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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 1  |  Page : 28-32

Effect of modified 5% sodium fluoride on the surface roughness and hardness of the enamel of primary incisors: An in vitro study


1 Former Post Graduate Student, Department of Pediatric Dentistry, Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Saudi Arabia
2 Dean of Postgraduate Studies and Research, Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Saudi Arabia

Date of Web Publication14-Feb-2017

Correspondence Address:
Mansour Assery
Riyadh Colleges of Dentistry and Pharmacy, Riyadh
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1658-6816.200136

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  Abstract 

Background: There has been interest over the past decade in the principle that additives that promote the formation of calcium hydroxyapatite can increase the efficacy of sodium fluoride varnishes (NaF).
Aim: This study aimed to compare in vitro; the protective effect of a commercially available 5% NaF varnish with the protective effects of 5% NaF varnishes enhanced with functional tricalcium phosphate (fTCP) and amorphous calcium phosphate (ACP).
Methodology: A total of 120 primary incisors were divided into four groups of 30 teeth. Group 1 comprised a control group that received no fluoride varnish, Group 2, teeth treated with 5% NaF varnish, Group 3, treated with 5% NaF enhanced with fTCP and Group 4, teeth treated with 5% NaF enhanced with ACP. Surface roughness before and after pH cycling was measured using a profilometer, whereas surface microhardness was measured after pH cycling.
Results: Teeth in Group 4 (ACP) and Group 3 (fTCP) showed significantly higher surface microhardness values than the other groups, but there existed a large variation in the range of values obtained. No Significant differences were observed in the change in surface roughness among all groups.
Conclusion: The large variation seen in the microhardness values suggest that the effects of the addition of ACP or FTCP to 5% NaF varnish may not be predictable in primary teeth.

Keywords: Amorphous calcium phosphate, fluoride varnishes, pH cycling, sodium fluoride, surface roughness, tricalcium phosphate


How to cite this article:
Baothman A, Assery M. Effect of modified 5% sodium fluoride on the surface roughness and hardness of the enamel of primary incisors: An in vitro study. Saudi J Oral Sci 2017;4:28-32

How to cite this URL:
Baothman A, Assery M. Effect of modified 5% sodium fluoride on the surface roughness and hardness of the enamel of primary incisors: An in vitro study. Saudi J Oral Sci [serial online] 2017 [cited 2019 Jul 19];4:28-32. Available from: http://www.saudijos.org/text.asp?2017/4/1/28/200136


  Introduction Top


Topical fluorides have been documented to be an effective means to prevent dental caries.[1],[2],[3],[4] In recent years, authors have tended to agree that fluoride varnishes, especially 5% sodium fluoride (NaF) varnishes, offer an effective means of not only preventing caries but also arresting early enamel lesions.[5],[6],[7]

Fluoride varnishes have a topical effect on the structure of the enamel, increasing its resistance to demineralization by the formation of fluorohydroxyapatite.[8] Over the years efforts have been made to improve the efficacy of fluoride varnishes by experimenting with combinations of minerals which could not only prevent demineralization, but also increase remineralization.[9],[10] Two of these products, functional tricalcium phosphate (fTCP) and amorphous calcium phosphate (ACP) have been considered the most promising.[11],[12],[13]

The polymorph of tricalcium phosphate (a-TCP or Ca3[PO4]2) is the only single solid calcium phosphate capable of expeditious hydrolysis for the formation of HAp.[8] This property is of significance as the hydrolysis and formation of HAp is accelerated in the presence of NaF, and the HAp formed by such hydrolysis tends to have a greater uptake of fluoride than conventional HAp.[8],[14]

ACP has been shown to greatly increase remineralization of human enamel in vitro.[15],[16],[17] Despite some evidence for the increased efficacy of NaF varnishes modified with either fTCP [9],[18] or ACP,[19] there is little available literature on the comparative efficacy of these two systems or their effect on primary teeth.

Surface roughness and hardness offer a useful tool to determine the effects of demineralization and have been used to study the effectiveness of both fluoride regimen and different forms of fluoride.[20],[21] This study aimed to compare, in vitro, the protective effect of a commercially available 5% NaF varnish (Durashield ®, Sultan Pharmaceuticals, USA) with the protective effects of 5% NaF varnishes enhanced with tricalcium phosphate (Clinpro ™ White, 3M-ESPE, Seefeld Germany) and ACP (Enamel Pro ®, Premier ®, Pltymouth Meeting PA, USA), by examining changes in surface microhardness and surface roughness of the enamel of primary teeth following pH cycling.


  Methodology Top


Ethical clearance for the study was obtained from the research center of Riyadh Colleges of Dentistry and Pharmacy, and the proposal was assigned the registration number PGRP/43235004/6. Sample power was calculated using G-power 3.1 sample power calculator (Universtat Kiel, Germany). A sample size of 30 in each group was required to obtain a (1-β) of 0.95 and α of 0.05 in order for the sample to have adequate power.

A total of 120 sound human extracted primary incisors were collected immediately after extraction and stored in artificial saliva until the time of testing. Teeth that had no intact enamel surface, developmental defects and evidence of cracks, hypoplasia, caries, or exposure to chemical agents were excluded from the study. All teeth were embedded in clear acrylic resin to stabilize the teeth for placement in the jig of the microhardness tester and profilometer. The labial surface of the incisors was coated with nail varnish save for a window of 2 inches, which win diameter was made on the labial surface of the incisor using a nail varnish to facilitate measurement of surface roughness and microhardness.

The prepared teeth were then divided into four groups of 30 teeth each; Group 1 (Control Group) received no surface coating, Group 2: teeth treated with 5% NaF varnish (Durashield ®, Sultan Pharmaceuticals, USA); Group 3: teeth coated with 5% NaF enhanced with fTCP varnish (Clinpro™ White, 3M-ESPE, Seefeld Germany). Group 4: Teeth treated with 5% NaF enhanced with ACP (Enamel Pro ®, Premier ®, Plymouth Meeting PA, USA). Surface roughness of all teeth was measured in the 2-inch window using a contact profilometer (Taylor-Hobson, USA) before pH cycling.

Teeth were kept in a remineralizing solution (CaCl2 1.5 mM, NaHPO4 0.9 mM, and KCl 0.15 mM; pH of 7.0; 15 mL/tooth) for 20 h. Teeth were washed in deionized water between solutions and placed in artificial saliva for 30 min (CaCl2 [15 mg], MgCl2 [5 mg], KCl [0.1 g], KSCN [10 mg], Na2 HPO4 [40 mg], sodium carboxymethylcellulose [1.0 g], methylparaben [0.1 g], and water [1 L]; pH of 7.0). Teeth were then kept in demineralizing solution (CaCl2 2.2 mM, NaH2 PO4 2.2 mM and acetic acid 0.05 M; pH of 4.5, adjusted with KOH 1M; 15 mL/tooth) for 3 and a half hours to complete the 24 h cycle.[22] This cycle was repeated for 10 days.

After pH cycling surface roughness was measured using the contact profilometer and micro-hardness measurements of primary dental enamel were made using a micro-hardness tester (Micromet 2100 series Microhardness Testers, USA) with a Vickers indenter and static load of 25 g and with 15 s of dwell time.

The roughness of the enamel of the different groups before and after pH cycling was compared using the one-way ANOVA and paired t-test. The microhardness of the enamel of the different groups after pH cycling was compared using the one-way ANOVA and the Scheffe's post hoc test was used to determine the significance of intergroup variation. All statistical analyses were performed using the SPSS version 20 data processing software (IBM corp. Armonk NY, USA).


  Results Top


pH cycling resulted in a significant increase in the surface roughness across all groups (t = −2.655, P = 0.009), however, when the post-pH cycling surface roughness values were compared the one-way ANOVA showed no significant differences in the surface roughness (F = 0.308, P = 0.891).

When the surface microhardness values across groups were observed it was seen that the 5% NaF enhanced with ACP (Group 4) showed the highest mean Vickers hardness number (VHN) while the control group (Group 1) showed the lowest mean VHN [Table 1]. The Scheffe's post hoc test showed that the mean VHN in Group 4 was significantly higher than all other groups. The mean VHN of Group 2 (5% NaF + FTCP) and Group 3 (5% NaF) were significantly lower than those of Group 4 but significantly higher than the control group [Table 2].
Table 1: Descriptive Statistics of Microhardness (VHN) and surface roughness

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Table 2: Homogeneous subsets of the Post hoc test for microhardness

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The wide range of values seen in both surface roughness and microhardness suggest a large variation in the action of the additives to the NaF varnish. Teeth in group 4 (5% NaF + ACP) showed both the highest (VHN = 618) and lowest (VHN = 124) scores. Similarly, the samples in this group also showed the greatest increase (−3.96 µm) and decrease (+3.02 µm) in surface roughness. The analysis of kurtosis and skew was done to determine whether these distributions were acceptable or not. The analysis of skew revealed an acceptable symmetry of distribution across groups. The analysis of kurtosis revealed that while the control group and the Group 2 (5% NaF) showed acceptable kurtosis the level of kurtosis seen in groups 3 (5% NaF + TCP).


  Discussion Top


The role of 5% NaF varnishes in the prevention of dental caries is today considered significant.[1] There are a series of studies and evidence from literature collected over the past decade that strongly supports the caries preventive role of fluoride varnishes; both, as an adjunct to already existing water and toothpaste fluoridation [23],[24],[25] and also as a stand-alone measure.[1],[26],[27] The role of additives such as tricalcium phosphate or ACP is, however, a topic of debate.

ACP wasfirst introduced by Reynolds in 1998, and there has been significant evidence of its effectiveness as a remineralizing agent. There is little evidence to show that it increases the efficacy of 5% NaF varnish. Although there is some evidence to show that low concentrations of NaF can improve the efficacy of ACP, the converse has not been proven.[28] Similarly, despite in vitro evidence to support the concept of increased microhardness of enamel when treated with fTCP additives to 5% NaF varnish, little is known about the impact such additives have on surface roughness. The aim of this study was to evaluate the impact of these two different additives on both surface microhardness and surface roughness when subjected to pH cycling.

When the changes in surface roughness were evaluated using a profilometer, it was seen that pH cycling induced an increased surface roughness across all groups. Furthermore, the lack of significant difference in surface roughness, across groups, suggests that despite their protective action on the enamel and increase in surface microhardness, fluoride varnishes are unable to cause or prevent changes in surface roughness induced in the enamel following pH cycling.

While the mechanism of action of fluoride is based on the interaction with calcium hydroxyapatite, studies have shown that the structure of enamel could influence the ultimate clinical efficacy of the fluoride.[1] Studies that have yielded positive results on in vitro bovine or rat models have often failed to produce similar results in human mouths.[29],[30] In this respect, there is a need to assess the impact of fluoride on primary enamel. Gatti et al. suggested that while the overall effects of fluoridated dentifrices on primary teeth were similar to those on permanent teeth, there were certain in vitro differences.[22] Primary enamel has a far greater amount of structure-less enamel making the transfer of fluoride ions across the crystals less pronounced than in permanent teeth. In this respect, the formation of new hydroxyapatite from the hydrolysis an uptake of tricalcium phosphate salts may be significant.[8] Our results showed compared across groups, it was seen that the ACP group showed the highest mean increase in surface hardness, followed by the fTCP group. The lack of statistical significance among the results, however, could be attributed to the large variations in surface hardness observed in the ACP group. While the presence of structure-less enamel could explain this in some part, consideration must also be given to the mechanism of action of ACP, fTCP, and the impact of pH cycling.

There have been previous attempts made to evaluate the effectiveness of additives to NaF varnishes. These have been based on research that showed that the provision of dissolved fluoride is the key to successful therapy. The source of this fluoride could either be fluorapatite or calcium fluoride (CaF2) (like) precipitates, which are formed on the enamel and in the plaque after application of topical fluoride.[31] However, the results with varnishes incorporating CaF2 have not been promising.[24] In their comparison of CaF modified varnish with 5% NaF, Ferreira et al. found that both varnish formulations tested produced similar clinical effects.[24] While there have been promising in vitro results with the addition of fTCP to NaF varnish,[32] there has been no in vivo confirmation of this. The results of our study show that while both ACP and fTCP greatly increase the mean surface hardness of the enamel, variations among the structure of these teeth make these results statistically insignificant. However, the wide variation between the different samples could explain why despite positive in vitro results, the clinical evidence on the benefit of these additives remains inconclusive.

The results of our study seem to indicate that while the addition of substances such as ACP and fTCP greatly improve the ability of some primary teeth to withstand demineralization induced by pH cycling, variations exist between teeth. Research is needed into the microscopic interaction between primary enamel and these additives to help standardize the action of fTCP and ACP in conjunction with 5% NaF varnish in protecting primary teeth.

NaF varnish with or without additives (either ACP or fTCP) are ineffective in reducing the surface roughness changes induced by acid attack.


  Conclusion Top


It can be stated that although not detrimental in any way, enhancement of the action of 5% NaF by either ACP or fTCP, seems to be unpredictable in primary teeth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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