Toothpastes and enamel erosion/abrasion – Impact of active ingredients and the particulate fraction

Abstract

Objectives

To investigate in vitro a range of differently characterised toothpastes with respect to their efficacy in an erosion/abrasion setting with special emphasis on the role of the particulate ingredients.

Methods

Human enamel samples were erosively demineralised with citric acid (2 min, 6×/day; 0.5%, pH 2.5; 10 days) and immersed in slurries (2 min, 2×/day) either without or with brushing (15 s, load 200 g). The toothpastes were eight NaF-toothpastes, three hydroxyapatite-toothpastes (one without and two with NaF), one fluoride-free chitosan-toothpaste and three Sn-toothpastes. Negative control was erosion only, positive control was SnF 2 gel. Tissue loss was quantified profilometrically.

Results

The SnF 2 gel was most effective (reduction of tissue loss of 79%). Most of the products reduced tissue loss significantly when applied as slurries (between 28 and 66%). Brushing increased tissue loss in almost all toothpastes, only 5 formulations (all Sn-toothpastes and 2 NaF-toothpastes) reduced tissue loss significantly when compared to negative control (between 33 and 59%). There was a non-linear association between abrasiveness and amount of particles in a formulation, the particle size had no impact.

Conclusions

Toothpastes had a protecting effect when applied as slurries but to a much lesser degree when applied with brushing. The particulate fraction may be a determinant for toothpaste efficacy in erosion/abrasion settings.

Clinical significance

Toothpastes are important carriers of active agents against erosion, but physical impacts through brushing modifies efficacy distinctly. Understanding the role of the particulate fraction in toothpastes may offer perspectives for designing effective formulations for patients with erosive lesions.

Introduction

Toothpastes are important carriers of agents for preventing oral diseases. In the context of dental erosion, however, the role of toothpastes remains unclear . Unlike caries lesions, erosive defects are surface phenomena located at tooth areas exposed to many chemical and physical impacts and acid challenges lead to a partially demineralised enamel surface which is more prone to abrasion . Therefore, not only the active ingredient but also the abrasivity of a toothpaste is of importance.

Studies investigating the efficacy of toothpastes reveal a wide range of effects and products containing the same fluoride compound and fluoride concentration provide distinctly different degrees of protection . The reasons for these findings may be manifold, e.g. in terms of excipients, but it is also well conceivable that the particulate fraction (often also referred to as abrasives) in a toothpaste formulation is an important modulator of efficacy. Such particles are mostly silica of various sizes and shapes and with different properties. Besides cleaning and polishing another function of silica is thickening, thus most toothpaste formulations contain varying mixtures of different types of particles in order to achieve the desired properties of a product depending on its indication.

So far, however, only few studies investigated the role of the particulate fraction in toothpastes in the context of erosion. In formulations without active agents, the most striking differences were found between particle-free and particle-containing formulations whereas the abrasivity in terms of REA (radioactive enamel abrasion) values in the latter were of minor importance . In contrast, in the presence of an active agent REA values seem to become much more influential .

Currently, the multitude of toothpaste brands increases with highly diversified marketing strategies aiming to provide product lines for specific indications. Amongst others formulations with special cleaning properties or formulations containing special active agents, e.g. hydroxyapatite, biopolymers or stannous ions are available, some of which claiming to be of particular efficacy in the field of erosion. The complex actions of such formulations when used in erosion/abrasion systems, however, are currently only poorly understood.

The aim of this study was to investigate the effects of a range of marketed toothpastes in an in vitro erosion/abrasion experiment with special emphasis on the role of the particulate fraction and the abrasiveness in terms of REA and RDA (radioactive dentin abrasion) values. The null-hypothesis was that three is no difference between the different toothpastes.

Material and methods

The experimental design was a standard procedure of our research group and published elsewhere . In brief, enamel samples deriving from formerly completely impacted human third molars were prepared and polished (diamond grinding and polishing discs, 30, 15 and 3 μm; Bühler GmbH, Düsseldorf, Germany) in order to achieve a flattened area of approximately 3 mm × 3 mm. A reference area was covered with light curing acrylic (Technovit 7230 VLC, Kulzer-Exakt, Wehrheim, Germany). A total of 510 enamel samples (between 2 and 3 samples per tooth) were prepared (n = 15 per group, 34 groups) and stored in 100% humidity until use.

The erosive demineralisation was performed with 0.5% citric acid; the storage solution was a mineral salt solution containing 4.08 mM H 3 PO 4 , 20.10 mM KCl, 11.90 mM Na 2 CO 3 and 1.98 mM CaCl 2 with a pH of 6.7.

The toothpaste and gel slurries were prepared by mixing 1 part of the toothpaste or gel with 3 parts of the mineral salt solution (by weight). The test products are described in Table 1 .

Table 1
Toothpastes (TP) under study (abbreviation used in the text in brackets), active agents and pH of the slurries, n.d. = not declared. The Emofluor Gel was the positive control.
Active agent pH
PositiveControl
Emofluor Gel a 1000 ppm F as SnF 2 5.1
Sn-TP
Emofluor Toothpaste a 1000 ppm F as SnF 2 4.6
Elmex Erosion Protection (Erosion Protection) b 1400 ppm F as AmF and NaF, SnCl 2 4.0
Oral-B ProExpert Enamel Shield (Enamel Shield) c 1450 ppm F as NaF, SnCl 2 6.2
Non-fluoride TP
Chitodent d Chitosan 6.3
Biorepair e Hydroxyapatite 8.7
Hydroxyapatite/NaF-TP
ApaCare f 1450 ppm F as NaF, Hydroxyapatite 7.4
ActiSchmelz g NaF (amount n.d.), Hydroxyapatite 8.2
NaF-TP
Sensodyne Pronamel (Pronamel) h 1450 ppm F as NaF 7.8
Sensodyne Multicare (Multicare) h 1450 ppm F as NaF 7.7
Elmex Sensitive (Sensitive) b 1400 ppm F as AmF 4.8
Theramed Natural White (Natural White) i 1450 ppm F as NaF 7.5
Theramed ProElectric (ProElectric) i 1450 ppm F as NaF 7.6
Theramed Original 2in1 (Original 2in1) i 1450 ppm F as NaF 7.7
Theramed Interdental (Interdental) i 1450 ppm F as NaF 7.3
Pearls&Dents j 1200 ppm F as AmF and NaF 6.0

a Dr Wild & Co. AG.

b CP GABA GmbH.

c Procter & Gamble Germany GmbH.

d Helmuth Focken Biotechnik.

e Dr. Kurt Wolff GmbH & CO. KG.

f Cumdente GmbH.

g Dirk Rossmann GmBH.

h GlaxoSmithKline Consumer Healthcare GmbH.

i Henkel AG.

j Rudolf Liebe Nachf. GmbH.

Material and methods

The experimental design was a standard procedure of our research group and published elsewhere . In brief, enamel samples deriving from formerly completely impacted human third molars were prepared and polished (diamond grinding and polishing discs, 30, 15 and 3 μm; Bühler GmbH, Düsseldorf, Germany) in order to achieve a flattened area of approximately 3 mm × 3 mm. A reference area was covered with light curing acrylic (Technovit 7230 VLC, Kulzer-Exakt, Wehrheim, Germany). A total of 510 enamel samples (between 2 and 3 samples per tooth) were prepared (n = 15 per group, 34 groups) and stored in 100% humidity until use.

The erosive demineralisation was performed with 0.5% citric acid; the storage solution was a mineral salt solution containing 4.08 mM H 3 PO 4 , 20.10 mM KCl, 11.90 mM Na 2 CO 3 and 1.98 mM CaCl 2 with a pH of 6.7.

The toothpaste and gel slurries were prepared by mixing 1 part of the toothpaste or gel with 3 parts of the mineral salt solution (by weight). The test products are described in Table 1 .

Table 1
Toothpastes (TP) under study (abbreviation used in the text in brackets), active agents and pH of the slurries, n.d. = not declared. The Emofluor Gel was the positive control.
Active agent pH
PositiveControl
Emofluor Gel a 1000 ppm F as SnF 2 5.1
Sn-TP
Emofluor Toothpaste a 1000 ppm F as SnF 2 4.6
Elmex Erosion Protection (Erosion Protection) b 1400 ppm F as AmF and NaF, SnCl 2 4.0
Oral-B ProExpert Enamel Shield (Enamel Shield) c 1450 ppm F as NaF, SnCl 2 6.2
Non-fluoride TP
Chitodent d Chitosan 6.3
Biorepair e Hydroxyapatite 8.7
Hydroxyapatite/NaF-TP
ApaCare f 1450 ppm F as NaF, Hydroxyapatite 7.4
ActiSchmelz g NaF (amount n.d.), Hydroxyapatite 8.2
NaF-TP
Sensodyne Pronamel (Pronamel) h 1450 ppm F as NaF 7.8
Sensodyne Multicare (Multicare) h 1450 ppm F as NaF 7.7
Elmex Sensitive (Sensitive) b 1400 ppm F as AmF 4.8
Theramed Natural White (Natural White) i 1450 ppm F as NaF 7.5
Theramed ProElectric (ProElectric) i 1450 ppm F as NaF 7.6
Theramed Original 2in1 (Original 2in1) i 1450 ppm F as NaF 7.7
Theramed Interdental (Interdental) i 1450 ppm F as NaF 7.3
Pearls&Dents j 1200 ppm F as AmF and NaF 6.0
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Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Toothpastes and enamel erosion/abrasion – Impact of active ingredients and the particulate fraction
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