Effect of Fluoride Varnish on Demineralization Adjacent to Orthodontic Brackets: An In vitro Comparative Study

INTRODUCTION

Orthodontics, a specialty, whose goal is to improve facial and dental esthetics, is posed with the problem of white spot lesion development adjacent to orthodontic brackets. Enamel decalcification remains common negative sequelae of orthodontic treatment in the absence of proper oral hygiene.¹ Various methods have shown to decrease white spot lesions like improving oral hygiene and diet modification to decrease the amount of fermentable carbohydrates, which solely rely on patient compliance.² Other non-compliant methods have been created to deliver fluorides adjacent to orthodontic appliances such as fluoride varnishes and bonding agents such as Glass Ionomer Cement (GIC).These have shown to decrease enamel demineralization both in-vitro and in clinical trials. Fluoride varnishes have the benefit of adhering to the enamel surface longer than other topical fluoride applications.²

GICs have been shown to release fluoride over a long term and generally at much higher levels than released by fluoride releasing composites. Although GICs have demonstrated high levels of fluoride release, they have shown poor bond strength and hence greater bond failure rates than composite resins. In an attempt to provide greater fluoride release and obtain adequate bond strength, combinations of GICs and composite resins have been developed. The Resin Modified GIC [RMGIC] is one such combination that is available.The fluoride releasing mechanism of resin modified GIC and Fluoride varnishes can help the orthodontists to minimize enamel demineralization in patients who do not comply with their dietary and hygienic recommendations.²

The aims & objectives of the present study was

1) To assess the role of fluoride varnish in reducing the white spot incidence around the orthodontic brackets.

2) To compare the effect of fluoridated Vs nonfluoridated bonding agents on demineralization of enamel.

3) To evaluate the combination of fluoride varnish with a fluoride containing bonding agent to reduce the incidence of white spot lesion.

MATERIALS AND METHODS

Freshly extracted caries free, 40 human premolars were used in this study. The extracted teeth were stored in 0.1% aqueous Thymol solution and later disinfected in tissue fixative. Calculus, bone and soft tissue were removed with a mixture of non-fluoridated pumice and water for around 2-3 seconds. A small hole was drilled near the apex of each tooth and dental floss was fed through the hole to facilitate suspension of teeth in different solutions.

The materials used in the present study were the bonding agents such as light cure Resin Modified Glass Ionomer Cement (Fuji ORTHO LC, GC ASIA DENTAL PTE Ltd, Singapore), light cure composite resin i.e. GLUMA Comfort bond (Heraeus Kulzer GmbH AND Co.KG, Hanau) , which acted as a nonfluoridated releasing control and Bifluorid-12 fluoride varnish (GROUP pharmaceuticals Ltd, Mumbai). Begg (TP Orthodontics) brackets were used to bond the teeth. Masking tape was used to cover the occlusal area adjacent to brackets and acid resistant varnish (nail polish) was used to paint the rest of tooth surfaces. By placing masking tape on the teeth, care was taken not to etch occlusal to where the brackets were to be positioned. The teeth were randomly assigned to 1 to 4 groups of 10 each.The bonding was done according to manufacturer's instructions.

Later the masking tape was removed and methanol was used to remove any residue from the tape. All teeth were painted with a thin layer of acid-resistant varnish (nail polish) to within a 1- mm area occlusal to each bracket, leaving an exposed window of enamel (Fig-1). The teeth were color coded inorder to differentiate them from various other groups.

After drying, the teeth in groups 2 and 4 received a thin coating of a Bifluorid-12 varnish containing 12 % fluoride (6% Calcium Fluoride + 6% Sodium Fluoride) placed over the exposed enamel windows. The fluoride varnish was allowed to dry for 5 minutes. Groups 1 and 3 received no other treatment. All groups were then placed in an artificial saliva solution of neutral pH consisting of 20 mmol/L NaHCO₃, 3 mmol/L NaH₂PO₄ , and 1 mmol/L CaCl₂ for a period of 11 hours. Later these teeth were subjected to artificial caries-producing solutionfor a period of 1 hour. The Cariesproducing solution consisted of 2.2 mmol/L Ca2+, 2.2 mmol/L PO₄-, and 50 mmol/L acetic acid at pH 4.4. The teeth were cycled between saliva and caries solutions twice dailyfor 31 days. 

The artificial saliva solution was changed twice weekly. After each caries challenge, the surface occlusal to the bracket was brushed for 5 seconds with a soft bristled toothbrush with no dentifrice to simulate normal mechanical wear of the fluoride varnish. The brackets were then removed, cusps were ground flat and each tooth was embedded in acrylic.

Longitudinal sections of tooth were made in bucco-lingual direction with the help of hard tissue microtome (Leica SP 1600) at Bapuji Dental College, Davangere, to yield sections of 100μm thick. The tooth slice was mounted on the glass slide using DPX. The tooth was observed and photographed under polarized light microscopy (Leica DMRB) at 25 times magnification. The depth of the lesion was measured using the calibration formula given by User manual by Leica DMRB. The lesion depth for each section was the average of 3 representative measurements (gingival, middle and occlusal) from enamel surface to the depth of the lesion.

The average depth of demineralization observed among 4 groups was analyzed for differences using analysis of variance (ANOVA). Alpha level was chosen to be 0.05. The Duncan multiple range test was used to show differences between the groups.

Figures 2, 3, 4 & 5 are photomicrographs of representative samples from group 1 through 4 respectively. 

RESULTS

This in-vitro study was conducted on forty extracted premolar teeth. Four different adhesive systems were compared to determine the amount of demineralization adjacent to orthodontic brackets (Table I consists of assignment of the samples to four different groups numbered 1 to 4). During sectioning, four teeth fractured and were not included in the measurements, leaving a sample number of nine in each group. The measurements were tabulated and statistical analysis was done using the SPSS package.

Table II consists of mean depth of the demineralized areas in the four adhesive system groups.The test of significance ANOVA conducted showed P≤ 0.0001. Duncan multiple variation tests showed differences among group 1, 3 & 4 and between groups 2, 3, & 4. Group 1 & 2 did not show significant changes. The largest lesion depth was found in Group 3 [114.68] (Composite resin without Fluoride varnish), followed by Group 4[87.11] (Composite resin with fluoride varnish), followed by Group 1 [65.33] (RMGIC without fluoride varnish) and least lesion depth was found to be in Group 2 [58.07] (RMGIC with fluoride varnish) [Table III & Graph-1].

In Group 2 where RMGIC with fluoride varnish was used , the lesion depth were found to be least towards gingival zone (39.20) when compared to middle zone (56.62) and occlusal zone (78.40)[Graph-2,3,4]. There was no difference between the gingival lesion depth of Group 1(39.20), and Group 2 (39.20) [Graph-4] & (Table IV). This study therefore indicates that Group 2 (RMGIC with fluoride varnish)  was best for bonding orthodontic brackets followed by Group 1(RMGIC without fluoride varnish). 

DISCUSSION

A. Effect of fluoride system on demineralization around Orthodontic brackets

The analysis of variance for the four groups for the mean lesion depths (occlusal, middle and gingival combined) showed a statistically significant difference between the four groups (p< 0.0001).

This indicated that Composite alone as a bonding agent has limited effect on minimizing demineralization adjacent to orthodontic brackets. This was in accordance with the findings of Corry A et al³ and Pascotto et al⁴ who demonstrated that the least protection to demineralization was afforded by the composite bonding agent used as the control in the study.

The results of the present study showed that Group 2, Glass Ionomer with fluoride Varnish had t h e ma x imum e ff e c t o n i n h i b i t i o n o f demineralization of enamel adjacent to orthodontic brackets. This is in harmony with the findings of Schmit et al,² and Corry et al³. When the four groups were compared in all the three zones with each other for statistically significant difference, the results of the Duncan's test showed that no statistically significant differences existed between Group 1 and 2. This indicated that Glass Ionomer and Glass Ionomer with fluoride varnish both are not significantly different in inhibiting demineralization adjacent to orthodontic brackets when used as adhesives.

Both RMGI groups had 50% smaller mean lesion depths when compared with the composite resin group without fluoride varnish. There was a significant difference between Group 1 (Glass Ionomer without fluoride varnish) and 3 (Composite without fluoride varnish) in their effect on demineralization. This was in agreement with the findings of Corry et al,³ Pascotto et al,⁴ Vorhies et al,⁵ Wheeler AWet al,⁶ and Marcusson Aet al.⁷

In the present study, Group 1 (Glass Ionomer cement without fluoride varnish) and Group 3 (Composite resin without fluoride varnish) showed significant differences with Group 2 (Glass Ionomer cement with fluoride varnish) and Group 4 (Composite resin with fluoride varnish) respectively in reducing the demineralization adjacent to orthodontic brackets, indicating that the use of fluoride varnish with the bonding agent has to some extent minimized the demineralization potential. This concurs with the findings of Todd et al.¹

The effect of Glass Ionomer cement with and without fluoride varnish was significantly greater compared to the other two groups, Composite resin and Composite resin with fluoride varnish in diminishing demineralization of enamel adjacent to orthodontic brackets. Regarding the effect of fluoride varnish, Groups 2 and 4 (with fluoride varnish) had a significantly greater effect in reducing demineralization than Groups 1 and 3 (without fluoride varnish). Between the two Glass Ionomer groups there was no difference in their inhibition effect on demineralization. Composite resin without fluoride varnish had a lesser effect in hindering demineralization compared to its use with fluoride varnish.

The effect of the adhesive system on inhibiting demineralization adjacent to orthodontic brackets can be summarized as follows:

Glass Ionomer = Glass ionomer + Fluoride Varnish > Composite + Fluoride Varnish > Composite.

This concurs with the findings of Vorhies BAet al⁵ .

B. The effect of fluoride varnish on the zone of demineralization in enamel adjacent to the bracket

The analysis of variance for the four groups for the gingival lesion depths, Middle lesion depths and occlusal lesion depths showed a statistically significant difference between the four groups (p< 0.0001). This was in accordance with the study conducted by Schmit JL et al² where they showed that fluoride release decreased from the edge of the bracket out to 1 mm away from the bracket.

The maximum demineralization was seen in the occlusal zone for all groups indicating the role of extraneous factors other than fluoride release in the demineralization. The least demineralization was seen in the gingival zone for all groups. Even in the various zones Glass ionomer cement and Glass ionomer cement with fluoride varnish showed the least demineralization compared to plain composite. The extraneous factors that may have influenced the release of fluoride into the different zones include, brushing, visible plaque and mutans streptococci and the level of oral hygiene.

Limitations of the study

1. Since this was an in-vitro study the effect of diet, temperature or other extraneous factors could not be estimated.
2. The use of calibrated Polarized light microscope for the measurement of crater depths may have yielded more precise recordings.

Clinical recommendations

1. The maintenance of oral hygiene measures by patients during orthodontic treatment is considered to be crucial as it may lead to the formation of white spot lesions, if ignored.
2. According to this study, it was found that use of Resin Modified Glass Ionomer Cement with fluoride varnish is very important to minimize the formation of white spot lesions adjacent to brackets.
3. Fluoride varnish should be used as an adjunct while either preventing the formation or progression of white spot lesions after initial bonding of orthodontic brackets.
4. Repeated applications of fluoride varnish are needed for its caries preventive effect. Semi-annual applications are the proven 8 treatment regimen.

CONCLUSION

1. Fluoride containing adhesives, Resin Modified Glass Ionomer cement (RMGIC) reduce the demineralization occurring adj a c ent to orthodonti c br a cke ts significantly, compared to non fluoride containing adhesives like Composite resins.
2. This effect of diminishing demineralization can be enhanced significantly by application of fluoride varnish during bonding procedure.
3. The demineralization of enamel adjacent to orthodontic brackets is significantly less in the area most near to the brackets and it increases as we move away from the bracket edges. This may most probably be due to extraneous factors like dental plaque, brushing, Streptococcus mutans etc.