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Year : 2016  |  Volume : 14  |  Issue : 3  |  Page : 344-347

Effect of different concentrations of fluoride varnish on enamel surface microhardness: An in vitro randomized controlled study

Department of Pedodontics and Preventive Dentistry, The Oxford Dental College and Hospital, Bengaluru, Karnataka, India

Date of Web Publication28-Jul-2016

Correspondence Address:
Priya Subramaniam
Department of Pedodontics and Preventive Dentistry, The Oxford Dental College and Hospital, Hosur Road, Bommanahalli, Bengaluru - 560 068, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2319-5932.187172

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Introduction: Dental caries occurs as a result of demineralization-remineralization phases occurring alternately at the tooth surface. Fluoride varnishes have a caries-inhibiting effect on teeth through remineralization. The resulting enamel is resistant to acid dissolution. Aim: The aim of this study is to assess enamel surface microhardness (SMH) following varnish application with different fluoride concentrations. Materials and Methods: Ninety freshly extracted, caries-free premolar teeth were used. Teeth were sectioned to obtain enamel blocks from the buccal surface of crown. The blocks were serially polished and flattened, embedded in acrylic blocks and smoothened to achieve a flat surface. The samples were divided into three groups, namely, A, B, and C consisting of 30 enamel blocks each. In Group A, Fluor Protector® varnish and in Group B, Bi-Fluorid 10® varnish was applied. Group C served as controls. All samples were subjected to a demineralization-remineralization cycle for 7 days. The SMH of enamel was measured. Data obtained was subjected to statistical analysis using the Student's t-test and one-way ANOVA. Results: The mean values of enamel SMH of Groups A and B were 496.99 ± 4.81 and 449.47 ± 7.37 Vickers Hardness Number, respectively. Conclusion: Fluor Protector varnish showed significantly higher enamel SMH than that of the other two groups (P < 0.05).

Keywords: Demineralization, enamel, fluoride, hardness, remineralization, varnish

How to cite this article:
Subramaniam P, Telegeti S. Effect of different concentrations of fluoride varnish on enamel surface microhardness: An in vitro randomized controlled study. J Indian Assoc Public Health Dent 2016;14:344-7

How to cite this URL:
Subramaniam P, Telegeti S. Effect of different concentrations of fluoride varnish on enamel surface microhardness: An in vitro randomized controlled study. J Indian Assoc Public Health Dent [serial online] 2016 [cited 2022 Dec 3];14:344-7. Available from: https://www.jiaphd.org/text.asp?2016/14/3/344/187172

  Introduction Top

Dental caries is a dynamic process that is caused by alternating periods of demineralization- remineralization. Demineralization refers to the loss of minerals (mainly calcium and phosphate ions) from dental hydroxyapatite due to exposure to acidic compounds.[1] There is a delicate balance in the demineralization-remineralization phase occurring at the tooth surface. Prolonged multiple exposures to cariogenic challenges results in an imbalance, leading to the formation of an early enamel lesion, which may progress or may remain stable and remineralize with time. Since enamel lacks a cellular repair mechanism, the events surrounding the development and reversal of caries are dependent on physiochemical interactions occurring at the tooth pellicle/plaque interface.[2]

Fluoride is the most reactive element in the periodic table and its presence in the biofilm is important in limiting demineralization and stimulating remineralization of the hydroxyapatite crystal. There is convincing evidence that fluoride has a major effect on demineralization and remineralization of dental hard tissue.[2] The source of this fluoride could either be fluorapatite (formed due to the incorporation of fluoride into enamel) or calcium fluoride-like precipitates, which are formed on the enamel and in the plaque after application of topical fluoride.[2]

Fluoride varnishes were developed as an alternative to conventional topical fluorides. Fluoride varnish is a professionally applied adherent material which consists of a high concentration of fluoride as a salt or silane preparation in a fast drying, alcohol, and resin-based solution. Fluoride varnishes are a useful tool for caries prevention.[3] The fluoride uptakein vitro and in vivo, acid resistance, and caries-preventing effect of fluoride varnishes have been investigated in laboratory, animal, and human experimental studies.[4] Studies have shown that varnishes supply fluoride more efficiently than other topical agents.[5],[6] With fluoride varnishes, the amounts of fluoride exposure can be better controlled, and less chair-time is required compared with conventional solutions and gels.[6] The outcome of a review suggested that fluoride varnishes have a substantial caries-inhibiting effect in both permanent and primary teeth.[7]

Enamel is the hardest and one of the most durable load-bearing tissues of the body. It has attracted considerable interest from both material scientists and clinical practitioners due to its excellent mechanical properties.[8] Since the hardness of enamel has been shown to have considerable local variations, methods using a microscratch or microindentation have been preferred.[9] Remineralization makes the enamel more resistant to acid dissolution and prevents structural breakdown. Although, there is much information on the use of fluoride varnishes to inhibit tooth demineralization and enhance remineralization,[10] there appears to be a paucity of literature on a comparison of enamel hardness per se following application of varnishes with different fluoride concentrations. Various microhardness tests were considered as a measuring technique suitable for direct or indirect mineral quantification of de- or re-mineralization of enamel.[11] Thus, the aim of this study was to investigate the surface microhardness (SMH) of enamel following the application of two commercially available varnishes of different fluoride concentrations.

  Materials and Methods Top

Thisin vitro randomized controlled study was conducted over a period of 6 months. The study protocol was approved by the Institutional Ethic Committee. Ninety freshly extracted premolar teeth that were extracted from healthy individuals aged 13–18 years, for the purpose of orthodontic treatment were collected for the study. Written informed consent was obtained from patients as well as parents for the use of these teeth in this particular study.

Teeth with intact enamel surfaces and without white spot lesions or signs of decalcification were included in the study. The soft tissue deposits and calculus was removed from the teeth with a surface scaler. Teeth were cleaned using slurry of pumice. All teeth were then stored in distilled water containing 0.2% thymol to inhibit the microbial growth until the study was carried out. The teeth were then sectioned using Silverstone–Taylor hard tissue microtome to obtain enamel blocks (3 mm × 3 mm) from the most prominent portion on the buccal surface of crown. The blocks were serially polished and flattened using polishing grits no. 800, 1000, and 1200. These blocks were embedded in acrylic blocks and smoothened to achieve a flat surface.

All the samples were further divided into three groups, namely, Groups A, B, and C consisting of 30 enamel blocks each. On the enamel blocks of Group A, a thin layer of varnish containing fluoride (Fluor Protector ® Ivoclar Vivadent, Mumbai, India) was applied according to manufacturer's instructions using a soft bristled applicator tip provided by the manufacturer. On the enamel blocks of Group B, a thin layer of varnish containing fluoride (Bi-Fluorid 10® Voco GmbH, Mumbai, India) was applied according to manufacturer's instructions using a soft sponge pellet provided by the manufacturer. Enamel blocks of Group C were used as a control group, and no varnish was applied. The principal investigator coded all the enamel blocks before the assessment of SMH which was carried out by the co-investigator, who was blind to the type of sample tested.

After 24 h, the varnish was removed carefully from enamel blocks belonging to Groups A and B. The blocks were then washed with deionized water for 1 min. All the samples from each group were subjected to a demineralization-remineralization cycle simulating a high caries challenge.

The enamel blocks were immersed in demineralizing solution (2.0 mmol/L calcium, 2.0 mmol/L phosphate in 0.075 mol/L acetate buffer, 0.02 μm F/mL, pH 4.7) for 3 h (35.5 mL per block).[12] After 3 h, all the samples were removed from demineralization solution and dried using a blotting paper. Following, all the samples were immersed in remineralizing solution (1.5 mmol/L calcium, 0.9 mmol/L phosphate, 150 mmol/L potassium chloride in 0.1 mol/L tris buffer, 0.03 μm F/mL, pH 7.0) for 21 h (17.75 mL per block).[12] This cycle was repeated every day for 7 days.[13] On 8th day, all the samples were taken out of the solution and dried using blotting paper and SMH was assessed.[12],[13],[14],[15] The modified pH-cycling model allowed the evaluation of changes on the outermost enamel layer during caries development.[14]

The SMH of enamel was measured using the microhardness tester machine (Shimadzu HMV-2000/Shimadzu Corporation, Kyoto, Japan). SMH of each sample was assessed by making an indentation on enamel by applying 25 mg of the load for 10 s.[14],[16] The value displayed on the machine was noted. Five such indentations were made on left upper, left lower, central, right upper, and right lower part of the enamel block. The average SMH of 5 indents was calculated for each sample. The values were expressed in Vickers Hardness Number (VHN).[16],[17]

Data obtained was tabulated and subjected to statistical analysis using one-way ANOVA and Tukey multiple post hoc test.

  Results Top

[Table 1] shows a comparison of enamel SMH among three groups (ANOVA). Enamel in the control group (Group C) showed the lowest SMH. There was a significant difference in mean VHN values of groups (P< 0.001). The mean VHN value of Group A (Fluor Protector ® varnish) was significantly higher than that of the other two groups (P = 0.0001) [Table 2].
Table 1: Comparison of enamel surface micro hardness among three groups

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Table 2: Comparison of the study groups using Tukey post hoc test

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  Discussion Top

Human enamel is composed mainly of hydroxyapatite and fluorapatite together with traces of delta calcium metaphosphate. The evaluation of early surface changes in dental enamel seems to be sensitive for measuring the fluoride efficacy and may present the greatest predictive value with respect to anticaries effectiveness.[15]

The main purpose of varnish application is to retain and prolong the close contact between fluoride and the tooth for a long period.[18],[19] Concentrated fluoride ions in fluoride varnish cause globules of calcium fluoride-like material on the tooth surface. This response lowers the solubility of calcium and phosphate ions, releasing fluoride ions and increasing the saturation of calcium and phosphate ions in the microenvironment of the tooth. This reaction helps to prevent dissolution of calcium and phosphate ions and/or increases re-precipitation or remineralization of these lost minerals.[20],[21]

The dissolution of the fluoride from calcium fluoride is pH dependent. At lower pH, the coating is lost and an increased dissolution rate of calcium fluoride occurs. There is a release of fluoride and calcium ions. The fluoride ions may remain in the saliva or settle in free spaces on the crystal lattice of the tooth structure, producing fluorapatite or hydroxyfluorapatite which is more acid-stable than hydroxyapatite. Calcium fluoride globules, therefore, act as an efficient source of free fluoride ions during a cariogenic challenge.[2],[22],[23] Plaque fluoride influences enamel dissolution in more than one-way. Simultaneous dissolution of hydroxyapatite and reprecipitation of fluorapatite may coat individual enamel crystals with a fluoride-rich layer so that, while the total fluoride content is rather low, its effective solubility is more like that of fluorapatite.[24]

Fluor Protector contains 0.9% difluorsilane in a polyurethane varnish base with ethyl acetate and isoamyl propionate solvents. The fluoride content is equivalent to 0.1%, or 1000 ppm in solution.[19] As the solvents evaporate, the fluoride concentration at the tooth surface will increase to much higher values (nearly 10 times higher). Bi-Fluorid 10® contains 5% sodium fluoride equal to 22,600 ppm of fluoride and 5% calcium fluoride. It permits an immediate high fluoride release through sodium fluoride.

Fluor Protector ® has been shown to exhibit higher demineralization inhibitory effect, in comparison to Bi-Fluorid 12®.[25] In this study, an increase in mineral content following application of both fluoride varnishes could be responsible for higher VHN values obtained in the two experimental groups. Formation of fluorhydroxy apatite or fluorapatite could be the probable reason because fluorapatite is harder and more resistant to acid dissolution than hydroxyapatite.[2],[26]

In spite of a high release of fluoride from Bi-Flourid 10® varnish, the enamel treated with Fluor Protector ® showed significantly higher SMH than enamel treated with Bi-Flourid 10® varnish. This difference may be due to the amount and the type of F compound formed on the surface. Bi-Fluorid 10® varnish has a higher viscosity than Fluor Protector ® which makes it adhere better to demineralized areas rather than intact tooth surfaces.[27] Whereas, Fluor Protector ® varnish contains polyurethane-based compound difluorosilane and forms a thin transparent film which readily adheres even on intact tooth surfaces.

The SMH of enamel in the control group, which was not subjected to fluoride varnish, was lower but comparable to that of the enamel treated with Bi-Fluorid 10® varnish. This could be due to inherent fluoride incorporation into the enamel structure of these teeth (before extraction) from other fluoride sources, mainly the regular use of fluoridated dentifrices.

The importance of formulation effects on the remineralization performance of a fluoride varnish should be given consideration.

The outcome of the presentin vitro study may be different when carried out in the presence of dynamic interactions occurring at the tooth surface in the oral cavity. Therefore,in vivo studies should be conducted to validate the observations of this study.

  Conclusions Top

The SMH of enamel was seen to be higher following application of both fluoride varnishes. Fluor Protector ® varnish showed a more significant increase in the SMH of enamel than Bi-Fluorid 10® varnish.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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[PUBMED]  Medknow Journal  
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  [Table 1], [Table 2]

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