Fluoride-Based Interventions for White Spot Lesion Prevention in Orthodontics: Varnish Versus Fissure Sealant

Dental caries are often present as white spot lesions (WSLs) in their early stages; a concern heightened during orthodontic treatment. This in vitro study was conducted using 60 caries-free premolars, aimed to compare different interventions in preventing WSLs around orthodontic brackets. Samples were divided into four groups: Control, Fluoride Varnish (FV), Fluoride-Releasing Fissure Sealant (FRFS), and Non-Fluoride Fissure Sealant (NFFS). Each group received respective treatments, and orthodontic brackets were bonded. Demineralization-remineralization cycles were applied, and enamel microhardness was measured at the end of the study using a Vickers microhardness tester. Statistical analyses were performed using one-way ANOVA and Tukey’s post hoc test. The FV and FRFS groups had significantly higher microhardness compared to other groups (P < 0.05). FV exhibited the highest microhardness. However, the NFFS group did not significantly differ from the control group (P= 0.984). Overall, both FV and FRFS effectively reduce WSLs around orthodontic brackets.

Dental caries is one of the most common chronic oral diseases worldwide, presenting in its initial stages as white spot lesions (WSLs) [1,2]. Orthodontic treatments are a major contributing factor to the development of these lesions, as they make it challenging to maintain proper plaque control around the brackets and alter the microbial ecology [3-5]. The increased risk of demineralization during orthodontic treatment underscores the need for effective preventive measures. Fluoride application has long been established as one of the most effective methods in the prevention of dental caries, owing to its ability to promote enamel remineralization [6,7]. Various studies have recommended the use of fluoride in the form of either fluoride varnish or fissure sealant to combat caries development. Fissure sealants, especially those that release fluoride, are widely regarded as one of the most effective ways to prevent occlusal caries, as the fluoride they release helps to inhibit the growth of cariogenic bacteria like Streptococcus mutants, which are major contributors to caries development [8]. Fluoride varnish, on the other hand, has shown significant effectiveness in preventing demineralization and the formation of white spot lesions around orthodontic brackets. Numerous studies have demonstrated its ability to reduce the risk of white spot lesions in patients undergoing orthodontic treatment, establishing it as a strong preventive measure in this population [9-11]. The rationale for conducting this study stems from the high prevalence of white spot lesions in orthodontic patients and the well-established role of fluoride in caries prevention. While various studies support the use of fluoride-based treatments, there are conflicting results regarding the comparative efficacy of fissure sealants and fluoride varnish in preventing white spot lesions around orthodontic brackets. Therefore, this study aims to compare the effectiveness of these two preventive strategies, hoping to identify the most effective measure for reducing dental caries and improving oral health outcomes in patients undergoing orthodontic treatment.

Sixty healthy, caries-free premolars, extracted for orthodontic purposes from systemically healthy patients less than six months ago, were selected for this in vitro experimental study. The sample size was determined based on the study power of 0.8 and a type I error of 0.05, and the mean and standard deviation from a previous similar study [10], resulting in 15 teeth per group.

The teeth were stored at room temperature in normal saline, with the solution replaced every two weeks. Prior to the experiment, the teeth were thoroughly cleaned using pumice and a brush, and the crowns were separated from the roots using a high-speed turbine. A rectangular window (3 × 4 mm) was prepared on the middle third of the buccal surface, and the remaining surfaces were covered with acid-resistant nail varnish (Moda Nail Polish). The samples were then mounted in self-cure acrylic (Marlic, Iran) and coded from 1 to 60. Before starting the experiment, the microhardness of the enamel in the buccal surface of each sample was measured using a Vickers microhardness tester (Roell, Zwick, Germany) with a 200 N force applied for 10 seconds at three different points. The values were recorded in data forms for each sample.

The 60 samples were randomly divided into four groups:

• Control Group: No material was applied around the orthodontic brackets.
• Fluoride Varnish Group: 5% sodium fluoride varnish containing xylitol (Alvand Shimi, under license from VERICOM) was applied around the orthodontic brackets.
• Fluoride-Releasing Fissure Sealant Group: Fluoride-releasing fissure sealant (Pulpdent, Embrace Wetbond, USA) was applied around the orthodontic brackets and cured for 30 seconds.
• Non-Fluoride Fissure Sealant Group: Non-fluoride fissure sealant (Masterdent, Dentonics, USA) was applied around the orthodontic brackets and cured for 30 seconds.

The samples were dried, and acid etching and bonding were applied. Orthodontic brackets were then bonded to the center of the window on the buccal surface of each tooth.

To mimic the caries process, the teeth underwent cycles of demineralization and remineralization. The demineralization solution (pH = 4.5) and remineralization solution (artificial saliva, pH = 7) were prepared according to the following formulations [12,13]:

Demineralization Solution: CaCl2 (2.2 mM), NaH2PO4 (2.2 mM), Acetic acid (50 mM), NaCl (100 mM), NaF (1 ppm), NaN3 (0.02%).

Remineralization Solution: KCl (0.04%), NaCl (0.04%), CaCl2.2H2O (0.09%), NaH2PO4.2H2O (0.069%), MgCl2.6H2O (0.008%), Urea (0.05%), Ascorbic acid (0.01%), H2O (10 cc), Methyl-p-hydroxybenzoate (0.15%), PEG 6000 (7%), Glucose (0.1%).

Each tooth was immersed in the demineralization solution for 3 hours, followed by a brief rinse with distilled water. The teeth were then immersed in artificial saliva for 21 hours. This 24-hour cycle was repeated daily for 14 days, and all procedures were performed in an incubator at 37°C.

On the 14th day, the brackets were removed using a bracket remover plier without damaging the tooth structure. The materials applied around the brackets were also carefully removed. The microhardness of the enamel around the brackets in all four groups was then re-measured at three points around the bracket area using the Vickers microhardness tester under the same conditions as the initial measurements (200 N force, 10 seconds). The results were recorded in data forms for statistical analysis.

The mean and standard deviation of the microhardness values for each group were calculated separately. Comparative analysis between the groups was performed using one-way ANOVA test and p-value of less than 0.05 was considered statistically significant. All statistical analyses were conducted using SPSS ver.29. The study was approved by the Ethical Committee of Shahid Beheshti University of Medical Sciences with the ethical code IR.SBMU.DRC.1397.057, ensuring adherence to all ethical considerations throughout the research process.

In this study, 60 premolar teeth were divided into four groups for comparative analysis. To assess the normality of data distribution and to select the appropriate statistical test, the Shapiro-Wilk and Kolmogorov-Smirnov tests were applied across all groups. Based on these normality tests, a significance level greater than 0.05 was observed in all groups, indicating a normal distribution of the data. Consequently, a one-way ANOVA was employed for comparative analysis. The obtained results indicated that, by the end of the study, at least one group exhibited a statistically significant difference from the others. Therefore, post hoc multiple comparisons between groups were subsequently conducted using Tukey’s test. The mean and standard deviation of enamel microhardness in the four groups at the start and end of the study are presented in Table 1.

Table 1: Mean and standard deviation of enamel microhardness in all groups at the start and end of the study.

This table provides detailed information, including mean, standard deviation, and the range of values (minimum and maximum), for each group, allowing for a comprehensive comparison across conditions. Moreover, to visually highlight the comparative differences in mean microhardness values between the start and end of the study, a bar chart (Figure 1) is also included.

The comparison of enamel microhardness among the four groups at the start of the study revealed no statistically significant differences between groups (P-values range from 0.314 to 0.991) (Table 2).

Table 2: Comparison of enamel microhardness among all groups at the start of the study.

The comparison of enamel microhardness between the four groups at the end of the study indicated statistically significant differences between all groups (P-values range from lessthan 0.001 to 0.004), except between the control group and the non-fluoride fissure sealant group (P-value = 0.984) (Table 3).

Table 3: Comparison of enamel microhardness between all groups at the end of the study.

The findings of the present study demonstrate that conventional (non-fluoride) fissure sealant had minimal impact in preventing caries, underscoring the critical role of fluoride in caries prevention. Our results showed significantly higher enamel microhardness around orthodontic brackets in the fluoride varnish and fluoride-releasing fissure sealant groups compared to the control group, indicating substantial effectiveness in preventing early caries initiation in the form of WSLs around brackets. In contrast, non-fluoride fissure sealant did not significantly differ from the control group in terms of enamel microhardness, which suggests that fluoride presence is a key factor in enhancing microhardness and resisting demineralization.

These findings align with the study by Layane et al., which reported a 58% reduction in the risk of WSLs around orthodontic brackets in patients using fluoride-releasing materials compared to those not using fluoride products [14]. Additionally, Demito et al. observed a 38% reduction in caries depth in patients treated with fluoride varnish versus the control group [11]. The study by Mary et al. also supports these findings, showing reduced demineralization in groups treated with fluoride-releasing composites [15]. Moreover, Sardana et al. emphasize the importance of effective at-home plaque control using fluoride-containing products during orthodontic treatment [16].

Conversely, the study by Benham et al. indicated that non-fluoride fissure sealant could significantly increase the risk of WSL formation in orthodontic patients [17]. However, in the present study, the non-fluoride fissure sealant group showed no significant impact on enamel microhardness, likely due to the sealant's protective barrier, which may suffice in limiting WSL formation in the short term. Differences in results could stem from in vitro conditions and shorter study durations in our experiment compared to the Benham et al. study.

The mechanism by which fluoride reduces WSLs and dental caries can be summarized as follows:

• Incorporation into enamel structure, increasing resistance [18].
• Enhancement of remineralization [19].
• Inhibition of demineralization [19].

Suppression of cariogenic bacteria through various mechanisms, including the reduction of acid production [20,21].

As such, fluoride-containing materials are recommended for patients undergoing orthodontic treatment to maintain optimal enamel health.

Notably, our study found a statistically significant difference in enamel microhardness in favor of fluoride varnish over fluoride-releasing fissure sealant by day 14. This suggests that fluoride varnish may offer a more potent reduction in caries progression under similar conditions.

Fluoride varnishes such as Duraphat in Europe and Duraflur in the United States have been widely adopted due to their ease of application, efficiency in reducing fluoride ingestion, and suitability for children and individuals with special needs. Skold et al. found that fluoride varnish effectively reduced proximal caries and provided an economic advantage [22]. Likewise, Sonesson et al. conducted a systematic review and found that regular applications of fluoride varnish during orthodontic treatment with fixed appliances significantly reduced the prevalence of WSLs [23]. Furthermore, Hu et al. highlighted the effectiveness of remineralizing agents, including fluoride varnish, in preventing and treating orthodontically induced WSLs [24]. Consistently, Wadih et al. demonstrated that fluoride varnishes significantly reduced demineralization around, but not beneath, orthodontic brackets [10].

Perrini et al. also noted the positive impact of fluoride varnish in preventing WSLs, though the effect was comparable to regular oral hygiene practices [25]. Furthermore, He et al. reported that fluoride varnish effectively enhances remineralization [26]. Moreover, Li et al. compared fluoride varnish and fluoride-releasing fissure sealant, finding both effective in reducing caries without, however, a statistically significant difference [27]. Overall, various fluoride-based interventions can be effective; however, their clinical impact may somewhat depend on the amount of fluoride uptake by the dental structure [27,28].

Fluoride varnish and fluoride-releasing fissure sealant can significantly reduce the incidence of white spot lesions and caries around orthodontic brackets. Among these, fluoride varnish demonstrated superior effectiveness compared to fluoride-releasing fissure sealant. The primary function of non-fluoride fissure sealant appears to be limited to its sealing properties, without a notable effect on enamel microhardness. These findings suggest that fluoride-based interventions play a crucial role in caries prevention for orthodontic patients.

Acknowledgements

None

Authors’ Contributions

MKB: Methodology, Investigation, Writing - Original Draft, Visualization.

FK: Conceptualization, Supervision, Data Analysis, Review & Editing.

Competing Interests

None.