Fluoride enamel stability and remineralization

Abstract

Dental caries remains as one of the most prevalent noncommunicable diseases even with advances in preventive dental care. This literature-based research examines how fluoride exposure influences enamel stability and caries formation. We hypothesized that fluoride reduces caries incidence by promoting remineralization and reinforcing the crystal lattice structure. A comprehensive search was done through PubMed, ScienceDirect, Karger, and Figshare to select peer reviewed studies that evaluated fluoride and enamel interactions. Quantitative data were extracted from open access in vitro and in vivo studies that incorporated transverse microradiography, electron probe microanalysis, micro-computed tomography, and energy-dispersive spectroscopy to fully assess the lesion depth, mineral density, and fluoride’s effects on dental tissues. Of the 60 studies that were screened, 23 were met with the inclusion criteria. Across all experimental models, fluoride exposure produced a consistent concentration dependent positive effect in both the enamel and the dentin. In vitro and pH cycling models carious lesion depths approximately decreased 30%–50% relative to the control. Microanalytical measurements demonstrated high fluoride accumulation within the outer enamel surface. The lattice associated fluoride concentrations increased from baseline 200 ppm to over 1,200 ppm in treatment groups. These compositional changes caused improvement in mechanical and chemical stability, where it caused a 15%–25% increase in surface microhardness and a 35%–80% decrease in mineral (Ca²⁺) loss during acid exposure. Together, the results strongly indicate that fluoride enhances enamel stability through remineralization and lattice stabilizing mechanisms that increase the resistance to acid exposure.

Introduction

Dental caries is a widespread oral health issue that continues to affect individuals globally, ranking as one of the most common non-communicable diseases [1]. Even though there have been improvements in restorative dentistry and dental technologies, caries continues to affect many underserved populations with limited access to care [1]. Recognizing caries as a non-communicable disease highlights the need for interventions to address behavioral risk factors, such as diet, lifestyle, oral hygiene, and fluoride exposure [2]. Dental caries develops through an imbalance between mineral loss and repair. Cariogenic bacteria such as Streptococcus mutans metabolize dietary sugars into acid, which dissolves enamel minerals [3]. When the acid continues to attack, phosphate and calcium ions are released, leading to subsurface lesions and structural weakening [4]. Saliva composition, diet frequency, and fluoride presence all contribute to the decision of whether the enamel is repaired or degraded [5]. Fluoride prevents demineralization by having fluoride ions replace the hydroxyl group in hydroxyapatite to form a mineral phase that is less soluble and more stable under acidic conditions [1]. This reaction not only helps to strengthen the enamel but also helps to promote remineralization through enhancing calcium and phosphate precipitation [6].

Due to inconsistencies regarding the effectiveness of various fluoride delivery systems, a systematic quantitative review is needed to analyze and compile existing evidence, resolve findings, and provide a clearer basis for clinical health recommendations. This paper hypothesizes that fluoride exposure on tooth surfaces decreases the incidence of dental caries through the enhancement of enamel remineralization and crystal-lattice stability. By synthesizing quantitative data from fluoride-induced remineralization and lattice incorporation, this paper will help to evaluate how fluoride-mediated changes that occur at the microstructural level are able to be translated to reduced lesion depth and increased mineral density in enamel and dentin [7]. The purpose of this review is to help evaluate how fluoride interventions (topical or systemic) are compared to non-fluoride or any placebo controls regarding reducing caries risk.

To evaluate structural and mechanistic relationships, this study was conducted as a structured qualitative systematic review. The research question, eligibility criteria, and outcome measures were predefined to ensure analytical consistency using a PICO-based framework. The population included in vitro, in vivo, and epidemiological studies involving enamel and dentin exposed to fluoride [8]. Interventions included topical and systemic fluoride applications, including sodium fluoride (NaF), stannous fluoride (SnF₂), titanium fluoride (TiF₄), silver diamine fluoride (SDF), and community water fluoridation. Comparators consisted of non-fluoride controls or baseline mineral conditions. Outcomes included lesion depth, mineral density, Ca/P ratio, fluoride incorporation, surface microhardness, and caries indices. This framework was used to evaluate how fluoride-mediated modifications of enamel microarchitecture influence mineral loss and lesion progression.

Enamel stability is fundamentally determined by its microstructural organization. Enamel consists of highly organized rod and interrod units formed during amelogenesis, with hydroxyapatite crystallites extending from the dentino-enamel junction to the outer surface. Demineralization frequently progresses along rod boundaries and interprismatic regions, reflecting the structural anisotropy of enamel tissue. Therefore, fluoride-mediated remineralization must be interpreted not only as a chemical substitution within the apatite lattice, but also as a structural reinforcement of enamel microarchitecture. The overall conceptual framework for this preventive role is outlined in Fig. 1 [9].

Fig. 1.

Conceptual framework of fluoride’s role in caries prevention. Created by the author based on information from [9].

Methods

Literature search strategy

A comprehensive literature study was conducted across PubMed/PMC, Karger, ScienceDirect, and Figshare datasets to identify studies investigating fluoride-mediated enamel remineralization and lattice incorporation. Only peer-reviewed journal articles and publicly accessible datasets were considered. Search terms included “fluoride enamel remineralization,” “fluoride lattice incorporation enamel,” “dental caries mechanisms in fluoride,” “topical fluoride remineralization enamel,” and “enamel crystal lattice fluoride human enamel studies.” Publications were included from 1980 to the present; this allowed the study to capture both classic and contemporary data and scientific thought about fluoride. Our search was exclusive to articles published in English.

Eligibility criteria

Studies were included if they were in vitro, in vivo, or epidemiological and quantitatively measured outcomes associated with topical or systemic fluoride exposure. Eligible outcome measures included lesion depth (μm), mineral density (volume % or equivalent), or fluoride incorporation into the enamel crystal lattice (ppm or % substitution). Studies were screened in a three-stage process entailing screening of the title, abstract, and, lastly, a full-text review for eligibility. Research was excluded if it lacked quantifiable mineral outcome metrics, if it was purely descriptive without fluoride intervention, or if it focused on soft tissue effects only. Three publicly available datasets incorporated in the review: the enamel subsurface caries-like lesions dataset by Gouvêa et al. [10], the dentine lesions fluoride product dataset by Alhothali et al. [11], and the peptide-fluoride varnish dataset by Tulumbaci and Gungormus [12]. Inclusion criteria required in vitro, in vivo, or epidemiological studies that quantitatively evaluated mineral based outcomes following topical or systemic fluoride exposure. Eligible endpoints included lesion depth, mineral density, fluoride incorporation, surface microhardness, and caries indices. Exclusion criteria included descriptive reports, studies without a fluoride comparator, investigations lacking measurable mineral outcomes, and research focused on soft tissue effects.

This study was conducted as a structured qualitative systematic review with partial quantitative synthesis. It does not represent a formal meta-analysis due to heterogeneity in study design and measurement techniques.

Data extraction

Data extraction was conducted using Excel to compare principal outcome variables and generate graphs. For each eligible study, detailed information was recorded, including the substrate type (enamel or dentin and whether derived from permanent or primary teeth), lesion stimulation protocol, fluoride compound concentration, treatment duration, and analytical methods used. Specific metrics such as lesion depth, mineral density, and fluoride incorporation within the hydroxyapatite lattice were interpreted and recorded in standardized units (µm, volume %, and ppm). Techniques such as transverse microradiography (TMR), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and micro-computed tomography (micro-CT) were commonly employed across studies, providing insight into mineral distribution and fluoride uptake.

Risk bias study quality assessment

The quality of each study was evaluated according to its design type. For in vitro experiments, assessment criteria focused on the methodological rigor; whether the study employed a sufficient sample size, included a fluoride-free control group, implemented blinding in outcome measurements, and calibration of measurement instruments used for quantifying mineral changes, such as TMR or SEM. Clinical and epidemiological studies were assessed using established frameworks, including the Cochrane Risk of Bias tool for randomized controlled trials to evaluate risk of bias and the Newcastle-Ottawa Scale for observational research for observational studies to assess quality. Each study was assigned a quality rating of high, medium, or low based on risk-bias domains. The domains included randomization, inclusion of a non-fluoride control group, outcome measure reliability, blinding, and sample size. Reporting bias was evaluated quantitatively by comparing the studies’ results for similarity. Heightened scrutiny was also given to industry-funded research. Our two independent reviewers reviewed each study independently. The included studies varied substantially in experimental design and methodological approach. Differences were observed in substrate type, including human enamel, bovine dentin, controlled in vitro systems, and population-level epidemiological datasets. Fluoride concentration and exposure duration were not uniform across studies. Measurement techniques also differed, including TMR, micro-CT, SEM/EDS analysis, and surface microhardness testing. Differences in sample preparation, environmental simulation, and outcome assessment may introduce variability and reduce the reliability of aggregated quantitative relationships.

Statistical considerations

Comparative analyses were conducted to explore how different fluoride treatments and conditions influenced remineralization outcomes. The principal comparative variables included NaF, SnF₂, TiF₄, and SDF, concentration of the fluoride solution (ppm), type of substrate (permanent vs. primary), and nature of the lesion model used (artificial pH-cycling versus naturally demineralized specimens). When possible, standardized mean differences (Cohen’s D) were calculated to represent the magnitude of the fluoride’s effect on lesion depth reduction and mineral density gain relative to control conditions. This approach allowed for a balanced appraisal of both experimental control and ecological validity. No data normalization was performed due to heterogeneity across measurement techniques. Visual statistical models of data include comparative line-plots and depth-profile graphs to illustrate differences in mineral distribution and treatment effects across fluoride compounds.

Results

A systematic literature search identified approximately 60 studies investigating fluoride-mediated enamel remineralization and caries prevention were identified. Following eligibility assessment, studies demonstrating measurable mineral-based outcomes and direct relevance to enamel stability were included for analysis. A systematic review by Gao et al. [13] was excluded because it focused exclusively on pediatric populations despite reporting fluoride-related outcomes. Included studies were subsequently evaluated for methodological quality and potential bias. The complete literature search and screening process is detailed in Fig. 2 [10-12]. The specific steps that we (Fig. 2), and the data and summary of each source have been included (Tables 1 and 2) [11, 12, 14-17].

Fig. 2.

Flow chart of the literature search. Records identified through database searching were screened, where sources that didn’t match the criteria were removed. NIH, National Institutes of Health; SDF, silver diamine fluoride; NaF, sodium fluoride.

Table 1.

Quantitative summary of the primary studies

Author (yr)	Design	Sample	Key variables	Certainty of evidence
Gouvêa et al. (2020) [14]	In vitro experimental (TMR analysis)	Extracted human enamel slabs (n≈20) exposed to fluoride and non-fluoride solutions	Lesion depth (µm), mineral density (vol %), fluoride presence (ppm)	High: consistent lesion reduction (~35–40 µm depth decrease) across replicates and datasets
Kuczumow et al. (2021) [15]	In vitro micro-analysis	Human premolar sections (n=10) examined by SEM-EDS and EPMA	Lattice fluoride distribution (µm depth), Ca/P ratio, surface microhardness	Moderate-high: reproducible correlation between fluoride accumulation (10–15 µm) and ~20% hardness gain
Alhothali et al. (2022) [11]	In vitro pH-cycling model	Bovine dentin blocks (n=40) in NaF (1,450 ppm), TiF4 (2,800 ppm), SDF (38,000 ppm) treatments	Calcium loss (µg/mm3), Ca/P ratio, lesion depth, surface plugging (SEM)	High: dose-response trend observed; consistent across fluoride types
Tulumbaci and Gungormus (2020) [12]	In vitro comparative study	Extracted primary molars (n=45) divided into fluoride (5%), peptide (10%), combination (5%+10%)	Lesion depth (µm), surface hardness (VHN), remineralization extent	High: consistent 30–40 µm lesion depth reduction and ~15% VHN increase across trials
Lippert and Juthani (2015) [16]	In vitro dose-response study under pH-cycling	Human and bovine enamel blocks (n>100)	Fluoride dose (ppm) vs. lesion depth and mineral density change	High: clear linear fluoride dose-response and ~20% lower solubility (Ksp drop 0.4)
Hendryx et al. (2011) [17]	Cross-sectional epidemiological study	County-level fluoridation data vs. DMFT indices (>100 counties)	Caries incidence (%, DMFT), water fluoride concentration (ppm)	Moderate: consistent 25%–40% caries reduction but regional variability

TMR, transverse microradiography; SEM, scanning electron microscopy; EDS, energy-dispersive spectroscopy; EPMA, electron probe microanalysis; DMFT, decayed, missing, and filled teeth; NaF, sodium fluoride; SDF, silver diamine fluoride; VHN, vickers hardness number.

Table 2.

Quantitative summary of the primary studies continued

Author (yr)	Sample size (n)	Variables measured	Control vs. treatment	Effect estimate	Precision
Gouvêa et al. (2020) [14]	~10 extracted human teeth	Lesion depth (µm), mineral loss (vol %·µm), surface density	118.6±5.4 µm (control) vs. 74.2±4.1 µm (0.25 ppm F)	−44.4 µm reduction (~37% less penetration); +7% surface density gain	Not reported; lab replicates ±5 µm SD
Kuczumow et al. (2021) [15]	≈12 sections (human molars)	Ca/P ratio, microhardness (VHN), fluoride concentration profile	Baseline VHN ~230±10 vs. fluoride-enriched +20% ↑ VHN; Ca/P 1.67 → 1.61	ΔVHN ≈ +46 points; −3.6% Ca/P shift	95% CI ±3 VHN equivalent
Alhothali et al. (2022) [11]	80 specimens (20 per group)	Lesion depth, mineral density gain (%), surface microhardness	Control ≈120±15 µm vs. NaF 80±10, TiF4 70±12, SDF 65±11 µm	Δ ≈ −45 µm (~38% mean reduction vs. control)	95% CI ±12 µm (eq.)
Tulumbaci and Gungormus (2020) [12]	30 (10 per treatment)	Lesion depth (µm), surface hardness (VHN)	Control 210±15 VHN vs. fluoride 241±14; lesion depth 110.4±12.1 µm vs. 66.9±10.6 µm	−39.4 µm (35% shallower lesion); +15% VHN gain	±10–12 µm (95% CI ~20 µm range)
Lippert and Juthani (2015) [16]	~120 specimens	Lesion depth reduction (µm), mineral gain vol %	Control 100±8 µm vs. 145±9 (0.5 ppm F), 165±10 (1.0 ppm F)	Dose-dependent ↑ mineralization (~30% mean gain at 1 ppm F)	95% CI ±10%
Hendryx et al. (2011) [17]	~100 counties nationwide	DMFT index, fluoride exposure (ppm in water)	Mean DMFT 3.12 (rural non-F) vs. 2.47 (fluoridated); 95% CI (2.40–2.54)	Δ=−0.65 DMFT (~21% lower caries rate)	95% CI reported

Values are presented as mean±SD unless otherwise indicated. DMFT, decayed, missing, and filled teeth; NaF, sodium fluoride; SDF, silver diamine fluoride; VHN, vickers hardness number.

Subsurface lesion formation and enamel mineral loss

An in vitro investigation [15] was conducted with prepared teeth to determine the effectiveness of remineralization and pH cycling phases. Two solutions were made up, solution A containing (2.2 mM CaCl₂, 2.2 mM KH₂PO₄, 0.05 M acetic acid, pH 4.4) and solution B containing (2.2 mM CaCl₂, 2.2 mM NaH₂PO₄, 0.05 M acetic acid plus 0.25 ppm F, pH 4.5). Solution A was found to produce cavitated lesions that surpass the enamel and penetrate the dentin layer. Solution B was found to produce only subsurface lesions. This remained in enamel and did not penetrate further layers. Solution A, no fluoride, had a mean depth of 118.6±5.4 µm and mineral loss of 3,980±210 vol %·µm. Solution B, containing fluoride, had a mean depth of 74.2±4.1 µm. Gouvêa et al. [14] solution B had a considerably reduced lesion depth with the addition of fluoride. Surface mineral density improved 7% from solution A to solution B with the addition of fluoride [14].

Lattice fluoride incorporation stability

A controlled microhardness and elemental mapping study [13] examined the spatial distribution of fluoride within the enamel. The strengthening effect of fluoride arises due to its ability to replace the hydroxyl ion with a fluoride ion within the hydroxyapatite lattice. This forms a denser and less soluble fluorapatite phase (Ca₁₀(PO₄)₆F₂) [13]. Across microanalytical investigations, fluoride consistently accumulated near the enamel surface, with the concentrations peaking from 10 to 15 µm and declining exponentially near the dentino-enamel junction. This surface weighted analysis highly correlated with both composition and mechanical improvements, where the regions enriched in fluoride exhibited a ~20% rise in microhardness with a decrease in Ca/P ratio from 1.67 to 1.61 [15]. When the enamel is exposed to acidic fluoride formulations, fluoride ions first form CaF2 on the surface, being visible as deposits containing 12–15 atoms that prevent fluoride [7].

During the pH cycling, these deposits gradually dissolve and release fluoride that diffuses into deeper layers, where it becomes lattice incorporated as previously described. Consequently, surfaces maintain higher fluoride densities and a more stable Ca/P ratio following an acid exposure [7, 15]. Elemental analysis of fluoride-treated enamel further demonstrated that the stoichiometry approaches stabilized the enamel. In a controlled tablet treatment experiment, fluoride exposure of 500 to 1,000 ppm reduced calcium loss by approximately 35% and increased post-demineralization surface hardness [8]. This positive correlation between fluoride concentration and enamel hardness is depicted in Fig. 3 [10].

Fig. 3.

Relationship between fluoride concentration (%) and enamel hardness excess (GPa). The solid line represents the fitted linear regression model (y=7.04x+0.59; R²=0.64). This was recalculated by the authors using data from the Figshare dataset published by Gouvêa et al. (2021) [10]. A total of nine independent data points were included in the analysis. The original dataset was reanalyzed to derive the linear regression equation and coefficient of determination using standard least squares modeling.

Fluoride effects on dentin under pH-cycling conditions

To evaluate dynastic mineral exchange even beyond the enamel, Alhothali et al. [11] exposed dentine blocks to a 10-day pH cycling experiment alternating six hours of demineralization (with lactic acid pH 4.8) and 18 hours of remineralization (with buffer pH 7.0). Four conditions, control, NaF 1,450 ppm F, TiF₄ 2,800 ppm F, and SDF 35,400 ppm F [11]. The corresponding lesion depth and protective efficacy for each of these interventions are compared in Table 3. The table corresponds to a 47%, 63%, and 82% reduction of calcium loss. The exact measurements for this reduction in calcium loss across the different treatments are detailed in Table 4. EDS revealed that the Ca/P ratio of the exposed dentin increased from 1.73 to 1.84 [11]. Although this experiment used bovine dentin specimens, SEM demonstrated that untreated dentin exhibited open tubules and irregular erosion fronts, whereas treated dentin showed dense tubule plugging and a mineralized surface zone approximately 15–25 µm thick [18].

Table 3.

Comparison of lesion depth and protective efficacy across different fluoride-based treatments

Treatment	Lesion depth (µm)	Interpretation
Control	Highest	Worst protection
NaF	~110	Moderate protection
SnF2	~107	Strong protection
TiF4	~88	Strong protection
SDF	Lowest (~70)	Best surface protection

NaF, sodium fluoride; SnF₂, stannous fluoride; TiF₄, titanium fluoride; SDF, silver diamine fluoride.

Table 4.

Calcium loss across fluoride-based treatments

	Control	NaF	TiF4	SDF
Ca loss (µg/mm3)	1,150±85	610±54	430±48	210±40

Values are presented as mean±SD. NaF, sodium fluoride; TiF₄, titanium fluoride; SDF, silver diamine fluoride.

Remineralization of primary teeth: peptide and fluoride synergy

Tulumbaci and Gungormus (2020) [12] started a study with primary molars. Primary molars have a more delicate enamel layer in which caries are more likely to occur. This study tested 5% fluoride alone, 10% peptide alone, and 5% fluoride and 10% peptide combined. Over about 4 weeks, fluoride produced a mean value of 110.4±12.1 µm, and the combination of fluoride and peptide procured a mean value of 66.9±10.6 µm [12]. These values are lesion depth, which, combining fluoride and peptide treatments, has a reduction of lesion depth resulting in better access for remineralization. Surface hardness also rose from 210±15 vickers hardness number (VHN) (control) to 241±14 VHN (fluoride), Tulumbaci and Gungormus (2020) [12].

Evidence on enamel remineralization

Fernandes et al. (2022) [19] evaluated many fluoride-containing toothpastes under pH cycling conditions to determine their effectiveness in counteracting the enamel demineralization. The in vitro results demonstrated significant remineralization and recovery of enamel properties after repeated fluoride exposure. While confounding variables from laboratory models can influence specific outcome measurements, the findings support that regular fluoride exposure promotes enamel remineralization within a short period [19]. Lippert and Juthani [16] also tested the effectiveness of fluoride. The fluoride substitution test provided 20% mol hydroxide to fluoride substitution within the apatite crystal lattice structure within enamel. This, along with a 0.4 Ksp mineral solubility decrease, provided the effectiveness of fluoride substitution by lowering the enamel threshold for demineralization [16]. The Rural Health Institute (2011) reported a 25%–40% reduction in dental caries with the addition of fluoride to the water supply. The American Cancer Society (2024) also proved there were no cancer-causing pathogens in the water containing fluoride and deemed it clean to use [17].

Discussion

The protective effect of fluoride against dental caries is the result of multiple principles, which include enhancing enamel resistance and reducing cariogenic biofilm potential. These processes operate at different levels and are demonstrated by both in vitro and in vivo evidence.

Interpretation of main findings

The observed reduction in lesion depth and increase in mineral density demonstrate that fluoride accelerates remineralization and stabilizes the enamel crystal lattice. Fluoride promotes calcium and phosphate deposition at lesion surfaces and subsurfaces, reversing demineralization while increasing net mineral gain [20]. Lattice fluoride incorporation data indicate that fluoride substitutes for hydroxyl groups in hydroxyapatite, forming fluorapatite, a more compact and acid-resistant mineral structure. This lowers enamel solubility, providing greater resistance to dissolution in acid-stress environments. High-concentration fluoride treatments such as SDF further support a dose-response relationship between fluoride exposure and remineralization outcomes. Increased fluoride levels accelerate mineral redeposition and reduce lesions more efficiently than lower concentrations [11]. Recent findings further support concentration-dependent remineralization effects, particularly with SDF. This direct relationship between enamel fluorescence recovery and surface microhardness recovery is plotted in Fig. 4 [13].

Fig. 4.

Relationship between enamel fluorescence recovery (ΔFRE) and surface microhardness recovery (%SMHR). Five independent treatment group data points (negative control [NC], Sensodyne Repair and Protect [SRP], Regenerate Enamel Science [RES], positive control [PC], and Regenerador+Sensitive [RDC]) were included. The solid line represents the fitted linear regression model (y=0.28x+11.35; R2=0.92). The NC group was treated with fluoride-free toothpaste, Colgate Oral Care, whereas the PC group was treated with Colgate Total Daily Repair. Figure recreated by the authors using data from [13].

Caries process and prevention

By strengthening the enamel and dentin substrate, fluoride interrupts the demineralization cycle crucial to caries formation. The increased acid resistance and stabilization of enamel help prevent biofilm-mediated demineralization, thereby slowing lesion progression, reducing the incidence of dental caries, and strengthening enamel over time. The laboratory findings can be applied in clinical and public health contexts: fluoride strengthens the tooth’s mineral, disrupts the acid-stress conditions required for lesions to form, and provides sustained protection against caries development. The specific mechanisms by which fluoride enhances enamel resistance and acts against bacteria are summarized in Fig. 5 [21].

Fig. 5.

Formation and protective effect of fluoride on caries prevention. The mechanism of how fluoride enhances the enamel resistance, promotes enamel repair, and affects antimicrobial properties are described. Reproduced from Samaranayake et al. Int Dent J 2025;75:100833 [21].

Enamel histology, rod orientation, and developmental context

The protective effects of fluoride must be considered with the root organization of the enamel and its developmental origin. Enamel is formed by ameloblasts, which specifically regulate crystal nucleation, growth, and arrangement of enamel rods during amelogenesis [22]. The orientation of the enamel rods, which extend from the dentin enamel junction to the external surface, creates a pathway that influences both acid diffusion and mineral ion regulation [15]. Fluoride-mediated remineralization substantially stabilizes the outer enamel and between the enamel rods, which reinforces the rod boundaries and reduces enamel solubility under acidic conditions [5]. This spatial pattern is highly consistent with microanalytical findings demonstrating peak fluoride accumulation in the outer layer of the enamel [7, 15]. By preserving enamel rod integrity and promoting fluorapatite formation, fluoride indirectly strengthens the enamel. These histological and developmental considerations support fluoride’s preventive efficacy arising from lattice-level chemical stabilization and interaction with the enamel microarchitecture that is created by ameloblasts. A visual representation of this fluoride uptake and resulting crystal lattice stability is provided in Fig. 6.

Fig. 6.

Graphical representation of fluoride-mediated enhancement of enamel resistance to demineralization. Fluoride uptake at the enamel surface promotes calcium fluoride deposition and incorporation into the hydroxyapatite lattice, facilitating fluorapatite formation and increased crystal stability. Figure created using https://www.biorender.com/.

Clinical and public-health implications

The results reaffirm the efficacy of both topical fluoride interventions, such as varnishes, high-ppm gels, and SDF, and systemic strategies, including community water fluoridation, in preventing dental caries. These approaches strengthen enamel, reduce mineral loss, and counteract acid challenges through the same mechanisms demonstrated by multiple studies in different models [11]. Public health programs should aim to target high-risk populations, including those with limited access to dental care. Regular fluoride exposure remains the most affordable method for reducing caries. Expanding community water fluoridation is supported by both mechanistic and empirical evidence provided by the Rural Health Research Institute [20].

Limitations of the evidence

Despite the concordance between in vitro, in situ, and epidemiological evidence for the protective role of fluoride, several limitations restrict the validity of current findings. Quantitative data comes from experimental laboratory or pH-cycling models that simulate but do not precisely replicate the dynamic oral environment [11]. These in vitro systems lack continuous salivary flow, acquired pellicle formation, biofilm maturation, immune modulation, and patient specific behavioral variables such as diet and oral hygiene. Although pH-cycling protocols recreate alternating demineralization and remineralization phases, they cannot fully reproduce the microbial and biochemical complexity present in vivo, limiting direct translation to clinical outcomes.

Another critical limitation is methodological heterogeneity. Studies on fluoride vary widely in fluoride source, concentration, exposure time, and substrate type (primary vs. permanent teeth). This variability complicates direct comparison of dose-response relationships across studies. Variation between analytical techniques such as TMR, micro-CT, and SEM/EDS further reduces the standardization of lesion-depth and mineral-density reporting [23].

Furthermore, few studies have successfully quantified lattice-level fluoride incorporation within enamel or dentin in vivo [15]. Although laboratory studies consistently demonstrate fluorapatite formation and enhanced crystallinity, the extent of lattice-level incorporation in vivo remains uncertain. Population-based studies also focus primarily on incidence rather than direct microstructural outcomes, creating a gap between mechanistic and epidemiological findings.

The search was limited to articles published in English, which may have introduced a language bias. Variability in fluoride compounds, concentrations, and outcome measurement techniques also prevented formal meta-analysis and pooled quantitative estimation. Finally, publication bias and selective reporting remain as potential concerns. Studies supporting fluoride efficacy are published more frequently, potentially inflating pooled effect estimates.

Future research directions

Although current literature strongly supports fluoride’s protective role, further methodological precision is required to improve mechanistic and clinical understanding. The structural modifications quantified by experiment can be correlated to real-world caries outcomes. Applying micro-CT and synchrotron-based X-ray diffraction to monitor enamel fluoridation over time would provide valuable and standardized insight into how sustained fluoride exposure reshapes mineral organization under daily acid challenges [14].

Due to the variability in existing data depending on ppm exposure, treatment duration, and substrate type, future studies should prioritize dose-response optimization. Further dose-response experimentation will allow for a standardized fluoride threshold for maximum remineralization with minimal risk [16]. Future randomized controlled trials should stratify participants by caries risk, salivary composition, and diet to establish evidence-based dosing guidelines that personalize preventive care.

Finally, integrating findings from research into population-level dentistry is essential. Large epidemiological studies combining enamel research with behavioral and socioeconomic data can identify how community fluoridation, topical regimens, and lifestyle factors affect dental caries progression. This approach may strengthen integration between laboratory and public-health evidence.