Printer Friendly

The effect of fluoride slow-releasing devices on fluoride in plaque biofilms and saliva: a randomised controlled trial.


The key element in the effort to tackle dental caries is prevention with the most widely used and most effective agent, fluoride (F). Interpretations of the available data on the anti-cariogenic effect of F are in favour of a local effect [Fejerskov, 2004; Hellwig and Lennon, 2004] and within the caries lesions themselves [Robinson et al., 2000]. Evidence for the effectiveness of a continuous supply in the oral cavity via fluoridated water has led to a search for an alternative F source capable of producing and sustaining elevated concentrations of F in the mouth over longer periods of time than the minutes associated with tooth brushing or rinsing. As a result of these investigations a F sustained slow-releasing device (FSSRD) was developed at Leeds University in 1984. This device, comprising a soluble fluoride containing glass, was shown to be capable of maintaining low levels of fluoride in saliva of ~0.1 ppm [Toumba, 1996; Toumba et al., 2009; Al-Ibrahim et al., 2010] i.e. up to 10 times that in normal control saliva [Pessan et al., 2008].

The anti-cariogenic effect of the FSSRD was shown by a double-blind clinical caries trial, with high caries-risk children over a period of two years. This study showed significantly fewer carious teeth using the F device compared with a control (placebo) device group. For dmft-DMFT there were 67% fewer new carious teeth and for dmfs-DMFS there were 76% fewer new carious surfaces [Toumba and Curzon, 2005].

With regard to the site of F action, it is now considered most likely that F operates primarily on the dynamics of demineralisation and remineralisation in the carious lesion [Wood et al., 2000]. The movement of fluoride through and possibly accumulation by plaque biofilms, overlying caries lesions, is therefore extremely important [Robinson et al., 2000]. With this in mind it is reasonable to hypothesise that the slow release from the device would increase F concentrations in saliva and possibly plaque or at least reduce loss of accumulated fluoride from plaque biofilm layers. To test this we have performed the following randomised controlled double-blind crossover study which aimed at investigating the effect of FSSRD on F levels in unstimulated saliva and undisturbed plaque biofilms over 7 days. The investigation also included a study of the effect of patient age on F concentrations in dental plaque biofilms and unstimulated saliva while using the FSSRD.

Materials and Methods

Clinical methods. Ethical approval was obtained from Bradford local ethics committee and an informed consent for each participant was obtained before the start of the study. Following the analysis of the results obtained from a pilot study, a power calculation showed the need for a minimum of 64 participants in order to achieve the study aims.

Seventy-seven participants took part in this randomised controlled double-blind crossover study. Twelve participants dropped out of the study due to difficulties attaching the devices to their teeth, devices being lost twice in the first leg of the study, or not being happy with the feeling of the devices in the mouth. Randomisation was achieved by two independent individuals who coded all of the FSSRD/placebo devices (PDs) used. The codes were not disclosed until all analyses were complete and the results produced. Neither the author nor the participants knew whether the device used for each leg was a FSSRD or a PD. The FSSRDs and the PDs were identical in shape and were indistinguishable from each other.

The FSSRD/PD (Ultradent, Salt Lake City, Utah, USA) in this study was made up of a fluoride containing glass bead and a bracket (Figure 1). The brackets containing the glass beads were attached to the tooth surfaces using composite resin. This carried with it the possibility of changing the glass bead without the need to de-bond the whole device (Figure 1).


Sixty-five participants aged between 6-35 years completed this study. The mean age of all the participants in the study was 19.2 years with 24 participants aged between 6-16 years of age (mean age=11.8 years) in the mixed and early adult dentition stage and 41 participants aged between 16-35 years of age (mean age=23.6 years) in the adult dentition.

Undisturbed plaque biofilms were recovered using a modification of the plaque-generating device (MPGD) described by Robinson et al. (1997) in which the nylon ring was replaced with a composite ring attached to the tooth using composite resin rather than cyanoacrylate adhesive. This provided firmer adhesion and eliminated loss of rings in vivo due to failure of adhesion of rings to the underlying enamel slab. This was especially important with child participants. A comparison of plaque bacterial composition and biofilm structure, in a previous study for both devices showed no significant difference between the two types of device [Abudiak, 2007].

Before the start of the first leg each participant had a washout period of 7 days followed by a second washout period of 7 days between the first and second legs of the study. During the whole study period (washout and legs) all participants were asked to use only non-fluoridated toothpaste and to avoid where possible high fluoride containing foods or drinks.

Whenever possible, the FSSRD/PD was attached to the second permanent molar, while the MPGD was attached to the first permanent molars in the same maxillary dental quadrant (Figure 2). For child participants with mixed or primary dentitions, the FSSRD/PD and the MPGD were attached to any available combination of molar/premolar permanent or primary teeth on the same maxillary dental quadrant with the FSSRD/ PD always attached distal to the MPGD.


At the end of the second leg, both devices were removed, teeth cleaned of remaining composite resin and Duraphat varnish 2.26% F (Colgate-Palmolive Ltd, UK) applied to the buccal surface of the teeth used for attachment of the devices. This was a prophylactic measure in case of any surface demineralisation that may have occurred following device attachment.

At the end of each leg of the study whole, mixed unstimulated saliva was collected from all participants which were then stored at -20[degrees]C for future analysis. This was achieved by asking the participants to allow saliva to collect in their mouth and drool into a tube after two minutes.

Statistical Methods

Statistical analysis using paired sample t-test was used to compare the results of F levels between test and control groups. Spearman's correlation coefficient was used to test the relationship between patient's age and plaque weight against F concentration in plaque and saliva using FSSRDs and PDs.

Laboratory Methods

Plaque samples. After recovery, the MPGDs were immediately snap frozen in liquid nitrogen, and then stored at -20[degrees]C prior to analysis. For analysis, total plaque was collected by scooping plaque from the inside of the MPGDs using sterile dental probes and placing this into acid washed Eppendorf tubes. Fluoride was extracted by immersion overnight in deionised water (DIW), using a water to plaque ratio of 100:1 (W/W) [Duckworth et al., 1994]. The supernatant was analysed for fluoride using micro ion exchange chromatography (IC). A Hamilton PrPx 110 column (column dimension= 150x4.1mm, column particle size= 7[micro]m, stable pH=0-14, Hamilton, USA) with 6mM NaOH eluent was used (flow rate= 1ml/min).

Saliva samples. The method described by [Benzo et al., 2002] was used to measure F in saliva. One hundred microlitres of saliva was added to 10 [micro]l of 2 M NaOH and 50 [micro]l of DIW after which the sample was shaken using a Vibrax shaker for 10 sec. To precipitate proteins, acetonitrile (200 [micro]l) was added to the mixture and the whole sample shaken again for 10 sec and then centrifuged at 13,300 rpm at room temperature (~20[degrees]C) for 10 min. One hundred microlitres of supernatant was then added to 500[micro]l DIW all of which was then injected using an autosampler (Triathlon, Spark, Metrohm Ltd., Herisau, Switzerland) into the IC using the same column used for plaque samples but with an eluent of 12 mM NaOH.


Saliva. There was no statistically significant difference in F concentration between the test and control groups when analysed using paired sample t-test (p>0.05) (Table 1). There was no correlation between patient's age and F concentration (p>0.05), in both the test and control groups as shown by Spearman's correlation coefficient (Table 2).

Plaque results. There was no statistically significant difference between the test and control groups when analysed using paired sample t test (p>0.05) (Table 1). Using Spearman's correlation coefficient, no relationship was found between patient's age and F concentration in natural plaque biofilms (p>0.05) (Table 2). Using Spearman's correlation coefficient, a reverse relationship was found between plaque wet weight and F concentration in natural plaque biofilms (p<0.05, r = -0.683 test,-0.485 control groups) (Table 2).

Discussion. In this study, we aimed at investigating the effect of the FSSRD after seven days on F concentrations in whole unstimulated saliva and natural undisturbed plaque in children and adults ranging from 6-35 years of age using a randomised controlled trial. The crossover design was chosen to reduce the number of participants needed as it was extremely difficult to recruit children. In addition, this design had the advantage of reducing patient variability as a factor in this study.

Plaque and saliva did not show a significant rise in F concentration from the FSSRD over 7 days. These negative results raise a number of important issues. First, this might suggest that 7 days may be insufficient to generate the increased fluoride concentrations which have been suggested by earlier studies. For example, when FSSRDs were used for longer periods of time [Toumba, 1996; Kapetania, 2004; Toumba and Curzon, 2005; Andreadis et al., 2006] salivary levels were shown to increase. Secondly, however, as well as the time difference, saliva was collected differently in these earlier studies when saliva was allowed to pool on the FSSRD for 2 min before collecting samples. This pooling over the device may have a considerable effect on elevating salivary fluoride as judged by the data of Tatsi (2006).

Tatsi [2006] used 2 FSSRDs attached to each maxillary first permanent molar in 10 participants. Unstimulated saliva was collected after 2 weeks and 3 months using the same methodology as the current study. As with our current study, no differences were found between the test and control groups. Furthermore, Tatsi also looked more closely at the difference in saliva sample collection techniques. Drooling after holding saliva for 2 min where the FSSRD was attached produced higher F concentrations in the samples than just drooling saliva in the floor of the mouth. Clearly the mode of saliva collection can have a significant effect on salivary fluoride concentration.

As well as saliva, there was no statistically significant differences in plaque F concentration between the test and control groups (p>0.05). This differs from some previous studies. Recovering the PGDs after 4 weeks of using the FSSRD, Kapetania [2004], using the same laboratory methodology as our study, showed a statistically higher plaque F concentration in a sample of adult participants. This implies that 7 days is not sufficient to permit significant fluoride accumulation. The reason could lie with the restricted penetration of plaque demonstrated previously [Robinson et al., 1997; Watson, 2005]. Even exposure to 1,000 ppm fluoride for 2 minutes showed restricted uptake with F mainly concentrated in the outer layers.

Some changes in plaque architecture with time have also been reported showing some reduction in porosity which may also affect F uptake. Wood and co-workers [2002] studied the effect of plaque age (two days, one week, two weeks and four weeks) on plaque structure viewed under the confocal scanning laser microscope. There was a tendency for plaque to become more compact over a period of 4 weeks. The effect of such a change on fluoride accumulation is not clear.

The significant inverse relationship between F concentration and plaque weight may also be related to structure. As fluoride tends to accumulate in the outer regions of plaque biofilms, thinner plaques with a greater proportion of surface will tend to show higher fluoride concentrations. Therefore a change in plaque weight/thickness recovered between the test and control groups might have contributed to the results attained. The above data may also suggest that the FSSRD anticariogenic effect [Toumba and Curzon, 2005] might not be related to plaque or saliva fluoride in a simple fashion. It might, for example, be due to the consistency of F concentrations in plaque, rather than absolute concentration.

Patient age had no relationship to F concentration in natural plaque biofilms or with F concentration in unstimulated saliva. To the author's knowledge, no studies are available discussing the effect of patient age on plaque F content.


Our data showed no effect of the FSSRD in raising F concentrations in dental plaque and unstimulated whole saliva after 7 days. Such levels may require longer periods to become established. One could also conclude that the mechanism and precise concentrations of fluoride needed to exert a protective effect may not only be related to time of exposure but also consistency of fluoride concentration. Further studies on the effect of plaque age and thickness on F concentration is crucial for the study of the effect of the FSSRD on dental plaque biofilms. There is no effect of patient's age on plaque and salivary F concentration collected after 7 days.


Abudiak H. Effect of fluoride sustained slow-release devices on fluoride, phosphate and calcium levels in plaque biofilms. PhD thesis at Child Dental Health. Leeds, University of Leeds, 2007.

Al-Ibrahim NS, Tahmassebi JF and Toumba KJ (2010). In vitro and in vivo assessment of newly developed slow-release fluoride glass device. European Archives of Paediatric Dentistry;11:131-135.

Andreadis, GA, Toumba, KJ, Curzon, ME. Slow-release fluoride glass devices: in vivo fluoride release and retention of the devices in children. Eur Arch Paediatr Dent. 2006;7:258-261.

Benzo, Z, Escalona, A, Salas, J, et al. Evaluation of select variables in the ion chromatographic determination of F-, Cl-, Br-, NO(-)3, SO(-2)4, and PO(3)4 in serum samples. J Chromatogr Sci. 2002;40:101-106.

Duckworth, RM, Jones, Y, Nicholson, J, et al. Studies on plaque fluoride after use of F-containing dentifrices. Adv Dent Res. 1994;8:202-207.

Fejerskov, O. Changing paradigms in concepts on dental caries: consequences for oral health care. Caries Res. 2004;38:182-191.

Hellwig, E & Lennon, AM. Systemic versus topical fluoride. Caries Res. 2004;38:258-262.

Kapetania, I. Effect of Fluoride Slow Release Glass Device on Salivary and Plaque Levels of Fluoride, Calcium, and Phosphate. Master's desertation at Child Dental Health. Leeds, University of Leeds, 2004.

Pessan, JP, Al-Ibrahim, NS, Buzalaf, MA, et al. Slow-release fluoride devices: a literature review. J Appl Oral Sci. 2008;16:238-246.

Robinson, C, Kirkham, J, Percival, R, et al. A method for the quantitative-site specific study of the biochemistry within dental plaque biofilms formed in vivo. Caries Res. 1997;31:194-200.

Robinson, C, Shore, RC, Brookes, SJ, et al. The chemistry of enamel caries. Crit Rev Oral Biol Med 2000; 11:481-495.

Tatsi, C. Effect of Fluoride Slow Release Glass Devices On Salivary And Gingival Crevicular Fluid Levels Of Fluoride. A Pilot Study. Master's Desertation at Child Dental Health. Leeds, University of Leeds, 2006.

Toumba, KJ. In vivo and in vitro evaluation of a slow-release fluoride glass for the prevention of dental caries in high-risk children. PhD thesis at Child Dental Health. Leeds, University of Leeds, 1996.

Toumba, KJ, Curzon, ME. A clinical trial of a slow-releasing fluoride device in children. Caries Res. 2005;39:195-200.

Toumba KJ, Al-Ibrahim NS, Curzon MEJ. A review of slow-release fluoride devices. Eur Arch Paediatr Dent; (2009) 10:175-182.

Watson, PS. The uptake and distribution of fluoride and triclosan in plaque biofilms formed in vivo using the Leeds in situ device. PhD thesis in Oral biology department. Leeds, Leeds University, 2005. Wood, SR, Kirkham, J, Marsh, PD, et al. Architecture of intact natural human plaque biofilms studied by confocal laser scanning microscopy. J Dent Res 2000; 79: 21-27.

Wood, SR, Kirkham, J, Shore, RC, et al. Changes in the structure and density of oral plaque biofilms with increasing plaque age. FEMS Microbiol Ecol 2002; 39: 239-244.

H. Abudiak *, C. Robinson **, M.S. Duggal *, S. Strafford *, K.J. Toumba *.

* Department of Paediatric Dentistry, Leeds Dental Institute, University of Leeds, UK. **Department of Oral Biology, Leeds Dental Institute, University of Leeds, UK.

Postal address: Dr H. Abudiak, Dept Paediatric Dentistry, Leeds Dental Institute, Clarendon Way, Leeds, LS2 9LU, UK.

Table 1. Plaque and saliva F concentrations (ppm) for the test
and control groups showing means, 95% confidence intervals for
the difference in means and significance based on paired sample

                                             95% Confidence
                                              Interval of
                          Mean               the Difference   Sig.

               Test leg (n)   Control (n)   Lower     Upper

Plaque (ppm)   0.588 (62)     0.571 (60)    -0.201    0.236   0.87
Saliva (ppm)   0.036 (64)     0.034 (65)    -0.0128   0.016   0.84

Table 2. Correlation between (patient's age (years) and plaque
wet weight (mg) against plaque F concentration (ppm)) and
(Patient's age (years) against salivary F concentration (ppm))
using Spearman's correlation coefficients.

                                           Plaque F concentration (ppm)

                                            Test group   Control group

Patient age in years     Correlation          -0.062        -0.167
                         Sig. (2-tailed)      0.641          0.246
                         N                      62            60

Plaque wet weight (mg)   Correlation          -0.683        -0.485
                         Sig. (2-tailed)      0.0 *          0.0 *
                         N                      62            60

                                           Saliva F concentration (ppm)

                                            Test group   Control group

Patient age in years     Correlation           -0.2          -0.05
                         Sig. (2-tailed)      0.113          0.695
                         N                      64            65

Plaque wet weight (mg)   Correlation
                         Sig. (2-tailed)

* Statistically significant (p< 0.05)
COPYRIGHT 2011 European Academy of Paediatric Dentistry
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2011 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Abudiak, H.; Robinson, C.; Duggal, M.S.; Strafford, S.; Toumba, K.J.
Publication:European Archives of Paediatric Dentistry
Article Type:Report
Geographic Code:4EUUK
Date:Jun 1, 2011
Previous Article:Use of the 'Hall technique' for management of carious primary molars among Scottish general dental practitioners.
Next Article:Disease outcome for children who present with oral manifestations of Crohn's disease.

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters