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formulation of dentifrice.
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Dentifrices are designed to be used with toothbrushes to remove dental stains, to introduce a fresh, pleasant and clean feeling, and to deliver active agents into the oral cavity. The dentifrices in today's market have a wide range of rheological properties and appearances. The most common rheology is that of a paste that is extruded from its container onto a toothbrush as a ribbon that can maintain its shape for the necessary time prior to brushing and then be easily dispersed during brushing. Although there are many different types of dentifrices available, most contain the same basic functional ingredients, which have a specific role to play within the formulation and these are described below.
Abrasives are the solid cleansing materials that aid in the removal of plaque, food debris and residual stains from the teeth. Some abrasives can also exert a certain amount of polish to the tooth surface. Abrasives will be discussed further in Section 6.1.
The humectant system comprises one or more liquids in which the other dentifrice ingredients are dispersed or dissolved in order to provide a stable paste. The liquids are usually sorbitol, glycerol or polyethylene glycols and are typically used in the 10–30% w/w range. The humectant does not crystallise and this helps prevent the formulation from drying out and causing an unacceptable increase in viscosity which, for example, can lead to the tube cap to stick to the nozzle.
The thickening agent primarily defines the rheological properties of the final formulation. It also acts as a binder to prevent the separation of liquid and solid ingredients on storage. Modern thickeners include silica, sodium carboxymethyl cellulose and xanthan gum. Usually, only small quantities are required (0.5–3.0% w/w).
The primary purpose of the surfactant is to generate foam and to impart a pleasant, smooth sensation during use. Indeed, a surfactant and foam-free dentifrice is generally unacceptable to consumers. The most commonly used surfactants are sodium lauryl sulphate, sodium N-lauroyl sarcosinate and sodium methyl cocoyl taurate, and are typically used at 1–3% w/w.
The flavour is the dominant factor in determining the sensory aspect of a dentifrice and is typically added at about 1% w/w. It gives the product an acceptable and characteristic taste, contributes to mouth freshness and to aftertaste. Most dentifrice flavours are based on peppermint and spearmint oils with top notes added to create unique flavours based on herbs, spices, fruits, etc. Menthol is a principal component of the mint flavours and gives a cooling sensation during use. Sweeteners are also added, such as sodium saccharinate, to aid in the overall pleasantness of the product during use.
Active agents can be added to dentifrices to give them other benefits such as anti-caries, anti-plaque, anti-gingivitis, anti-calculus and anti-sensitive teeth benefits. For example, when fluoride is added to a compatible dentifrice formulation, it can significantly reduce the incidence of dental caries [59]. Arguably, the widespread use of efficacy-proven fluoridated dentifrice is the single measure to have provided the greatest overall improvement in dental public health to date. Typical sources of fluoride are sodium fluoride, sodium monofluorophosphate and stannous fluoride. More recently, anti-bacterial ingredients such as triclosan in combination with zinc citrate have been shown to be effective anti-plaque agents and, more importantly, these have been proven to provide a significant anti-gingivitis benefit [48]. Anti-calculus benefits can be derived from pyrophosphate and zinc salts [60]. Benefits for sensitive teeth can be derived from strontium salts, which have been suggested as blocking exposed dentine tubules, or potassium salts, which reduce the dentine nerve excitation. Both routes may reduce the overall observed pain when dentine is exposed to, for example, hot or cold stimuli [7].
Dentifrices may also contain opacifying agents to make the paste look white (e.g. titanium dioxide), an effective preservative to achieve microbiological stability, colours and buffering agents to stabilise the pH of the formulation. For further details, a number of authors have listed dentifrice formulations based on the above principles [4,5,61,62].
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