Year : 2010 | Volume
: 28 | Issue : 2 | Page : 84--90
Effect of fluorides from various restorative materials on remineralization of adjacent tooth: An in vitro study
MS Baliga1, SS Bhat2,
1 Reader, Department of Pedodontics and Preventive Dentistry, K.D. Dental College and Hospital, Mathura, India
2 Professor and Head, Department of Pedodontics and Preventive Dentistry, Yenepoya Dental College and Hospital, Mangalore, India
M S Baliga
Department of Pedodontics and Preventive Dentistry, K.D. Dental College and Hospital, Mathura
The aim of the study was to evaluate the extent of surface zone remineralization and the effect of fluoride at the inter-proximal adjacent tooth surface, using restorative materials FusionAlloy, Ketac-Fil and Heliomolar. Ninety extracted molar teeth were used of which 45 were placed in artificial caries for 10 weeks. The remaining 45 teeth were filled with the respective restorative materials, mounted with the artificial carious teeth in proximal contact with plaster and placed in artificial saliva for a period of 28 days. Finally, sectioning of artificially carious teeth was done mesio-distally and observed under the optical microscope and scanning electron microscope. Comparison among the groups was done by one-way analysis of variance [ANOVA] and Fischer«SQ»s F test. Intercomparison between the groups was done by using Dunnett«SQ»s t-test. Results obtained from transmitted electron microscopic and scanning electron microscopic observations were almost similar with the Ketac-Fil and Heliomolar showing better results in surface zone remineralization compared to FusionAlloy. Also, Ketac-Fil is a good material in releasing fluoride to remineralize enamel when compared to Heliomolar and FusionAlloy. Thus, it can be used mainly in class II cavity restorations of primary and permanent dentitions due to the potential ability of fluoride containing glass ionomer cements and composite resins to remineralize incipient carious lesions on adjacent teeth.
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Baliga M S, Bhat S S. Effect of fluorides from various restorative materials on remineralization of adjacent tooth: An in vitro study.J Indian Soc Pedod Prev Dent 2010;28:84-90
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Baliga M S, Bhat S S. Effect of fluorides from various restorative materials on remineralization of adjacent tooth: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2020 May 27 ];28:84-90
Available from: http://www.jisppd.com/text.asp?2010/28/2/84/66742
The role of fluoride in preventive dentistry was established as early as 1892 when Sir James Crichton Browne found the direct relationship between fluoride ions and caries experience of the community. Since then it has been conclusively proved that fluoride increases the resistance of enamel to caries. Fluoride is one of those remarkable elements that have not only chemical qualities but also physiological properties of great interest and importance to the dentist. The beneficial effects of fluoride on human dentition have led to its incorporation into restorative materials, which elevated its anticariogenic effect. Varying data are available suggesting that leached fluoride is in part subsequently taken up by tooth structure.
The aim of the study was to evaluate the effect of fluoride at the inter-proximal adjacent tooth surface using different restorative materials. The restorative materials used were FusionAlloy, Ketac-Fil and Heliomolar.
The objectives of this study were to
Determine the extent of surface zone remineralization and thus the efficiency of various restorative materials in releasing fluorides to enhance remineralization andDetermine whether fluorides from restorative materials help in remineralization of artificially created enamel carious lesions of interproximal adjacent tooth surface.
Materials and Methods
Sample collection and preparation
[Table 1] shows the materials used in this study. Ninety human mandibular permanent molar teeth were collected from oral surgery department. After extraction, each of the 90 teeth were scrubbed, cleaned and checked for developmental defects, enamel cracks or caries. The teeth were then stored in thymol and were retained in the same solution until the study was initiated. Before use, the teeth were washed in water and cleaned with an aqueous slurry of pumice using a hand piece and rubber cup.
Forty-five teeth collected were painted with acid-resistant varnish leaving a window of around 3 mm diameter on the proximal contact area. The teeth were then immersed in acidified gelatin gel (artificial caries) for storage at room temperature for a period of 10 weeks. The acidified gelatin gel was changed at 3-4 week intervals. The parameter used in preparing gelatin media was as specified by Hattab et al. in 1989. The gel contained 20% gelatin, 1 g/L hydroxyapatite and 0.10% thymol adjusted to pH 4 by adding lactic acid.
Proximal box preparation and restoration
The remaining 45 teeth stored in thymol were removed and an identical proximal box was prepared measuring 2.0 mm mesio-distally, 2 mm occluso-gingivally and 2 mm in depth on the contact enamel surface with a diamond bur fitted in a high-speed hand piece with constant water spray. The size of the cavities was standardized using a divider, graduated scale and a calibrated periodontal probe. The bur was always held at right angles to the tooth surface to produce a cavosurface angle close to 90°.
The teeth were equally divided into three groups with 15 specimens in each group. They are as follows.
Group I: Cavities were prepared of the proper dimensions. Fusion Alloy was mixed according to manufacturer's instructions, condensed into the cavities and burnished.
Group II: The cavities were conditioned with 10% polyacrylic acid for 20 seconds using a cotton pellet. They were rinsed with water for 10 seconds and blotted dry with tissue paper. Ketac-Fil glass ionomer cement was mixed according to manufacturer's instruction, filled into the cavities and contoured using Mylar strip. The Mylar strip was removed after the material was set and Fuji glass ionomer varnish was coated onto the surface of restorations.
Group III: The cavities were dried and an acid etchant containing 37% orthophosphoric acid was applied on the enamel surface of prepared cavity for 30 seconds. It was rinsed with water for 15 seconds and blow dried with air free of oil or water contamination. The acid-etched enamel had a dull frosty white appearance. One drop of adhesive was applied with a clear brush in a uniform layer on the etched enamel. The excessive adhesive was removed by gentle airblow and curing was done for 10 seconds with a visible light source. Heliomolar (R) was duly filled into the cavities and adapted using Mylar strip. Light curing was done for 40 seconds according to manufacturer's instructions with spectrum light source as close as possible and the Mylar strip was removed. All the specimens were stored in normal saline at room temperature for 48 hours after which finishing and polishing were carried out.
Mounting of samples
These teeth were then mounted with the artificial carious lesion having an inter-proximal contact with the adjacent tooth restoration on plaster model. These 45 pairs of teeth were placed in artificial saliva prepared with 20 mM sodium bicarbonate, 3 mM sodium dihydrogen phosphate and 1 mM calcium chloride. In 4-week interval during which the saliva was replenished every 2 weeks, all the teeth were made to undergo thermocycling in a waterbath for 500 cycles maintained at 5ΊC and 55ΊC with a dwell time of 30 seconds to simulate oral hygiene conditions. After 28 days, the mounted teeth were separated and sectioned mesio-distally using a diamond disc and lathe with continuous water supply. Any irregularities in the tooth structure unsuitable for measurements were discarded.
Ground sections were made by rubbing against the Arkansas stone. Samples were mounted on glass slide using DPX solution and viewed under the transmitted light microscope to detect the depth of outer surface zone termed as remineralization caused due to release of fluorides from various restorative materials. Measurements were made using eyepiece graticule and stage micrometer. Comparison among the groups was done by one-way analysis of variance [ANOVA] and Fischer's F test. Intercomparison between the groups was done by using Dunnett's t-test.
Scanning electron microscope analysis
For scanning electron microscope (SEM) analysis, the polished samples (with alumina slurry) were mounted on a metallic stub coated with gold in an ion-sputtering unit and viewed under the SEM at different magnifications.
Transmitted light microscopic analysis
Group I: Enamel adjacent to FusionAlloy showed a surface zone (remineralization) depth with a range of 0.0038-0.0190 mm [Figure 1].
Group II: Enamel adjacent to Ketac-Fil showed a surface zone (remineralization) depth with a range of 0.0798-0.1140 mm [Figure 2].
Group III: Enamel adjacent to Heliomolar showed a surface zone (remineralization) depth with a range of 0.0228-0.0494 mm [Figure 3].
F= 374.613 and P < 0.001 determined by ANOVA were very highly significant.
[Table 2] shows the quantitative measurement of the surface zone remineralization between the three groups (in millimeters).
[Table 3] is given the quantitative analysis of the surface zone remineralization between the three groups.
[Table 4],[Table 5],[Table 6] show the comparison between the groups [Dunnett's t-test]. [Table 4] shows the comparison between FusionAlloy and Ketac-Fil and a t value of 14.965 and a P value of <0.001 is very highly significant.
[Table 5] shows the comparison between FusionAlloy and Heliomolar and a t value of 10.411 and a P value of <0.001 is very highly significant.
[Table 6] shows the comparison between Heliomolar and Ketac-Fil and a t value of 26.32 and a P value of <0.001 is very highly significant.
Scanning electron microscopic analysis
Studies done under SEM revealed that the different samples showed distinguishable features in the extent of remineralization seen in the surface zone of enamel. The values obtained from these studies showed the extent of remineralization to be approximately 0.00384 mm for FusionAlloy [Figure 4], 0.01296 mm for Ketac-Fil [Figure 5] and 0.00664 mm for Heliomolar [Figure 6].
Smooth surface inter-proximal caries radiographically presents as a single lesion, or often as inter-proximal lesions involving both the teeth that are in contact. With tooth cavity preparation of a single lesion it was observed that the adjacent tooth that did not exhibit radiographic caries often has a visible white spot incipient lesion. The inhibition of incipient caries offers an excellent opportunity for fluoridated materials in preventive dentistry, as they appear to improve caries inhibition over nonfluoridated materials.
A sustained fluoride release and an intimate contact of restoration to the tooth margins are needed to facilitate the exchange of fluoride with the hydroxyapatite of enamel.  Continual high frequency, low concentration fluoride release has been recommended as a desirable treatment strategy to prevent tooth demineralization and enhance the remineralization. 
Glass ionomer cements and composite resins exhibit a promising future in the field of preventive restorative dentistry and appear to fulfill the demands of an ideal restorative material possessing adequate anticariogenic properties.  Various studies have reported fluoride-releasing properties of self-cure glass ionomer cements in vitro and in vivo., Studies conducted by Reteif et al. have proved the ability of enamel adjacent to glass ionomer restoration for fluoride uptake and resisting demineralization. In vitro studies in an acidified gel medium by Hattab et al. and Dionysopoulos et al. have shown significantly less demineralization around the restoration and absence of recurrent wall lesion in teeth filled with glass ionomer cements when compared with the teeth filled with composite and amalgam. However, in vitro studies by Temin  have shown appreciable fluoride uptake by the adjacent enamel proving its ability to have adequate anticariogenic properties.
At present, there is a tremendous resurgence in the interest of glass ionomer and composite resin restorative material with its latest developments. There is limited information in the literature regarding the efficacy of these materials in preventing incipient inter-proximal lesions. This study was conducted for comparative evaluation of incipient inter-proximal lesion inhibition by different restorative materials that are being used in daily clinical practice.
Studies conducted by Silverstone , in 1966 and 1968 have shown that artificial caries lesions exhibit histologic characteristics similar to that of naturally occurring lesions. Two basic systems exist inducing artificial caries like lesion, i.e., chemical system and bacterial system. Simplest type of chemical system is to use an acid buffer that produces demineralization at a faster rate, but this does not resemble caries.  Bacterial system was not found as well defined as acid gel system because of the problems encountered by a rapid drop in pH.
Acidified gelatin gel technique is found to be a valuable tool in creating artificial caries like lesion; when examined under polarized microscope, it appears indistinguishable from natural lesion. This technique was preferred over other caries media in this study because a constant pH can be maintained. Viscosity of gel stimulates a layer of plaque, and moreover, it is a simple technique. The gel was maintained at pH 4 and thymol was added to prevent bacterial growth. Addition of hydroxyapatite serves as a reservoir of calcium and phosphorous in the media.
Surface zone of enamel caries in natural as well as artificial caries remains intact and well mineralized. This is due to calcium and phosphorous deposition from subsurface dissolution of plaque. One of the modes of action of fluoride in an enamel microenvironment is to stimulate conversion of calcium and phosphorous to fluoridated apatite. Gelatin gel surrounding the teeth serves as in-vitro plaque, acting as a reservoir of fluoride leached out from restorative material, and helps in surface remineralization. Hals et al. have reported that caries lesion develops as early as 3 weeks in gelatin gel. Other studies have reported formation of caries like lesion between 8 and 15 weeks. ,,, In this study, tooth specimens were subjected to an artificial caries challenge for 10 weeks.
The specimens were ground to approximately 50 μm and were examined under transmitted light microscope. The lesion consisted of an outer surface zone showing features of remineralization. In this study, all the specimens examined showed the presence of an outer surface zone, though the depth of the zone varied with type of restorative material used. Depth of outer surface zone was measured in millimeters and varied from 0.0798 to 0.1140 mm for Ketac-Fil, from 0.0228 to 0.0494 mm for Heliomolar and from 0.0038 to 0.0190 mm for FusionAlloy. This study revealed maximum depth of outer surface zone for Ketac-Fil while FusionAlloy showed minimum outer surface zone depth.
In general, the caries inhibitory effect of self-cure glass ionomer was found to be superior when compared with that of composite and amalgam. Several authors have reported a comparative reduction in depth of outer surface lesion in-vitro around fluoride-releasing restorative materials. ,,,
It is well known that the progression of caries depends on several factors other than the local environment. The mineral content of enamel, particularly the amount of calcium, phosphorous, fluoride, magnesium and carbonate content, the structure of and variation in enamel rods, presence of enamel cracks and lamella play an important role in caries progression.  A comparative evaluation of depth measurement with other studies at different places may not be valid. The ability of glass ionomer and composites to resist caries like attack at the tooth restoration interface appeared to be of great importance in the prevention of incipient inter-proximal caries. The apparent caries resistance in enamel adjacent to these restorations may be due to the availability of fluoride at the tooth restoration interface. The anticaries activity of fluoride is contributed in several ways. Two major aspects of fluoride action are
The inhibition of demineralization at the crystal surfaces within the tooth andThe enhancement of subsurface remineralization resulting in the arrest or reversal of caries lesions.
Fluoride present in the aqueous phase at the apatite crystal surface may play a determining role in the inhibition of enamel or dentin demineralization.
Two factors that may affect fluoride absorption by enamel are
The amount of fluoride available andThe ability of enamel to accept additional fluoride.
In this study, remineralization of enamel adjacent to Ketac-Fil and Heliomolar was seen. Various authors have reported similar results. ,, None of the specimens restored with amalgam showed resistance to demineralization at tooth restoration interface. Ketac-Fil showed maximum remineralization, whereas composite showed intermediate amalgam showed no mineralization.
The mounted teeth were placed in artificial saliva as these materials release more fluoride in artificial saliva than in distilled water  and de-ionized water  and fluoride release from these materials in water does not represent what actually takes place in the oral environment.
Amalgam containing no fluoride showed no remineralization in the adjacent enamel surface. This coincides with the results of Bynum and Donly  where nonbrushed amalgam group exhibited a considerable amount of demineralization whereas the amalgam group that was brushed with a fluoridated dentifrice remained relatively stable with little remineralization.
Ketac-Fil glass ionomer cement showed maximum values in terms of total remineralization on the outer surface of adjacent enamel. This result coincides with those of Bynum and Donly  and Marinelli  where maximum remineralization was observed as a result of fluoride from Ketac-Fil. Young  reported a 10-fold fluoride increase in Ketac-Fil material compared to Heliomolar for the same duration. This may be due to the presence of soluble fluoride in which ion exchange can readily occur not only on the surface, but also possibly some small distance into the material.  Studies have shown that fluoride release from glass ionomer materials is more in acidic conditions  and it may be affected by other factors  including the setting time and mixing time; however, the amount of fluoride released from these materials may be linked to the structure of glass powder used. 
The observation that Heliomolar, a composite resin, released fluoride and helped to reduce demineralization coincided with the results of Bynum and Donly  and Donly and Gomez.  Heliomolar resins have hygroscopic properties and studies have shown that fluoride release could be through diffusion.  Composite resin material Heliomolar contains around 9 vol.% total fluoride that is adequate to obtain maximum enamel demineralization reduction.  This remineralization occurred maximally from fluoride release, which diffuses through fluid and plaque from the composite to the adjacent enamel surface.  But fluoride release from this dissolved form of fluoride in Heliomolar may be pH dependent.  Thus, fluoride releasing glass ionomer cements and composites compared to amalgam appear to have a local positive effect in the future for the prevention of incipient inter-proximal caries.
Though we made an attempt to recreate clinical conditions, an in-vitro experiment does not fully reflect oral conditions. The artificial caries study measures only the resistance of enamel and dentin to withstand acidic attack. The effect of bacterial assaults, demineralization, remineralization cycles and potential for recharging with external sources of fluoride in clinical conditions were not determined. So, it is essential to conduct clinical investigation to correlate with in-vitro studies in an attempt to select an ideal restorative material.
Results obtained from scanning electron microscopic evaluation were almost similar with those obtained from transmitted electron microscope analysis. A more detailed study using the SEM, with adequate sample size, and statistical analysis is required to compare the extent of remineralization in the enamel surface zone due to fluoride release from restorative materials.
These findings from this in-vitro study suggest the potential ability for glass ionomer cements and composite resins to remineralize incipient carious lesions on adjacent teeth and thus it can be used in mainly class II cavity restorations of primary and permanent dentitions.
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