Objectives: Sodium Tripolyphosphate (STP) is commonly incorporated into toothpastes for stain removal where its mild chelating properties interfere with stained pellicle integrity. However, these chelating properties may negatively impact on enamel surface finish. This study investigated the effects of STP treatment on the surface finish of polished and roughened enamel with and without tooth-brushing.
Methods: Bovine enamel specimens (n=8/group) were prepared to either 1200-grit SiC and 3µm diamond finish (Polished group), P800-ground finish, or P320-ground finish and soaked or brushed (Oral B P35), using an in vitro tooth-brushing simulator (5-60m brushing), in STP solutions of concentrations (w/w) 2.5%, 5.0% or 10.0% STP. Gloss changes were measured with a Novo-Curve glossmeter and surface roughness and wear depth determined by profilometry.
Results: There were no significant changes in surface roughness and wear depth after brushing in STP for 5-60m. Small gloss decreases occurred for all polished and roughened specimens, which were of greater magnitude with prolonged soaking or brushing. Brushing in STP did not exacerbate the gloss loss relative to soaking for equivalent times. There was no clear linear relationship between STP concentration and gloss change after soaking or brushing reflecting the small gloss changes taking place.
Conclusion: Minor decreases in enamel surface gloss following extensive soaking in STP did not cause greater susceptibility to wear during tooth-brushing. Only minimal changes in enamel surface finish occurred after exposure to STP, even with highly polished surfaces, and its stain removal properties potentially provide positive benefits for oral hygiene.
Effective cleaning of the tooth surface through good oral hygiene is central to both the prevention of oral and dental disease and the appearance of the dentition. Clear causal links are well established between the presence of dental plaque, caries and periodontal disease. The appearance of the teeth, particularly whiteness, is of great importance to patients and tooth discolouration is a common dental complaint. It has been reported, depending on the population examined, that personal dissatisfaction with the appearance of the dentition ranges from 17.9 to 52.6% [1-5]. Extrinsic staining of the tooth can arise from a variety of sources including smoking, red wine consumption, cationic compounds such as chlorhexidine or stannous salts [6-9]. Stain removal can be challenging, thus, oral hygiene strategies need to address both the removal of dental plaque and extrinsic stain.
While a variety of tooth whitening procedures are used professionally [10-13], they are costly and labour intensive [14], and some of these procedures do not contribute to oral hygiene. There is considerable demand for ‘Over-The-Counter’ (OTC) tooth-whitening products that can be integrated into a normal oral hygiene regime, and whitening toothpastes are the dominant delivery format [15]. In general, whitening toothpastes provide tooth whitening by abrasive removal of extrinsic stain and dental plaque and the chemical action of constituents such as Sodium Tripolyphosphate (STP), Sodium pyrophosphate, sodium hexametaphosphate, hydrogen peroxide, as well as the enzymes papain and bromelain [3].
Sodium Tripolyphospahte (STP) is a linear condensed phosphate that is commonly incorporated in whitening toothpastes for effective stain removal [16], where its mild chelating properties interfere with stained pellicle integrity [17-19]. However, increasing interest in enamel surface finish and polishing raises questions as to whether these chelating properties may negatively impact enamel surface finish. There are not many studies in the literature regarding the effect of STP on the surface roughness and gloss at varying concentrations. The present in vitro study investigates the effects of STP treatment on the surface finish of polished and roughened bovine enamel, with and without tooth brushing.
Bovine enamel has been used in this pilot study due to the reported and extensive similarities between bovine and human teeth. Indeed a recent study, which compared teeth from several species, indicated that on the basis of their chemical and morphological composition, bovine teeth should be the first choice as substitutes for human teeth in research [21].
Sodium tripolyphosphate, a sodium salt of triphosphoric acid, has been widely used for water treatment, detergency and in the food industry [22,23]. Its surfactant and chelating properties have led to its use in whitening toothpastes for stain removal. In vitro studies with crystalline Hydroxyapatite (HA) powder showed that STP was effective in removing existing stain and inhibiting stain formation through inhibition of the adsorption of salivary protein or tea stain and the desorption of existing protein and stain from HA surfaces [15,24]. In vivo trials also reported significant extrinsic stain removal efficacy for a dentifrice containing STP versus the baseline [18] and a reduction in dental stain by a chewing gum containing STP [25]. These beneficial effects for stain removal and inhibition depend in part on the chelating properties of STP, the latter of which may, however, negatively impact on enamel surface finish.
In the present study, the effects of STP on several parameters of enamel surface finish have been examined to determine whether its chelating properties have any adverse effects. Furthermore, exposure of enamel to STP has been investigated both by simple soaking of specimens in STP solutions and also, following tooth-brushing with STP solutions under clinically relevant exposure time conditions. Any significant chelating action of STP may be expected to show exaggerated enamel surface loss when exposure occurs under brushing conditions due to the physical abrasion from brushing on a softened surface. Surface gloss of enamel represents a very sensitive parameter of change to the surface finish of this tissue. Soaking or brushing of enamel specimens in STP for periods of 5 – 60 mins resulted in only small decreases in surface gloss, with little difference between the two treatments, suggesting that any chelating action of STP caused minimal tissue loss from the enamel surface. Both surface roughness and wear depth values did not show any change after exposure of specimens to STP for up to 60 mins. The starting finish of an enamel surface (polished vs ground) influences its available surface area, but the lack of influence of this on gloss, surface roughness or wear depth emphasizes the minimal effects of STP on enamel surface finish, as does the lack of influence of STP concentration. Interestingly, a lack of influence of STP concentration on stain desorption from hydroxyapatite has also been reported [24].
Mechanistically, it has been suggested that the main action of STP in both the inhibition of salivary protein adsorption to hydroxyapatite and desorption of bound salivary proteins is through competitive binding to the crystal surface, although the chelating action of STP has been proposed as a possible additional factor [24]. Data from the present study indicate that chelating effects of STP on intact enamel are minimal under clinically relevant exposure times, implying that chelation may be of minor importance when considering adsorption/desorption of salivary proteins and stains to enamel.
In summary, the present study has demonstrated that exposure of enamel to STP, either by soaking or with brushing, results in only minimal changes to surface gloss and has no statistically significant effect on surface roughness or wear depth. Thus, several parameters of enamel surface finish indicate that any chelating action of STP on enamel is minimal under clinically relevant conditions underpinning the positive benefits from its use for stain removal from teeth.
The authors gratefully acknowledge financial support from GSK Consumer Healthcare for this research.
The authors are not aware of any competing interests for this study.
Citation: Wang C, Lucas R, Cooper PR, Smith AJ (2017) Effect of Sodium Tripolyphosphate on Polished and Roughened Bovine Enamel. J intern Med Prim Healthcare 2: 004
Copyright: © 2017 Changxiang Wang, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
