomic factors. Moderate fluorosis predominated among the participants and dental caries were highly prevalent, with 90.3% of subjects exhibiting DMFT scores greater than zero. There is no association between fluorosis severity and caries risk after adjusting for confounders.

ETHICAL APPROVAL:
The study was approved from the Research Ethics Committee of Liaquat University of Medical and Health Sciences, Jamshoro, Pakistan (Letter No: LUMHS/REC-152).

PATIENTS’ CONSENT:
Written consent was obtained from all the participants inclu-ded in the study.

COMPETING INTEREST:
The authors declared no conflict of interest.

AUTHORS' CONTRIBUTION:
FAK, SY: Contributions to the conception and design of the manuscript.
MM, SS, PR: Provision of study materials or patients, data collection, assembling of the data, analysis, and interpre- tation.
NK: Data analysis and manuscript writing.
All authors approved the final version of the manuscript to be published.

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