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Keywords:

  • Remineralisation;
  • fluoride;
  • children;
  • toothpaste

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Objective

To evaluate the ability of a range of low abrasivity experimental toothpastes designed for use by children at different stages of their development (typically ages 0–2 years, 3–5 years and 6+ years) to promote fluoride uptake and remineralisation of artificial caries lesions.

Methods

pH cycling study: demineralised human permanent enamel specimens were subjected to a daily pH cycling regime consisting of four 1-minute treatments with toothpaste slurries, a 4-hour acid challenge and remineralisation in pooled whole human saliva. Surface microhardness (SMH) was measured at baseline, 10 days and 20 days, and the fluoride content determined at 20 days. Enamel Fluoride Uptake (EFU): these studies were based on Method #40 described in the US Food and Drug Administration (FDA) testing procedures. Abrasivity: relative enamel abrasivity (REA) and relative dentine abrasivity (RDA) were measured using the Hefferren abrasivity test. Bioavailable fluoride: the bioavailable fluoride was determined for all experimental toothpastes from slurries of one part toothpaste plus 10 parts deionised water.

Results

Enamel remineralisation measured by changes in SMH correlated with enamel fluoride content. A statistically significant fluoride dose response was observed for all toothpastes tested across all age groups (P < 0.05). The fluoride content of specimens in the pH cycling model correlated with the EFU testing results. The enamel and dentine abrasivities were low and the level of bioavailable fluoride was high for all experimental toothpastes.

Conclusion

A series of low abrasivity experimental toothpastes were developed which were effective at promoting fluoride uptake and remineralisation of artificial caries lesions.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

In children, the deciduous or primary teeth typically begin to erupt at 6–8 months of age. However, from around the age of 6 years, these teeth start to be replaced by permanent teeth. At this stage, the mouth will contain both deciduous and permanent teeth until the last deciduous tooth is lost at around 12 years of age[1, 2].

There are a number of important differences between deciduous and permanent enamel. Specifically, deciduous enamel contains more organic material[3], is generally less mineralised in the outer enamel layers[4] and has a higher porosity[5]. This makes deciduous enamel more susceptible to acid-mediated dissolution than permanent enamel[6-8]. In addition, deciduous enamel is softer and therefore less mechanically resistant than permanent enamel. Consequently, tooth wear owing to abrasion can be more pronounced in deciduous than in permanent teeth[9].

Childhood caries is recognised as being a major public health problem among the general population. According to the National Health and Nutrition Examination Survey carried out from 1999 to 2004 in the USA, 42% of children aged 2–11 years have had dental caries in their primary teeth and 21% of children aged 6–11 years have had dental caries in their permanent teeth[10]. A number of comprehensive reviews of caries clinical trial data in children and adolescents concluded that there was strong evidence that daily use of fluoride (F)-containing toothpastes can reduce the incidence of caries compared with a placebo or with non-brushing[11, 12]. These effects were also improved with supervised brushing and increased frequency of brushing[11].

Mechanistic studies have shown that the anti-caries effect of fluoride is through the prevention of demineralisation and enhancement of remineralisation[13]. In addition, fluoride has been shown to interfere with bacterial metabolism in vitro, which may inhibit plaque acid production[14].

A series of guidelines have been established by the US Food and Drug Administration (FDA), the American Dental Association (ADA) and FDI World Dental Federation to ensure that marketed toothpastes are safe and effective[15-17]. Caries clinical trials are considered to be the ultimate proof of anti-caries effectiveness, however, because of the long duration and high costs associated with these types of studies, a number of preclinical methods known as bioequivalence studies have been developed to evaluate fluoride efficacy[18]. In these studies, the experimental toothpaste is tested against a clinically proven control toothpaste containing the same active ingredient at the same nominal concentration.

The maximum permitted concentrations of fluoride for toothpastes in different markets are governed by regulatory requirements; however, fluoride concentrations for specific child age ranges are generally set by national guidance via health authorities or dental associations.

A new range of toothpastes have been developed for use by children at different stages of their development (typical ages are 0–2 years, 3–5 years and 6+ years) containing different concentrations of fluoride and for different markets. The aim of the present studies was to evaluate the efficacy of these toothpastes to (1) promote lesion remineralisation under dynamic demineralising/remineralising conditions simulating in vivo caries formation, and (2) promote enamel fluoride uptake. The enamel and dentine abrasivities of these toothpastes were also determined relative to the ADA reference abrasive.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

Materials

The experimental toothpastes and commercial toothpaste controls evaluated are shown in Tables 1 and 2, respectively. The placebo toothpastes were fluoride-free variants of the corresponding experimental toothpastes.

Table 1. Typical age ranges, fluoride concentrations, abrasive, pack type and intended markets for each experimental toothpaste
Age rangeFluoride concentration (ppm) and sourceAbrasivePack typeIntended market
  1. a

    Matched placebo formulation.

  2. b

    Matched dose response control.

0–2 years0a, 500 or 1,000 (as sodium fluoride (NaF))SilicaTubeNon-US
3–5 years0a, 250b, 500, 1,000 or 1,450 (as NaF)SilicaTubeNon-US
6+ years0a, 500b, 1,450 (as NaF)SilicaTubeNon-US
2–5 years1,150 (as NaF)SilicaTube and pumpUS
6+ years0a, 250b, 1,150 (as NaF)SilicaTubeUS
Table 2. Age ranges, fluoride concentrations, abrasive and current market for each commercial toothpaste control
ToothpasteAge rangeFluoride concentration (ppm) and sourceAbrasiveMarketManufacturer
Odol-Med3 Milchzahn0–6 years500 (as NaF)SilicaGermanyGlaxoSmithKline
Aquafresh Milk Teeth0–3 years1,000 (as sodium monofluorophosphate (SMFP))SilicaUKGlaxoSmithKline
Aquafresh Little Teeth4–6 years1,000 (as NaF)SilicaSouth AfricaGlaxoSmithKline
Aquafresh Kids Bubble Fresh2 years and older1,100 (as SMFP)ChalkUSGlaxoSmithKline
Aquafresh Big Teeth6+ years1,400 (as NaF)SilicaUKGlaxoSmithKline
Aquafresh Little Teeth4–6 years1,400 (as NaF)SilicaUKGlaxoSmithKline
Aquafresh Fresh and MintyNot specified1,450 (as NaF)SilicaUKGlaxoSmithKline
USP Reference ToothpasteN/AConcentration not specified (as NaF)SilicaN/ANot specified
pH cycling

The method used was based on the model of White[19, 20] which was subsequently modified by Schemehorn et al.[21-23]

Specimen preparation

Enamel specimens (3 mm diameter) were removed from extracted human permanent teeth and mounted on rods. The specimens were initially ground by hand on a lapidary wheel (600 grit wet/dry paper). Following hand grinding the specimens were mounted on a counter rotational grinding/polishing apparatus and finally ground for 3 minutes with the same paper. The specimens were then polished on the same apparatus with 0.05 μm Gamma Alumina (Buehler, Lake Bluff, IL, USA) against a urethane pad using a force of 0.1 N for 1 hour.

Baseline surface microhardness

The initial baseline surface microhardness (SMH) of the sound enamel specimens was determined using a Vickers hardness indenter at a load of 200 g for 15 seconds. The average baseline specimen SMH was determined from four indentations. Only specimens with a sound SMH range of 300–360 Vickers hardness numbers (VHN) were accepted.

Initial demineralisation

Artificial lesions were formed in the enamel specimens by a 68-hour immersion into a solution of 0.1 m lactic acid and 0.2% w/v Carbopol C907 which had been 50% saturated with hydroxyapatite and adjusted to pH 5.0 with potassium hydroxide. The initial SMH of the demineralised specimens was determined using the procedure described above. Only specimens with a lesion SMH range between 25 and 45 VHN were accepted into the studies. Specimens were balanced into groups and subgroups based on their post-demineralisation SMH values. Thirty specimens per treatment group were used in this study.

Treatment slurries

During the treatment period, the specimens were immersed in toothpaste slurries to simulate daily exposure to toothpaste. The slurries were prepared by adding 5.0 g of toothpaste to 10.0 g of pooled human saliva in a beaker with a magnetic stirrer bar. All treatments were stirred at 350 rpm. A fresh slurry was prepared immediately before each treatment period.

Treatment regimen

The pH cycling regimen consisted of a 4 hour per day acid challenge in the lesion forming solution and 4 × 1-minute treatment periods with toothpaste slurries. After the treatments, the specimens were rinsed with running deionised water. During remineralisation periods, specimens were stored in pooled human saliva. This regimen was repeated for 20 days. The treatment schedule is shown in Table 3.

Table 3. pH cycling regimen
Time of dayTreatment
  1. a

    On the first day this treatment was not given; the study started with the saliva treatment to allow a pellicle to form.

08:00–08:01Toothpaste treatmenta
08:01–09:00 Saliva treatment
09:00–09:01Toothpaste treatment
09:01–10:00Saliva treatment
10:00–14:00Acid challenge
14:00–15:00Saliva treatment
15:00–15:01Toothpaste treatment
15:01–16:00Saliva treatment
16:00–16:01Toothpaste treatment
16:01–08:00Saliva treatment
Post-treatment surface microhardness

After 10 days and 20 days of treatment, the average specimen SMH was determined from four indentations on each specimen, next to the baseline indentations. The difference between the SMH following treatment and the initial lesion SMH indicated the ability of that treatment to enhance remineralisation after 10 days and 20 days of treatments.

Fluoride analysis

At the end of the 20-day treatment regimen, the fluoride content of each enamel specimen was determined using the microdrill technique to a depth of 100 μm. The diameter of the drill hole was also determined. The enamel powder from the drill hole was collected and dissolved in 20 μl of perchloric acid (HClO4) followed by the addition of 40 μl of citrate/ethylenediaminetetraacetic acid (EDTA) buffer and 40 μl of deionised water. Solutions were analysed for fluoride using an ion-selective electrode by comparison with a similarly prepared standard curve. Fluoride content was calculated as μg F/cm3.

Enamel fluoride uptake (EFU)

The methodology was identical to the one identified as Method 40 in the US Anti-Caries Monograph[18] except that the lesions were formed using a solution of 0.1 m lactic acid containing 0.2% w/v Carbopol 907 and 50% saturated with hydroxyapatite (pH 5.0).

Sound, upper, central, bovine incisors were selected and cleaned of all adhering soft tissue. A core of enamel 3 mm in diameter was prepared from each tooth by cutting perpendicular to the labial surface with a hollow-core diamond drill bit. Each specimen was embedded in the end of a Plexiglas rod using methyl methacrylate and polished with 600 grit wet/dry paper followed by 0.05 μm Gamma Alumina (Buehler, Lake Bluff, IL, USA). Twelve specimens per group were used in this study.

Each enamel specimen was etched by immersion into 0.5 ml of 1 m HClO4 for 15 seconds with continuously agitation. A sample of each solution was then buffered with a total ionic strength adjustment buffer (TISAB) to a pH of 5.2 (0.25 ml of sample, 0.5 ml of TISAB and 0.25 ml of 1 m sodium hydroxide) and the fluoride content determined by comparison to a similarly prepared standard curve (1 ml standard and 1 ml TISAB). This data formed the baseline fluoride concentration of each specimen before treatment.

The specimens were once again ground and polished as described above. An incipient lesion was formed in each enamel specimen by immersion into 0.1 m lactic acid containing 0.2% w/v Carbopol 907 and 50% saturated with hydroxyapatite (pH 5.0) for 24 hours at room temperature. These specimens were then rinsed with deionised water and stored in a humid environment until used.

The treatments were performed using supernatants of the toothpaste slurries. The slurries were prepared by adding 9.0 g of toothpaste to 27.0 ml of deionised water. The slurries were mixed well and then centrifuged. The specimens were then immersed into 25 ml of their assigned supernatant with constant stirring (350 rpm) for 30 minutes. Following treatment, the specimens were rinsed with deionised water and etched with 0.5 ml of 1 m HClO4 for 15 seconds with continuous agitation. The etch solution was analysed for fluoride as outlined above. The baseline fluoride concentration of each specimen was then subtracted from the post-treatment value to determine the change in enamel fluoride due to the test treatment.

Relative dentine abrasivity (RDA)

The procedure used in this study was the Hefferren abrasivity test[24] recommended by the ADA and described in ISO 11609:2010[15] for determination of toothpaste abrasiveness in dentine.

Eight human dentine specimens were subjected to neutron bombardments resulting in the formation of radioactive phosphorus (32P)[15]. The specimens were mounted in methyl methacrylate and placed into a V-8 cross-brushing machine (Sabri Dental Enterprises, Inc., Downers Grove, IL, USA). The specimens were brushed for a 1,500 stroke, precondition run using a slurry consisting of 10 g ADA reference material [calcium pyrophosphate (Ca2P2O7)] in 50 ml of a 0.5% w/v carboxymethylcellulose (CMC)/10% w/v glycerine solution. The brushes used were those specified by the ADA (Oral-B P-40) with a brushing force of 1.5 N.

Following the precondition run the test was performed using the above parameters (1.5 N and 1,500 strokes) in a ‘sandwich design’. Before and after brushing with the test toothpaste (25 g product/40 ml deionised water) each tooth set was brushed with the ADA reference material. This dilution produces a final slurry volume and a concentration similar to those of the reference abrasive slurry. The procedure was repeated so that each toothpaste was assayed on each tooth set.

RDA calculations

One millilitre samples were taken, weighed and added to 5 ml of ‘Ultima Gold’ scintillation cocktail. The samples were mixed well and immediately put on a liquid scintillation counter for radiation detection. The counts per minute (CPM) values for the test and reference products were measured.

The RDA of the test toothpaste is calculated using Equations 1 and 2:

  • display math(1)

where

Gmr = mean reference net CPM per mass of slurry (g)

Gpre = pre-net CPM per mass of slurry (g)

Gpost = post-net CPM per mass of slurry (g)

  • display math(2)

where

Gmt = mean test toothpaste net CPM per mass of slurry (g)

Gmr = mean reference net CPM per mass of slurry (g)

100 = Dentine abrasivity of the ADA reference material

Relative enamel abrasivity (REA)

The procedure was identical to that used for determination of RDA except that human enamel was used instead of dentine. In addition, specimens were brushed for 5,000 strokes. In this test, the ADA reference material was assigned a value of 10.

Determination of bioavailable fluoride

Toothpaste slurries were prepared by homogenisation for 10 minutes of one part test toothpaste with 10 parts (w/w) deionised water. The slurries were centrifuged at ca. 3000 g to obtain the supernatant. The supernatants were diluted with water such that the range of the working standard bracketed the concentration of the fluoride ion. These solutions were analysed by Dionex Ion Chromatography (Dionex Corporation, Camberley, UK) with suppressed conductivity detection. Fluoride concentrations were determined by external standardisation.

Statistical analysis

Statistical analyses were conducted using an analysis of variance model (anova) (Sigma Stat Software, Version 3.1, Systat Software, Chicago, IL, USA). Where significant differences were found, additional pair-wise comparisons were performed using a Student–Newman–Keuls test (P < 0.05).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

pH Cycling Studies

The change in hardness (ΔVHN), fluoride content and slurry pH data from the pH cycling studies are shown in Tables 4-7. The pH of all toothpaste slurries tested as one part test product with two parts (w/w) pooled human saliva ranged from 7.06–8.07.

Table 4. Summary of ΔVHN and enamel fluoride content after pH cycling with experimental toothpastes (ages 0–2 years/non-US) toothpastes (n = 30). The pH of the toothpaste slurry is also reported
TreatmentΔVHN10 dayΔVHN20 dayEnamel fluoride content (μg F/cm3)pH of toothpaste slurry
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

0 ppm F−1 (0.7)a3.6 (1.0)a585 (19)a7.04
500 ppm F12 (1.0)b17.3 (1.0)b2,259 (101)b7.11
1,000 ppm F14.2 (0.9)b24.2 (1.2)c3,181 (131)c7.20
Table 5. Summary of ΔVHN and enamel fluoride content after pH cycling with experimental toothpastes (ages 3–5 years/non-US) toothpastes (n = 30). The pH of the toothpaste slurry is also reported
TreatmentΔVHN10 dayΔVHN20 dayEnamel fluoride content (μg F/cm3)pH of toothpaste slurry
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

0 ppm F0.6 (0.7)a−3.2 (0.9)a352 (12)a7.15
250 ppm F11.2 (0.7)b14.3 (0.8)b1,484 (56)b7.16
500 ppm F13.3 (0.8)b19.0 (0.9)c1,692 (62)c7.20
1,000 ppm F15.7 (0.9)c20.1 (1.1)c1,886 (86)d7.21
1,450 ppm F17.3 (0.9)c20.7 (0.8)c2,301 (68)e7.21
Table 6. Summary of ΔVHN and enamel fluoride content after pH cycling with experimental toothpastes (ages 2–5 years and 6+ years/US) toothpastes (n = 30). The pH of the toothpaste slurry is also reported
TreatmentΔVHN10 dayΔVHN20 dayEnamel fluoride content (μg F/cm3)pH of toothpaste slurry
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

0 ppm F ( 6+ years)5.9 (0.9)a9.5 (0.8)a365 (15)a7.06
250 ppm F (6+ years)11.7 (1.2)b18.5 (1.1)b,c1,062 (56)b7.13
1,150 ppm F (2–5 years)15.3 (1.1)b23.9 (1.5)d1,539 (59)c7.16
1,150 ppm F (6+ years)22.7 (1.5)c22.6 (1.4)c,d1,655 (66)c7.11
USP Reference Toothpaste14.9 (1.3)b20.7 (2.5)b,c,d1,633 (67)c7.09
Aquafresh Kids Bubble Fresh15.5 (0.7)b16.8 (0.9)b1,048 (39)b8.07
Table 7. Summary of ΔVHN and enamel fluoride content after pH cycling with experimental toothpastes (ages 6+ years/non-US) toothpastes (n = 30). The pH of the toothpaste slurry is also reported
TreatmentΔVHN10 dayΔVHN20 dayEnamel fluoride content (μg F/cm3)pH of toothpaste slurry
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets

0 ppm F8.0 (0.8)a5.8 (0.7)a582 (20)a7.09
500 ppm F14.7 (0.9)b17.6 (0.9)b2,029 (51)b7.15
1,450 ppm F20.2 (1.2)c23.2 (1.4)c3,074 (146)c7.20

Ages 0–2 years (Non-US toothpastes)

All fluoride-containing toothpastes were significantly more effective at promoting remineralisation compared with the fluoride-free placebo after 10 days and 20 days (Table 4). A significant difference in ΔVHN between the 500 and 1,000 ppm F toothpastes was only observed after 20 days. All differences in the enamel fluoride content between toothpaste treatments were significant.

Ages 3–5 years (non-US toothpastes)

All fluoride containing toothpastes were significantly more effective at promoting remineralisation compared with the fluoride-free placebo after 10 days and 20 days (Table 5). After 10 days, all ΔVHN treatment differences were significant with the exception of the 250 versus 500 ppm F and 1,000 versus 1,450 ppm F toothpastes. After 20 days, a statistically significant dose response in ΔVHN was only observed up to 500 ppm F. While there were no statistically significant differences between the 500, 1,000 and 1,450 ppm F toothpastes at this timepoint, the differences were directional. All differences in the enamel fluoride content between toothpaste treatments were significant.

Ages 2–5 years and 6+ years (US toothpastes)

All fluoride containing toothpastes were significantly more effective at promoting remineralisation compared with the fluoride-free placebo after 10 days and 20 days (Table 6). At both timepoints, a statistically significant dose response was observed for ΔVHN, however, there were no statistically significant differences between the 250 ppm F dose response toothpaste, the current US Aquafresh Kids Bubble Fresh toothpaste and the USP reference toothpaste. After 20 days, there were no significant differences between the two experimental toothpastes containing 1,150 ppm F and the USP reference toothpaste. The enamel fluoride content data show a statistically significant dose response; however, the differences between the two experimental toothpastes containing 1,150 ppm F and the USP reference toothpaste were not significant.

Ages 6+ years (Non-US toothpastes)

At both the 10-day and 20-day time-points, all differences in ΔVHN and enamel fluoride content between the 0, 500 and 1,450 ppm F toothpastes were statistically significantly (Table 7).

EFU

The EFU results for the US and non-US experimental toothpastes with commercially available controls are shown in Tables 8 and 9 respectively. All fluoride containing toothpastes promoted significant fluoride uptake into demineralised enamel compared with the fluoride free placebo. The fluoride uptake data in Table 8 show that there were no significant differences between the three US experimental toothpastes. However, these toothpastes were significantly more effective at promoting fluoride uptake than the USP reference toothpaste. The order of fluoride uptake was 0 ppm F < Aquafresh Kids Bubble Fresh < USP reference toothpaste < 1,150 ppm F (ages 2–5 years (Tube) = 1,150 ppm F (ages 2–5 years (Pump) = 1,150 ppm F (ages 6+ years).

Table 8. Enamel fluoride uptake data for US experimental and commercial toothpastes using FDA method #40 (n = 12)
TreatmentPack fluoride concentration (ppm)Mean enamel fluoride concentration (ppm)
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

Experimental Toothpaste (6+ years)08 (2)a
Experimental Toothpaste (2–5 years/tube)11501,779 (59)b
Experimental Toothpaste (2–5 years/pump)11501,730 (37)b
Experimental Toothpaste (6+ years)11501,818 (53)b
USP standardN/A1,296 (51)c
Aquafresh Kids Bubble Fresh1100748 (17)d
Table 9. Enamel fluoride uptake data for non-US experimental and commercial toothpastes using FDA Method #40 (n = 12)
TreatmentPack fluoride concentration (ppm)Mean enamel fluoride concentration (ppm)
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

Experimental Toothpaste (3–5 years)040 (6)a
Aquafresh Milk Teeth1,000617 (20)b
Odol-med 3 Milchzahn5001,000 (21)c
Experimental Toothpaste (0–2 years)5001,383 (27)d
Experimental Toothpaste (3–5 years)5001,521 (42)e
Aquafresh Little Teeth1,4001,540 (72)e
Experimental Toothpaste (0–2 years)1,0001,648 (46)e,f
Aquafresh Little Teeth1,0001,758 (36)f,g
Experimental Toothpaste (3–5 years)10001,860 (35)g,h
Aquafresh Big Teeth1,4501,919 (54)h,i
Experimental Toothpaste (3–5 years)1,4501,959 (41)h,i
Experimental Toothpaste (6+ years)1,4502,035 (53)i

For all non-US toothpastes, the fluoride uptake data showed a dose response (Table 9). The fluoride uptake from the experimental toothpastes was either equivalent to or statistically higher than the commercial controls containing the same fluoride concentration. For the 500 and 1,000 ppm F experimental toothpastes, fluoride uptake from toothpastes for ages 3–5 years was significantly higher than from toothpaste for ages 0–2 years.

RDA & REA

The RDA and REA data for the experimental toothpastes and the commercial controls are shown in Table 10. The products evaluated in this study have a wide range of RDA values (from 31.14–103.97) whereas the range of REA values is considerably smaller (from 0.93–4.58). The statistical analysis showed that while there were no differences between the experimental toothpastes for both RDA and REA, there were significant differences between the commercial control toothpastes.

Table 10. Relative enamel and dentine abrasion results for experimental and commercial toothpastes (n = 8)
TreatmentREARDA
  1. Letter superscripts represent the different statistical groupings. Standard error in brackets.

Aquafresh Fresh and Minty4.58 (0.23)a77.10 (2.13)a
Aquafresh Kids Bubble Fresh2.49 (0.11)b103.97 (1.90)b
Experimental Toothpaste (6+ years/non-US)2.26 (0.17)b,c38.29 (1.60)d
Experimental Toothpaste (0–2 years/non-US)2.25 (0.18)b,c36.54 (1.88)d
Aquafresh Big Teeth2.03 (0.12)b,c,d68.46 (1.20)c
Experimental Toothpaste (2–5 years/US tube)2.02 (0.12)b,c,d35.90 (1.21)d
Experimental Toothpaste (6+ years/non-US)2.00 (0.17)b,c,d38.00 (1.65)d
Experimental Toothpaste (2–5 years/US pump)1.76 (0.21)c,d36.76 (1.13)d
Experimental Toothpaste (6+ Years/US)1.64 (0.18)c,d37.59 (1.35)d
Aquafresh Milk Teeth1.49 (0.08)d78.82 (1.87)a
Odol-Med 3 Milchzahn0.93 (0.19)e31.14 (2.96)d
Bioavailable fluoride

The bioavailable fluoride data for the experimental toothpastes is shown in Table 11. All placebo formulations contained ≤ 4 ppm fluoride. For all other toothpastes, the concentration of bioavailable fluoride was high and similar to that of the on-pack fluoride concentration.

Table 11. Bioavailable fluoride results for experimental toothpastes
Age rangePack fluoride concentration (ppm)Bioavailable fluoride (ppm)
0–2 years04
0–2 years500471
0–2 years1,000956
3–5 years0None detected
3–5 years250249
3–5 years500463
3–5 years1,000920
2–5 years1,150 (Tube)1,040
2–5 years1,150 (Pump)1,041
3–5 years1,4501,311
6+ years02
6+ years250238
6+ years500457
6+ years1,1501,079
6+ years1,4501,335

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

The range of experimental toothpastes evaluated in this study have been developed for use by children at the different stages of their development. The formulations for the three age groups are different; specifically, in the level of surfactant and the type of thickening gums used. In addition, flavour and colour variations are present across the three formulations. The rationale for these differences is discussed by Stovell et al.[25] These toothpastes were designed to maximise fluoride availability, minimise abrasivity and incorporate levels and types of surfactant that will minimise interference with fluoride delivery.

In vitro pH cycling models are frequently used to replicate the dynamics of demineralisation and remineralisation involved in caries lesion formation and daily toothpaste usage[26]. The pH cycling model described in this paper has been previously used to investigate the effect of fluoride containing toothpastes on remineralisation of artificial caries lesions[27, 28]. The cycling studies described here used permanent human teeth because of the difficulty in obtaining sufficient numbers of deciduous teeth. Furthermore, deciduous teeth are smaller and so there is less surface area for experimental manipulation[26]. While there are a number of distinct differences between deciduous and permanent enamel, it has been reported that remineralisation of initial caries lesions is similar in both substrates[29]. This means that permanent enamel can be used as a surrogate for deciduous enamel in these studies. The lesions used in this study represented early stage lesions where the mineral loss was confined to the outer regions of the enamel where fluoride is considered most effective[30].

The changes in specimen hardness following pH cycling were less that those reported by Newby et al. using the same experimental protocol[28]. These differences may be explained by compositional variations in the saliva used as the remineralisation medium. As saliva varies from person to person, and the composition of an individual's saliva can vary depending on the time of collection[31], the saliva used in these studies was pooled from at least five individuals in an attempt to mitigate this variability.

In this paper, the enamel remineralisation neared a plateau in the range of 250–500 ppm F, however, in most cases the dose response continued to be significant up to higher fluoride concentrations. Similar remineralisation plateaux have been observed by other authors for shallow lesions[32]. In addition, while net remineralisation increased from 10 days to 20 days for all fluoride-containing toothpastes, the changes were small. A plausible explanation could be a surface-zone blocking effect, which reduces the number of diffusion pathways to the lesion body. This effect has been demonstrated during mechanistic studies in vitro[33, 34].

The fluoride source in all experimental toothpastes and the majority of the commercial control toothpastes is NaF. Only the Aquafresh Kids Bubble Fresh and Aquafresh Milk Teeth Toothpastes use SMFP as a fluoride source. To be effective in the mouth, the fluoride ion needs to be freely available. While this is the case for NaF, the SMFP must be initially hydrolysed by salivary or microbial phosphatases in order to release the fluoride ion[35]. As a result, the toothpaste slurries used in the pH cycling studies were prepared in human saliva in order to initiate hydrolysis. It is worth noting that whilst the in vitro pH cycling data has shown that treatment with both experimental toothpastes (US) produced greater lesion remineralisation and a higher enamel fluoride content than the Aquafresh Kids Bubble Fresh toothpaste, a number of caries clinical trials have shown no significant differences in the anti-caries effectiveness of toothpastes containing fluoride as either NaF or SMFP[36].

Fluoride uptake has long been accepted as a positive indicator of the anti-caries activity of fluoride toothpastes. All experimental toothpastes contain a high level of bioavailable fluoride and were effective at delivering this fluoride to demineralised enamel. However, not all toothpaste containing an equivalent fluoride source and concentration produced the same fluoride uptake. This demonstrates that fluoride uptake can be influenced by different toothpaste excipients[25]. In both EFU studies, the fluoride uptake was higher from NaF than from SMFP toothpastes containing equivalent fluoride ion concentrations. For comparison, Arends et al.[37] and de Rooij et al.[38] reported similar findings using sound enamel. For the US experimental toothpastes, the fluoride uptake was either equivalent to or greater than the USP reference toothpaste and therefore satisfies this part of the monograph testing requirements[18]. However, as the EFU method does not incorporate biological factors that in vivo would promote SMFP hydrolysis, it is not possible to make any inference from this study as to the efficacy of the Aquafresh Kids Bubble Fresh toothpaste relative to the USP reference toothpaste. Although not reported in this paper, the Aquafresh Kids Bubble Fresh toothpaste fulfils all testing requirements listed in the anti-caries monograph. The fluoride uptake results were consistent with those measured in the pH cycling studies.

Abrasives are added to toothpastes to remove plaque and further to remove the stained pellicle on the tooth surface and thus it is important to ensure that the abrasive will not cause mechanical damage to the teeth[39, 40]. In vitro abrasivity tests are routinely performed to provide information on the abrasive potential of toothpastes; however, the protective nature of the pellicle towards toothpaste abrasion means that any extrapolation of in vitro data to levels of in vivo abrasive wear should be treated with caution[41]. While no specific REA and RDA limits have been established for children's toothpaste, ISO 11609:2010 sets toothpaste abrasivity limits of 250 for RDA and 40 for REA. As RDA is not a predictor of REA and vice versa, both abrasivity tests were conducted. In consideration of the differences between primary and permanent enamel with regard to its abrasion resistance, all children's toothpastes have been designed to have low levels of abrasivity. The results show that all toothpastes were below the recommended abrasivity limits and are therefore considered safe for everyday use.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References

In conclusion, a range of toothpastes have been developed for use by children at different stages of their development and contain different concentrations of fluoride for different markets. These toothpastes were specifically formulated to maximise fluoride availability and have low abrasivity.

The in vitro findings reported here demonstrate that the experimental toothpastes were effective at promoting fluoride uptake and remineralisation of artificial caries lesions. Toothpastes for the US market were shown to comply with the in vitro testing requirements of the US anti-caries monograph.

Conflict of interest

Author Churchley is employed by GlaxoSmithKline Consumer Healthcare. Author Schemehorn is employed by Therametric Technologies Inc., an independent research facility that received funding from GlaxoSmithKline Consumer Healthcare for this work.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. References
  • 1
    Tooth structures. In: Berkowitz BKB, Holland GR, Moxham BJ, editors. Color Atlas and Textbook of Oral Anatomy. Chicago: Year Book Medical Publishers Inc, 1977. pp. 1734.
  • 2
    Tooth eruption, succession and replacement. In: Atkinson ME, White FH, editors. Principles of Anatomy and Oral Anatomy for Dental Students. Edinburgh London Madrid Melbourne New York and Tokyo: Churchill Livingstone, 1992. pp. 469475.
  • 3
    Stack MV. Variation in the organic content of deciduous enamel and dentine. Biochem J 1953 54: XV.
  • 4
    Wilson PR, Beynon AD. Mineralisation differences between human deciduous and permanent enamel measured by quantitative microradiography. Arch Oral Biol 1989 34: 8588.
  • 5
    Linden LA, Bjorkman S, Hattab F. The diffusion in vitro of fluoride and chlorhexidine in the enamel of human deciduous and permanent teeth. Arch Oral Biol 1986 31: 3337.
  • 6
    Featherstone JDB, Mellberg JR. Relative rates of progress of artificial carious lesions in bovine, ovine and human enamel. Caries Res 1981 15: 109114.
  • 7
    Wang LJ, Tang R, Bonstein P et al. Enamel demineralisation in primary and permanent teeth. J Dent Res 2006 85: 359363.
  • 8
    Shellis RP. Relationship between human enamel structure and the formation of caries –like lesions in vitro. Arch Oral Biol 1984 29: 975981.
  • 9
    Lussi A, Schaffner M, Jaeggi T. Dental erosion – diagnosis and prevention in children and adults. Int Dent J 2007 57: 385398.
  • 10
    Dental Caries (Tooth Decay) in Children (Age 2 to 11). National Health and Nutrition Examination Survey, 1999–2004.
  • 11
    Twetman S. Caries prevention with fluoride toothpaste in children: an update. Eur Arch Paediatr Dent 2009 10: 162167.
  • 12
    Marinho VCC, Higgins JPT, Logan S et al. Fluoride toothpastes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev 2003 Issue 1 Art No: CD002278.
  • 13
    Featherstone JDB. Prevention and reversal of dental caries: role of low level fluoride. Community Dent Oral Epidemiol 1999 23: 3140.
  • 14
    Marquis RE, Clock SA, Mota-Meira M. Fluoride and organic weak acids as modulators of microbial physiology. FEMS Microbiol Rev 2003 26: 493510.
  • 15
    International Standards Organization ISO 11609, Dentistry – toothpastes – requirements, test methods and marketing 2010.
  • 16
    Guidelines for the acceptance of fluoride containing dentifrices. J Am Dent Assoc 1985 110: 545547.
  • 17
    Guidance on the assessment of the efficacy of toothpastes. Int Dent J 1999 49: 311316.
  • 18
    24 CFR Parts 310, 355 and 369, Anti-caries Drug Products for Over-the-Counter Human Use; Final Monograph; Final Rule, Federal Register, 1995 Vol.60, No 194
  • 19
    White DJ. Reactivity of fluoride dentifrices with artificial caries I. Effects on early lesion: F uptake, surface hardening and remineralisation. Caries Res 1987 21: 126140.
  • 20
    White DJ. Reactivity of fluoride dentifrices with artificial caries II. Effects on subsurface lesions: F uptake, F distribution, surface hardening and remineralisation. Caries Res 1988 22: 2736.
  • 21
    Schemehorn BR, Farnham RL, Wood GD et al. A bovine enamel model for in vitro remin/demin tests. J Dent Res 1990 69: 260. (Abstract 1213)
  • 22
    Schemehorn BR, Farnham RL, Wood GD et al. Fluoride uptake and remineralization in human and bovine enamel. J Dent Res 1992 71: 186. (Abstract #644)
  • 23
    Schemehorn BR, Roberts JA, Wood GD. An in vitro remin/demin model showing a fluoride dose response. J Dent Res 1994 73: 241. (Abstract #1117)
  • 24
    Hefferren JJ. A laboratory method for assessment of dentifrice abrasivity. J Dent Res 1976 55: 563573.
  • 25
    Stovell AG, Newton BM, Lynch RJM. Important considerations in the development of toothpaste formulations for Children. Int Dent J 2013 63 (Suppl 2): 5763.
  • 26
    Buzalaf MAR, Hannas AR, Magalhaes AC et al. pH Cycling models for in vitro evaluation of the efficacy of fluoridated dentifrices for caries control: strengths and limitations. J Appl Oral Sci 2010 18: 316334.
  • 27
    Karlinsey RL, Mackey AC, Walker ER et al. Remineralisation potential of 5000 ppm fluoride dentifrices evaluated in a pH cycling model. J Dent Oral Hyg 2010 2: 16.
  • 28
    Newby EE, Newby CS, Wood GD et al. Surface hardness changes and enamel fluoride uptake in a 20 day in vitro caries cycling model. Caries Res 2007 41: 328. (Abstract 173)
  • 29
    Hellwig E, Altenburger MA, Attin T et al. Remineralisation of initial carious lesions in deciduous enamel after application of dentifrices of different fluoride concentrations. Clin Oral Invest 2010 14: 265269.
  • 30
    Bjarnason S, Finnbogason SY. Effect of different fluoride level in dentifrice on the development of aproximal caries. Caries Res 1991 25: 207212.
  • 31
    Edgar WM. Saliva: its secretion, composition and functions. Br Dent J 1992 172: 305312.
  • 32
    Ten Cate JM, Exterkate RAM, Buijs MJ. The relative efficacy of fluoride toothpastes assessed with pH cycling. Caries Res 2006 40: 136141.
  • 33
    Silverstone LM, Wefel JS, Zimmerman BF et al. Remineralisation of natural and artificial lesions in human dental enamel in vitro. Caries Res 1981 15: 138157.
  • 34
    Ten Cate JM, Duijsters PP. Alternating demineralisation and remineralisation of artificial enamel lesions Caries Res 1982 16: 201210.
  • 35
    Bowen WH. The role of fluoride toothpastes in the prevention of dental caries. J Royal Soc Med 1995 88: 505507.
  • 36
    Volpe AR, Petrone ME, Davies R. Clinical anticaries efficacy of NaF and SMFP dentifrices: overview and resolution of the scientific controversy. J Clin Dent 1995 6: 128.
  • 37
    Arends J, Lodding A, Petersson L. Fluoride uptake in enamel – in vitro comparison of topical agents. Caries Res 1980 14: 403413.
  • 38
    de Rooij JF, Arends J, Kolar Z. Diffusion of monofluorophosphate in whole bovine enamel at pH 7. Caries Res 1981 15: 363368.
  • 39
    Barbakow F, Lutz F, Imfeld T. Abrasives in dentifrices and prophylaxis pastes. Quintessance Int 1987 18: 1722.
  • 40
    White DJ. Development of an improved whitening dentifrice based on ‘stain specific soft–silica’ technology. J Clin Dent 2001 12: 2529.
  • 41
    Dorfer CE. Abrasivity of dentifrices from a clinical perspective. J Clin Dent 2010 21(Spec Iss): S4.