Toothpaste seems to improve every day. We have anti-cavity toothpastes, extra-whitening toothpastes, toothpastes with mouthwash, toothpastes for sensitive teeth, toothpastes with stripes, clear toothpaste, even liver flavored toothpaste for dogs.
A modern toothpaste has many things to do. It must have abrasives to scour off bacterial films. It must have fluorides to harden the teeth against decay. It must have a strong enough flavor to hide the bad tastes of decaying bits of previous meals, and the awful taste of some of the other ingredients, such as detergents and phosphates.
Toothpaste must have thickeners to stay on the toothbrush, and squeeze out of the tube. It must have detergents to remove fatty films, and water softeners to make the detergents work better, and sweeteners, preferably non-nutritive, so bacteria are not encouraged.
The most recognized toothpaste ingredient is probably the class of compounds known as fluorides. Stannous fluoride was the first to be used in toothpaste, because it could be used with the abrasive most common at the time, calcium phosphate. The calcium prevents sodium fluoride from being effective.
Later, sodium monofluorophosphate was used, as it also could be used with abrasives common at the time.
When hydrated silica became the abrasive of choice, sodium fluoride could be used, and is the most widely used fluoride in toothpastes at this time.
Hydrated silica is the transparent abrasive used in gel toothpastes, and in the clear parts of striped toothpaste. It has become common to use it in white opaque toothpastes as well, because of its compatibility with sodium fluoride.
Fluorides work better in combination with surfactants, which help the remineralization process. The most common are the lauryl sulfates, such as sodium lauryl sulfate, or ammonium lauryl sulfate.
Surfactants (detergents) also help clean the teeth, and provide a foam that helps to carry away debris. Moreover, lauryl sulfates have significant anti-bacterial properties, and they can penetrate and dissolve plaque.
Lauryl sulfates can irritate oral membranes, and so a similar detergent, lauryl sarcosinate often replaces some or all of the lauryl sulfate. Allantoin is sometimes added to relieve the irritation caused by detergents, alkalies, and acids.
The sequestering agent tetrasodium pyrophosphate (TSPP) removes calcium and magnesium from the saliva, so they can't deposit on teeth as insoluble deposits called tartar, (calcified plaque). In this respect it acts as a water-softening agent. It won't remove tartar that already exists.
TSPP is slightly alkaline, and has a bitter taste, requiring additional flavorings to mask it. Also, additional detergents must be added to keep it in solution. All of these factors can irritate oral membranes and cause sensitivity.
Polymers such as the acrylic PVM/MA copolymer are added to prevent bacteria from breaking down pyrophosphates. Other long polymers used are polyethylene glycol (PEG) in various weights (i.e. PEG-6, PEG-8, PEG-40, etc.), and polypropylene glycol (PPG).
Sodium bicarbonate (baking soda) is added for taste and mouth feel. It combines with acids to release carbon dioxide gas, adding to the foam produced by brushing. It is a mild abrasive. It may reduce the numbers of acid loving bacteria in the mouth, although this effect lasts only as long as the mouth stays alkaline.
Sodium carbonate peroxide is added to "peroxide" toothpastes as a whitener. It breaks down into sodium carbonate (washing soda) and hydrogen peroxide. The hydrogen peroxide bleaches the teeth, and kills germs.
Sweeteners such as sodium saccharin are added for taste. Other flavors are usually strong essential oils in the mint family.
The anti-bacterial agent Triclosan is added to kill plaque-forming microbes.
Various gums are used to thicken the paste, but also to retain moisture, so the toothpaste does not dry out if the top is not replaced.
In white pastes, titanium dioxide is used to make the paste opaque and white.