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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 13  |  Issue : 2  |  Page : 63-67

Effect of fluoride agents on the color stability of esthetic restorative materials


1 Department of Dental Materials, Ziauddin College of Dentistry, Ziauddin University, Karachi, Pakistan
2 Department of Dental Materials, Jinnah Sindh Medical University, Karachi, Pakistan
3 Department of Statistics, Dow University, Karachi, Pakistan

Date of Submission29-Mar-2016
Date of Acceptance30-Mar-2016
Date of Web Publication23-Aug-2016

Correspondence Address:
Nazish Fatima
Ziuddin Dental College, Dental Materials, c-1, 1st Floor, Anjum Complex, Pechs 2, Karachi, Sindh 74200
Pakistan
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-8574.188911

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  Abstract 


Objective
The aim of the study was to estimate the effect of acidulated phosphate fluoride (APF) gel and fluoride varnish on the color stability of esthetic restorative materials.
Methodology
The materials included were glass ionomer cement, resin-modified glass ionomer cement, and composite resin. A Teflon matrix (12×2 mm) mold was used to fabricate 108 specimens from all restorative materials. Further, 36 disks of each restorative material were then randomly divided into three groups (n = 12) according to the fluoride application: deionized water (control), APF (1.23%), and fluoride varnish. Color change was measured by means of a spectrophotometer using a CIE L*a*b* (Comission International l´Eclairage) system before and 24 h after fluoride treatment. Statistical comparisons were made using first mixed model repeated measure analysis of variance on the transform ranked data under the assumption of non-normal data and to see which main or interaction effect was significant.
Results
In control groups, when the baseline and final readings of glagg ionomer cement, resinmodified glass ionomer cement, and composite materials were compared for color changes, similar values were observed and hence results were nonsignificant. When all materials were compared for color changes before and after the application of APF, highly significant mean differences were found among the groups. Hence, application of APF results in a highly significant color change in all materials compared with varnish application.
Conclusion
Topical fluoride agents – either fluoride varnish or APF gels – cause discoloration in all esthetic restorative materials. However, this discoloration is not visually perceptible.

Keywords: acidulated phosphate fluoride, color stability, dental composite, glass ionomer cement, varnish


How to cite this article:
Fatima N, Nayab T, Farooqui WA. Effect of fluoride agents on the color stability of esthetic restorative materials. Tanta Dent J 2016;13:63-7

How to cite this URL:
Fatima N, Nayab T, Farooqui WA. Effect of fluoride agents on the color stability of esthetic restorative materials. Tanta Dent J [serial online] 2016 [cited 2017 Jun 27];13:63-7. Available from: http://www.tmj.eg.net/text.asp?2016/13/2/63/188911




  Introduction Top


Tooth color restorative materials have attained popularity because of their esthetic value and effectiveness in tissue preservation. In dentistry, glass ionomer cements are recommended for occlusal, proximal, labial, and lingual restorations as well as for the generation of sealants, orthodontic bands, tunnel restorations, and cementation of stainless steel crowns [1]. Similarly, composites are in wide demand because of their excellent esthetics, adequate strength, and moderate cost compared with ceramics, and their ability to micromechanically bond with the tooth structure [2]. In patients at moderate to high risk of developing caries, topical application of fluoride (TAF) from different sources can improve the condition and its effectiveness has been widely accepted and studied [3],[4]. Several types of topical fluoride preparations are available, such as 1.23 or 2% gels, 0.05% solutions for daily mouth rinsing, and varnishes indicative for intensive therapy [5]. According to the recommendations, patients susceptible to dental caries should receive TAF for prevention; 1.23% acidulated phosphate fluoride (APF) gel and 2% neutral fluoride gel should be applied on the teeth for 2 min every 6 months [6],[7]. Despite the benefits of professionally applied remineralizing agents some factors need to be considered: APF, stannous fluoride, and sodium fluoride can etch and stain esthetic restorative materials because of microleakage of fluoride and changes in surface morphology due to erosion of restorations [8]. Various in-vitro studies have confirmed that the surface of GIC, COMPOSITE AND CERAMICS materials such as glass ionomer cement and composite and dental ceramics can be distorted by the use of TAF, as it reduces their microhardness, and increases surface roughness and porosity, allowing dye penetration and hydrolysis of the polymeric matrix. The fluoride ions of sodium fluoride present in topical fluoride solutions and hydrofluoric acid are commonly present in acidulated phosphate gel, which dissolves the surface layer of restorative materials and promotes surface roughness, which consequently reduces the color stability [9],[10].

Thus there is a need to find whether this discoloration of restorative material is within clinically acceptable limits and whether the effects of etching and staining can be modified if artificial saliva is used as storage solution. Therefore, the main aim of the current study was to determine the effect of fluoride varnish and APF gel on the color stability of esthetic restorative materials.

The hypothesis tested was that APF gel makes the surface of restorative materials rougher, affecting light reflection and promoting more color alteration compared with fluoride varnish.


  Methodology Top


A total of 108 disk specimens of all three restorative materials were prepared. Thirty-six disks for glass ionomer cement (Vitrofil; FAS: aluminum fluorosilicate glass, PPA: polyacrylic acid, water Brazil, DFL dental product), Thirty six discs of resin-modified glass ionomer cement (Vitremer; FAS: aluminum fluorosilicate glass, PMAA: polymethacrylic acid, HEMA: hydroxyethylmethacrylate 3M dental products; St Paul, Minnesota, USA), and thirty six discs of composite resin [Filtek Z350 resin composite matrix: Bis-GMA, UDMA, Bis-EMA, and TEGDMA filler: (zirconia/silica) nanofillers of silicon (5–75 nm), zircon/silicon nanoclusters (0.6–1.4 μm) – nanofiller 78.5% wt, 59.5% vol 3M ESPE dental product (USA)] were fabricated.

Disc preparation

A polyethylene sheet and glass slide were placed under the mold. Vitremer and Vitrofil were mixed manually according to the manufacturer's instructions. These mixed materials and unset pastes of composite were placed in the polytetrafluoroethylene (Teflon) mold (10 × 2.5 mm). After filling the mold, mylar strips and glass slides were placed over the filled mold and light pressure was applied. Vitremer and composite were light cured at a distance of 1 mm for 40 s on each side with LED curing lamp Mectron (intensity 1.000 mW/cm 2 starlight pro-led curing lamp; Mectron straight pro-led Carasco, Italy). Vitrofil specimens were left undisturbed for 5 min for setting. After setting, glass slides and mylar strips were removed. Discs with voids, bubbles, and an uneven rough surface texture were excluded from the study.

Groups

Each group contained 36 discs, which were further divided into three subgroups, each containing 12 samples, as shown in [Table 1].
Table 1: Division of subgroups is given

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Fluoride application

The control groups (A1, B1, and C1) were not coated with any fluoride agent. In the control groups, the test specimens were immersed in artificial saliva at 37°C during the entire period of the experiment and saliva was changed after 24 h. In the experimental groups (A2, B2, and C) specimens were treated with fluoride varnish. A soft minibrush was used to apply fluoride varnishes (Prevident; Colgate Oral Pharmaceutical Inc., 300 Park Avenue, New York). Upon coating, each specimen was suspended in air to dry for ∼5 min. All specimens were then individually cleaned for 2 min with a toothbrush and immersed in deionized water at 37°C for 30 min to obtain chemical equilibrium at the material surface, to provide an intermediate period between tests later on; it was stored in artificial saliva. In groups A3, B3, and C3, the fluoride gel 1.23% APF (Gelato fluoride gels; Keystones Industry, Gibbstown NJ, USA) was applied in two cycles of 4-min application, simulating 1 year of clinical use. After this period, the test specimens were washed and immersed in deionized water at 37°C for 30 min to obtain chemical equilibrium at the material surface to provide an intermediate period between tests later on; it was stored in artificial saliva.

Color evaluation

Baseline color measurements were taken with a spectrophotometer (Data color; SF 600; Plus-CT; USA) using a CIE L*a*b* system (Comission International l´Eclairage). The analyzed color parameters were the values for L*, a*, and b*, where L* is the luminosity, a* represents the color variation between green-red, and b* represents the color variation between blue-yellow. The spectrophotometer was calibrated before each color analysis session of specimens in accordance with the manufacturer's instruction. For color analysis, each specimen was placed inside the central orifice of the white, opaque Teflon matrix. A mortise device was placed on the white Teflon, which was positioned over the specimen to standardize the contact of the tip from the spectrophotometer to the specimen surface at a 900 angle. Color values were measured before and after fluoride application. The total color variation was ΔE. It was calculated as per the following equation:



Statistical analysis

Data were analyzed using IBM SPSS, version 22.0, and the results were presented as mean±SD with confidence interval. Statistical comparisons were made using first mixed model repeated measure analysis of variance on the transform ranked data under the assumption of non-normal distribution of data and to analyze which interactive effect was significant. Followed by wilcoxon rank test for intragroup comparisons. Partial η2 was also computed to see which main or interaction factor had a more significant effect. A P value of 0.01 or less was considered statistically significant. It was noticed that in computation of P value for all comparisons of intragroup, as our hypothesis was to test average change in length of color stability after application was greater than the average change in length of color stability before application.


  Results Top


Mean square values have been provided if any researcher wants to calculate the sample size from this study in the future, as shown in [Table 2]. Repeated measure analysis of variance was applied to test the significance of differences within specimens. [Table 3] shows the overall main and interaction effect of significance. Highly significant differences were found among all interactions, except application with materials, as it showed only 7% contribution in affecting color change. There was a larger contribution from topical fluoride agents (69%). Mean square values have been provided if any researcher wants to calculate the sample size from this study in the future, as shown in [Table 2].
Table 2: Tests of within-specimen contrasts

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Table 3: Comparison of change in color stability between GIC, RMGIC and composite following fluoride application of varnish, acidulated phosphate fluoride

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[Table 3] shows all combinations of groups, their mean, and SD. For any topical fluoride agent, all specimens gave similar results in the control group when the baseline and final color readings of GIC, RMGIC and composite materials were compared. Therefore, initial and final measurements are not depicted in the table, although readings were noted for controls. After the application of APF, highly significant mean differences were found among the groups. The results obtained showed that APF application resulted in a larger significant change in all materials instead of varnish application. However, composite material give the same and least mean difference when compared for color changes before and after the application of APF or varnish. Almost the same difference was found when the GIC and RMGIC materials were compared for color changes before and after the application of fluoride varnish or APF.


  Discussion Top


The two major groups of tooth color restorative materials used by dentists over the past 30 years are glass ionomer cements, composites, and variants of these materials [1],[11]. Application of fluoride remineralizing agents to the tooth surface was effective in preventing dental caries. The most common professionally applied remineralizing agents are fluoride varnishes and APF gel. In the present study, the limit of clinical acceptance adopted for direct restorative materials was ΔE less than 3.3. Therefore, the alternative hypothesis of the current study was accepted, as there was significant color alteration after fluoride agent application. Application of fluoride varnish on the restorative materials resulted in a significant change in color. These results were comparable with those obtained in other studies [12],[13]. Researches have also reported that the composition and size of the filler particles affect both color and surface roughness of the restorative material. Moreover, the relative susceptibility of glass ionomer to color change could be attributed to the porosity, cracking, and surface roughness of the glass particles. Another possible reason was that rough surfaces mechanically retain stains more efficiently compared with smooth ones [12]. In this study, application of APF gel on the GIC and RMGIC materials resulted in significant change in color at the end of the experimental period, and increase in surface roughness of the GIC material. These results corroborated those of other studies in which APF treatment increased the surface roughness of the GIC material [14],[15]. The application of APF gel on the composites resulted in a significant change in color as composite formulation affected the color stability of composites. Furthermore, TEGDMA-based composites absorb more water than UDMA-based composites, which in turn absorb less water than Bis-GMA-based types [16],[17]. However, according to Choi and colleagues, the combination of Bis-GMA and TEGDMA monomers provides less color stability to the composite. In the current study the composite contained a combination of Bis-GMA and TEGDMA monomers [18]. The solvent inside the resin matrix may cause deterioration of the resin matrix/filler interface, a phenomenon called plasticization, causing bond relaxation among polymer chains resulting in altered color. Moreover, fluoride solutions can also cause significant oxidation to the residual carbon–carbon double bonds (C=C) because of their high reactivity, which leads to the possible formation of formaldehyde, thus causing the plasticization of the polymeric network [19]. Therefore, the longer the action of fluoride solution on the composites, the greater will be its color alteration, which justifies the results of the present study. Moreover, fluoride ion may cause depolymerization of the resin matrix/filler interface, breaking chemical bonds inside the composite, allowing water and/or solvent penetration and further degrading of the resin matrix. The greater the action of fluoride ions at the resin matrix/filler interfaces in the composite, the greater the physical–mechanical properties affected [20]. The smaller size of filler in the composite increases its color stability. Hosoya and colleagues had observed in their study that APF gel application did not cause significant color alteration in nanospherical filler composites. This did not agree with the findings of the present study, as in our study the composite had also shown significant color change [21]. APF etches enamel, allowing better penetration of fluoride. However, hydrogen ions from phosphoric acid and fluoride ions from sodium fluoride were also present in the composition of this gel, which can react and form hydrofluoric acid that dissolves the surface of restorative materials that have inorganic components in their composition, such as ceramics, glass ionomers, and particularly composite, creating gaps and increasing the surface roughness [10],[20].


  Conclusion Top


Topical fluoride agents, either fluoride varnish or APF gels, cause discoloration of all esthetic restorative materials. However, this discoloration is not visually perceptible.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3]



 

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