Toothpaste

I had to write a report on toothpaste as part of a project for school.  Since I did a fair bit of research into how toothpaste works and what the various ingredients actually do, I figured I'd post it here.

Overview of Tooth Decay
To understand the importance of toothpaste one must first understand the process by which bacteria cause cavities. The bacteria in a person's mouth form a colorless, thin, sticky film called plaque. The bacteria use carbohydrates present in the mouth after meals as fuel. The population grows and they produce acid as a waste of their metabolism.

While teeth are the hardest substance in the human body, they are very susceptible to acid. The acid from bacteria causes the pH level in the mouth to lower. This causes demineralization, and causes the teeth to soften, which in turn reduces their resistance to abrasion. Once the pH level returns to a higher level, minerals naturally present in saliva cause the softened teeth to gradual remineralize. The critical pH level is 5.5. Below this level demineralization occurs, above it remineralization (Dawes).

As long as the process of remineralization is faster than the loss of minerals from acid there will be no decay. However, when carbohydrates are frequently consumed the bacteria can produce more acid than the body can counteract. This leads to tooth decay. Once tooth decay has occurred the body can not repair the damage.

Ingredients
Abrasives
Toothbrushing removes the plaque film that covers one's teeth. This is accomplished through the mechanical action of brushing. It was long thought that toothpaste provided additional abrasive qualities that enhanced this process. Substances like hydrated silica are added to toothpaste to increase its abrasiveness. However recent studies have shown plain water to be as effective at removing plaque as toothpaste (Paraskevas). On the other hand, other studies have shown an additional benefit to using toothpaste (Putt). It is therefore impossible to drawn any definitive conclusions. Toothpaste, however, has numerous other benefits.

Raising pH Level
Since the problem with bacteria is the acid they produce, raising the pH level to make the mouth more basic will neutralize some of the acid and delay tooth decay. Sodium bicarbonate is often used as both an abrasive and to raise the pH of the toothpaste. Since it is slightly basic, it increases the pH in the mouth for some time after use. In addition to directly neutralizing acid, the basic environment makes it harder for the bacteria to grow, which further reduces acid levels.

Cosmetic Additives
One of toothpaste's most obvious benefits is the cosmetic impression of cleaning it has. While a mouth brushed with just water is perhaps as clean as one brushed with toothpaste, there is no doubt that toothpaste leaves the mouth with a sensation of cleanliness. The foaming action of toothpaste is associated with cleaning in general. Surfactants are added to toothpaste to enhance this foaming action.

The flavor of toothpaste is also associated with a clean mouth. While there are a wide variety of flavors the most popular are peppermint, spearmint, and wintergreen. Toothpastes also come in either paste or gel form. The option of paste of gel doesn't change the effectiveness of the toothpaste and the choice is a personal one based on preferences.

Fluoride
Toothpaste is also useful as a delivery mode for numerous chemicals that enhance oral health. The most significant of these being fluoride. Fluoride has a large body of evidence backing up its positive effects for teeth. Studies have shown that fluoride reduces cavities by 24% (Marinho). Furthermore, increasing the fluoride concentration generally decreases the cavity rate (Walsh). There are three forms of fluoride commonly used in toothpaste: sodium fluoride (NaF), sodium monofluorophosphate (Na₂PO₃F), and stannous fluoride (SnF₂). While NaF and Na₂PO₃F have been shown to be equally effective, SnF₂ has been shown to be less effective, and is thus less commonly used today (DePaola; Beiswanger).

Fluoride has three positive effects. First, it reduces the rate that bacteria are able to metabolize carbohydrates into acids. This effect lasts for some hours after using toothpaste with fluoride. Secondly, fluoride enhances the rate at which teeth are remineralized. This offsets a larger carbohydrate intake, for a net reduction in decay. Lastly, fluoride reacts with the minerals (hydroxyapatite) in teeth to form a protective coating (fluorapatite). This coating is more resistant to acid than the naturally occurring material. Specifically, the following reaction takes place when using sodium fluoride:

Ca₁₀(PO₄)₆(OH)₂ + 2 NaF → Ca₁₀(PO₄)₆F₂ + 2 NaOH

The result is that fluorapatite forms on the outside of teeth and resists future acid attacks more readily. However, this coating is very thin and wears off after several hours to a day. This requires regular applications of fluoride.

Surfactants
The use of fluoride in toothpaste is nearly universal. However, there are several other additives which are found in toothpaste to various degrees. Surfactants are added to toothpaste to act as detergents and cause the foaming action of toothpaste. This has already discussed benefits in perception of cleanliness. However, it also has been shown to enhance fluorides ability to penetrate into deeper crevices in the teeth, the result being a reduction in cavities (Caslavska).

Antibacterial
Triclosan is an antibacterial agent which was patented by Colgate for use in its Total brand of toothpastes. This patent expired in 2008 and triclosan has since spread to other toothpastes. Triclosan has been shown to cause a modest reduction in cavities and a 30% reduction in gingivitis (Feller; Garcia-Godoy). Its effect on plaque continues to work for hours or days after use (Jenkins).

Xylitol is a nonfermentable sugar that is used in chewing gums and sometimes added to toothpaste. Xylitol, not only will not increase bacteria counts, it can actually have a net negative effect on bacteria counts. This is because xylitol is chemically similar to sucrose, which causes bacteria to attempt to metabolize it. This, in effect, starves the bacteria and kills them. The result is a proven reduction in plaque levels (Milgrom).

Remineralization
Calcium phosphate has been shown to enhance the remineralization process, when used with fluoride it has a greater effect than fluoride alone (Shen). Similarly, nano-hydroxyapatite is a new technology that also enhances remineralization (Tschoppe). These two additives have proven benefits, and are currently only found in specialty toothpastes.