Effects of topical fluoride agents on enamel surface in cooperation with bleaching agents

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Considering enamel abrasion, the calcium/ phosphate precipitation from saliva results in hardening of porous enamel which gradually may return to its initial situation if the process continues. The amount of the fluoride in the tooth's surface is also an important factor for the changes that could occur after the bleaching process. It has been shown that fluoride has the potential to inhibit demineralization which means that less surface changes would occur. To avoid these unfavorable effects of bleaching treatments, it is recommended to use fluoride containing remineralization agent incorporation with bleaching agents in order to decrease surface solubility (Akal N et al., 2001; Chen et al.,2008)

Taking this suggestion into consideration Tezel et al (Tezel et al., 2011) used artificial saliva to reflect the oral conditions and "after bleaching mousse" containing fluoride to maintain clinical schedule in their study mentioned above. This procedure gave them the potential effects of the topical fluoride agent for remineralization. As mentioned before, fluoride has been admitted to remineralize softened enamel by increasing resistance to acid attacks by forming a calcium fluoride layer to inhibit demineralization (Attin et al., 1997; Ten Cate&Arends,1977; Featherstone et al.,1982). It accumulates in the plaque fluid and as calcium fluoride on the enamel surface. During the acid challenge, calcium fluoride is dissolved (Axellson, 2000). It may be a question if the calcium loss could be from the dissolved calcium fluoride or not. Fundamentally, the source of calcium for calcium fluoride is from the enamel. Depending on this fact, the measured calcium loss after the acidic challenge should be from the enamel either directly or indirectly from the dissolved calcium flouride. Nevertheless, further studies are required to estimate this fact.

In another study (Tezel et al., edited to be published) which is still being edited to be published, the effects of different fluoride agents on the caries-like lesion formation and Ca2+ loss from the enamel surfaces after bleaching with 38% hydrogen peroxide have been examined. Teeth were divided into four pieces and randomly divided into four groups; three of them being the test groups and the last one being the control. The test groups were then bleached with 38% hydrogen peroxide leaving the control group untreated. Then two out of three test groups were treated with fluoride agents with different concentrations; 1% titanium tetrafluoride (TiF4) and 1.1% sodium flouride (NaF). Immediately after the application of the bleaching and fluoride agents for prescribed time, the specimens of each group were subjected to erosive demineralization with acetic acid buffered with 0.34M sodium acetate (pH=4). The specimens were demineralized four times for four days. The amount of Ca2+ released from the specimens was detected with atomic absorption spectrometer. When the results were examined it was clearly observed that there was a decrease in the Ca2+ release in the fluoride-treated groups after bleaching. When these two groups (TiF4 and NaF) were compared, it was determined that at the end of the test period (16 days) the amount of Ca2+ in the buffer solution of TiF4-treated samples was less than that of NaF-treated samples and the difference was statistically significant (Table 5, 6). Regarding this result, it can be assumed that TiF4 may be effective in preventing the bleached enamel surface against the acid attacks. Furthermore, there was no Ca2+ release from three specimens during the first four days, and during the second 4-day interval. This result can be a result of the glaze layer formed just after the application of TiF4.

N

4th Day

8th Day

12th Day

16th Day

Total

Mean

3.59

3.20

3.72

4.55

15.07

Control

10

Std Dev

0.54

0.59

1.23

0.89

1.81

Group

Min.

3.01

2.46

2.46

2.74

12.60

Max.

4.93

4.38

6.58

5.75

18.36

Mean

5.75

5.18

5.56

5.95

22.44

38% HP

10

Std Dev

1.60

1.52

0.71

0.37

2.52

Min.

3.83

3.01

4.66

5.48

18.36

Max.

7.95

8.50

6.85

6.58

27.68

Mean

2.05

3.15

3.94

4.52

13.67

38% HP+

10

Std Dev

0.83

0.58

1.01

0.83

1.86

NaF

Min.

0.82

2.19

2.46

3.29

10.68

Max.

3.01

4.11

5.75

6.03

15.61

Mean

1.15

1.94

2.66

3.37

9.12

38% HP+

10

Std Dev

0.92

1.54

0.63

0.48

2.40

TiF4

Min.

0

0

1.64

2.46

4.93

Max.

2.46

4.11

3.56

3.83

11.50

Table 5. Ca2+ release from the bleached specimens treated with 1% TiF4 and 1.1% NaF in mm2 (|J,g/ml).

Table 5. Ca2+ release from the bleached specimens treated with 1% TiF4 and 1.1% NaF in mm2 (|J,g/ml).

In a previous study, Tezel et al (Tezel et al., 2002) reported that TiF4 was found to be more effective than Duraphat (NaF, 2.26% F) or Elmex (amine fluoride, 1.25% F) in preventing artificial enamel lesion formation. Attin et al (Attin et al., 1999) reported that, fluoridation was effective in increasing resistance of enamel against demineralization by erosive substances. Similarly, the findings of this present study demonstrated that the resistance of enamel against the erosive demineralization caused by 38% HP application was increased after 1% TiF4 treatment.

When the Ca2+ losses from the test groups which were bleached with 38% HP were compared, there was also a decrease in Ca2+ losses of 1.1% NaF treated group indicating that NaF could also prevent enamel surfaces against acid attacks during the first four days (p<0.05). Addition of sodium fluoride to hydrogen peroxide solutions leads to formation of fluoridated hydroxyapatite and calcium fluoride when applied on hydroxyapatite samples (Tanizawa, 2005). In the present study, although NaF was effective against acid attacks on enamel surfaces, its influence was not as strong as TiF4 (Table 6; Figure 8).

Materials

4th Day

8thDay

12th Day

16th Day

Total

Control X 38% HP

*

*

*

*

*

Control X 38% HP + NaF

*

NS

NS

NS

NS

Control X 38% HP + TiF4

*

NS

NS

*

*

38% HP X 38% HP + NaF

*

*

*

*

*

38% HP 38 X 38 % HP + TiF4

*

*

*

*

*

38% HP + NaF X 38% HP + TiF4

NS

NS

*

*

*

* Statistically significant differences between the groups (p<.05) NS No statistically significant differences (p>.05)

Table 6. Statistical differences between test groups.

Table 6. Statistical differences between test groups.

Different topical fluoride agents (sodium fluoride, acidulated phosphate fluoride, stannous fluoride, amine fluoride or titanium tetrafluoride) to human tooth enamel are widely used in caries prevention. Topically applied fluoride may reduce the solubility of the surface enamel, render the tooth surface harder, more resistant to demineralization, and more prone to remineralization (Skartveit et al., 1990). The inhibiting effect of sodium fluoride on caries is well documented and a protective effect against dental erosion has been shown in vitro (Sorvari et al., 1994; Ganss et al., 2001). Fluoride varnishes provide long contact periods between the dental tissues and the fluoride agent resulting in high fluoride uptake and the formation of calcium fluoride deposits that act as fluoride reservoirs (Arends J & Schuthof, 1975; Grobler et al.,1983; de Bruyn,1987; Petersson,1993). It has been reported that during the application of titanium tetrafluoride, a glaze layer was formed on the tooth surface (Mundorff et al., 1972). TiF4, has been shown to reduce articifial caries lesion formation and enamel solubility enabling high fluoride uptake (Tezel et al.,2002; Buyukyilmaz et al., 1997).

Generally, fluoride uptake in demineralised enamel is higher when compared to sound enamel (Attin et al., 2006) It is assumed that the porous structure of the demineralised enamel allows better diffusion and penetration of the applied fluoride and that the porosity offers a higher number of possible retention sites for the fluoride. The application of highly concentrated fluoride favors the formation of the calcium-fluoride like layer (Attin et al., 1977). This deposit is later dissolved, allowing fluoride diffuse into the underlying enamel, the saliva, or a plaque layer covering the tooth. It is assumed that some of the fluoride is supporting the remineralization of the enamel. The results of a previous study confirmed that the calcium fluoride layer on the enamel was coated by phosphates and proteins from saliva as a pH-controlling reservoir that acts to decrease demineralization and promote remineralization (Rolla&Saxegaard, 1990).

Fig. 8. Cumulative calcium (Ca2+) release from the bleached specimens in the buffer solution after treatment with 1% TiF4 and 1.1% NaF on the 4th, 8 th, 12 th and 16 th days (^g/ml).

VanRijkom et al (VanRijkom et al., 2003) compared the erosion-inhibiting effect of the topical fluoride treatment based on the deposition of CaF2-like material using 1% NaF and 4% TiF4. It was concluded that the reduction of Ca2+ loss was more stable for TiF4 than the NaF group and the reduction appeared to be smaller for the longer acid exposure times. Recently, Magalhaes et al (Magalhaes et al., 2008) have stated that a TiF4 varnish showed better results than 2 commercial NaF varnishes in reducing enamel erosion. Based on the results of Tezel et al's (Tezel et al., edited to be published) study, it was shown that topical fluoride applications decreased Ca2+ loss from the 38% HP treated enamel surfaces. It may be concluded that the application of fluoride agents may reduce the risk of erosion-like lesions caused by bleaching and remineralize the bleached enamel surfaces. The findings of this in vitro study demonstrated that TiF4 may act better than NaF solution in preventing acid attacks.

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