SUMMARY

OBJECTIVE:

To evaluate the effectiveness of daily tooth brushing with high-fluoride toothpaste on white spot lesion (WSL) formation in adolescents during treatment with fixed orthodontic appliances (FOA).

MATERIALS AND METHODS:

Four hundred and twenty-four healthy 11- to 16-year-old patients, referred to five Orthodontic Specialist Clinics, were randomized to use either toothpaste containing 5000 ppm fluoride or regular toothpaste with 1450 ppm fluoride. To be eligible for inclusion, the patients had to be scheduled for bimaxillary treatment with FOA for an expected duration of at least 1 year. The primary and secondary outcome measures were prevalence and incidence of WSL, as registered from digital photos of the maxillary incisors, canines, and premolars taken before onset and immediately after debonding. The photos were evaluated separately by two blinded and calibrated clinicians using a 4-step score. A random sample of 50 cases was reassessed to check intra- and interexaminer reliability (Kappa = 0.70; 0.74).

RESULTS:

The use of high-fluoride toothpaste resulted in fewer WSL (P = 0.042) with a prevented fraction of 32%. The lateral incisor was most commonly affected in both groups.

CONCLUSION:

To prevent WSL during treatment of FOA, daily use of high-fluoride toothpaste may be recommended.

Introduction

The development of white spot lesions (WSL) during orthodontic treatment with fixed appliances remains an unwanted clinical problem with a reported incidence of 15–85% (Mitchell, 1992; Chapman et al., 2010; Richter et al., 2011; Shungin et al., 2010). As such lesions have limited ability to improve after bracket removal, the final aesthetical result may be severely impaired (Mattousch et al., 2007). Systematic and narrative reviews have examined various strategies to prevent WSL development and found some evidence that topical fluoride (rinses, varnishes, gels, toothpaste) or fluoride-containing bonding materials could reduce the occurrence and severity of WSL adjacent to bands and brackets (Derks et al., 2004; Benson et al., 2005; Bergstrand and Twetman, 2011). There was, however, little evidence on which fluoride supplement, or combination of methods, that was the most effective (Benson et al., 2005). Among the self-applied fluoride products available, toothpaste is thought to be most important (Marinho et al., 2003; Twetman, 2009). The availability of fluoride from toothpaste is influenced by several factors, such as the concentration of fluoride, the amount of toothpaste used, and the post-brushing behaviour (Davies and Davies, 2008; Zero et al., 2010). The fluoride concentration in toothpaste has traditionally been limited to 1450 ppm F, but in recent years, a high-fluoride toothpaste containing 5000 ppm F for special need patients is available. Previous clinical studies with high-fluoride toothpaste have shown beneficial effects on root caries (Baysan et al., 2001; Ekstrand et al., 2008) and proximal caries progression in caries-active adolescents (Nordström and Birkhed, 2010). The effect of regular brushing with 5000 ppm fluoride toothpaste during treatment with fixed orthodontic appliances is to our knowledge yet scarcely studied. Alexander and Ripa (2000) suggested a better caries-protective effect of a high-concentrated dental cream and gel in orthodontic patients, and a study by Al-Mulla et al. (2010) showed that high-sodium-fluoride toothpaste had a greater anti-caries potential than a standard formula in patients with orthodontic bands. More high-quality clinical research is however required into the different modes of delivering fluoride to the orthodontic patient. The aim of the present investigation was therefore to evaluate the effectiveness of daily tooth brushing with high-fluoride toothpaste on WSL development in adolescents during treatment with fixed orthodontic appliances. The null hypotheses were that the prevalence and incidence of the lesions would not differ from a control group using standard fluoride toothpaste.

Materials and methods

The investigation was conducted as a randomized controlled multicentre trial with two parallel arms. The study design was approved by the Regional Ethical Review Board in Lund, Sweden (Dnr 417/2007) and registered in/at Clinical Trials.gov Identifier (NCT01768390).

Participants

The study group consisted of 482 healthy adolescents, 11–16 years of age, referred for orthodontic treatment to four public specialist clinics in southern Sweden (Jönköping, Malmö, Värnamo, and Nässjö) and one University clinic (Faculty of Odontology, Malmö University) who also had the coordinating function of the trial. Each centre had to contribute with at least 50 patients. The recruitment started in 2008, and the trial was completed in May 2012. To be eligible for inclusion, the adolescents had to be scheduled for bimaxillary treatment with fixed orthodontic appliances according a standard straight-wire concept (McLaughlin et al., 2001) for an expected duration of at least 1 year. Subjects with special needs such as chronic diseases and/or disabilities were excluded.

Informed consent was obtained from 424 subjects, as well as from one of their custodians. An independent person, not involved in the treatments or data analyses, randomly allocated the subjects to one of the study groups with aid of a computer, generating sequentially numbered opaque envelopes. A detailed flowchart is presented in Figure 1.

Figure 1

Flow chart for participants and dropouts in the trial.

Figure 1

Flow chart for participants and dropouts in the trial.

Test and reference groups

Patients allocated to the test group were provided with toothpaste containing 5000 ppm sodium fluoride (Duraphat, Colgate-Palmolive, Glostrup, Denmark) and instructed to apply 2cm (approximately 1g) on the brush and then brush their teeth for 2min, twice daily, after breakfast and before bedtime, during the period of orthodontic treatment. The patients of the reference group received regular toothpaste with 1450 ppm sodium fluoride (Colgate Caries Control, Colgate-Palmolive, Glostrup, Denmark) with the same flavour and consistency and given the same instructions. The participants were supplied with two tubes of the designated toothpaste at baseline and then two new tubes every 3rd month during the entire treatment period. They were also supplied with a standardized toothbrush at baseline and every 3rd month throughout the trial. The fluoride content in the piped drinking water was less than 0.3 ppm F in all communities from where the test and reference groups were recruited. The subjects were encouraged to immediately report any perceived side effect to their regular dental team. The compliance was regularly encouraged through interviews by the clinicians and any violation of the protocol was noted in the records.

Clinical procedures

All subjects were thoroughly examined prior to the onset of the fixed appliances. After polishing with a rubber cup and fluoride-free pumice paste, the presence of visible WSL or hypomineralizations on all facial surfaces of the maxillary premolars, canines, and incisors was recorded. Three digital photos (one frontal and two laterals) were exposed in a standardized way and stored on CD discs for future comparisons with the status after debonding. At the time of debonding, at least 12 months after onset, the remaining composite material on the surfaces was carefully removed with a slowly rotating carbide bur, followed by polishing with a rubber cup and pumice paste. After drying with air, a new series of frontal and lateral digital photos was taken and stored on a disc.

Outcome measure

The primary and secondary outcome measures were the prevalence and incidence of WSL at the time of debonding, as registered with a 4-step score from digital photos. The pre- and post-treatment photos were projected on a screen (Hewlett Packard ProBook 6650b, Palo Alto CA, USA) in a dark room and the incidence and severity of enamel demineralization was registered independently by two experienced and calibrated orthodontists (MS and LB) according to the index of Gorelick et al. (1982). The labial surfaces of the maxillary incisors, canines, and premolars were considered and scored as follows: 1 = no white spot formation; 2 = slight white spot formation (thin rim): 3 = excessive white spot formation (thicker bands); 4 = white spot formation with cavitation. When in doubt, the lower score was chosen.

The examiners were not involved in the treatment of the patients and blinded for the group assignment. In case of disagreement, the photos were re-examined until consensus was reached. Unreadable follow-up photos (i.e. poor contrast, technical errors) were counted as dropouts. A random sample of 50 cases was reassessed after 1 month in order to check the intra- and interexaminer reliability.

Sample size estimation

The sample size was calculated on the basis of the WSL incidence reported by Stecksén-Blicks et al. (2007). With the alpha and beta values set at 0.05 and 0.2, respectively, 172 subjects per group were needed to disclose a 30% difference between the treatment groups in the proportion of participants with new demineralized lesions at debonding. An anticipated 20% attrition rate increased the sample size, totalling at least 412 subjects (206 in each arm) to be enrolled and randomized.

Statistical analysis

All data were processed with the IBM-SPSS software (version 19.0, Chicago, IL, USA) and the group allocation was not unveiled until after the statistical calculations. Proportions and categorized scores were compared by Pearson’s chi-square test with Yate’s correction for continuity. The mean number of WSL’s was compared with analysis of variance. Continuous data (age and treatment duration) were processed by t-test. Inter- and intra-individual agreement was calculated with Cohen’s Kappa correlation. The level of significance was set to 5% (P < 0.05).

Results

The groups were similar in age and gender at baseline; the mean age in the test group was 14.8 years [standard deviation (SD) 1.70] and 14.6 years (SD 1.65) in the reference group. The sex distribution was 66% girls and 34% boys in the reference group and the corresponding figures were 65% and 35% in the test group. There were no significant differences in prevalence of WSL at onset of fixed orthodontic appliance or at debonding between the five centres that participated in the trial. The mean duration of the orthodontic treatment was 1.8 years (SD 0.53) in both groups, and the dropout rate was 10.4% in the test group and 9.6% in the reference group (Figure 1). Eighteen participants did not comply with the study protocol, but otherwise, the performance was uneventful and no side or adverse effects were reported. The dropouts were proportionally distributed among the centres and did not differ from the final material considering age, gender, or geographic area. The interexaminer Kappa value was 0.74, and the intraexaminer values were 0.70 (good) and 0.80 (very good), respectively.

The prevalence of WSL at onset of the fixed orthodontic appliance and at debonding is shown in Tables 1 and 2. There was no significant difference between the groups at baseline but the prevalence was significantly lower at individual level in the high-fluoride toothpaste group at debonding (P = 0.04). The WSL incidence was 18.1% in the high-fluoride group compared with 26.6% in the reference group, corresponding to a prevented fraction (risk reduction) of 32%. As shown in Table 2, there was a significantly increased relative risk for having new demineralized lesions in the reference group at debonding (odds ratio 1.64; 95% confidence interval 1.03–2.68; P = 0.049). The vast majority of all new WSL were thin rims (score 2) in both groups, while more severe lesions (scores 3 and 4) were found in 1.2% and 2.3% in the test and reference groups, respectively. The lateral incisors were the most commonly affected teeth in both groups, followed by the canines and premolars.

Table 1

Prevalence (proportion of patients with at least one white spot lesion) and mean number (standard deviation) of white spot lesion at onset and debonding of the fixed orthodontic appliance.

 Test group (N = 188) Reference group (N = 192) P value 
Prevalence, % Mean (SD) Prevalence, % Mean (SD) 
Onset 16.5 0.3 (1.0) 18.7 1.0 (1.8) 0.66 
Debond 34.6 0.4 (1.0) 45.3* 1.2** (1.8) 0.04 
 Test group (N = 188) Reference group (N = 192) P value 
Prevalence, % Mean (SD) Prevalence, % Mean (SD) 
Onset 16.5 0.3 (1.0) 18.7 1.0 (1.8) 0.66 
Debond 34.6 0.4 (1.0) 45.3* 1.2** (1.8) 0.04 

*Statistically significantly difference compared with the test group; *chi-square test; **analysis of variance.

Table 2

Two-by-two table showing the incidence of white spot lesion (patients showing at least one new lesion) in the test and reference groups.

New white spot lesion Test group Reference group Total 
Yes (negative outcome) 34 51 85 
No (positive outcome) 154 141 295 
Total 188 192 380 
New white spot lesion Test group Reference group Total 
Yes (negative outcome) 34 51 85 
No (positive outcome) 154 141 295 
Total 188 192 380 

Values in the table denotes the number of subjects. Odds ratio = 1.64 (95% confidence interval 1.03–2.68; P = 0.049).

Discussion

It is generally considered that adolescents treated with fixed orthodontic appliances are at risk for enamel demineralization adjacent to the brackets due to an accumulation of aciduric and acidogenic bacteria (Chapman et al., 2010; Andrucioli et al., 2012). To our knowledge, this is the first multicentre randomized clinical trial (RCT) specifically designed to evaluate the use of high-fluoride tooth paste on the prevalence and incidence of WSL adjacent to fixed appliance in adolescents. The rational for the multicentre approach was to include a sufficient and large number of participants in a reasonable time period. The pharmacological approach for the project was that toothpaste with high-fluoride content could decrease the metabolic activity of the biofilm by hampering the enzyme enolase needed for bacterial glucolytic activity (Marquis et al., 2003; Takahashi and Washio, 2011) and subsequently diminish the acid stress. Although, the outcome was in favour for the high-fluoride toothpaste and the null hypotheses could be rejected, we have no microbial data to support further speculations on the mechanism of action. It is, however, well established that topical fluorides, even in low concentrations, act locally in the biofilm–tooth interface by reducing enamel demineralization and enhancing remineralization (Buzalaf et al., 2011; ten Cate, 2013).

There were, however, some study limitations. First, the use of clinical digital photos for the evaluation of WSL development was an indirect scoring method and may somewhat underestimate the true occurrence of enamel demineralization due to remnants of composite bonding materials and contamination of moisture. On the other hand, it allowed a blind, unbiased, and independent evaluation of the scores, a fact that is often overlooked in clinical trials. Secondly, we were unable to secure a true double-blind performance of the study because it was not possible for the manufacturer to produce identical packing of the two different toothpastes. Even if the participating subjects were not informed on the different toothpaste characteristics, it was not unlikely that they became aware of their assignment during the study period, especially since the diameter of the tube openings differed. Nevertheless, this multicentre RCT has several strengths compensating bias; the large material size, random assignment and small attrition rate ensured equivalence of both groups at baseline and sufficient power. Furthermore, the good/very good inter- and intraexaminer agreement suggested a strong validity of the outcome measure.

An interesting observation was that the lateral incisors were more frequently affected than the central incisors, canines, and premolars in both the test and the reference groups. This has been reported earlier (Stecksén-Blicks et al., 2007), but the reason for this ‘vulnerability’ is not fully clear. One explanation could be the lateral incisors in many orthodontic cases have an initial palatal position and thereby conceivably subjected to heavier plaque accumulation due to difficulties in cleaning. Another more hypothetical explanation could be that local differences in the salivary defence system in the incisor area might occur.

The prevented fraction (the difference between the incidence in the reference and test groups, divided by the incidence in the reference group × 100) in this study was 32% that was statistically significant but clearly lower than in a previous study with a similar design but using fluoride varnish (Stecksén-Blicks et al., 2007). Although the net WSL incidence was of the same magnitude in both studies, results from one trial cannot directly be compared with another. For example 5000 ppm fluoride toothpaste is a home-care procedure with a great potential of being cost-effective but heavily relying on compliance. Fluoride varnish, on the other hand, is a professional procedure that can be applied regularly without need of the individual patient’s involvement. However, an indirect way to compare the effectiveness of various interventions is to calculate the number needed to treat (NNT). In this study, the NNT was close to 12 compared with 5.5 in a trial using fluoride varnish (Stecksén-Blicks et al., 2007). This indicates that the interventions may not differ significantly in terms of cost-effectiveness when direct and tangible costs are added. Other fluoride options to consider in terms of health economy are fluoride mouth rinses and fluoride gels.

Conclusions

Following conclusions could be drawn from the present investigation:

  1. Daily use of high-fluoride toothpaste can significantly reduce the prevalence and incidence of white spot lesions adjacent to fixed orthodontic appliances in adolescents.

  2. High-fluoride toothpaste should be considered as one of several alternative fluoride supplements for patients subjected to a temporarily increased caries risk.

Funding

The Swedish Patent Revenue Fond 2007.

Acknowledgements

The authors gratefully acknowledge Dr Krister Bjerklin, Dr Eva Josefsson, Dr Lars-Göran Lindström and Dr Stefan Norén for their coordination and support at the public orthodontic specialist clinics. The authors would also like to thank Susanne Andersson, Ingrid Carlin, Pia Jensen, Gunilla Jeppson, Annelie Johansson, Elisabeth Kaiser, Ingela Karlsson, Birgitta Magnusson, Karin Nerbring, Marie Nilsson, Marie Rosenlind, Marita Svensson, Anette Timén and Jessica Wilén for their excellent clinical work. The study was supported by a grant from The Swedish Patent Revenue Fond. The authors have no conflict of interest related to this research. Toothpaste and toothbrushes for the study were generously donated by Colgate-Palmolive, Denmark, but the company played no part in the design of the trial, in the statistical analysis, drafting of the manuscript, or in the approval of the final wording.

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Supplementary data