Effects of various toothpastes on remineralization of white spot lesions

Abstract

INTRODUCTION

Enamel demineralization is a significant consequence of orthodontic treatment in patients with poor oral hygiene and its prevention is one of the greatest challenges faced by clinicians despite recent advances in caries management. Fixed orthodontic appliances not only make conventional oral hygiene procedures difficult but also increase the number of plaque-retentive sites on the surfaces of teeth that are normally less susceptible to caries development. ¹ After such appliances are introduced into the oral cavity, the microbial flora of plaque exhibits a rapid shift toward acidogenic bacteria, most notably Streptococcus mutans and Lactobacilli. ^{2, 3} Therefore, caries progression is faster in patients with fixed orthodontic appliances. In particular, the development of white spot lesions (WSLs) around brackets is attributed to prolonged plaque accumulation. ^{4, 5, 6, 7, 8} WSLs become noticeable within 1 month of bracket placement, whereas caries development usually takes at least 6 months. ⁹ These lesions are commonly seen on the buccal surfaces of teeth with brackets, especially in the gingival region. ^{4, 8, 10}

Fluoridated toothpastes are considered the most effective agents for preventing enamel demineralization. The efficacy of the conventional toothpaste (1,000-ppm fluoride) has been documented in many studies; evidence suggests that toothpaste containing 5,000 ppm fluoride can further reduce demineralization and enhance remineralization. ^{11, 12} However, complete elimination of WSLs is unlikely because of rapid remineralization of the enamel surface in the presence of high fluoride concentration, which restricts the passage of ions into the deeper, more affected layers. Therefore, direct application of a high concentration of fluoride is not recommended. ¹³

Another preventive method is application of low levels of fluoride and calcium ions, which can penetrate deep into WSLs, such as in the form of a casein phosphopeptide. amorphous calcium phosphate complex (CPPACP). CPP-ACP maintains a supersaturated state of calcium and phosphate to enhance enamel remineralization. ¹⁴ At present, CPP-ACP is available in a variety of gels, creams, and mousses and can also be incorporated into chewing gum.

Some initial reports have shown that Clinpro™ Tooth Creme (3M ESPE, St. Paul, MN, USA), a 0.21% (w/w) sodium fluoride (950-ppm fluoride) anticavity toothpaste containing functionalized β-tricalcium phosphate (fTCP), is useful for reducing WSLs. fTCP is produced by milling TCP with sodium lauryl sulfate. This process prevents undesirable interactions between calcium and fluoride, which could render both inactive. fTCP stabilizes fluoride in solution and maintains high concentrations concentrations of calcium phosphate and fluoride in WSLs. Therefore, it could prevent and resolve enamel demineralization during orthodontic treatment.

Quantitative light-induced fluorescence (QLF™; Inspektor Research Systems, Amsterdam, Netherlands) is a validated instrument for assessing the mineral contents of smooth-surface lesions. ¹⁵ The aim of this in vitro study was to examine the effects of fluoridated, CPP-ACP-containing, and fTCP-containing toothpastes on remineralization of WSLs by using QLF-D Biluminator™ 2 (Inspektor Research Systems), which is a new QLF™ system used in combination with high-definition digital single-lens reflex (DSLR) imaging.

MATERIALS AND METHODS

RESULTS

Mean ΔF _initial was not significantly different among the groups. However, mean ΔF was higher in the fTCP and CPP-ACP groups than in the fluoride and control groups. The fluoride group did not show a significant difference from the control group ( Table 2). The percent increase in fluorescence after the treatment was 0.480%, 0.500%, 0.940%, and 1.446% in the control, fluoride, CPP-ACP, and fTCP groups, respectively. Figures 1, 2, 3, 4 show the pretreatment and post-treatment light-induced fluorescent images of one specimen from each group.

DISCUSSION

WSLs are not unique to orthodontic patients: they are observable in 3-82% of the children who have not received orthodontic treatment. ^{16, 17, 18, 19} In the orthodontic population, however, the prevalence rate of WSLs ranges from 8.5% to 44% on the anterior teeth and 7.7% to 71% on the posterior teeth. ²⁰ The results of the present study indicate that application of fTCP- or CPP-ACP-containing toothpaste may reduce WSLs, compared with use of 1,000-ppm fluoride-containing toothpaste.

In the present study, the application of CPP-ACP-containing toothpaste resulted in a significant increase in fluorescence. The remineralization of WSLs with CPP-ACP has been previously studied with conflicting results. Bröchner et al., ²¹ in a prospective clinical trial, found that WSL regression was comparable between CPP-ACP-containing and traditional toothpastes. They reported that application of CPP-ACP-containing toothpaste after debonding of orthodontic appliances resulted in significantly increased fluorescence and reduced lesional area after 4 weeks of treatment, as assessed by QLF™. The improvement was however not superior to "natural" regression occurring with daily use of fluoridated toothpaste. By using laser fluorescence, Bhat et al. ²² found that application of CPP-ACP-containing cream with and without fluoride for 14 and 21 days, respectively, led to significant differences in remineralization of incipient enamel lesions. However, by using a pH-cycling model of early caries in bovine enamel, Ogata et al. ²³ reported insufficient remineralization of enamel subsurface lesions with CPP-ACP. Polarized light photomicrographs and microradiographs did not reveal significant differences in mineral gain between CPP-ACP-treated and control groups; addition of low levels of fluoride was needed to observe lesional regression. The conflicting results of these studies may be related to the different methods of specimen preparation, treatment periods, and additional application of fluoride.

In the fTCP group, we used 950-ppm sodium fluoride toothpaste containing fTCP, which, according to the manufacturer, is an innovative calcium-based additive that can help to remineralize enamel. By in vitro pH-cycling experiments designed to mimic remineralization of incipient enamel lesions, Karlinsey and Mackey ²⁴ reported that the combination of sodium fluoride with fTCP in a simple aqueous solution produces significantly greater surface and subsurface rehardening of WSLs than use of fluoride alone. This result is similar to our findings.

Use of higher-concentration (1,500-5,000 ppm) fluoride toothpastes and gels twice daily during orthodontic treatment has a demineralization-inhibiting tendency. ²⁵ However, such high doses of fluoride have negative effects, so the Korea Food and Drug Administration has recommended that the total fluoride content of toothpaste should be less than 1,000 ppm. Further, although use of high doses of fluoride completely arrests the carious process, which is ideal for posterior carious lesions, WSLs of orthodontic origin present a cosmetic challenge and regression is the therapeutic goal. If a high dose of fluoride is used locally, the arrested lesion will remain the same size and frequently becomes stained with organic debris. Moreover, natural remineralization produces greater resistance to further dissolution because components are replaced with less-soluble substances having larger crystals during remineralization. ²⁶ This phenomenon has been reported as plugging of the diffusion pathways of enamel by hydroxyapatite crystals and as hyper-remineralization. ⁶

To the best of our knowledge, this study is the first direct comparison of the remineralization effects of 1,000-ppm fluoride-, CPP-ACP-, and fTCP-containing toothpastes on WSLs, although quantitative assessment of fluoridated and CPP-ACP-containing toothpastes has been reported. The better findings in the CPP-ACP and fTCP groups than in the fluoride group may be attributable to the lack of rinsing in the former groups. Further, the CPP-ACP- and fTCP-containing toothpastes were applied for longer than the actual clinical usage and the saliva solution was changed once a day. This study improves our understanding of the preventive potential of the products, but it cannot reproduce all the complexities of the living oral cariogenic environment. Well-designed controlled clinical trials studies are required to examine the potential benefits of CPP-ACP with fluoride and microabrasion with fTCP on remineralization.

CONCLUSION

fTCP- and CPP-ACP-containing toothpastes seem to be more effective in reducing WSLs than 1,000-ppm fluoride-containing toothpastes.

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References