Is toothpaste afraid of water? Will it be ineffective if you dip it in water?

There is a long-standing topic on the Internet: should you dip toothpaste in water before use? At present, most people think that it is better not to dip it in water. There are many reasons for this: some people think that toothpaste will produce a lot of foam after dipping it in water, which will reduce the friction of the abrasive on the one hand, and make people mistakenly think that they can brush their teeth quickly, and end up brushing them hastily. Both of the above situations will have an adverse effect on the cleaning effect of teeth; some people also think that the special effects of toothpaste will be greatly reduced after dipping it in water, such as whitening toothpaste or desensitizing toothpaste.

But, are these seemingly reasonable views really reasonable?

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01

Water is one of the three main ingredients in toothpaste

Toothpaste is a sticky paste, so it may be difficult for people to associate it with water. But in fact, water (15-50%), abrasives (25-60%), and moisturizers (20-60%) are the three main ingredients of toothpaste.

Given that the ultimate purpose of toothpaste is to increase the friction between the toothbrush bristles and the tooth surface, abrasives in toothpaste are also one of the main ingredients.

But it is obvious that if toothpaste only has one ingredient, abrasive, the solid particles in it are either like "a pile of loose sand", unable to work together and thus unable to play the expected cleaning role; or because they are relatively hard, they "collide head-on" with the teeth, which may eventually cause serious damage to the teeth.

Therefore, liquid water is added to toothpaste as a "comrade-in-arms" that can "fight side by side" with abrasives. First, it can "condense" abrasive particles, and second, it can buffer the friction between abrasive particles and teeth. Of course, the water in toothpaste is not ordinary water, but distilled water and deionized water. It is worth noting that, except for baking soda, most abrasives are difficult to dissolve in water, so the addition of water usually does not have a substantial effect on the decontamination ability of abrasives.

However, it is not enough to just have water in the toothpaste. Not only does the water evaporate slowly, but it also tends to separate from the abrasive particles, so a humectant needs to be introduced into the mixture. When the abrasive particles, water and humectant are mixed together, they become one. And these three ingredients are the most basic ingredients of all toothpastes.

From this we can see that toothpaste is not insulated from water, but cannot live without water.

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02

Are the effective ingredients in toothpaste “afraid” of water?

Although the basic ingredients of toothpaste are not "afraid" of water, is it possible that the effective ingredients are "afraid" of water?

As mentioned earlier, there are many claims that whitening toothpaste and desensitizing toothpaste will become ineffective if used with water.

Not to mention that the amount of water that toothpaste comes into contact with after being dipped in water is limited. From the perspective of efficacy alone, whether it is whitening toothpaste, desensitizing toothpaste, or the fluoride toothpaste we are very familiar with, they all "require" water.

One of the ways to whiten teeth with whitening toothpaste is to use peroxide to bleach teeth. Since hydrogen peroxide is unstable, hydrogen peroxide is not necessarily added directly to whitening toothpaste, but peroxides such as calcium peroxide may be used. Calcium peroxide can only decompose into hydrogen peroxide that can ultimately play a role when it meets water (only in terms of the situation in the oral environment, not from a purely chemical reaction perspective). The reaction equation is CaO2 + 2H2O→Ca(OH)2 + H2O2.

One of the ways to desensitize toothpaste is to use potassium ions in the drug to numb the pain nerves. Its effective ingredients are mainly soluble potassium salts. Soluble potassium salts can only dissociate into potassium ions when they come into contact with water.

Similarly, the fluoride in fluoride toothpaste must be a soluble fluoride such as sodium fluoride. For this reason, in the formula of sodium fluoride toothpaste, the abrasive usually uses hydrated silica instead of calcium carbonate, in order to avoid the ineffectiveness of fluoride ions due to the reaction of sodium fluoride and calcium carbonate to form insoluble calcium fluoride.

To sum up, the effective ingredients are not only not afraid of water, but also need the cooperation of water to work.

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So, after knowing this, do you still think that toothpaste cannot be used with water? Of course, considering the moisture in the saliva in the mouth of healthy people, it doesn't matter whether the toothpaste is used with water or not, as long as it is chosen according to personal habits. However, if the saliva secretion is abnormal, or the toothpaste is relatively viscous, dipping it in water may be a more appropriate choice.

References:

1. Hu Deyu, editor-in-chief. Oral Preventive Medicine (6th Edition) [M]. Beijing: People's Medical Publishing House, 2012.

2. Epple M, Meyer F, Enax J. A critical review of modern concepts for teeth whitening[J]. Dent J (Basel), 2019, 7(3): 79.

Author | Rich

Review | Si Yan, Chief Physician and Associate Professor, Department of Oral Preventive Health Care, Peking University School of Stomatology

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