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White lesions after orthodontic treatment: does low fluoride make a difference?

School of Clinical Dentistry, University of Sheffield, UK

Address for correspondence: D. R. Willmot, Department of Oral Health and Development, School of Clinical Dentistry, University of Sheffield, Claremont Crescent, Sheffield, S10 2TA, UK. Email: D.Willmot{at}Sheffield.ac.uk

Received December 15, 2003; accepted March 19, 2004

	Abstract

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

 
Objective: To compare and measure the changes in size of post-orthodontic demineralized white lesion enamel lesions treated with a low fluoride (50 ppm) versus a non-fluoride mouthrinse/toothpaste regime.

Study design: An experimental double-blind prospective randomized clinical controlled trial.

Setting: A university dental school orthodontic clinic (Sheffield, UK).

Participants: Twenty-six patients identified as having post-orthodontic demineralized white lesions on removal of their fixed appliance.

Method and interventions: The participants were randomly and blindly assigned to either a low fluoride mouthrinse/toothpaste treatment regime or an inactive control. Computerized image analysis of calibrated photographic images taken under polarized light were used to measure the lesions.

Outcome measures: Lesion size and proportion (DWL%t) and percentage reduction (ADPR) at debond, and at 12 and 26 weeks later.

Results: Five participants dropped out of the study, 12 had the low fluoride regime and 9 did not. As a percentage of the total labial tooth area (DWL%t) the mean size of the lesions at debond was 8.1% (SD 3.7). After 12 weeks the mean size of lesion had reduced to 4.6% (SD 2.6), which was a significant reduction (p=0.03). After 26 weeks the mean size was 3.5% (SD 2.1), which was a very significant reduction (p<0.003). This confirmed statistically that post-orthodontic demineralized white lesions do reduce in size with time reflecting remineralization or other enamel surface changes. Intervention using a test low fluoride mouthrinse/toothpaste combination at 26 weeks showed an average difference percentage reduction (ADPR) of 54.3% (Upper 95% CI=62.08, Lower 95% CI=46.44%) compared with a non-active control combination, which showed an ADPR of 66.1% (Upper 95% CI=77.74, Lower 95% CI=54.51%). This failed to show any differences or therapeutic affect.

Conclusions: Post-orthodontic demineralized white lesions reduced in size during the 6 months following treatment by approximately half the original size. There was no clinical advantage in using the low fluoride formulation of mouthrinse/toothpaste in this study.

Key words: White spots, demineralization, fluoride mouthrinse

	Introduction

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Enamel demineralization and white lesions occur during and sometimes remain after orthodontic treatment.^1,2 This phenomenon has become a particular clinical problem since directly bonded orthodontic brackets were introduced.³ O’Reilly and Featherstone⁴ and Ogaard^5,6 have shown that visible white lesions can develop within 4 weeks of the fitting of a fixed bonded orthodontic appliance. Melrose et al.⁷ have shown that similarly early enamel carious lesions can form associated with orthodontic bands in periods as short as 4 weeks. Clearly, the best approach during orthodontic treatment is to prevent lesions occurring. It has been concluded that fluoride preparations, oral hygiene instruction and dietary control have the greatest effect on reducing demineralization.⁸ Once formed, many of these early lesions appeared to be surface demineralization, rather than a sub-surface lesion with an intact surface zone. Remineralization of these white lesions is a natural phenomenon resulting in the partial reversal of what is an early caries lesion. The factors involved are discussed in the proceedings of a workshop by Leach.⁹ The mineral of the dental enamel is in equilibrium with its environment and saliva contains all the necessary elements for hydroxyapatite crystal growth. In the natural state there is natural demineralization and remineralization continually taking place. An excellent example of this is the maturation of tooth enamel that occurs shortly after a tooth erupts.¹⁰ This study examined a group of 9 year old children revealed 72 carious white lesions, which were carefully recorded. Six years later 50% of those lesions had disappeared, inferring that remineralization had taken place. Melrose et al.⁷ commented that the superficial lesions seen after orthodontic treatment will tend to remineralize more rapidly and completely than deeper lesions on removal of the cariogenic challenge. Remineralization varies considerably from subject to subject and from site to site in the mouth.¹¹ These studies have shown an average remineralization of 20–30% over 2 weeks (measured as a percentage mineral change). Sometimes the amount of remineralization cannot totally overcome the amount of demineralization even with an effective agent present. Following removal of the appliance, some regression of post-orthodontic lesions is known to occur provided other aetiological factors are favorable. Ogaard et al.⁶ warned against treating visible white lesions on labial surfaces with concentrated fluoride agents, since this arrests the lesion (hypermineralization). Instead, they advocated allowing remineralization by saliva, as this results in greater repair and a less visible lesion.

Remineralization also produces a greater resistance to further dissolution and this is due to the fact that during remineralization, components are replaced with less soluble substance that may have larger crystals.¹² This has been reported⁴ as plugging of diffusion pathways of enamel by hydroxyapatite crystals as hyper-remineralization. Workers in this field have, however, recommended the remineralization of small lesions with low fluoride preparations.^13,14 They have shown that lesions smaller then 60 µm deep can be remineralized using these preparations. In order to avoid arresting the lesion and obtunding the surface layer several workers have recommended low dose fluoride applications to enhance sub-surface remineralization. Lee Linton¹³ showed that a 50 ppm F mouthrinse had a higher efficiency for remineralization than a control solution or a regular mouthrinse containing 250 ppm. For lesions on surfaces other than on the visible labial surface, application of concentrated fluoride was suggested to prevent further progression. It has been suggested that acid etching of fluoride-treated lesions could facilitate remineralization of the lesion by oral fluids of synthetic remineralizing fluids.¹⁵

The purpose of the study was to examine and measure, in a randomized longitudinal prospective clinical study of post-orthodontic demineralized white lesions, the changes in size, and subsequent prognosis and fate of these lesions. In addition to compare the fate of post-orthodontic demineralized white lesions when subjected to intervention with a rinsing/toothpaste regime of either a specially formulated low fluoride mouthrinse/toothpaste test combination or a control fluoride-free mouthrinse/toothpaste combination, using an experimental double blind prospective randomized controlled trial.

The study was designed to test the following hypotheses:

• that post-orthodontic white enamel demineralized lesions reduce in size in the post-treatment period.
  
• that a low fluoride remineralizing mouthwash leads to a greater reduction in size of visible post-orthodontic white lesions compared with a no fluoride mouthrinse.
  

	Participants and methods

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

 
Study design
The study was an experimental double blind prospective randomized clinical controlled trial with 2 parallel groups. Participants who had suffered post-orthodontic demineralized white lesions following comprehensive fixed appliance therapy were offered the opportunity to enroll into the trial and if in agreement provided with either a test (low-fluoride) or a control (fluoride-free) mouthrinse/toothpaste combination for use on a daily basis according to a specified regime. The trial was double blind and the test and control interventions were randomized, the contents being unknown to the researcher at the time of both imaging and measurement. Ethical approval was obtained from South Sheffield Research Ethics Committee (reference no. SSR 98\002) All patients were treated according to the declaration of Helsinki.¹⁶

Inclusion criteria
To be accepted into the study the participants must have had:

• at least 12 months fixed appliance therapy;
  
• at debond post-orthodontic demineralized white lesions identified by the debonding clinician;
  
• lesions were not present at start of treatment when compared with pre-treatment clinical photographs;
  
• be possible to acquire the first images close to the date of debond;
  
• demineralized white lesions present on at least one of the anterior 8 upper or lower teeth including the most anterior remaining premolar.
  

Agreement that participants would undertake to use interventions provided by the researchers and would be content with the structure of the clinical trial.

Sample
Sample size calculations were carried out. Using the data from a previous study of demineralized white lesions, assuming a significance level of 0.05 and a 2-sided t-test, statistical advice from the Statistical Services Unit, University of Sheffield, UK, using nQuery software gave the opinion that with an expected reduction in lesion area of 40% in the control group and 70% in the test group (i.e. a 30% difference) this could be detected with n=11 in each group.

Recruitment of participants
Participants in the randomized controlled clinical trial were recruited from patients consecutively completing comprehensive fixed appliance therapy in the Orthodontic Clinic at the Charles Clifford Dental Hospital, Sheffield. At debond patients were referred to a regular research clinic when the orthodontist completing orthodontic treatment suspected post-orthodontic demineralized white lesions. Patients attending this clinic agreed to attend the research clinic regularly, and were prepared to enter the clinical trial and have their teeth imaged by photography. Participants were given an appropriate explanation of the study and informed consent obtained by the principal researcher. They were issued with an information sheet and clear instructions on how to use the mouthrinse/toothpaste combination.

The interventions under test and randomization
The mouthrinse/toothpaste combinations comprised of a low sodium fluoride test mouthrinse or an identical control mouthrinse with no sodium fluoride, plus a fluoride-free toothpaste. Sodium fluoride was present in the test mouthrinses in very low concentrations as recommended by various authorities^13,5 to promote remineralization. The mouthrinse had an effective NaF content of 50 ppm. The control mouthrinse contained all the same ingredients except sodium fluoride. All participants in the study were given a fluoride free toothpaste and were instructed to use this toothpaste throughout the study and not their regular toothpaste. Packs of mouthrinse and toothpaste were prepared by a dental products company (Boots Contract Manufacturing, Beeston, Nottingham NG2 3AA, UK). The participants were issued with 3–4 months supply in packs of 3x200 g tubes of paste and 3x1 litre of mouthrinse. Packs were numbered 1 onwards by the pharmaceutical company and the test/control packs were randomized by that company according to a table of random numbers held by the company. The code was placed in a sealed envelope until the conclusion of both the trial and measurements. Participants were instructed to keep all empty bottles and tubes, and return them to the researcher at their next visit. Participants and the researcher were unaware as to whether an intervention or control mouthrinse was being supplied. Clear written instructions were given to each participant on how to use the interventions and also about the clinical trial procedure in general as requested by the Ethics committee. Participants were instructed to use the mouthrinse twice a day after brushing their teeth in the morning and in the evening before bed. They were instructed to swish the mouthrinse around their teeth for 30 seconds.

Image acquisition
Images were acquired in a darkened dental surgery using polarized light from flashlights and polarizing lenses attached to a 35-mm system.¹⁷ Previous work has shown the techniques of image acquisition is repeatable and enables the distinction of dimensional changes in lesions.¹⁸ Images were acquired within a few days of debonding and at approximately monthly intervals up to and beyond 26 weeks in some cases.

Selection of lesions
For each subject included in the clinical trial, all 8 upper anterior teeth and all 8 lower anterior teeth were examined for discreet white lesions. They were known not to be pre-existing when compared with pre-treatment clinical photographs and they were associated with the position of the previously placed fixed appliances. Depending upon the remaining lesions, up to a maximum of 4 lesions were selected from each patient, representing a range of different teeth. Each lesion was measured independently for each image, which had been previously calibrated as part of the following protocol.

Processing protocol
The images were processed on a Pentium II PC (300 mHz) with a 64 MB RAM. Initially, the 35-mm colour slides were scanned by a Fotovix converter (Fotovix IIIS, Model TF-156WE, Tamron Co., Japan) set to standard repeatable settings and converted into TIFF files as colour (RGB) images. The TIFF files were then processed using Image Pro-Plus (Version 4, Media Cybernetics, Ca., USA) as color images. The image was opened and, if necessary, adjusted for brightness using a contrast enhancement process. A processing procedure of ‘sharpen’ filter (set at minimum 3x3, one pass) was used to improve margin integrity of the teeth and lesions. Calibration (spatial) was via a modified plastic bite gauge held between the subject’s teeth. All data was collected via the clipboard to a Microsoft Excel spreadsheet for storage and processing. At each visit made by the patient during the months following debond the area of demineralized white lesion (ws) and the area of the labial surface of the tooth under study (t) were measured.

Statistical analysis and outcome measures
In order to make understandable comparisons between groups, it is necessary to have a key number for each subject for any one parameter. Variation of enamel response between participants, rather than between teeth was the aim of this study. There are advantages in measuring more than one demineralized white lesion per subject and calculating the average per subject. We can then compare that figure for the whole subject with other participants in the clinical trial in order to compare test and control groups. Following examination of the curves and data seen in the earlier clinical longitudinal studies,^17,18 difference in lesion as a proportion of total tooth area (DWL%t) for A–B (where A=start and B=end) expressed as a percentage reduction (DPR), would a good measure. For participants with multiple lesions, the differences for up to four lesions were measured and averaged to give the average difference in percentage reduction (ADPR). For participants with only one tooth with a lesion, a single measurement was used. The average difference in percentage reduction (ADPR) thus calculated was compared between groups at defined points of time calculated from XY plots. For this study the ADPR at 12 and 26 weeks were agreed as outcome measures. If ADPR is normally distributed within a group, then 2-group t-tests could be used. If the data is not normally distributed, then a Mann-Whitney test should be used.

Outcome measures
The following measurements were calculated to be used as outcome measures:

• DWL%t—The demineralized white lesion as a percentage area of the visible labial surface of the tooth calculated by:
  
  

  
  

• DPR(x)—The difference in percentage reduction at x weeks for each tooth. The difference of DWL%t for A–B, where A=Start and B=End (x weeks). This parameter was calculated for each tooth at 12 and 26 weeks; Figure 1 illustrates the methodology of this calculation.
  
• ADPR(x)—The average difference in percentage reduction for each subject at between debond and x weeks. Calculated from the mean of XY plots for each tooth against time of DWL%t. This was calculated for 12 and 26 weeks for each subject.
  Figure 2 shows the method of calculation for one subject in the study.
  

View larger version (19K): [in this window] [in a new window]   Figure 1 Illustrates the calculation of the difference of the demineralized white lesion as a percentage of area of the labial surface of the tooth (t) which in this hypothetical case is 7–3%=4% at 26 weeks [(DWL%t(0) – DWL%t(26)=DPR(26)]

View larger version (14K): [in this window] [in a new window]   Figure 2 A typical graph of change in DWL%t with time for four teeth in one subject. The thick black plot shows the change in DWL%t with time as the mean of the lesions on the four teeth 12, 11, 42 and 41. From the mean curve the DWL%t at 0, 12 and 26 weeks has been identified. The difference between 0–12 and 0–26 weeks can then be calculated. For this case ADPR(12) was 11.8–5.6=6.2% and ADPR(26) was 11.8–4.3=7.5%

	Results

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

View larger version (36K): [in this window] [in a new window]   Figure 3 CONSORT diagram to show flow of participants through each stage of the randomized trial

View larger version (19K): [in this window] [in a new window]   Figure 4 Average difference in percentage reduction (ADPR) at 12 weeks for all cases in the clinical trial. (The greater the value of ADPR the more the lesions have remineralized and reduced in size)

View larger version (21K): [in this window] [in a new window]   Figure 5 Average difference in percentage reduction (ADPR) at 26 weeks for all cases in the clinical trial. (The greater the value of ADPR the more the lesions have remineralized and reduced in size.)

	Discussion

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

The drop out rate of 19.2% was higher than desirable. A feature of trials on patients who have suffered post-orthodontic demineralization is a high drop out rate.^4,11 These participants may well have their lesions because of their lack of compliance and many of the participants may well have been ‘burnt’ after prolonged orthodontic treatment.

There was a wide variation in response between the participants in both groups. On the face of it the control group fared better than the test group, but these values were not significantly different when subjected to a 2-sample t-test. The fact that the control group appeared to actually fare better then the test group by a small amount indicates that there is unlikely to be any useful clinical difference (e.g. >30%) between the groups even in a larger multi-center study. There may be many factors influencing the wide variation in response. Failure to comply with the treatment regime may explain some of the variation. The lack of therapeutic effect seen with the treatment regime that has been reported as successful in previous studies¹⁴ may reflect either this lack of compliance or, of course, a true lack of therapeutic effect of low dose fluoride.

The size reduction with time measured as a proportion plotted as graphs in the clinical trial showed the general exponential reduction in demineralized white lesion area seen in earlier longitudinal studies and reported in experimentally induced caries.²⁰ There was a wide variation in response. Consistently, all lesions reduced in size with time. Natural enamel remineralization and tooth wear seem the most likely cause. In 4 cases, after 6 months (26 weeks) very little further size reduction appeared to occur. On average, in all participants studied the difference in percentage reduction showed a reduction in lesion area of about a third after 12 weeks and a half after 26 weeks. The reductions are similar to those reported using the very different measurement technique of quantitative light induced fluorescence (QLF).²¹ Benson et al.^22,23 in a comparative in vitro study that both methods would be applicable to a clinical trial, and this present work validates both methodologies and outcome. These reductions were statistically significant when comparing the demineralized white lesion as a percentage of labial tooth area (DWL%t) at both 0–12 weeks (p=0.03) and 0–26 weeks (p=0.003).

	Conclusions

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

 

• This prospective randomized controlled clinical trial confirmed, using larger numbers and an improved methodology than in the previous longitudinal studies, that there was a general exponential reduction in demineralized white lesion area. There was a statistically significant reduction in lesion area measured proportionally at 12 weeks (p=0.03) and 26 weeks (p=0.003).
  
• In the period after removal of orthodontic appliances there was a wide variation in the response of post-orthodontic demineralized white lesions, but consistently lesions reduced in size with time. On average, in all participants studied the difference in percentage reduction showed a reduction in lesion area of about a third after 12 weeks and a half after 26 weeks.
  
• Numbers recruited to the study were sufficient to confirm any effect above 30% change in lesion area, if it did indeed exist.
  
• The fate the lesions subjected to intervention using a test low fluoride mouthrinse/toothpaste combination compared with a non-active control combination failed to show any differences or therapeutic affect.
  

	Contributors

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

 
Derrick Willmot was responsible for study design, obtaining funding, logistics, administration, recruitment of participants, data interpretation, drafting, critical revision and final approval of the article. Darren Lath was responsible for technical support. Philip Benson was responsible for critical revision, and final approval of the article. Derrick Willmot is the guarantor.

	References

Top Abstract Introduction Participants and methods Results Discussion Conclusions Contributors References

 
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2 Artun J, Brobakken BO. Prevalence of carious white spots after orthodontic treatment with multibanded appliances. Eur J Orthod 1986; 8: 229–34.[Abstract/Free Full Text]

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4 O’Reilly MM, Featherstone JDB. Demineralization and remineralization around orthodontic appliances: an in-vivo study. Am J Orthod Dentofac Orthop 1987; 92: 33–40.[CrossRef][Medline]

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6 Ogaard B, Rolla G, Arends J, Ten Cate JJ. Orthodontic appliances and enamel demineralization Part 2: prevention and treatment of lesions. Am J Orthod Dentofac Orthop 1988; 93: 123–8.

7 Melrose CA, Appleton J, Lovius BBJ. A scanning electron microscope study of early enamel caries formed in-vivo beneath orthodontic bands. Br J Orthod 1996; 23: 43–7.[Abstract]

8 Millet DT, Nunn JH, Welbury RR, Gordon PH. Decalcification in relation to brackets bonded with glass ionomer cement or a resin adhesive. Angle Orthod 1999; 69: 65–70.[Medline]

9 Leach SA. Factors relating to demineralisation and remineralisation of the teeth, Proceedings of a Workshop, Anatalya, Turkey. Oxford: Pub IRL Press, 1985.

10 Backer-Dirks O. Post eruptive changes in dental enamel. J Dent Res 1966; 45: 503–22.[Abstract/Free Full Text]

11 Mellberg JR, Chomicki WG, Mallon, DE, Castrvince LA. Remineralisation in vivo of artificial caries lesions by a mono-fluorophosphate dentifrice. Caries Res 1985; 19: 126–35.[Medline]

12 Silverstone LM. Remineralisation and enamel caries: significance of fluoride and effect on crystal diameters. In Leach I, Edgar WM (Eds) Demineralisation and Remineralisation of the Teeth, pp. 185–205. Oxford: IRL Press Ltd, 1983.

13 Lee Linton J. Quantitative measurements of remineralization of incipient caries. Am J Orthod Dentofac Orthodont 1996; 104: 590–7.

14 Lagerweij MD, Damen JJM, Stookey GK. Remineralisation of small lesions by fluoride. J Dent Res 1997; 76(Special issue): 16.

15 Hicks MJ, Silverstone LM, Flaitz CM. A scanning electron microscopic and polarised light study of acid etching of caries like lesions in human enamel treated with sodium fluoride in-vitro. Arch Oral Biol 1984; 29: 765–72.[CrossRef][Medline]

16 World Health Organisation. Declaration of Helsinki. Br Med J 1996; 313: 1448–9.[Free Full Text]

17 Willmot DR, Brook AH. Changes in area of post-orthodontic enamel lesions measured by polarized illumination and image analysis. J Dent Res 2002; 31: 81.

18 Willmot DR, Benson PE, Pender N, Brook AH. Reproducibility of quantitative measurement of white enamel demineralization by image analysis. Caries Res 2000; 34: 175–81.[CrossRef][Medline]

19 Altman DG, Schulz KF, Moher D et al. The revised CONSORT statement for reporting randomized clinical trials: an explanation and elaboration. Ann Intern Med 2001; 134: 663–94.[Abstract/Free Full Text]

20 Ogaard B, Ten Bosch JJ. Regression of white spot enamel lesions. A new optical method for quantitative longitudinal evaluation in-vivo. Am J Orthod Dentofac Orthop 1994; 106: 238–42.[Medline]

21 Al-Khateeb S, Forsberg CM, De Josselin de Jong E, Angmar-Mansson B. A longitudinal laser fluorescence study of white spot lesions in orthodontic patients. Am J Orthod Dentofac Orthop 1998; 113: 595–602.[CrossRef][Medline]

22 Benson PE, Pender N, Higham SM. Quantifying enamel demineralization from teeth with orthodontic brackets — a comparison of two methods. Part 1: repeatability and agreement. Eur J Orthod 2003; 25: 149–58.[Abstract/Free Full Text]

23 Benson PE, Pender N, Higham SM. Quantifying enamel demineralization from teeth with orthodontic brackets — a comparison of two methods. Part 2: validity. Eur J Orthod 2003; 25: 159–65.[Abstract/Free Full Text]

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